JP4632116B2 - Ceramic circuit board - Google Patents

Description

  The present invention relates to a ceramic circuit board used in a power semiconductor module, and more particularly to a ceramic circuit board in which a metal plate for forming a circuit pattern is bonded to at least one surface of a ceramic substrate via a brazing material layer.

  In recent years, power semiconductor modules (IGBT modules) capable of high voltage and large current operation have been used as inverters for electric vehicles. As a substrate used for a power semiconductor module, a ceramic circuit substrate in which a metal plate such as a copper plate or an aluminum plate (hereinafter referred to as a copper plate) is joined to a ceramic substrate made of aluminum nitride or silicon nitride is widely used. Has been. For example, a semiconductor substrate or the like is mounted on one surface of a ceramic substrate, and a copper plate serving as a circuit is bonded, and a heat radiating copper plate is bonded to the other surface. A ceramic circuit board is formed by forming a metal circuit pattern made of a plurality of copper plates on the side of the circuit copper plate by etching along a circuit pattern to be a circuit portion.

As a means for integrally bonding the ceramic substrate and the copper plate, a so-called copper direct bonding method (DBC method: Direct Bonding Copper) in which a copper plate is directly bonded onto the ceramic substrate using a eutectic liquid phase such as Cu—Cu ₂ O. Method), a refractory metal metallization method in which a refractory metal such as Mo or W is baked on a ceramic substrate, and a brazing material layer containing an active metal such as a group 4A element or a group 5A element on the ceramic substrate. An active metal method or the like is used that is formed by coating and heat-treated at an appropriate temperature while being pressed between the copper plates and applying pressure. These ceramic circuit boards obtained by the DBC method or the active metal method all have advantages such as a simple structure, low thermal resistance, and compatibility with large-current and highly integrated semiconductor chips.

  In addition, as a means for forming a copper plate circuit pattern, a direct mounting method in which a copper plate having a circuit pattern shape obtained in advance by pressing or etching is bonded onto a ceramic substrate via a brazing material layer, or soldering is performed on almost the entire surface of the ceramic substrate. A multi-stage etching method in which a metal layer is formed, a copper plate is joined so as to cover it, and then an unnecessary portion of the patterned copper plate is etched together with the brazing material layer to form a metal circuit pattern, or a desired circuit pattern A brazing material layer is applied and formed along the shape, and then a method using both the brazing material pattern printing and the etching method to form a metal circuit pattern by etching an unnecessary portion of the copper plate in the same manner as the multistage etching method (hereinafter, This is called a pattern printing etching method).

  In recent power semiconductor modules, high output and high integration have rapidly progressed, and thermal stress repeatedly applied to the ceramic circuit board tends to increase. Failure to withstand this thermal stress causes problems such as warping and cracking of the ceramic substrate. Conventionally, among the above-mentioned means for connecting the ceramic substrate and the metal plate, high strength, high sealing property, etc. can be obtained, so the eutectic composition of Ag and Cu (72 mass% Ag-28 mass% Cu) is used. An active metal method using a brazing paste in which an active metal such as Ti is added to the eutectic brazing filler is generally used. However, when the pattern printing etching method is adopted in this active metal method, there is no solid-liquid coexistence region because of the eutectic composition, and all the brazing filler metals that exist are melted above the melting point temperature. May flow out to the non-joined part of the circuit, and adjacent circuit patterns may come into contact with each other to cause a short circuit failure. For this reason, the following proposals have been made on the connection structure of ceramic circuit boards that can withstand thermal stress and the guarantee of insulation.

  Patent Document 1 discloses a brazing material layer containing Ag, Cu, Ti on at least one surface of a ceramic substrate made of an aluminum nitride sintered body or a silicon nitride sintered body for the purpose of suppressing the occurrence of cracks in the ceramic substrate. And joining the metal plate, it is desirable to form a so-called protruding portion in which the brazing material layer protrudes from the end portion of the metal plate within a range of 0.1 to 1.0 times the thickness of the metal plate. Are listed.

  Patent Document 2 discloses a ceramic substrate made of an aluminum nitride sintered body or a silicon nitride sintered body with a brazing material layer containing Ag, Cu, Ti for the purpose of preventing cracks in the ceramic substrate and improving bending strength. The metal plate is joined, and the metal plate is etched to form a circuit pattern, and the protruding portion is formed in the same manner as described above so that the brazing material layer protrudes outward from the side surface of the circuit pattern. It also describes that the side surface of the metal circuit pattern is formed so as to be inclined into a smooth curved surface.

  In Patent Document 3, a mixture containing 40 to 80% by weight of Ag and 20 to 60% by weight of an active metal powder such as Cu, Ti, Zr, and Hf in order to prevent the brazing material from flowing out during the bonding heat treatment. It is described that brazing material made of powder is used, and it is effective to control the ratio of particles having a particle size of 5 μm or less in the active metal powder constituting the brazing material to 5% by weight or less.

  Patent Document 4 discloses a brazing material that has a small thermal shock to the ceramic substrate and can suppress distortion during bonding, and includes 50 to 85% by weight of Ag, 1 to 5% by weight of Ti, and 0. It describes a brazing material for ceramics comprising 1 to 7.5% by weight of In and the balance Cu.

  Patent Document 5 discloses that in a metal / ceramic bonding substrate, the generation of corona discharge can be suppressed by controlling the void diameter of the bonding layer to 0.65 mm or less, and the withstand voltage to the bonding substrate can be 4 kV or more. Is described.

  Patent Document 6 aims to suppress the peeling phenomenon that occurs between the metal circuit board and the brazing material due to the stress generated by the difference in thermal expansion of the metal circuit board of the ceramic substrate. There is a description that a ceramic circuit board that functions stably and reliably can be provided by setting the porosity in the inner region 5 mm from the outer periphery to 5%.

  In Patent Document 7, it is found that by providing a specific gap in the bonding layer at the interface between the metal circuit and the metal heat dissipation plate and the ceramic substrate, the thermal stress caused by the difference in thermal expansion between them can be absorbed, and as a technique therefor The above voids can be easily formed by increasing the amount of the organic binder in the brazing paste to be used by increasing the amount by 3 to 5 times, or by printing in a stripe or grid pattern of a specific size, or both. There is a description that it can be done.

JP-A-10-190176 JP 11-340598 A JP-A-11-29371 JP-A-6-107471 JP-A-2001-48671 Japanese Patent Laid-Open No. 2001-210948 Japanese Patent No. 3260224

  As described above, ceramic circuit boards are required to have sufficient bonding strength and durability against thermal stress and thermal cycle, as compared with conventional ceramic circuit boards. In this regard, the inventions disclosed in Patent Document 1 and Patent Document 2 are designed such that when a metal circuit board is connected to a ceramic substrate via a brazing material layer, the brazing metal has a predetermined length from the end face (side face) of the metal board. It is disclosed that the thermal stress concentration on the joint surface between the ceramic substrate and the metal circuit board end face can be reduced by providing the protruding portion of the material layer, and the end face of the metal circuit board is inclined to a smooth curved surface. This shows that the concentration of thermal stress can be further relaxed. Certainly, the effect of providing the protruding portion can be expected. However, on the other hand, in recent ceramic circuit boards, an improvement in integration density is also required. For example, although the interval between copper plates differs depending on the withstand voltage, an accuracy of about ± 0.1 mm is required at about 1.0 mm or less, Further narrowing is required. In this way, it is difficult to perform the etching process with a narrow interval with accuracy, but in the case of the pattern printing etching method in particular, the effect of the brazing filler metal layer due to the influence of the liquid phase of the brazing filler metal layer at the time of joining and the pressing force. A flow-out phenomenon is likely to occur, and a short circuit failure is likely to occur. Patent Document 1 and Patent Document 2 do not mention any recognition and solution for such problems.

  In this regard, according to Patent Document 3, it is possible to prevent the brazing material from flowing out by controlling the particle size of the active metal powder. Specifically, it is effective to suppress the powder having a particle diameter of 5 μm or less among the added Ti powder to 5% by mass or less, and surplus active metal powder by suppressing the content of relatively fine particles. It is to be able to prevent the outflow. However, according to the study by the present inventors, scale-like irregularities are formed on the surface of the brazing material layer by the heat treatment during joining, and when joining the copper plate for circuit formation, the copper plate, the brazing material layer, and the brazing material are joined. It was found that many voids due to the scale-like irregularities remain at each interface between the material layer and the ceramic substrate. As a result, there is a fatal problem that the bonding strength is weakened, and when a high voltage load is applied to the front and back sides of the circuit board, corona discharge is generated at the locations where the microvoids exist. In this regard, the ceramic circuit board using the brazing material disclosed in Patent Literatures 1 to 4 has a problem that the shape and area ratio (existence ratio) of the microvoids cannot be consciously controlled.

  According to Patent Document 5, in order to eliminate corona discharge under a high voltage, the relationship between the void diameter at the joint interface between the metal plate and the ceramic substrate was investigated, and the corona discharge starting voltage and the starting voltage affected the void size. It has been confirmed that if the void is 0.65 mm or less, the start voltage and the end-to-end voltage can be set to 4 kV or more. However, there is no disclosure of detailed methods for controlling the void diameter, such as the amount of brazing agent, pressure, and temperature range. In addition, there is no mention of the relationship between the durability against a cooling cycle load and the void diameter and void ratio at the joint interface, which are necessary as a power module substrate.

Further, according to Patent Document 6, by setting the porosity of the ceramic circuit board to 5% from the outer periphery of the metal circuit board and the inner area 5 mm from the outer periphery, the stress generated by the difference in thermal expansion of the metal circuit board of the ceramic substrate There is a description that it is possible to suppress the peeling phenomenon that occurs between the metal circuit board and the brazing material. However, although there is a description of the porosity, the relationship between the void diameter at the bonding interface between the metal plate and the ceramic substrate for eliminating the corona discharge under the high voltage described in Patent Document 5, and the bonding to repeated cooling and heating There is no disclosure of the relationship between the interface strength reliability and the void diameter.

  In this regard, according to Patent Document 7, it has been found that by providing a specific gap in the bonding layer at the interface between the metal circuit and the metal heat sink and the ceramic substrate, it is possible to absorb the thermal stress due to the difference in thermal expansion between them, The occupation ratio of voids having a diameter of 1 mm or more existing in the bonding layer is defined as 0.3% to 3% with respect to the entire volume of the bonding layer. Furthermore, as a method for controlling the size and occupation ratio of the voids, the amount of the organic binder in the brazing paste used for bonding is increased by 3 to 5 times, or is printed in a striped or grid pattern having a specific size. In addition, it is explained that the above-mentioned void can be easily formed by both or both. However, increasing the amount of the organic binder in the brazing paste increases the volatile content in the temperature rising process, especially when using brazing agents containing active metals such as Ti, Zr and Hf. In order to exhibit the effect of these active metals, the degree of vacuum during heat treatment is essential. Therefore, in order to maintain the degree of vacuum in the furnace, a constant holding pattern is required for the temperature rising pattern to recover the degree of vacuum. Invite expansion of equipment for setting or exhaust capacity. Furthermore, since the frequency with which the ashed organic binder is deposited on the furnace wall increases, it is necessary to frequently clean the inside of the furnace, which causes a decrease in productivity. Moreover, paste printing in a striped pattern or a lattice pattern leads to a linear void remaining in the bonded layer after bonding, and it is possible to control a void having a diameter of 1 mm or more within a predetermined porosity range. However, it is impossible to uniformly finely disperse microvoids of 1.0 mm or less that exhibit an effect of mitigating crack propagation in the brazing filler metal layer against repeated cooling and heating within a predetermined porosity.

  The present invention has been made in view of such problems, and is intended to prevent cracking of the ceramic substrate and improve the bonding reliability at the metal plate / ceramic substrate interface against repeated cooling and cooling. An object of the present invention is to provide a ceramic circuit board in which the uneven shape on the surface of the brazing material layer and the shape and area ratio (existence ratio) of the microvoids at the bonding interface are controlled without impairing the above.

  In order to solve the above-mentioned problems, the inventors of the present application first paid attention to the composition and distribution of the brazing filler metal powder to be used, and repeated sincerity studies with a focus on controlling the uneven shape of the brazing filler metal layer surface after the heat treatment. . That is, by adding an appropriate amount of Ag powder particles or Cu powder particles having an appropriate particle size and particle size distribution to an alloy powder using an Ag—Cu—In—Ti brazing material as a base material, It is possible to control the uneven surface of the brazing material layer surface generated by the heat treatment before joining, and it can also be controlled by the heat treatment temperature at the time of brazing, and thereby the shape of the microvoids at the metal plate / ceramic substrate interface after brazing and joining. The present inventors have found that it is possible to control the area ratio and that the reliability of bonding at the metal plate / ceramic substrate interface for repeated cooling and cooling is improved in each stage.

That is, the first invention of the present application is a structure in which a metal plate is joined to at least one surface of a ceramic substrate via a brazing material layer, and the brazing material layer includes a joining range of the metal plate and is in a wider range. In the ceramic circuit board to be formed, the brazing material layer is made of Ag: 85 to 55% by mass, In: 5 to 25% by mass, Ti: 0.2 to 2.0% by mass, the remainder Cu and inevitable impurities. It consists of an Ag-Cu-In-Ti brazing material in which 5 to 30% by mass of Ag powder particles or Cu powder particles having an average particle size of 1 to 15 µm is further added to an alloy powder having an average particle size of 15 to 40 µm. It has a concave-convex surface made of a Cu-Ti phase and a maximum length of less than 1.0 mm and a convex portion consisting mainly of an Ag-In phase and a Cu-In phase, and has a void ratio of 0.5% or more and 10 % Or less, maximum diameter of void The ceramic circuit board is 1.0 mm or less.

According to the second invention of the present application, between the ceramic substrate and the metal plate, Ag: 85 to 55% by mass, In: 5 to 25% by mass, Ti: 0.2 to 2.0% by mass, the balance Cu and inevitable impurities. A circuit pattern using an Ag-Cu-In-Ti brazing material in which 5-30 mass% of Ag powder particles or Cu powder particles having an average particle diameter of 1-15 μm is further added to the alloy powder having an average particle diameter of 15-40 μm A brazing filler metal layer is formed in a wider range including the bonding range of, and the ceramic substrate and the metal plate are brazed by heat treatment, and the brazing filler metal layer is mainly composed of a Cu-Ti phase and has a maximum length. Is provided with a concave-convex surface composed of a concave portion of less than 1.0 mm and a convex portion composed mainly of an Ag-In phase and a Cu-In phase, and a void having a maximum diameter of 1.0 mm or less is 0.5% to 10%. And containing the metal plate. This is a method for manufacturing a ceramic circuit board in which the circuit pattern is formed by ching.
In the third invention of the present application, Ag: 85-55 mass%, In: 5-25 mass%, Ti: 0.2-2.0 mass between the ceramic substrate and a metal plate previously formed in a predetermined circuit pattern. Ag-Cu-In-Ti in which 5 to 30% by mass of Ag powder particles or Cu powder particles having an average particle size of 1 to 15 μm is further added to an alloy powder having an average particle size of 15 to 40 μm consisting of%, the balance Cu and inevitable impurities A brazing filler metal layer is used to form a brazing filler metal layer in a wider range including the bonding range of the circuit pattern, and the ceramic substrate and the metal plate are brazed by heat treatment, and the brazing filler metal layer is mainly composed of Cu. A concave / convex surface made of a Ti phase and having a maximum length of less than 1.0 mm and a convex portion mainly composed of an Ag-In phase and a Cu-In phase is provided, and a void having a maximum diameter of 1.0 mm or less is provided. 0.5% or more 10 % Is a method for producing a ceramic circuit board.

  In the present invention, the brazing filler metal layer has an average particle diameter of 15 to 40 μm composed of Ag: 85 to 55% by mass, In: 5 to 25% by mass, Ti: 0.2 to 2.0% by mass, the balance Cu and inevitable impurities. The alloy powder is preferably made of a brazing material obtained by adding 5 to 30% by mass of Ag powder particles or Cu powder particles having an average particle diameter of 1 to 15 μm.

  Here, the Ag powder particles or Cu powder particles to be added later are those having an average particle diameter of 1 to 15 μm added in the range of 5 to 30% by mass, and more preferably 3 to 5 μm Ag powder or Cu powder. It is adding -20 mass%. When the average particle size is less than 1 μm, the particle size difference between the alloy powder and the Ag powder or Cu powder becomes large, the dispersion state of the Ag powder or Cu powder in the brazing material paste becomes non-uniform, and the printed pattern unevenness after screen printing Inconvenience occurs. If the thickness exceeds 15 μm, the difference in melting point between the Ag powder or Cu powder and the alloy powder becomes remarkable, which is not preferable because of nonuniform melting. If the amount is less than 5% by mass, there is no effect of reducing the scale-like irregularities on the surface of the brazing material layer. If the amount exceeds 30% by mass, the effect of reducing the scale-like irregularities on the surface of the brazing material layer can be exhibited, Is added, the Ag component diffusing into the metal plate (Cu plate) increases, and the spreading behavior of the brazing material flowing out along the surface of the metal plate cannot be suppressed. Further, excessive addition of Ag component is not preferable because it causes an increase in melting temperature. On the other hand, when Cu powder is added, if it exceeds 30% by mass, the effect of alleviating the scaly irregularities on the surface of the brazing material layer can be exhibited, but in this case as well, the melting point difference from the alloy powder increases. , Which is not preferable because of non-uniform melting.

  The average particle diameter of the Ag—Cu—In—Ti alloy powder, which is the base material of the brazing material, is 15 to 40 μm, and the 1 to 15 μm Ag powder particles are filled so as to fill the gaps between these alloy powder particles. Alternatively, the effect is enhanced by filling the Cu powder particles. Further, it is desirable to adjust the particle size distribution by setting the average particle diameter d50 of the powder particles to 1 to 15 μm, d10 to 0.2 to 0.5 μm, and d90 to 10 to 25 μm. As shown in FIG. 1, the alloy powder alone has many voids between the powders (see FIG. 1 (B)), and by adding Ag powder or Cu powder of the above specifications to this, the filler density of the brazing material is increased. In particular, by specifying the particle size distribution of the Ag powder or Cu powder to be added as described above, the closest packing of the brazing material can be achieved. Due to these effects, it is possible to control the coating amount during paste printing and promote the reactivity between particles during the brazing process. All of these are necessary in terms of enhancing the bonding strength between the metal plate and the ceramic substrate, and thus improving the bonding reliability against thermal shock.

  Here, the effect of the void will be described. The uniformly dispersed voids can improve the fatigue life against repeated cooling and heating without deteriorating the interface strength and without causing corona discharge due to voltage concentration. In the ceramic circuit board, after brazing, stress concentration occurs at the interface between the end part of the metal circuit and the ceramic substrate due to a difference in thermal expansion between the metal plate and the ceramic substrate. Along with repeated cooling and heating, microcracks are generated on the ceramic side of this portion, and further, the crack progresses through the substrate as the number of cycles increases, and eventually breaks (metal circuit board) peeling. In the present invention, by uniformly dispersing microvoids maintaining an appropriate shape and area occupancy in the bonding interface, it is possible to suppress the progress of cracks by relaxing the plastic strain received by the brazing material layer, As a result, it has been found that the reliability of ceramic circuit boards can be improved. In other words, if the void ratio exceeds 10%, the bonding strength at the metal plate / ceramic substrate interface decreases, the bonding reliability against repeated cooling and heating deteriorates significantly, and when a high voltage load is applied between the circuit boards. In addition, there is a fatal problem that a corona discharge is generated at a location where the microvoid exists. If it is less than 0.5%, the bonding strength after the brazing treatment can be sufficiently ensured, but the fatigue life of the bonding interface in the repeated heating and cooling is reduced. Further, if the microvoid exceeds 1.0 mm, it acts as a starting point of fracture and the bonding strength is lowered, so that there is a problem that the bonding reliability against repetitive cooling is remarkably deteriorated. Furthermore, there is a problem that the frequency of corona discharge due to the increase in the size of the microvoids becomes significant. Furthermore, the void shape is not a single sphere, but is characterized by a shape having many curvatures. Although this shape has a form like a sugar-compound-like shape, since there are many curvature parts, the effect which relieves the plastic distortion which a brazing material layer receives is remarkable. This makes it possible to suppress the development of cracks that can occur due to repeated cooling and heating.

  In the present invention, the range of the heat treatment temperature for brazing the ceramic substrate and the metal plate is important for controlling the area ratio and shape of the microvoids, and it is desirable to carry out at 730 to 800 ° C. When the heat treatment temperature is less than 730 ° C., the brazing filler metal component cannot be sufficiently dissolved, the void ratio at the joining interface exceeds 10% and the void diameter exceeds 1.0 mm, and the above-described problems occur. On the other hand, when the temperature exceeds 800 ° C., the void ratio is less than 0.5% and the initial bonding strength is ensured, but there is a problem that the fatigue life of the bonding interface is reduced due to repeated cooling and heating. In addition, after the brazing process, there is a problem that the brazing material component flows out to the surface portion of the metal circuit board. Therefore, by performing the brazing heat treatment temperature at 730 to 800 ° C., generation of voids can be reduced and microvoids can be dispersed minutely.

  According to the present invention, unevenness on the surface of the brazing material layer can be suppressed, and the shape and area ratio (existence ratio) of the microvoids can be controlled. As a result, the bonding strength after the brazing treatment is ensured, and further, the bonding reliability against repeated cooling and heating is improved. In addition, when used as a ceramic substrate for a semiconductor element, cracks are less likely to occur in the substrate due to repeated cooling and heating cycles accompanying the operation of the semiconductor element, and the thermal shock resistance and thermal cycle performance can be significantly improved.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited by these Examples.
First, the brazing material will be described. The brazing material used in the ceramic circuit board of the present invention is a quaternary system in which the base alloy is Ag-Cu-In-Ti, Ag is 85 to 55% by mass, In is 5 to 25% by mass, It is composed of 0.2 to 2.0% by mass of Ti, 35 to 20% by mass of Cu and inevitable impurities. The alloy powder is produced by gas atomization so that the average particle diameter d50 value is 50 μm, and the powder of 50 μm or more is cut by sieving, and the powder under 50 μm is used. Here, the average particle of the alloy powder is used. The diameter d50 is 28 μm. The alloy powder can also be produced by a low-cost water atomization method, but in order to prevent oxidation of Ti acting as an active metal, the oxygen content in the alloy powder is 0.5% by mass or less in this case. It is important to control.

The composition ratio of Ag and Cu, excluding In and Ti in the mixed powder (alloy powder and added Ag powder), is 100% by mass of Ag and Cu (100% for Ag and Cu). When used, Ag is preferably 95 to 75% by mass and Cu is preferably 5 to 25% by mass. In the range of this composition ratio, there is an effect in suppressing the uneven shape of the brazing filler metal surface portion after heating and cooling, and moreover, Ag-- than the eutectic composition (72% Ag-28% Cu) in the Ag-Cu phase diagram. In the rich solid-liquid coexistence composition range, by arbitrarily selecting the processing temperature, it is possible to adjust the amount of melt at the time of the joining process, and thereby it is possible to suppress the flow-out phenomenon of the brazing material. . The alloy powder made of Ag—Cu—In—Ti used here preferably has an average particle size of 45 μm or less, and 10 to 30 μm in order to suppress pattern printing accuracy when screen printing is performed and flow out to the copper plate to be joined. A thing of a grade is more suitable.

  As the active metal, an element belonging to Group IVa of the periodic table can be used, and generally titanium, zirconium, and hafnium are used. Among these, in particular, titanium is highly reactive with an aluminum nitride substrate or a silicon nitride substrate, and can have a very high bonding strength. Therefore, titanium (Ti) is used in the present invention. Furthermore, if a hydride of titanium, that is, titanium hydride is used, oxidation due to the influence of oxygen during the bonding process is unlikely to occur, and a more preferable bonding state can be obtained. This is because titanium hydride releases hydrogen only after heat treatment in the bonding process to become active metallic titanium, which reacts with an aluminum nitride substrate or a silicon nitride substrate. Furthermore, when these active metal components are preliminarily contained in the alloy powder, the ratio of Ag-Cu-In-Ti becomes uniform, and the local melting of the brazing filler metal powder printed on the substrate or metal plate at the time of heating and heating. This is desirable because unevenness can be suppressed and Ti that diffuses in the brazing filler metal melt can be easily controlled. The addition amount of the active metal powder with respect to 100% by mass of the total amount of Ag, Cu and In is 0 in order to keep the bonding strength between the aluminum nitride substrate / silicon nitride substrate-brazing material-copper plate by the active metal powder sufficiently. .2 to 2.0% by mass is preferable. More preferably, it is 0.6-1.5 mass%.

  In the present invention, 5 to 30% by mass of Ag powder particles or Cu powder particles having an average particle diameter of 1 to 15 μm is further added to the base alloy powder. The reasons for these prescriptions are as described above. Further, it is desirable that the Ag powder particles or the Cu powder particles have a uniform particle size distribution, and in order to set the average particle diameter d50 to 1 to 15 μm, d10 is set to 0.2 to It is suitable that 0.5 μm and d90 be 10 to 25 μm. Here, the particle size distribution of the Ag powder is defined as follows. When d10 is less than 0.2 μm, the reactivity of the Ag powder becomes high, and it becomes difficult to control the flow-out phenomenon of the brazing material. This is because there is a problem that the flow of the Ag—In component to the copper plate surface frequently occurs. On the other hand, if d90 is more than 25 μm, the gap of the Ag—Cu—In—Ti alloy after screen printing cannot be filled with Ag powder, which greatly contributes to void formation after brazing. It becomes difficult to control the material printing amount. Furthermore, since Ag powder itself has a higher melting point than alloy powder, coarse particles are particularly inferior in reactivity, and some of the Ag powder particles remain undissolved. In this case, adhesion strength after brazing treatment is increased. Cause a decline. From the above, the particle size distribution of the Ag powder particles to be added is desirably such that d10 is 0.2 to 0.5 [mu] m and d90 is 10 to 25 [mu] m.

  In addition, when Cu powder is added later, the particle size distribution of Cu powder is defined as follows. When d10 is less than 0.2 μm, the reactivity of Cu powder becomes high, and an Ag—Cu melt is locally generated. This makes it difficult to control the flow-out phenomenon of the brazing material. For this reason, it is because the circuit part collapses and the malfunction that the flow of the Ag-In component to the copper plate surface frequently occurs. On the other hand, if d90 is more than 25 μm, the gap of the Ag—Cu—In—Ti alloy after screen printing cannot be filled with Cu powder, and it will greatly contribute to void formation after brazing. It becomes difficult to control the material printing amount. Furthermore, since the Cu powder itself has a higher melting point than the alloy powder, especially coarse particles are inferior in reactivity, and some of the Cu powder particles remain undissolved. In this case, the adhesion strength after brazing treatment Cause a decline. In view of the above, it is desirable that the particle size distribution of the Cu powder particles to be added is d10 of 0.2 to 0.5 μm and d90 of 10 to 25 μm.

  d10 is 0.2 to 0.5 μm, d90 is 10 to 25 μm, and FIG. 1 (A) shows the form of the brazing material particles after adding 15% of Ag powder particles having an average particle diameter of 5 μm. B) shows the form of the brazing filler metal particles with no added Ag powder. In both figures, the left side is a 100 times SEM photograph, and the right side is a 1000 times SEM photograph. As can be seen by comparing the two, in (B), a gap (paste organic component) that appears black between the base alloy particles having a size of 30 to 50 μm is seen throughout, but in (A), the addition of Ag powder Thus, the gap portion is filled and the filling density of the brazing filler metal powder is increased. This is considered to be effective in alleviating unevenness on the surface of the brazing filler metal layer described later, improving the linearity of the outer edge, and the like. In addition, the same form is confirmed also when adding Cu powder particle.

The particle size of Ag particles or Cu particles and the weight ratio of Ag powder or Cu powder in the mixed powder can be easily measured by using a liquid phase precipitation method. In the liquid phase precipitation method, when the powder form is irregular, the major axis and the minor axis cannot be distinguished and the average value is regarded as the particle size. In this specification, this average value is regarded as the particle size. No distinction is made between the major axis and the minor axis regarding the particle diameter. The particle size in this patent refers to the primary particle size, not the aggregated particle size. This can be easily measured by dispersing the powder in a solvent with ultrasonic waves.
Further, as shown in FIG. 1, the ratio of the alloy powder and the added Ag powder or Cu powder per unit area in the SEM image observed at an observation magnification of 1000 after printing the brazing paste on the substrate or copper plate. Can be evaluated by area occupancy. In addition, in order to discriminate between Ag powder or Cu powder having the same particle size and Ag—Cu—In—Ti alloy powder, when Ag powder is added after using an energy dispersive X-ray analyzer (EDX) The presence or absence of the Cu component can be determined by evaluating the presence or absence of the Ag component by surface analysis when the Cu component is added later.

  In addition, as a method for mixing Ag powder or Cu powder and alloy powder constituting the brazing material raw material powder, each component is mixed in a powder state using a stirrer such as a ball mill or an attritor, or an organic solvent or binder is added. It can be blended and mixed using a ball mill, a planetary mixer, a three-roll mill or the like to form a paste. In general, since it is difficult to form a pattern on a substrate in the form of metal powder, it is desirable to use it by kneading it into a paste. When making the paste, methyl cellosolve, ethyl cellosolve, isophorone, toluene, ethyl acetate, terpineol, diethylene glycol monobutyl ether, texanol, etc. are used as the organic solvent, and the binder is polyisobutyl methacrylate, ethyl cellulose, High molecular compounds such as methyl cellulose and acrylic resin are used.

  In order to screen-print a good brazing material pattern, the viscosity of the paste is preferably controlled to 20 to 200 Pa · s. By blending the organic solvent in the paste in the range of 5 to 15% by mass and the binder in the range of 1 to 5% by mass in the total paste, a paste having excellent printability can be obtained. In addition, blending the binder within the above range is preferable because the binder can be quickly removed in the degreasing step after printing. Moreover, when it is set as a paste, in order to improve the dispersibility of each component, a dispersing agent can also be added. The printed film thickness of the brazing material layer is preferably 20 to 80 μm in order to develop good adhesive strength.

Further, the metal plate used for bonding to the aluminum nitride or silicon nitride substrate is not particularly limited as long as the brazing material can be bonded and the melting point of the metal plate is higher than the melting point of the brazing material. In general, use copper, copper alloy, aluminum, aluminum alloy, silver, silver alloy, nickel, nickel alloy, nickel-plated molybdenum, nickel-plated tungsten, nickel-plated iron alloy, etc. Is possible.
Among these, copper is most preferably used as a metal member from the viewpoints of electrical resistance and stretchability, high thermal conductivity (low thermal resistance), and low migration.
In addition, the use of aluminum as a metal member has electrical resistance and high thermal conductivity (low thermal resistance), which is inferior to copper, but has the mounting reliability against the thermal cycle by utilizing the plastic deformability of aluminum. Is preferable.
In addition, it is also preferable to use silver if importance is attached to electrical resistance. When considering reliability after bonding rather than electrical characteristics, if molybdenum or tungsten is used, the thermal expansion coefficient of the metal is aluminum nitride. Since it is close to silicon nitride, the thermal stress during bonding can be reduced, which is preferable.

  Next, FIG. 2 shows a configuration example of the ceramic circuit board. In FIG. 2, reference numeral 7 denotes a ceramic substrate (hereinafter referred to as a silicon nitride substrate) made of a silicon nitride sintered body having a thickness of 0.3 to 0.6 mm, a thermal conductivity of 70 W / m · K or more, and a bending strength of 600 MPa or more. ). Copper plates 3, 4, 5 are joined to one surface (main surface) of the silicon nitride substrate 7 via the brazing material layers 8, 9, 10 made of the brazing material described above. On the other hand, a flat copper plate 11 for heat dissipation is joined to the other surface (lower surface) of the silicon nitride substrate 7 via a brazing material layer 12. The brazing filler metal layers 8, 9, 10, and 12 have a protruding portion 20 that protrudes from the outer peripheral end surfaces of the copper plates 3, 4, 5 and the copper plate 11 by a predetermined amount. The protruding length L of the protruding portion is at least 0.2 mm or more, preferably 0.3 to 1.2 mm, so that heat concentrated on the end surfaces of the silicon nitride substrate 7, the copper plates 3, 4, 5 and the copper plate 11 is concentrated. Stress can be relaxed. In addition, inclined surfaces 3 a, 4 a, 5 a, and 11 a are formed on the entire peripheries of the end surfaces of the copper plates 3, 4, 5 and the copper plate 11. The inclination angle of the inclined surface may be set to 30 ° to 60 ° and formed into a curved surface. The inclined surfaces 3a, 4a, 5a, and 11a may be formed by an etching process after joining the copper plates, or may be formed in advance by pressing a copper plate.

Then, this invention is demonstrated with the manufacturing method of a ceramic circuit board.
Silicon nitride powder having an average particle size of 0.2 to 3.0 mm: mixed powder was prepared by adding a sintering aid of MgO: 3% by mass and Y ₂ O ₃ : 1% by mass to 96% by mass. . Next, the mixed powder and silicon nitride balls as grinding media were put into a ball mill resin pot filled with an ethanol / butanol solution to which 2% by mass of an amine-based dispersant was added, and wet mixed for 48 hours. Next, 12.5% by weight of a polyvinyl organic binder and 4.2% by weight of a plasticizer (dimethyl phthalate) are added to 83.3% by weight of the mixed powder in the pot, and then wet for 48 hours. Mixing was performed to obtain a slurry for forming a sheet. The molding slurry was defoamed and the viscosity was adjusted by solvent removal, and then a green sheet was molded by the doctor blade method. Next, the formed green sheet is heated in air at 400 to 600 ° C. for 2 to 5 hours to sufficiently degrease (remove) the organic binder component, and then the degreased body is in a nitrogen atmosphere of 0.9 MPa (9 atm). In the case of baking at 1900 ° C. for 5 hours and warping of 50 μm / inch or more occurred, the heat treatment was performed again at 1800 ° C. for 5 hours in the same nitrogen atmosphere, and then cooled to room temperature. The surface properties of the obtained silicon nitride sintered body sheet were adjusted by sandblasting to obtain a silicon nitride substrate having a length of 50 mm × width of 30 mm × thickness of 0.63 mm.

Next, as shown in FIG. 3, the brazing material paste described above is screen-printed on the main surface of the silicon nitride substrate 7 in a predetermined mesh so that its thickness becomes 30 to 50 μm along the circuit pattern shape designed in advance. Is selected and applied to form the brazing material layers 8, 9, and 10. At this time, the range in which the brazing material is applied to the main surface of the silicon nitride substrate 7 protrudes to the outside by the protruding portion length L from the range in which the copper plates 3, 4, 5 are joined. In addition, it is important to apply the paste uniformly. As an application method, any method such as a screen printing method, a metal mask printing method, a roll coating method, spraying, and transfer can be considered. In general, the screen printing method is the simplest and easy to adopt. If there are coarse particles in the paste, the screen may be clogged and the desired pattern may not be printed. Therefore, the coarse powder is not included. When printing a finer wiring pattern, a fine mesh screen must be used, and clogging is more likely to occur. For example, when using a # 300 mesh screen, the maximum particle size of the powder It is preferable to control the diameter to 50 μm or less. In the case of the multistage etching method, the brazing material layer is applied to the main surface of the silicon nitride substrate regardless of the pattern.

After applying the paste, the binder component is generally removed by degreasing. The processing conditions such as heating temperature and time during degreasing vary depending on the binder component. However, the active metal is changed by processing in a non-oxidizing atmosphere such as nitrogen or argon or in vacuum. Suitable without being oxidized. Even in an oxidizing atmosphere, if the active metal is not oxidized more than necessary by limiting the amount of oxygen, a suitable bonding state can be obtained even if degreasing is performed in a trace oxygen concentration or in a wet atmosphere. Here, the wet atmosphere is an atmosphere formed by passing a non-oxidizing atmosphere gas through water or hot water and then supplying it to the processing chamber. However, in order to exhibit the effect of the active metal, it is important that the amount of oxygen in the brazing filler metal powder is 0.5% by mass or less.
In addition, by selecting a binder for the brazing material paste, the degreasing and brazing processes can be performed simultaneously by holding at a predetermined temperature in the temperature rising process of the brazing process without providing a separate degreasing process. In this case, binder selection is important.For example, when α-tenepineol is used as a solvent and polyisobutyl methacrylate, diethylene glycol monobutyl ether is used, even in heat treatment under high vacuum, ashed carbon does not remain, Bond strength is obtained. In the present invention, simultaneous processing of degreasing and brazing is performed.

When the metal plate is formed by a multistage etching method or a pattern printing etching method, a copper plate similar to a ceramic substrate is prepared.
On the other hand, in the case of the direct mounting method, a copper plate having a circuit pattern similar to the pattern of the brazing material layers 8, 9, and 10 as shown in FIG. 4 is prepared. The circuit patterns 3, 4 and 5 of the copper plate are integrally formed by pressing through some bridging portions 6a to 6d. Further, as a method for forming a circuit pattern in advance as shown in FIG. 4, an etching method, electric discharge machining, or the like may be used in addition to press working. The size of the copper plates 3, 4, and 5 is slightly smaller so that the protruding portions by the brazing material layers 8, 9, and 10 are formed, and the end portions have inclined surfaces 3 a to 5 a that narrow upward. .

Next, the members are overlapped so that the brazing material layer is disposed between the copper plate and the silicon nitride substrate. That is, on the main surface of the silicon nitride substrate 7 coated with the brazing material layer 8, 9, 10, so that the end faces brazing material layer 8, 9, 10 from the entire circumference of the copper plate 3, 4 and 5 protrude more distance L While aligning, a rectangular circuit copper plate is placed so as to cover the brazing material layer. On the other surface (lower surface) of one silicon nitride substrate 7, a heat radiating copper plate 11 is placed so that the brazing material layer protrudes, and each is held in a pressurized state.

Next, the silicon nitride substrate 7 on which the circuit copper plate and the heat radiating copper plate are mounted is heat-treated for a predetermined temperature and time, and then cooled, whereby the circuit board and the heat radiating plate are placed on the silicon nitride substrate 7 as shown in FIG. The copper plate is firmly joined via the brazing material layer.
In the present invention, the range of the heat treatment temperature for brazing the ceramic substrate and the metal plate is important for controlling the area ratio and shape of the microvoids, and it is desirable to carry out at 730 to 800 ° C. When the heat treatment temperature is less than 730 ° C., the brazing filler metal component cannot be sufficiently dissolved, the void rate at the bonding interface exceeds 10% and the maximum void diameter exceeds 1.0 mm, and the bonding strength is deteriorated. Corona discharge Problems such as the occurrence of. On the other hand, when the temperature exceeds 800 ° C., the void ratio is less than 0.5% and the initial bonding strength is ensured, but there is a problem that the fatigue life of the bonding interface is reduced due to repeated cooling and heating. In addition, after the brazing process, there is a problem that the brazing material component flows out to the surface portion of the metal circuit board. Therefore, by performing the brazing heat treatment temperature at 730 to 800 ° C., generation of voids can be reduced and microvoids can be dispersed minutely.
In addition, with respect to factors other than the control of microvoids, the brazing material sufficiently wets the silicon nitride substrate and the copper plate, the circuit pattern is not crushed, and the brazing material located at the end of the circuit forms a protruding portion. In order to prevent a decrease in thermal shock resistance due to residual stress due to a difference in thermal expansion, it is important to set the bonding temperature within the above range. In addition, when the atmosphere is processed in a vacuum, the active metal powder, the copper powder, and the copper plate can be obtained in a good bonding state without being oxidized. In particular, the bonding should be performed at a vacuum degree of 10 ⁻² Pa or less. Is desirable. Furthermore, by applying an appropriate load at the time of joining, the copper plate and the brazing material and the silicon nitride substrate and the brazing material can be more reliably brought into contact with each other, and a good joining state can be obtained. As the weight, a load of 20 to 150 g / cm ² can be adopted.

  Now, the influence of the brazing material layer by the heat treatment was examined. The photograph which observed the brazing filler metal layer after heat processing is shown in FIG. FIG. 6 (A) shows the surface property of the brazing filler metal layer using the brazing filler metal according to the present invention and adding 15% Ag powder particles having an average particle diameter of 5 μm. FIG. 6B shows the surface property of a brazing material layer which is a conventional example and is the same brazing material but not added with Ag powder. In both figures, the left side is a 1.7 × magnification microscopic photograph, and the right side is a 13.5 × magnification. Thus, in (B) without addition of Ag particles, scaly irregularities are generated on the entire surface, and the maximum length of the concaves reaches 1.2 to 2.5 mm. The brazing material layer was subjected to a peel strength test in order to evaluate the bonding strength between the metal plate and the ceramic substrate. In the peel strength test, one end of the copper plate protrudes to the outside of the substrate by about 5 mm, and the bonding area is 10 mm × 10 mm, and the unit per length unit required to pull it up 90 degrees. The power of was evaluated. When an adhesion strength test between the metal plate and the ceramic substrate was performed by this method, the peel strength was 10 (kN / m) or less, and it was confirmed that the adhesion strength was weak.

On the other hand, the scale-like irregularities are eliminated from the brazing material layer of the present invention in FIG. As a result of component analysis using a wavelength dispersive X-ray analyzer (WDX) for the scale-like uneven portion in FIG. 6, the main component is the Cu—Ti phase in the concave portion, and the convex portion is the Ag—In phase and It has been found that the frequency of formation of the recesses increases as the amount of Ti added increases with the Cu—In phase. That is, in the cooling process, a Cu—Ti phase having a high melting point first precipitates and shrinks as the temperature decreases. Subsequently, an Ag—In phase and a Cu—In phase are precipitated. Since these contain low melting point In, the liquid phase is maintained up to a lower temperature region than the Cu—Ti phase. For this reason, a shrinkage difference occurs between the Ag—In phase, the Cu—In phase, and the Cu—Ti phase, resulting in an uneven shape. Therefore, in the present invention, by adding Ag powder to the Ag-Cu-In-Ti alloy powder, an Ag-In phase having a relatively high melting point is precipitated, and the shrinkage difference from the Cu-Ti phase that has been precipitated first is suppressed. It is thought that there is an effect in doing. On the other hand, when Cu powder is added, contrary to Ag powder addition, a large amount of Cu—In phase having a relatively high melting point is precipitated, and the effect of suppressing the shrinkage difference from the previously precipitated Cu—Ti phase is effective. It is what I thought there was.
The formation of the Cu—Ti phase is greatly related to the Ti amount in the alloy powder and the Ag / Cu ratio when the alloy powder and the Ag powder are mixed. The larger the Ti amount, the more the Ag / Cu ratio. The lower the value, the higher the value, and the higher the generation frequency of the scale-like irregularities. Therefore, in order to suppress this scale-like uneven part, it is important to increase the Ag / Cu ratio by adding Ag powder and to control the Ti amount to 0.2 to 2.0% by mass. I understood. On the other hand, when Cu powder is added, the Ag / Cu ratio is lowered and the formation of the Cu—Ti phase is promoted, but by defining the Ti amount to 0.2 to 2.0 mass%. In addition, it is possible to suppress the formation of scale-like irregularities by keeping the generation of the Cu—Ti phase within a certain range and controlling the generation ratio of the Cu—In phase and the Cu—Ti phase to be generated instead.

As for the adhesion strength in FIG. 6A as well, it was confirmed that the peel strength was over 20 (kN / m) and the adhesion strength was improved. From these facts, it was found that the scale-like irregularities are strongly involved in the adhesion strength, and quantitatively, if the maximum length of the recess is less than 1.0 mm, sufficient adhesion strength can be secured. For example, when the thickness is less than 5 μm, it can be achieved by reducing the amount of In in the alloy powder. In this case, however, the liquid phase is instantaneously cooled in the cooling process at the Ag-Cu alloy eutectic temperature of 780 ° C. or lower. Solidification occurs, local nucleation occurs, and non-uniform solidification proceeds. In this process, local differences also occur in the shrinkage behavior, and shrinkage cavities tend to occur between the brazing material and the copper plate, leaving large voids having a maximum diameter exceeding 1.0 mm. This large void is a fatal defect for a circuit board, and a leak current is generated when a high voltage load is applied, leading to a decrease in insulation. Therefore, in order to ensure sufficient adhesion strength, maintain the dielectric strength of the circuit board, and maintain bonding reliability against repeated heating and cooling, the void ratio in the bonding layer is 0.5% to 5% and the maximum diameter is It is necessary to finely disperse the voids controlled to 1.0 mm or less. For this purpose, it is preferable to control the maximum length of the recesses to be less than 1.0 mm in terms of scale.
The following examples show the correlation between the average particle diameter of Ag particles or Cu particles and the roughness of the uneven surface, the maximum diameter of microvoids, the void ratio, and the adhesion strength depending on the addition amount.

  Finally, an etching process is performed. As the etching resist, there are an ink type and a sheet type in which a thermosetting type and a UV curable type can be used. The former application method is a screen printing method, and circuit formation can be designed in various ways according to the shape of the printing mask. In the latter, a desired resist pattern is formed by coating the surface of a metal plate and subsequently exposing and developing. Then, the sample which joined the copper plate to the upper and lower surfaces is etched. The etching apparatus is transported by a belt conveyor and has a specification in which an etching solution is sprayed from above and below. In addition, a ferric chloride (FeCl3) solution (46.5Be) was used as the copper plate etching solution, and the solution temperature was set to 50 ° C. The etching processing time depends on the thickness of the copper plate on the circuit side. For example, it takes about 15 minutes for a thickness of 0.3 mm and about 60 minutes for a thickness of 1.0 mm.

Hereinafter, the present invention will be specifically described with reference to examples and comparative examples.
(Example)
An alloy powder composed of Ag: 58.8% by mass, Cu: 27.5% by mass, In: 12.5% by mass, Ti: 1.2% by mass, and unavoidable impurities, Ag particle powder and Cu shown in Table 1 below. After adding powder particles and blending 6% by mass of α-tenenepineol, 5% by mass of diethylene glycol monobutyl ether, 5% by mass of polyisobutyl methacrylate, and 0.1% by mass of a dispersant in the proportion of the total paste, a planetary mixer is used. And a paste of 120 Pa · s was prepared. The average particle size of the base alloy powder used was 30 μm.
This paste is screen-printed on a substrate made of a silicon nitride sintered body having dimensions of 50 mm in length, 30 mm in width, and 0.63 mm in thickness so that the protruding portion L becomes 0.3 mm in a pattern as shown in FIG. 3 and a thickness of 25 μm. It was applied to. Here, the amount of brazing material protruding is 0.25 mm or more as a design value, but this is a value that maximizes the effect of relaxing stress concentration on the ceramic substrate near the edge of the metal circuit board. Stress concentration can be reduced to about 60%.
Thereafter, the substrate is dried in the atmosphere at 120 ° C. for 30 minutes, and subsequently superposed on the copper plate for circuit—silicon nitride substrate—copper plate for heat dissipation, and then in vacuum (10 ⁻² Pa) while applying a load of 70 g / cm ^2. The copper plate and the silicon nitride substrate were joined by performing a heat treatment at 760 ° C. for 10 minutes. The thickness of the copper plate used is the warpage of the circuit board after etching, the module mounting shape after solder reflow, and the circuit board and heat dissipation board (for example, Cu, Cu-W, Mo, Cu-Cu0, Al- In consideration of prevention of defective solder defects of SiC or the like, the circuit side is 0.3 mmt and the heat radiation side is 0.2 mmt. Thereafter, in order to obtain the pattern of FIG. 4, a resist pattern was printed in consideration of etching tolerances, and unnecessary portions of the copper member were removed to prepare each ceramic circuit board.

The roughness (the maximum length of the recesses), the maximum void diameter, and the void ratio of each ceramic circuit board were evaluated with an ultrasonic microscope. The results are shown in Table 2. Here, the roughness of the concavo-convex surface was evaluated by using the brazing filler metal powder shown in Table 1 and Table 2 on a silicon nitride substrate and evaluating the length of the concave portion with respect to the concavo-convex surface of the brazing filler metal layer portion after the heat treatment. In addition, the ultrasonic exploration imaging device used is Mi-Scope manufactured by Hitachi Construction Machinery Co., Ltd. Although the evaluation conditions differ depending on the type and thickness of the metal circuit board and the type and thickness of the ceramic substrate, in the present invention, the metal circuit board is made of Cu with a circuit board thickness of 0.3 mm, a heat sink thickness of 0.2 mm, The ceramic substrate is silicon nitride and has a thickness of 0.6 mm. The probe used was 50 MHz.
The void ratio of the bonding interface was binarized by setting the threshold value for a black and white 256-gradation evaluation image to 92, and the ratio of the white part to the evaluation area (black part) was evaluated by a reflection method. As for the void diameter, the maximum length was evaluated for the total number of microvoids existing in the evaluation area. 7A and 7B show an ultrasonic exploration image and a binarized image of the bonding interface in the circuit board of the present invention. The void fraction in this example is 0.8% and 5.0% for (A) and (B), respectively. FIGS. 7C and 7D show comparative examples. The void ratios in these examples were 0.4% and 18.0%, respectively. Further, the microvoid shape of the present invention is not a single spherical shape as described above, but is characterized by a shape having many curvatures.
Further, the bonded copper plate was pulled in a 90 ° direction with respect to the silicon nitride substrate, and the peel strength was measured to obtain the adhesion strength.
In addition, the evaluation of the thermal cycle resistance at the bonding interface of the circuit board is as follows: 1 temperature increase / decrease cycle with cooling at −40 ° C. for 20 minutes, holding at room temperature for 10 minutes and heating at 125 ° C. for 20 minutes. This was repeatedly applied, and the number of cycles until the void ratio at the bonding interface became 1.5 times or more of the initial value was measured.

(Comparative example)
The production of the brazing material paste, the printing on the silicon nitride substrate, the brazing conditions, etc. were performed in the same manner as in the above example, and the alloy powder and Ag powder or Cu powder shown in Sample Nos. 51 to 61 and 71 to 81 in Table 1 were used. Added. About these, the item similar to the above was measured.

The following knowledge was obtained from Examples Nos. 1 to 24 and 31 to 48 in Table 1.
No. Nos. 1 to 24 are cases where the Ag powder was added to the alloy powder. 31-48 are the results when Cu powder is added to the alloy powder.
Ag: 85 to 55% by mass, In: 5 to 25% by mass, Ti: 0.2 to 2.0% by mass, the average particle size of 1 to 40 μm composed of the balance Cu and inevitable impurities, and the average particle size of 1 When the peel strength at the interface between the metal circuit board and the silicon nitride substrate was measured for a circuit board using a brazing material mixed powder to which 5 to 30 mass% of Ag powder particles and Cu powder particles of -15 μm were added, both were 20 ( It was confirmed that it has a high bonding strength of kN / m) or more. Moreover, the void ratio at the Cu / Si3N4 interface of the ceramic substrate could be controlled to 0.5% to 10% and the void diameter could be controlled to less than 0.5 mm by relaxing the unevenness on the surface of the brazing material layer. The reliability evaluation of the circuit board manufactured under these conditions is carried out by performing a heat resistance cycle test, cooling at −40 ° C. for 20 minutes, holding at room temperature for 10 minutes, and heating at 125 ° C. for 20 minutes. The temperature-falling cycle was defined as one cycle, which was repeatedly applied, and the number of cycles until the void ratio at the bonding interface became 1.5 times or more of the void ratio before the start of the test was measured. As a result, even after 3000 cycles, the expansion of the void and the increase in the void ratio are negligible, and there is no cracking of the silicon nitride-based sintered body substrate or peeling of the copper circuit board, and excellent durability and reliability. It was confirmed that the Moreover, the withstand voltage characteristics did not deteriorate even after 3000 cycles.

On the other hand, Nos. 51 to 61 and Nos. From 71 to 82, the following findings were obtained. No. Nos. 51 to 61 are cases where the Ag powder was added to the alloy powder. 71 to 82 are results when Cu powder is added to the alloy powder.
In No. 51, the Ag content in the alloy powder was 90%, exceeding 85%, and there was a problem that brazing material flowed out on the surface of the copper plate after brazing and joining. In addition, the void ratio was less than 0.5%, and the number of cold-heat test cycles remained at 2000 cycles.
In No. 52, the Cu content in the alloy powder is 36.8%, which is more than 35%. In this case, the reactivity of the brazing filler metal powder is poor during the heating process. Thus, a sufficient amount of the brazing filler metal melt could not be produced, and there were many unjoined parts. At this time, the peel strength was reduced to 15.0 (kN / m). Along with this, the number of cold heat test cycles decreased to 1000 cycles.
In the case of no addition of the Ag powders of No. 53 and No. 54, the unevenness of the brazing filler metal surface portion was over 1.0 mm, the adhesion strength was less than 20 (kN / m), the maximum void diameter was over 1.0 mm, and the void ratio was 10 %, And the number of cold and heat cycle cycles was significantly reduced.
In No. 55, the amount of Ag powder added was more than 30%, and there was a problem that brazing material flowed out on the surface of the copper plate after brazing and joining. In addition, the void ratio was less than 0.5%, and the number of cold-heat test cycles remained at 2000 cycles.

In No. 56, when the In content in the alloy is less than 5%, the unevenness on the surface of the brazing material is reduced, but in this case, the melting point of the brazing material is increased. There were many joints and the adhesion strength decreased to 16.0 (kN / m). The maximum void diameter exceeded 1.0 mm and the void ratio exceeded 10%, resulting in a decrease in the number of cold-heat cycles.
In No. 57, when the In content in the alloy exceeds 25%, the unevenness of the brazing material surface portion is reduced, but in this case, the melting point of the brazing material is lowered. There was a defect in the pattern, and there was a problem that the brazing material flowed out on the surface of the copper plate after brazing and joining. The maximum void diameter exceeded 1.0 mm, and the number of cold-resistant cycles decreased.

In No. 60, which is a reference example, the average particle diameter of the alloy powder is less than 10 μm. At this time, the reactivity of the brazing filler metal powder is increased during the heating process, and the brazing material flows out to the copper plate surface after brazing and joining. There was a problem that caused.
In No. 61, the average particle diameter of the alloy powder is more than 55 μm, and in this case, the reactivity of the brazing filler metal powder is poor in the heating process, and the brazing filler metal melt sufficient for joining in the brazing treatment at 700 ° C. to 800 ° C. The maximum void diameter exceeds 1.0 mm and the void ratio exceeds 10%, resulting in a large number of unbonded portions. At this time, the peel strength decreases to 18.5 (kN / m). became. As a result, the number of cold-resistant cycles decreased to 800 cycles.

In No. 71, the Ag content in the alloy powder was 90%, which is more than 85%, and there was a problem that the brazing material flowed out on the copper plate surface after brazing and joining. In addition, the void ratio was less than 0.5%, and the number of cold-heat test cycles remained at 2000 cycles.
In No. 72, the Cu content in the alloy powder is 36.8%, which is more than 35%. In this case, the reactivity of the brazing filler metal powder is poor during the heating process. Insufficient brazing material melt can be produced, and by adding 5% Cu powder, these tendencies become more prominent and there are many unjoined parts, and the peel strength also decreases at this time. 15.0 (kN / m). Further, the length of the concave portion on the brazing filler metal surface was 2.0 mm, the maximum void diameter was 1.8 mm, the void ratio was 20%, and the number of cold-heat test cycles was reduced to 500 cycles.
In the case of no addition of Cu powder of No. 73 and No. 74, the unevenness of the brazing filler metal surface portion exceeds 1.0 mm, the adhesion strength is less than 20 (kN / m), the maximum void diameter exceeds 1.0 mm, and the void ratio is 10 % And the number of cold-resistant cycles decreased.

In No. 75, the amount of Cu powder added is more than 30%, and the melting point of the brazing material composition is increased, so that brazing treatment at 700 ° C. to 800 ° C. produces a brazing material melt sufficient for bonding. There were many unjoined parts, and the peel strength was reduced to 15.0 (kN / m).
Thereby, the number of heat-resistant cycles was reduced to 500 cycles.
In No. 76, the In content in the alloy is less than 5%. In this case, the melting point of the brazing material is increased, and in the brazing treatment at 700 ° C. to 800 ° C., there are many unbonded portions, and the adhesion strength decreases. .0 (kN / m)
It became. As a result, the number of cold and heat resistant cycles remained at 800 cycles.
In No. 77, the In content in the alloy is more than 25%. In this case, the melting point of the brazing material is lowered, and in the brazing treatment at 700 ° C. to 800 ° C., there is a circuit pattern breakage. There was a problem that brazing material flowed out on the surface of the later copper plate.

In No. 80, which is a reference example, the average particle size of the alloy powder is less than 10 μm. At this time, the reactivity of the brazing filler metal powder increases during the heating process, and the brazing material flows out to the copper plate surface after brazing and joining. There was a problem that caused.
In No. 81, the average particle size of the alloy powder is more than 55 μm. In this case, the reactivity of the brazing filler metal powder is poor during the heating process, and the brazing filler metal melt sufficient for joining in the brazing treatment at 700 ° C. to 800 ° C. In this case, the peel strength decreased to 18.5 (kN / m). As a result, the number of cold-resistant cycles decreased to 800 cycles.

It is a SEM photograph which shows the particle | grain form which comprises a brazing material, Comprising: (A) shows the brazing material of one Example of this invention, (B) shows the example without the conventional Ag particle or Cu particle | grain addition. It is a side view which shows one Embodiment of the ceramic circuit board of this invention. It is a top view which shows the brazing material layer apply | coated to the ceramic substrate of FIG. It is a top view which shows the example of the metal plate (Cu) previously formed in the predetermined circuit pattern. It is a top view which shows the state which joined the copper plate of FIG. 4 to the ceramic substrate of FIG. The aspect of the brazing filler metal layer by heat processing at the time of joining a copper plate to a ceramic substrate is shown, (A) is an example of the present invention, and (B) is a conventional example. The form of the filter-bonding interface after bonding a copper plate to a ceramic substrate is shown, (A) and (B) are examples of the present invention, and (C) and (D) are conventional examples.

Explanation of symbols

1: Circuit metal plates 3, 4, 5: Metal (copper) plates 3a, 4a, 5a: Inclined surfaces 3b, 4b, 5b: Bonding surfaces 3c, 4c, 5c: Bonding surfaces 7 with a ceramic substrate : Ceramic substrates 8, 9, 10: Brazing material layer 11: Metal (copper) plate 12: Brazing material layer 20: Overhanging portion

Claims (5)

It is a structure in which a metal plate is bonded to at least one surface of a ceramic substrate via a brazing material layer, and the brazing material layer is a ceramic circuit substrate formed in a wider range including the bonding range of the metal plate. ,
The brazing filler metal layer is made of an alloy powder having an average particle diameter of 15 to 40 μm composed of Ag: 85 to 55% by mass, In: 5 to 25% by mass, Ti: 0.2 to 2.0% by mass, the balance Cu and inevitable impurities. Further, it is made of an Ag—Cu—In—Ti brazing material added with 5 to 30% by mass of Ag powder particles or Cu powder particles having an average particle diameter of 1 to 15 μm, and the main component is a Cu—Ti phase and has a maximum length. It has a concave-convex surface composed of a concave portion of less than 1.0 mm and a convex portion composed mainly of an Ag-In phase and a Cu-In phase, a void ratio of 0.5% to 10%, and a maximum void diameter of 1.0 mm. A ceramic circuit board characterized by: The ceramic circuit board according to claim 1, wherein the adhesion strength (peel strength) between the ceramic substrate and the metal plate is 20 (kN / m) or more. The temperature increase / decrease cycle in which cooling at −40 ° C. for 20 minutes, holding at room temperature for 10 minutes and heating at 125 ° C. for 20 minutes is one cycle, and this is repeatedly applied. 3. The ceramic circuit board according to claim 1, wherein the number of cycles until the value becomes 1.5 times or more of the initial void ratio exceeds 3000. 4. Between the ceramic substrate and the metal plate, Ag: 85 to 55% by mass, In: 5 to 25% by mass, Ti: 0.2 to 2.0% by mass, balance Cu and inevitable impurities, average particle diameter of 15 to 40 μm In addition to this, the circuit pattern bonding range is obtained by using an Ag-Cu-In-Ti brazing material in which 5 to 30% by mass of Ag powder particles or Cu powder particles having an average particle diameter of 1 to 15 μm is added to the above alloy powder. A brazing material layer is formed over a wide range, and the ceramic substrate and the metal plate are brazed by heat treatment, and the brazing material layer is mainly composed of a Cu-Ti phase and has a maximum length of less than 1.0 mm. And an irregular surface composed of a convex portion composed mainly of an Ag-In phase and a Cu-In phase, and containing a void having a maximum diameter of 1.0 mm or less from 0.5% to 10%, Etch the circuit A method of manufacturing a ceramic circuit board, comprising forming a pattern. Between a ceramic substrate and a metal plate previously formed in a predetermined circuit pattern, Ag: 85 to 55% by mass, In: 5 to 25% by mass, Ti: 0.2 to 2.0% by mass, remaining Cu and inevitable impurities A circuit using an Ag-Cu-In-Ti brazing material in which 5 to 30% by mass of Ag powder particles or Cu powder particles having an average particle size of 1 to 15 μm is further added to an alloy powder having an average particle size of 15 to 40 μm. A brazing material layer is formed in a wider range including the bonding range of the pattern, and the ceramic substrate and the metal plate are brazed by heat treatment, and the brazing material layer is mainly composed of a Cu-Ti phase and has a maximum length. A concave and convex surface having a concave portion with a diameter of less than 1.0 mm and a convex portion mainly composed of an Ag-In phase and a Cu-In phase is provided, and a void having a maximum diameter of 1.0 mm or less is 0.5% to 10%. Contains A method for producing a ceramic circuit board, characterized by: