JP2642574B2 - Manufacturing method of ceramic electronic circuit board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a joined body of metal and ceramics, and more particularly to a method of manufacturing an aluminum-ceramic composite electronic circuit board suitable for mounting a high power electronic device such as a power module. It is about.

[0002]

2. Description of the Related Art A metal-ceramic composite electronic circuit board formed by bonding a metal to the surface of a ceramic substrate is used as a mounting substrate for a high power device such as a power module. Composite substrates of copper and alumina or aluminum nitride ceramics are currently mainly used.

[0003] As a joining method of copper and ceramics, there are a direct joining method and a brazing method. The former is a technique developed for joining oxide ceramics and copper.When joining, a copper plate containing oxygen is used to heat in an inert atmosphere or oxidize using oxygen-free copper. This is a method of joining copper and ceramics by heating in a neutral atmosphere. When joining a non-oxide ceramic and copper by this method, an oxide layer must be formed on the surface of the non-oxide ceramic in advance. For example, as disclosed in JP-A-59-3077, about 1000
After treating the aluminum nitride substrate at a temperature of ° C. to form an oxide on the surface, copper and aluminum nitride are joined by the above-described method. The brazing method is a method of joining an active metal brazing material between copper and ceramics. In this method, an Ag-Cu-Ti-based brazing material is generally used.

[0004] Despite the widespread use of copper-ceramic composite substrates, there are several problems during production and in practice. The most serious problem among them is dielectric breakdown between the front and back of the substrate caused by cracks generated inside the ceramic substrate during mounting and use of electronic components.

[0005] In order to bond a ceramic substrate and copper,
The ceramic substrate and copper are heated to nearly 1000 ° C, and when mounting electronic components such as power modules,
The copper-ceramic composite substrate is heated to nearly 400 ° C. Since the coefficient of thermal expansion of copper is about one order of magnitude higher than that of ceramics, when the composite substrate is cooled to room temperature, a large thermal stress is generated inside the substrate due to the difference in the coefficient of thermal expansion. Further, the temperature of the substrate constantly changes due to the use environment of the electronic component and the heat generated during use, and the thermal stress acting on the substrate also changes correspondingly. Cracks occur in the ceramic substrate due to the action of these thermal stresses. For this reason, heat cycle resistance, which is one of the important evaluation items for ceramic electronic circuit boards, is that cracks occur in the board when the board is repeatedly heated and cooled in a temperature range from -40 ° C to 125 ° C. The characteristic value evaluated by the number of repetitions until occurrence is 20 times for the copper-alumina composite substrate manufactured by the direct bonding method, but this characteristic value of the same substrate manufactured by the brazing method is 10 times or less. is there.

[0006] There has long been a concept of using aluminum having excellent electrical and thermal conductivity similar to copper as a conductive circuit material (for example, such a concept is described in JP-A-59-121890). . Aluminum is softer than copper. Its yield strength is about 1/4 of copper. Therefore, it can be predicted that if aluminum is used as a circuit material, the residual stress generated inside the composite substrate can be greatly reduced. However, the above-mentioned JP-A-59-121890 describes
No specific method of joining aluminum and ceramics was disclosed in the invention of the above-mentioned publication. JP-A-3-1254
No. 63, JP-A-4-12554 and JP-A-4-187
Reference numeral 46 discloses a method for producing an aluminum-ceramic composite substrate by a brazing method. According to these documents, the heat cycle resistance of the manufactured aluminum-ceramic substrate is 200 times or more, which is about 10 times that of the copper-ceramic substrate.

However, there are the following problems when manufacturing an aluminum-ceramic composite substrate by the brazing method as disclosed in the above-mentioned publication, and when using the substrate thus prepared.

1) Since aluminum is easily oxidized, the method disclosed in the above publication must be performed in a vacuum or in a high-purity inert gas atmosphere.

2) The melting point of aluminum is as low as 660 ° C.
When the brazing temperature is brought close to this, all of the aluminum melts and loses its shape or melts locally, causing a brazing defect called insect bite. On the other hand, if the brazing temperature is lowered, the reaction between the brazing material and the ceramic hardly occurs, so that the strength of the joined body is low. As shown in the embodiments of the present invention, when an Al-Si brazing alloy is used, the brazing must be performed within a temperature range of 590 ° C. or more and 640 ° C. or less. According to the inventor's experience, in the case of mass production, especially when manufacturing a composite substrate in a vacuum (since the heat from the heating element is transmitted only by radiation and conduction and there is no convection), the temperature in the furnace is uniformly controlled. It is very difficult to do.

3) When a composite substrate is manufactured by the brazing method, the brazing temperature must be lower than 660 ° C., the melting point of aluminum. However, at such a temperature, the wettability between the aluminum brazing material and the ceramic is not good. Therefore, when manufacturing a composite substrate by this method,
Unconnected defects are likely to occur.

4) Although an alumina substrate can be directly brazed, in the case of an aluminum nitride ceramic substrate, the surface of the aluminum nitride substrate must be oxidized in advance, as in the case of directly bonding copper. This method not only complicates the process, but the aluminum nitride substrate was originally developed to meet the demand for high thermal conductivity, but if oxides were formed on the surface, the thermal conductivity characteristics were adversely affected. Needless to say, give.

5) Similar to the case of the copper-ceramic composite substrate, it is considered that the heat cycle resistance of the substrate manufactured by the brazing method is lower than that of the substrate manufactured by the direct bonding method. This is because the brazing alloy used to make the substrate is harder than pure metal,
This is because plastic deformation is unlikely to occur, which adversely affects stress relaxation.

[0013]

As described above, in the process of manufacturing an aluminum-ceramic composite substrate by the brazing method, there are problems such as stability and the like. In the case of this, there is a problem that the manufacturing process becomes complicated. Further, it is considered that the composite substrate thus manufactured is not necessarily optimal in terms of bonding strength, heat resistance characteristics, and the like.

The present invention overcomes these problems and provides a stable and convenient manufacturing method for manufacturing an aluminum-ceramic composite substrate having better bonding strength, thermal conductivity, and heat resistance. With the goal.

[0015]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above problems, and as a result, have found a novel manufacturing method for manufacturing an aluminum-ceramic composite substrate, and have provided the present invention. did it.

That is, in the present invention, firstly , in the production of a ceramic electronic circuit board having a metal conductor on one side of a ceramic substrate, the aluminum or aluminum alloy for forming the conductor is placed in a vacuum or an inert gas. in after <br/> dissolved to give a melt, vacuum or inert said melt
Contact with the ceramic substrate in the mold in gas ,
At this time, the melt and the ceramic substrate are
One side of the ceramic substrate is held and cooled by direct contact without intervening the oxide film on the metal surface.
Made of aluminum or aluminum alloy in the metal guide
Method of manufacturing a ceramic electronic circuit board, characterized in that to firmly bond the conductor; the second, the ceramic substrate
Metal conductors are placed on both sides separately from each other.
In the production of ceramic electronic circuit boards,
Aluminum or aluminum alloy for forming the conductor
Gold melted in vacuum or inert gas to obtain melt
Thereafter, the melt is placed in a mold in a vacuum or inert gas.
To make contact with the ceramics substrate.
Lamix substrate and an oxide film on the metal surface at their interface
Hold and cool with direct contact without intervention
Aluminum or both sides of the ceramic substrate
The metal conductor made of aluminum alloy is strongly bonded.
Then, remove the conductor at the part connecting the conductors on the front and back.
Metal on both sides characterized by removal by etching
A method for producing a ceramic electronic circuit board having a conductor ;
Third, the method for manufacturing a ceramic electronic circuit board according to any one of the first to second aspects, wherein the ceramic substrate is one selected from alumina and aluminum nitride; For direct contact, a melting temperature of 7
Method of manufacturing a ceramic circuit board according to any one of the first to the third, characterized in that in a range of 00-1,000 ° C.; Fifth, the direct contact, the melt temperature 750
4. The method according to the fourth aspect, wherein the heat treatment is performed in a temperature range from to 1000 ° C.
The present invention relates to a method for manufacturing the above ceramic circuit board .

[0017]

According to previous studies by the inventors, when heated in air, a thick oxide (alumina) layer is formed on the surface of aluminum, so that aluminum cannot be bonded to ceramics. Aluminum and ceramics can be bonded in a vacuum and inert atmosphere, but a thin oxide layer is detected at the bonding interface, and aluminum and ceramics are bonded via a thin oxide film on the aluminum surface. Recognize. Since aluminum covered with alumina does not have good wettability with respect to ceramics, a non-contact portion is easily formed at the interface portion of the thus-formed bonded body, and the bonding strength varies.

In order to suppress such an adverse effect due to the oxide film, the inventors have previously made aluminum alloy element S
i, Ti, etc. were added, and the effect was examined. Si has the effect of thinning the oxide film on the surface, and Ti has the role of promoting the reaction at the interface. It was also confirmed that simultaneous addition of Si and Ti is most effective for improving the strength and stability of the joined body. However, in each case, oxide was detected from the interface of the joined body, and it was found that aluminum and ceramics were still joined via the oxide film.

The oxide alumina on the aluminum surface is chemically very stable and hardly reacts with other substances. Therefore,
If this exists at the interface, it is conceivable that the bonding between the aluminum and the ceramic substrate is hindered.

In a study on a sintered body of aluminum and ceramic powder conducted by the inventors in the past, an oxide film was not interposed between aluminum and ceramic powder, and there was a part directly joined, and aluminum was interposed therebetween. It has been found that a reaction product of the material and the ceramic has been formed. This is presumably because the oxide film on the surface of the aluminum powder was broken when the powder was mixed and pressed, and the aluminum powder was heated in a state of being in direct contact with the ceramic powder. This suggests the possibility of direct joining of aluminum and ceramics.

The present inventors have made various attempts to remove the oxide film on the aluminum surface and produce a high-quality metal-ceramic composite substrate, but have found that the following means is effective.

1) Relative motion was caused between the molten metal and the ceramic substrate to melt the metal and break the oxide film on the surface of the molten metal. More specifically, a ceramic substrate is placed in a predetermined place of a mold before casting a molten metal, or by inserting a ceramic substrate into a molten metal that has been cast, thereby converting the ceramic substrate into a molten metal. Cause relative movement between

2) If the temperature increases, the oxide film on the metal surface is easily decomposed, so it is preferable to increase the temperature of the molten metal. However, heating the molten metal to a high temperature requires extra energy, and at the same time, unfavorable effects such as evaporation of the molten metal and intense reaction between the molten metal and the mold occur. Below ℃,
In this temperature range, a sound composite substrate can be manufactured.

3) In order to suppress oxidation of the molten metal surface as much as possible, the casting of the molten metal and the insertion of the substrate are performed as quickly as possible. The production may be carried out in the air, but the melting and casting are preferably carried out in a vacuum or an inert atmosphere to prevent oxidation.

In the method of forming a pattern of an electronic circuit, a pattern of a circuit pattern is formed in a mold in advance, and a circuit pattern is directly formed or a solid aluminum layer is formed, and then a circuit pattern is formed by an etching method. There is a way to do that.

[0026]

Embodiment 1 As shown in FIG.
A 635 mm alumina (ceramics) substrate 2, an aluminum raw material 3 and a graphite piston 4 were installed, and these were placed at 700 ° C. (experiment 1), 800 ° C. (experiment 2), 900 ° C. (experiment 3), and 1000 ° C. (experiment 4), respectively. In a heated furnace. After the aluminum raw material was melted and penetrated into the portion where the alumina substrate was placed by the weight of the piston, the mold was taken out of the heating furnace and cooled to room temperature. In this example, heating and cooling were performed in a nitrogen atmosphere in order to prevent oxidation of the graphite mold. 0.5mm on one side made in this way
Mechanical and electrolytic polishing of the composite substrate having a thick aluminum layer, observing the aluminum structure with an optical microscope,
A 4 mm wide sample for peel strength measurement was cut out from the composite substrate and subjected to a 90 ° peel strength test.

In the composite substrate manufactured at any temperature, the structure of the aluminum portion is very dense, and the pores,
There were no common defects such as nests. Further, as shown in Table 1, since the strength of the composite substrate was 35 kg / cm or more, and the fracture occurred not in the interface but in the aluminum, it was found that the aluminum was strongly bonded to the alumina substrate. Further, there were some unconnected defects in the samples prepared at 700 ° C., but none of the samples prepared at 800 ° C. or higher.

In these examples, a composite substrate was produced using an alumina substrate. However, it was confirmed that an aluminum nitride composite substrate could be produced by the same method.

[0029]

[Table 1] From the contents described in this specification, it will be easily understood that the method shown in the above-described embodiment is not the only method and should not be limited to the conditions shown in this embodiment.
It is possible to manufacture composite substrates by various methods such as high-pressure casting, die casting, continuous casting, etc., prolonging the holding time at the manufacturing temperature, and alloying elements that help decompose and activate surface oxides in aluminum, Alternatively, an alloying element for lowering the melting point, for example, Si, Ge, Ti, Mg, or the like is added, and the sintering aid in the ceramic substrate is made to have a composition that easily reacts with aluminum, and if measures are taken to increase the amount, It is easily conceivable that a composite substrate can be produced at a lower temperature.

[0030]

Comparative Examples 1 to 6 For comparison, aluminum-ceramic composite substrates were produced by the brazing method.

The aluminum plate and the ceramic substrate were set such that two aluminum plates having a thickness of 0.5 mm sandwiched a ceramic substrate having a thickness of 0.635 mm from above and below via a brazing material. A weight was further placed thereon, and kept at 650 ° C. for 20 minutes in a vacuum of 10 ⁻⁵ to braze the aluminum plate and the ceramic substrate. The ceramic substrates used were two types of alumina and aluminum nitride substrates, and the brazing material was three types of Al-Si-Ti alloy foils having a thickness of 0.2 mm. Its composition is shown in Table 2. The evaluation of the composite substrate was performed by the same method as that described in the examples.

[0032]

[Table 2] Table 1 also shows the evaluation results of the composite substrate. HS
The aluminum plate itself melted and the shape of the composite substrate soldered with the brazing material was lost. Although the aluminum plate was not completely melted in the composite substrate brazed with MS and LS brazing material, a considerable part was melted, and bug bite brazing defects occurred. The peel strength of these samples is 30kg / cm
Below, especially for aluminum nitride substrates, the brazing strength
2.5kg / cm or less, peel strength required for substrate
It was lower than 5kg / cm. The area of the non-contact portion of these composite substrates was approximately 10% or more.

[0033]

Comparative Examples 7 and 8 In order to prevent the dissolution of the aluminum plate,
The brazing temperature was lowered by 10 ° C. to 640 ° C., and an attempt was made to produce an aluminum-alumina composite substrate using LS and MS brazing material. However, as shown in Table 1, at this temperature, LS
Brazing with brazing material was not possible. Although brazing was possible with the MS brazing material, the brazing strength was lower than that at brazing at 650 ° C., and the above-mentioned insect biting and non-contact defects were still generated. Lower temperatures may eliminate bug-eating defects, but may result in more open defects.

[0034]

Comparative Examples 9 to 10 An attempt was made to lower the brazing temperature to the melting temperature of the HS brazing material (about 580 ° C.) to produce an aluminum-alumina composite substrate. However, at such a low temperature, the ceramic substrate and the brazing material were not joined. Also 590
When brazing at a temperature of ° C., the aluminum plate partially melted, causing insect bite defects. It was found that the temperature could not be raised any more.

As can be seen from the above comparative examples, the aluminum-ceramic composite substrate manufactured by the brazing method has lower bonding strength and a higher probability of occurrence of unconnected defects than the one manufactured by the direct bonding method of the present invention. .

[0036]

According to the method of the present invention as disclosed in the present specification, soldering defects such as non-contacting in the case of manufacturing by the conventional soldering method are eliminated, and high reliability between aluminum and the ceramic substrate is achieved. , High strength bonding can be realized. by this,
A high-quality aluminum-ceramic composite substrate having excellent heat cycle resistance can be manufactured.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention.
It is sectional drawing of a casting_mold | template at the time of producing a ceramics composite substrate.

[Brief description of reference numerals]

 1 graphite mold 2 ceramic substrate 3 aluminum raw material 4 graphite piston

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-103992 (JP, A) JP-A-59-227781 (JP, A) JP-A-2-207633 (JP, A) JP-A 50-50 103429 (JP, A) JP-A-58-135691 (JP, A) JP-A-59-121890 (JP, A) JP-A-5-170578 (JP, A) JP-A-5-235388 (JP, A)

Claims (5)

(57) [Claims] 1. A metal substrate is provided on one side of a ceramic substrate.conductorTo
In the production of ceramic electronic circuit boards,
the aboveconductorAluminum or aluminum alloy for forming
MoneyIn vacuum or inert gasDissolveGot the melt
rear,Place the melt in a mold in vacuum or inert gas
handContact with the ceramic substrate,At this time, the melt and sera
The mixed substrate has an oxide film on the metal surface at the interface between them.
Without beingHolding and cooling with direct contact
Therefore, the ceramic substrateOn one side ofAluminum or
Aluminum alloyStrong bonding of metal conductor made of gold
ToManufacturing method of ceramic electronic circuit board characterized by the following:
Law. 2. The method according to claim 1 , wherein both sides of the ceramic substrate are separated from each other.
Ceramics each having a metal conductor in a separated state
In the manufacture of electronic circuit boards,
Vacuum or inert aluminum or aluminum alloy
After melting in a reactive gas to obtain a melt, the melt is evacuated to a vacuum.
Or a ceramic substrate in a mold in an inert gas
The melt is brought into contact with the ceramic substrate.
Direct contact at these interfaces without intervening oxide film on metal surface
By holding and cooling as
Aluminum or aluminum alloy on both sides of substrate
Metal conductors that are firmly joined together,
Remove the conductor at the part connecting the body by etching
A ceramic having a metal conductor on both sides.
Manufacturing method for electronic circuit boards. 3. The method for manufacturing a ceramic electronic circuit board according to claim 1, wherein said ceramic substrate is one type selected from alumina and aluminum nitride. 4. The method according to claim 1, wherein the direct contact is performed at a melting temperature of 700 to 10.
The method according to claim 1, wherein the method is performed at a temperature of 00 ° C. 5. 5. The method according to claim 1, wherein the direct contact is performed at a melting temperature of 750 to 10
5. The method according to claim 4, wherein the temperature is within a range of 00 ° C.
Lamix circuit board manufacturing method.