JPH06232549A - Manufacture of metal base board - Google Patents

Abstract

PURPOSE:To obtain a metal base board which is excellent in heat dissipating properties and enhanced in adhesion between a flame spraying ceramic layer and a metal board and between a flame spraying ceramic layer and a conductor layer by a method wherein an adhesive agent is interposed between the flame spraying metal layer of the metal plate and the flame spraying ceramic layer of a copper foil. CONSTITUTION:One surface of an aluminum board 1 is roughened, composite powder of nickel and aluminum is flame-sprayed on the roughened surface of the board 1 to form a nickel-aluminum layer 2 on the board 1. Then, alumina is flame-sprayed on the roughened surface of a copper foil 3 to form an aluminum layer 4 on it, whereby the copper foil 3 provided with the aluminum layer 4 on its one side can be obtained. Anhydride hardening epoxy resin is applied onto the surface of the aluminum layer 4 of the copper layer 3, the aluminum board 1 provided with the nickel-aluminum layer 2 is made to overlap the applied anhydride hardening epoxy resin making the aluminum layer 4 confront the nickel-aluminum layer 2 to form a laminate, and the laminate is pressed into a metal base board composed of the copper foil 3, the aluminum layer 4, the nickel-aluminum layer 2, and the aluminum board 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a metal base board used for a printed wiring board.

[0002]

2. Description of the Related Art Recently, as electronic devices have become smaller and higher in density, components mounted on a printed wiring board have been changed from a conventional insertion type to an imposition type. Therefore, the surface mounting method is becoming the mainstream as the mounting method on the printed wiring board. Furthermore, the components to be mounted are becoming smaller and higher in output, and the mounting density is also increasing. Therefore, how to deal with the heat emitted from the components has become a big problem.

In response to this problem, an organic substrate such as a glass cloth-based epoxy resin laminated plate, which is widely used as a printed wiring board, has a very low thermal conductivity and thus has a poor heat dissipation property, and thus is mounted. It is not suitable for mounting components that generate a large amount of heat because the heat generated from the components cannot be quickly processed.

Therefore, for such applications, an insulating layer is provided on the surface of a ceramic substrate typified by an alumina substrate, which has a higher thermal conductivity than that of an organic substrate and is excellent in heat dissipation, or a metal plate. A metal base substrate is used. However, the demand for high heat dissipation is becoming stronger, and higher heat dissipation is also required for these substrates.

[0005]

In order to meet the demand for high heat dissipation, a ceramic substrate has a higher thermal conductivity than conventional alumina substrates, such as beryllia substrate, aluminum nitride substrate,
Alternatively there is a silicon carbide substrate. However, the beryllia substrate has a problem of toxicity, and the aluminum nitride substrate and the silicon carbide substrate have a problem of high price, so that they have not been widely used. Regarding the ceramic substrate, there is a limit to the size of the substrate due to firing,
There is a problem that a large substrate cannot be formed.

On the other hand, the metal base substrate is a metal plate having a high thermal conductivity such as copper or aluminum, on the surface of which an insulating layer such as epoxy resin or glass cloth base material epoxy resin is formed. Due to the presence of the above, the heat dissipation property is higher than that of the conventional organic substrate. However, since the insulating layer on the surface is mainly composed of resin with low thermal conductivity, it is not possible to fully utilize the high thermal conductivity of the metal plate below it, and further improvement of heat dissipation is required. There is. In order to meet this demand, there is a resin in which an insulating layer is highly filled with ceramic powder such as alumina powder, and it is already widely used. However, although it is possible to increase the filling amount by this method,
In the case of a metal plate or conductor, there is a limit to the amount of filler that can be added due to the adhesiveness between the foil and the insulating layer, and it is not possible to meet the ever-increasing demand for high heat dissipation.

On the other hand, as in JP-A-49-68255 and JP-A-57-73991, ceramics are sprayed on the surface of a metal plate as a base to form a ceramic layer, and a metal is sprayed thereon. Many metal base substrates have been proposed in which a circuit is produced by a method of forming a plating layer. However, looking at these, the ceramic layer formed by thermal spraying has pores, which causes a large decrease in insulation characteristics when absorbing moisture.When the circuit is formed by thermal spraying, the electrical resistance is also due to the presence of pores. High, it is difficult to form a fine pattern, and further, the adhesion of the ceramic sprayed layer to the metal plate and the adhesion of the copper sprayed layer or the copper plated layer to the ceramic sprayed layer are There are drawbacks such as not being high enough to withstand reliability testing. Regarding the pores of the ceramic sprayed layer, see, for example, JP-A-55-1563.
No. 92 and JP-A-57-122593, a method of impregnating and sealing a resin has been invented, but after impregnation, a resin layer having a low thermal conductivity remains on the surface, This lowers the heat dissipation of the substrate. To improve this, post-treatment such as polishing and removal of the resin layer on the surface is required, which complicates the process and is disadvantageous for mass production.

In order to solve these drawbacks, the inventors of the present invention have previously formed a ceramic by spraying a ceramic on the same foil as a conductor, and adhere the ceramic to a base metal plate via an adhesive. He invented the method and filed a patent application. According to this method, all the drawbacks of the metal base substrate using the previously proposed ceramic spraying can be improved by this method. That is, the adhesive can impregnate the pores of the ceramic sprayed layer and seal the pores, and further, the adhesive can reach the interface between the copper foil and the ceramic sprayed layer through the continuous pores of the ceramic sprayed layer. Therefore, the adhesiveness between the copper foil and the ceramic sprayed layer is strengthened, and the adhesive layer is provided between the metal plate and the ceramic sprayed layer, so that the adhesiveness between them is also secured. Further, since the circuit can be formed by etching the copper foil on the surface similarly to the conventional metal base substrate, it is easy to form a fine pattern.

However, even in this method, a ceramic layer having a high thermal conductivity is provided just below the circuit, but an epoxy resin having a low thermal conductivity or a glass cloth base epoxy resin is still present between the ceramic layer and the metal plate. There is a layer mainly composed of the above resin. Therefore, the high thermal conductivity of the base metal cannot be fully utilized. Therefore, if the adhesive layer is made as thin as possible, the heat dissipation is improved, but the adhesion between the base metal and the ceramic layer is reduced.

The present invention has been made in view of the above problems, and is excellent in heat dissipation by using a ceramic layer as an insulating layer,
Moreover, it is an object of the present invention to provide a method for producing a metal base substrate having excellent adhesion between the ceramic sprayed layer and the metal plate and the ceramic sprayed layer and the conductor layer.

[0011]

The structure of the present invention for achieving the above object will be described with reference to FIG. 1 corresponding to an embodiment. According to the present invention, a metal sprayed layer is formed on a metal plate serving as a base. First step, second step of spraying ceramic on copper foil to form ceramic sprayed layer, thermocompression-bonding the metal sprayed layer obtained in the above step and ceramic sprayed layer with an adhesive interposed It is characterized by integrating as one.

As the base metal plate, metals such as copper, aluminum, iron, nickel, molybdenum, 42 alloy, Invar, stainless steel, or alloys thereof can be used. Among them, copper or aluminum, which has high thermal conductivity, is suitable for achieving high heat dissipation.

As the metal sprayed on the surface of the metal plate, simple metals such as nickel, aluminum, copper, iron, silver, molybdenum, tungsten, chromium, zinc, lead and alloys thereof can be used. Plasma spraying Method, gas spraying method, arc spraying method or the like. Further, in order to further improve the adhesion between the metal sprayed layer and the metal plate, blasting of the metal plate, which is a base material that is widely used in general thermal spraying, or roughening treatment with a chemical solution or plating, a resin is used. A roughening treatment in which a highly filled powder of ceramic, metal, or the like is applied as an agent by spraying or the like can be performed.

Ceramics that are sprayed onto copper foil include silica, alumina, cordierite, zirconia, mullite, spinel, calcia, magnesia, steatite,
An electrically insulating ceramic powder such as forsterite can be used, and among them, alumina having a high thermal conductivity is suitable for improving heat dissipation. The thickness of the ceramic sprayed layer is not particularly limited, but is preferably in the range of 20 μm to 300 μm. If the thickness is less than 20 μm, the ceramic layer is less likely to be continuous, and the insulation reliability between the conductor layer and the base metal is likely to be insufficient.
This is because as the thickness becomes thicker, the heat resistance becomes higher and the high heat dissipation property is hindered.

Epoxy resin is suitable as the adhesive resin for adhering the metal sprayed layer and the ceramic sprayed layer from the viewpoint of adhesive strength, electrical characteristics, heat resistance, chemical resistance, etc. A thermosetting resin such as a saturated polyester resin, a melamine resin or a vinyl ester resin, or an engineering thermoplastic resin such as a polyether ether ketone, polysulfone or polyphenylene oxide can be used.

As a filler for the resin of the adhesive, metal powder such as copper, aluminum, silver, nickel, iron, or alumina, magnesia, silica, zirconia, aluminum nitride, silicon carbide, titania, spinel, mullite,
The thermal conductivity can be further increased by adding a ceramic powder such as zircon or a mixture thereof.

The adhesive may be applied to either one or both of the metal sprayed layer on the metal plate and the ceramic sprayed layer on the copper foil. In this way, the metal sprayed layer and the ceramic sprayed layer are superposed with an adhesive agent interposed therebetween, and thermocompression bonded by a hot press or a heat roll to integrate them. By thermocompression bonding, the adhesive impregnates the pores of the metal sprayed layer and the ceramic sprayed layer,
The pores are sealed.

[0018]

[Function] When a ceramic sprayed layer of copper foil having a ceramic sprayed layer is adhered to a base metal plate, good adhesion can be obtained unless an adhesive layer having a certain thickness is provided between the ceramic sprayed layer and the metal plate. Absent. This is because when the adhesive layer becomes thin, there is no adhesive layer between the ceramic sprayed layer and the metal plate, and there are more portions where the ceramic sprayed layer and the metal plate are in direct contact with each other. Therefore, if the adhesive layer is thick enough to obtain sufficient adhesion, the heat dissipation of the substrate is reduced due to the low thermal conductivity of the adhesive layer, and the high thermal conductivity of the ceramic layer and the base metal plate. You will not be able to utilize the rate effectively.

On the other hand, when the metal sprayed layer is formed on the base metal plate as in the present invention and the ceramic sprayed layer is formed on the metal sprayed layer through the adhesive, the adhesive may be thinned. Adhesion can be obtained. That is, the metal sprayed layer and the ceramic sprayed layer have pores, and the adhesive impregnates these pores. Therefore, even if the adhesive layer between the metal sprayed layer and the ceramic sprayed layer becomes extremely thin, they will be connected by the adhesive impregnated into the pores of each other, and the adhesiveness will not decrease. Therefore, the adhesive layer, which causes a decrease in heat dissipation, can be made as thin as possible, and it is possible to obtain a highly heat-dissipative metal base substrate that takes advantage of the high thermal conductivity of the ceramic layer and the base metal plate. Further, when the adhesive is filled with metal powder or ceramic powder, the thermal conductivity of the adhesive layer left thinly between the metal sprayed layer and the ceramic sprayed layer can be increased, so that the heat dissipation of the obtained substrate can be improved. It can be further increased.

The adhesive between the metal sprayed layer and the ceramic sprayed layer impregnates pores during thermocompression bonding, and since the pores of the sprayed layer are continuous pores, the adhesive almost completely seals each pore. Reach the foundation. Therefore, the adhesion between the copper foil and the ceramic sprayed layer and the adhesion between the metal plate and the metal sprayed layer become stronger. Here, the thermal spray layer formed on the base metal plate may be a ceramic in addition to the metal, but the use of a metal improves the adhesion to the base metal and the heat dissipation of the obtained substrate. It can be anything. That is, the adhesiveness of the thermal sprayed layer to the metal is higher in the metal thermal sprayed layer than in the ceramic thermal sprayed layer. Generally, when forming a ceramic sprayed layer on a metal, a metal sprayed layer of nickel, aluminum or the like is formed as a base spray to improve adhesion. This is because the metals are the same kind of material, so they are more compatible with each other and the thermal expansion coefficients do not differ greatly. Further, since metal has a higher thermal conductivity than ceramic, metal spraying can improve the heat dissipation of the substrate.

In the conventional metal base substrate having a ceramic sprayed layer as an insulating layer, there is a problem in that the ceramic sprayed layer has pores, so that the insulating property is greatly deteriorated when absorbing moisture. On the other hand, in the method of the present invention, when bonding the metal plate having the metal sprayed layer on the surface and the copper foil having the ceramic sprayed layer with the adhesive, the adhesive impregnates the pores of the ceramic sprayed layer, To seal. Therefore, the insulation characteristics are not deteriorated when absorbing moisture, and the electric characteristics such as withstand voltage are good.

Further, in the circuit formation in the conventional method, a metal mask having an inverse pattern of the circuit shape is brought into contact with the surface of the ceramic sprayed layer, or a resist agent used at the time of etching the copper foil is printed and the copper is then applied. Has been used, a method of applying a copper or silver based paste on the ceramic sprayed layer and firing, or a method of forming a copper circuit by electroless plating. However, these methods have various problems. That is, although this is a method of spraying copper, the sprayed copper has pores and is partially oxidized, so that the electric resistance is increased. Therefore, in order to obtain a pattern of low electric resistance required as a circuit, a certain thickness and width are required. Further, when a metal mask is used, copper wraps around between the mask and the ceramic sprayed layer, which makes it difficult to form a fine pattern. Further, the adhesion with the ceramic sprayed layer is not sufficient. The method of coating and firing the conductor paste on the ceramic sprayed layer and the method of performing electroless plating have problems such as complicated processes and low adhesion to the ceramic sprayed layer.

On the other hand, in the present invention, since there is a copper foil having a strong adhesiveness with the ceramic sprayed layer by the adhesive which has already impregnated the pores of the ceramic sprayed layer,
Circuits can be easily formed by printing an etching resist on a copper foil and etching as in the case of conventional metal-based substrates, which is significantly superior to conventional methods in terms of process and formation of fine patterns. There is.

[0024]

EXAMPLES Examples of the present invention will be described below. Example 1 One surface of an aluminum plate 1 having a thickness of 1 mm was sandblasted to roughen it, and then 80% by weight of nickel was applied to the surface.
A composite powder consisting of 20% by weight of aluminum (Showcoat MA-81, manufactured by Showa Denko KK) was sprayed with a plasma spraying machine (Plasmadyne System 3600-80R, manufactured by US Plasmadyne Co., Ltd.) to a thickness of 20 μm. A roux aluminum layer 2 was formed. Next, a plasma sprayer (Plasma Dyne System 3600-80) was applied to the roughened surface of the electrolytic copper foil 3 (manufactured by Furukawa Circuit Kit Foil Co., Ltd.) having a thickness of 35 μm.
Alumina (Showcoat K-16T, Showa Denko KK) was sprayed by R type, manufactured by Plasmadyne Co., USA to form an alumina layer 4 having a thickness of 100 μm, and a copper foil having an alumina layer on one side was obtained. It was

An acid anhydride-curable epoxy resin (KE-578, manufactured by Hitachi Chemical Co., Ltd.) was coated on the surface of the alumina layer of the copper foil having the alumina layer thus obtained, and nickel-coated on it. An aluminum plate having an aluminum sprayed layer is laminated so that the alumina layer and the nickel-aluminum layer face each other, and the pressure is 20 Kgf / cm ² and the temperature is 1
Press molding was carried out at 30 ° C. for 1 hour to cure the epoxy resin to obtain a metal base substrate having a structure shown in FIG. 1 consisting of a copper foil, an alumina layer, a nickel-aluminum layer and an aluminum plate. Table 1 shows the measured values of thermal resistance, copper foil peeling strength, thermal shock resistance, normal state of the insulating layer and insulation resistance after boiling of this metal base substrate.

Example 2 A metal base substrate was prepared in the same manner as in Example 1 except that the epoxy resin of Example 1 mixed with 30% by volume of copper powder was used as an adhesive. The characteristics of this product are shown in Table 1. Comparative Example 1 A mixture of 50% by volume of alumina in an epoxy resin is applied on the surface of an aluminum plate, a copper foil is laid on the surface of the aluminum plate, and pressure bonding is performed with a hot roll to form a metal base substrate having an insulating layer with a thickness of 100 μm. did. Comparative Example 2 After sandblasting an aluminum plate, alumina was sprayed thereon to form an alumina layer having a thickness of 100 μm, and further copper was sprayed thereon to a thickness of 50 μm to prepare a substrate. Comparative Example 3 After sandblasting an aluminum plate, the thickness of alumina is 1
Thermal spraying to 00 μm, applying epoxy resin on it,
Vacuum impregnation was performed to seal the pores of the sprayed layer. After curing, an epoxy resin layer having a thickness of 20 μm was present on the surface of the alumina layer. Next, electroless copper plating was performed on the surface of the epoxy resin layer to form a copper layer.

Comparative Example 4 After applying an epoxy resin to the alumina layer of the copper foil having the alumina layer obtained in the example, aluminum plates were laminated and press-molded. The thickness of the adhesive layer between the alumina layer and the aluminum plate was 5 μm, and there were many parts where the alumina layer and the aluminum plate were in direct contact. Comparative Example 5 A glass cloth-based epoxy resin prepreg having a thickness of 50 μm was placed on the surface of an aluminum plate, and the copper foil having the alumina layer obtained in the example was placed thereon so that the alumina layer was in contact with the prepreg. Then, the metal base substrate was prepared by hot press molding. As shown in Table 1, the metal base substrate produced by the method of the present invention has low heat resistance and excellent heat dissipation, and further, the adhesion between the conductor and the insulating layer and the adhesion between the insulating layer and the metal plate serving as the base. Was high, and the insulation characteristics when absorbing moisture were also good.

[0028]

[Table 1]

[0029]

As described above, according to the present invention, it is possible to obtain a metal base substrate having a high heat dissipation property that cannot be obtained by the conventional method, and further, a high heat dissipation is achieved by using the conventional ceramic spraying method. That was a problem when manufacturing a metal base substrate with high thermal conductivity, the adhesion between the ceramic sprayed layer and the base metal plate or conductor layer was insufficient, and the insulation characteristics when absorbing moisture due to the presence of pores in the sprayed layer It is possible to solve the problem that the decrease is large, and further that the thermal conductivity is decreased due to the presence of the adhesive when the layers are bonded, and the high thermal conductivity of the ceramic layer and the base metal cannot be fully utilized.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a substrate obtained in Example 1 of the present invention.

[Explanation of symbols]

1. Aluminum plate 2. Nickel-aluminum layer 3. Copper foil 4. Alumina layer

Claims (4)

[Claims] 1. A metal plate obtained in the first step of forming a metal sprayed layer on the surface of a metal plate, the second step of spraying ceramic on a roughened surface of a copper foil to form a ceramic sprayed layer, and the metal plate obtained in the first step. Of the metal base substrate, which comprises a third step of thermocompression-bonding an adhesive between the metal sprayed layer and the ceramic sprayed layer of the copper foil obtained in the second step, and integrating them. Production method. 2. The method for producing a metal base substrate according to claim 1, wherein the adhesive contains an epoxy resin as a main component. 3. The method for manufacturing a metal base substrate according to claim 1, wherein the adhesive contains metal powder and / or ceramic as a filler. 4. The method for producing a metal base substrate according to claim 1, wherein the ceramic to be sprayed has alumina as a main component.