JPS607195A - Method of producing high thermal conductive metal base printed board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing a printed circuit board having a highly thermally conductive metal base with good heat dissipation properties and used in electronic equipment.

Conventional configurations and their problems In recent years, the field of electronic equipment has been trending toward smaller size and lighter weight, and the major issue has been how to dissipate heat from high heat generating components such as ICs, MSIs, LSIs, etc. and mount them in high density. It is becoming.

Conventionally, organic polymer materials such as paper phenolic resin laminates or glass aqueous epoxy resin laminates, and ceramic materials such as alumina substrates have been used as substrate materials for printed wiring boards, heat sinks, etc. However, due to their low thermal conductivity and insufficient heat dissipation, they had the disadvantage that high heat generating components such as ICs, MSIs, and jSIs could not be mounted in a high density.

Therefore, highly thermally conductive metal-based printed circuit boards based on metals with excellent heat resistance and thermal conductivity have been developed.

Hereinafter, a conventional method for manufacturing a highly thermally conductive metal-based printed circuit board will be described with reference to the drawings. Figure 1 (
a) and (b) are cross-sectional views in the manufacturing process of a conventional highly thermally conductive metal-based printed circuit board. The conventional method for producing a highly thermally conductive metal-based printed circuit board (as shown in Figure 1(a)) first involves bonding an epoxy resin-based or phenolic resin-based organic polymer to a conductor 1 using copper foil. The material coated with the insulating layer 2 is pressed and bonded to the metal base 3 shown in FIG. 1) while heating. The method of applying the organic polymer adhesive to the conductor 1 as the insulating layer 2 is generally carried out by coating the long conductor 1 with a roll coater.
The process is carried out efficiently using a conveyor system that applies the coating, goes through a drying process, and then winds it up.

These conventional highly thermally conductive metal-based printed circuit boards are made of only an organic polymer adhesive as the insulating layer 2, so it is possible to apply a thin (3011 m to 4 Q m) organic polymer adhesive with a low viscosity as the insulating layer 2. In addition, due to its flexibility, the conductor is actually coated with five layers of organic polymer adhesive using a roll coater, which is most suitable for mass production.

However, in recent years, in order to further improve the heat dissipation characteristics of printed circuit boards having a highly thermally conductive metal base,
An insulating layer 2 in which a highly thermally conductive filler is dispersed in an adhesive organic polymer is being developed. in this case,
A large amount of highly thermally conductive filler is dispersed in order to improve heat dissipation characteristics. Therefore, compared to an insulating layer made only of an organic polymer adhesive, the viscosity at the time of application is extremely high, and the cured insulating layer is brittle. Furthermore, since it is necessary to use a material with a high dielectric constant as a highly thermally conductive filler, it is necessary to apply the highly thermally conductive filler thickly to reduce the electrical capacity. However, the above-mentioned conventional method of coating the conductor side with a roll coater is unsuitable because it does not allow for thick coating, and there are problems such as the conductor warping after coating and drying, and the insulating layer cracking.

Furthermore, printed circuit boards that have this type of highly thermally conductive metal base in which a highly thermally conductive filler is dispersed require a thick coating of a highly viscous, highly thermally conductive adhesive as described above.
Second, the compatibility between the organic polymer and the highly thermally conductive 6B filler particles is not perfect, and air bubbles are likely to be mixed in during application. Therefore, the metal base and the conductor are bonded together with the air bubbles mixed in, resulting in defects in dielectric strength characteristics. Due to these problems, in order to mass produce this type of highly thermally conductive metal-based printed circuit board in which a highly thermally conductive filler is dispersed in an adhesive organic polymer, it is necessary to find a coating method that is suitable for mass production with a high yield. The big issue is how to develop a construction method.

Purpose of the Invention In view of the above-mentioned drawbacks, the present invention aims to improve the yield rate during mass production of a printed circuit board having a highly thermally conductive metal base, which is an insulating layer with good heat dissipation in which a highly thermally conductive filler is dispersed in an adhesive organic polymer. A delicious pudding!・Provides a method for manufacturing a substrate.

Structure of the Invention The method for manufacturing a highly thermally conductive metal-based printed circuit board of the present invention is characterized in that the insulating layer of the highly thermally conductive metal-based printed circuit board, which is composed of a metal base, an insulating layer, and a conductor, has a high thermal conductivity in an adhesive organic polymer. A highly thermally conductive adhesive having a filler dispersed therein, the manufacturing method of which is a highly thermally conductive adhesive in which the conductor is coated after the high thermally conductive adhesive is coated on the metal base side at least twice. The manufacturing method consists of a process of laminating layers and heat-pressing them, and as a result, there are manufacturing problems that could not be avoided when using this type of highly thermally conductive adhesive. In other words, due to the dielectric constant, it is necessary to apply a thick coating. If applied to the conductor side, the conductor may warp or the insulating layer may crack during the coating and bonding process with the metal base.
This solves problems such as the generation of bubbles and facilitates mass production.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIGS. 2(a) to 2(C) are cross-sectional views of each step up to completion of the printed circuit board in a method of manufacturing a printed circuit board according to an embodiment of the present invention.

In FIGS. 2(a) to 2(c), reference numeral 4 indicates a metal base, 5 indicates a hardened insulating layer, 6 indicates an adhesive insulating layer, and 7 indicates a conductor.

The method for manufacturing the printed circuit board of this embodiment configured as described above will be described below. First, the second
In Figure (a), a highly thermally conductive adhesive in which a highly thermally conductive filler is dispersed in an adhesive organic polymer is applied to the metal base 4 by screen printing, metal mask printing, a blade coater, etc., and then dried and cured. Hardened insulating layer 5 through process
form. Next, in FIG. 2(b), using the same high thermal conductive adhesive and coating method as described above, the adhesive insulating layer 6 is laminated and coated on the cured insulating layer 5 soil, and the adhesive 11 is in an uncured state. dry. Then, as shown in FIG. 2(c), a conductor 7 such as copper foil is laminated on the applied adhesive insulating layer 6,
The conductor 7 is bonded to the adhesive insulating layer 6 by pressing while heating with a heat press that can raise the temperature, thereby producing a printed circuit board having a highly thermally conductive metal base.

As described above, according to this example, the highly thermally conductive adhesive is
A high-viscosity base is applied to the metal base 4 side that does not bend or warp during the coating, drying, and curing processes, and screen printing and metal masks that are suitable for coating, that is, the thickness distribution of the coated surface, and small variations in thickness from coating to coating, are used. Coating using methods such as printing or a blade coater may cause the cured insulating layer 6 and the adhesive insulating layer 6 to crack or damage the metal base 4.
A word expression that is distorted. In the manufacturing process of this embodiment, the cured insulating layer 5 and the adhesive insulating layer 6 are coated twice, but by laminating and coating the insulating layers several times in this way, the cured insulating layer 5 and the adhesive insulating layer 6 are coated twice. The dielectric strength problem caused by air bubbles remaining in the insulating layer consisting of the adhesive insulating layer 6 and the adhesive insulating layer 6 is also solved. In this case, the insulating layer 6 is first coated at least once, dried and cured, and the adhesive insulating layer 6 is laminated and coated on the cured insulating layer 5. This is also for better management of the combined thickness of the cured insulating layer 5 and adhesive insulating layer 6.

That is, the cured insulating layer 6 is cured by a drying and curing process until it is completely cured after applying a highly thermally conductive adhesive with the main purpose of ensuring the thickness of the insulating layer. Therefore, depending on the thickness of the insulating layer, the number of coatings may be increased.

On the other hand, the adhesive insulating layer 6 is naturally included in the thickness of the insulating layer, but its main purpose is to bond with the conductor 7.
The highly thermally conductive adhesive is dried to an adhesive, uncured state in a drying process after application. By distinguishing the cured insulating layer 5 and the adhesive insulating layer 6 and coating them in multiple layers, it is possible to eliminate problems with dielectric strength caused by air bubbles remaining in the insulating layer, and also to improve the strength of the insulating layer. A stable product with varying thickness can be obtained.

Next, a case where screen printing is used as a coating method among the embodiments of the present invention will be described with reference to the drawings.

Figures 3(-) to (d) show a method for manufacturing a highly thermally conductive metal-based printed circuit board in which a highly thermally conductive adhesive is applied twice by screen printing. 3
Manufactured through the process in Figure (d) t, 8 is a metal base,
9 is a cured insulating layer, 10 is an adhesive insulating layer, and 11 is a conductor. In FIG. 3(a), a metal base 8 made of aluminum, anodized aluminum, or iron, with a thickness of 0.6 to 6 degrees, is shown.
The above-described highly thermally conductive adhesive is screen-printed using a 100-30011-ku Jimetsch mask, and a cured insulating layer 8 is formed through a drying and curing process. Next, in FIG. 3(b), a highly thermally conductive adhesive is laminated and coated on the cured insulating layer 9 by screen printing similar to the above, and dried to an adhesive and uncured state.
form 0. In FIG. 3(C), a conductor 11, typically made of copper foil, is laminated on the adhesive insulating layer 10, and then heated for 30 minutes at a temperature of 150° C. or higher and a pressure of 10 to 50 kg/2 using a heat press. Heat pressing is performed for ~2 hours, and the conductor 11 is bonded together with the adhesive insulating layer 10 being cured. After completing the process shown in FIG. 3(C), the printed circuit board having a highly thermally conductive metal base is cut into a required size and completed as shown in FIG. 3(d).

When screen printing is used as a coating method as described above, an advantage is that printing materials with higher viscosity can be used than with other coating methods.

That is, a larger amount of highly thermally conductive filler can be incorporated into the adhesive organic polymer, and a highly thermally conductive adhesive with higher thermal conductivity can be applied. However, on the other hand, air bubbles are likely to form due to the mesh marks on the screen, especially as the viscosity becomes higher, and bonding the conductor with one coating will leave air bubbles in the insulating layer, so at least as shown in this example, It is necessary to apply the layer twice. In addition, when applying by screen printing, air bubbles are likely to be formed due to the mesh marks on the screen, so as a countermeasure, it is better to have a smaller mesh wire diameter, that is, 10
A screen as fine as 0 mesh or less is preferable. However, the finer the mesh, the thinner the coating thickness of the highly thermally conductive adhesive becomes.Therefore, in order to thicken the insulating layer, it is necessary to increase the number of laminated coatings. It is preferable to use a coating agent having a concentration of 1 to 300 mesosyus. When the mesh of the screen is set to 300 meshes on the upper limit side, there is a limit to the particle size of the highly thermally conductive filler dispersed in the highly thermally conductive adhesive.

That is, the highly thermally conductive filler must have a maximum particle size not exceeding 503 to 71 m so that the screen can be coated in an optimal state without clogging. They are not particularly related to the type of highly thermally conductive filler, but rather during the kneading process to make the highly thermally conductive adhesive, the particles of said highly thermally conductive filler are crushed, and before the screen printing application. The adhesive may be a highly thermally conductive adhesive having a maximum particle diameter of 60 μm or less.

Next, the highly thermally conductive adhesive used in the present invention will be explained. The highly thermally conductive adhesive of the present invention is a Banbury mixer in which a highly thermally conductive filler is mixed with various additives and a curing agent in an adhesive organic polymer.

It is a paste-like composition that is kneaded using a mixer such as a roll mill. Here, the organic polymer with adhesive properties must be of a high temperature curing type that causes a curing reaction at 100°C to 200°C and is heat resistant. Cyanate ester resin compositions such as acid ester-maleimide resins, cyanate ester-maleimide-epoxy resins, and phenol resins.

Thermosetting resins such as epoxy resins, melamine resins, unsaturated polyester 14° resins, polyimide resins, polyvinyl butyral, butadiene resins, acrylonitrile resins, etc.
Cyanate ester resin modified with thermoplastic resin such as butadiene resin, cyanate ester-maleimide 'ffm
Examples include cyanate ester-maleimide-epoxy resin. On the other hand, highly thermally conductive fillers include alumina and boron nitride.

Examples include silicon nitride, aluminum nitride, magnesium oxide, and silicon carbide. Among them, alumina and boron nitride are suitable in terms of thermal conductivity and electrical properties (insulation resistance, dielectric strength, etc.). However, although boron nitride has higher thermal conductivity than alumina, when it is dispersed in the organic polymer mentioned above, its adhesive strength as a highly thermally conductive adhesive is extremely reduced, so there is a problem that it cannot be blended in high proportions. In this respect, alumina particles can be blended in an extremely large amount compared to the other fillers. Among them a-
Known as alumina powder, those with particle shapes close to spherical have the characteristic that they can be dispersed in the highest proportions. Therefore, the high thermal conductive adhesive according to the present invention can be formulated with at least 16 particles of alumina alone or in combination as a high thermal conductive filler, resulting in a high thermal conductive adhesive with high thermal conductivity. is obtained.

The method of manufacturing a printed circuit board having a highly thermally conductive metal base according to the present invention involves laminating and bonding a conductor to a highly thermally conductive adhesive coated on the metal base side at least twice. mainly described the example of screen printing coating in order to use a high viscosity and high thermal conductive adhesive with the highest thermal conductivity as an insulating layer, but there are other methods such as metal mask printing, coating methods using a blade coater, and It is also possible to use a rod coater, knife coater, etc. -1 If the metal base is made of aluminum or alumite-treated aluminum to improve heat dissipation, a printed circuit board with excellent heat dissipation can be obtained at the lowest cost. Furthermore, a method for improving heat dissipation includes applying a highly thermally conductive adhesive as a cured insulating layer, and adding a step of pressing the cured insulating layer to the next step of drying or curing in the drying and curing process. There is a way.

As a result, the particles of the highly thermally conductive filler dispersed in the cured insulating layer are compressed to a high density, resulting in a cured insulating layer with further improved heat dissipation properties. However, in this case, even if the cured insulating layer is completely cured and then pressed, the effect will be weak, so a dry or semi-cured state is preferable.

Effects of the Invention As is clear from the above explanation, the present invention has a metal base,
The insulating layer of a highly thermally conductive metal-based printed circuit board consisting of an insulating layer and a conductor is made of a highly thermally conductive adhesive in which a highly thermally conductive filler is dispersed in an adhesive organic polymer. After coating the adhesive on the metal base side at least twice, the conductor is laminated on the coated high thermal conductive adhesive layer and heat pressed to produce this type of high thermal conductive adhesive. There are certain manufacturing issues that cannot be avoided when using a metal base, such as the need to apply a thick coating due to the dielectric constant, and if the coating is applied to the conductor side, the conductor may warp during the process from coating to bonding with the metal base9. This solves problems such as cracking of the insulating layer and generation of bubbles, and provides an excellent effect of facilitating mass production.

Additionally, at least two coats of highly thermally conductive adhesive are applied to the metal base.
In the multilayer coating process, by separating the cured insulating layer and the adhesive insulating layer and applying the multilayer coating, it not only eliminates dielectric breakdown voltage defects caused by air bubbles that occur during coating, but also eliminates variations in the thickness of the insulating layer. You can get something stable.

In addition, by using screen printing, metal mask printing, and a blade coater as coating methods, even high-viscosity, high-thermal conductive adhesives containing high thermally conductive fillers can be easily applied as an insulating layer. This has the effect of providing a highly thermally conductive metal-based printed circuit board with excellent heat dissipation even with a thick insulating layer. Furthermore, heat dissipation is further improved by adding a step of pressing the dried or semi-cured cured insulating layer during the process of applying, drying and curing a highly thermally conductive adhesive as a cured insulating layer. There are effects such as the ability to obtain a hardened insulating layer.

181.・−

[Brief explanation of drawings]

FIGS. 1(a) and (b) are cross-sectional views showing the steps of a conventional printed circuit board manufacturing method, and FIGS. FIG. 2 is a cross-sectional view and a perspective view for explaining a method of manufacturing a printed circuit board in one embodiment. 4.8...Metal base, 6,9...Insulating hardened layer, 6.1o...Insulating adhesive layer, 7,11
······conductor. Name of agent: Patent attorney Toshio Nakao and one other person

Claims (1)

[Claims] (1) An insulator made of a highly thermally conductive adhesive in which a highly thermally conductive filler is dispersed in an adhesive organic polymer is applied at least once to a metal base and cured to form a cured insulating layer. death,
Furthermore, an insulator made of a highly thermally conductive adhesive of the same quality as the above-mentioned highly thermally conductive adhesive is applied to the cured insulating layer, dried to an uncured state to form an adhesive insulating layer, and a conductor is laminated on the adhesive insulating layer. and (2) the method for manufacturing a highly thermally conductive metal-based printed circuit board according to claim 1, which comprises applying a highly thermally conductive adhesive by using screen printing, metal mask printing, or a blade coater alone or in combination. . (a) A method for manufacturing a highly thermally conductive metal-based printed circuit board according to claim 1, wherein a highly thermally conductive adhesive is applied by screen printing with a screen of 100 to 300 meshes. (4) Metal Claim 1 using aluminum or anodized aluminum as the base
A method for manufacturing a highly thermally conductive metal-based printed circuit board as described in . A method for manufacturing a highly thermally conductive metal-based printed circuit board according to claim 1. (6) A method for manufacturing a highly thermally conductive metal-based printed circuit board according to claim 1, wherein a high temperature curing type is used as the adhesive organic polymer. (h) The method for manufacturing a highly thermally conductive metal-based printed circuit board according to claim 1, wherein the highly thermally conductive filler contains at least alumina particles alone or in combination. (8) A method for manufacturing a highly thermally conductive metal-based printed circuit board according to claim 1, wherein an organic polymer having high temperature curing adhesive properties is used as the highly thermally conductive adhesive. 3 Mi -゛