JPH05291751A - Manufacture of board with metal core for printed wiring - Google Patents

Abstract

PURPOSE:To improve heat dissipation and heat resistance and to eliminate formation of through holes by inserting a metal piece for electrically connecting a surface layer circuit and a metal plate having heat dissipation, and molding with a molding material using thermosetting resin. CONSTITUTION:A metal piece 4 for electrically connecting a surface layer circuit and a heat dissipating metal plate 5 are so disposed as not to be brought into contact with one another in a cavity 3 formed of an upper mold 1 and a lower mold 2. In this case, a metal foil 6 for forming the circuit may be additionally disposed, and the piece 4 is so disposed as to be brought into contact with an inner surface of the cavity 3 or the foil 6 via a contact surface 4a. The piece 4 for electrically connecting a surface circuit and the plate 5 having heat dissipation are inserted and molded of a molding material using thermosetting resin, and hence a board with a metal core which has excellent heat dissipation and heat resistance and in which the step of molding through holes is eliminated is obtained. Accordingly, this board is entirely eliminated for the steps of drilling, plating of the holes, thereby reducing a manufacturing cost.

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 printed wiring board used in electronic equipment and the like which requires heat dissipation.

[0002]

2. Description of the Related Art Conventionally, a printed wiring board used for electronic equipment is laminated with paper or glass cloth (prepreg) impregnated with phenol resin, epoxy resin or the like and a metal foil, and heated and pressed by a press. Obtained. Such a substrate made of paper or glass cloth and resin has a low thermal conductivity and cannot be directly mounted with a large power semiconductor element or the like that generates a large amount of heat, but must be mounted separately on a heat sink or the like. On the other hand, there is a metal core wiring board as a wiring board having heat dissipation property, which is obtained by applying a resin on the surface of a metal plate to form an insulating layer and bonding a metal foil. With such a metal core substrate, circuits can be formed on both front and back surfaces, but it is difficult to form through holes for electrically connecting these because the metal plate is an electrical conductor. On the other hand, a method of filling an insulating resin in a hole made in a metal plate and then laminating it with a prepreg (for example, JP-A-59-105216) or a method of filling an excessive resin in the prepreg in a hole made in a metal plate Such methods (for example, JP-A-59-213431 and JP-A-59-213432) have been proposed. However, since these methods use prepreg,
The resin filled in the holes does not contain a base material, and the physical properties such as the coefficient of thermal expansion are different from those of the insulating layer portion, and the electrical reliability of the through hole portion remains uneasy.

[0003]

The substrate using the prepreg as described above requires a step such as a drilling process to form the through hole of the through hole. This processing process requires a great deal of time and labor and occupies a large proportion in terms of cost. Especially when glass cloth is used as the substrate,
The processing blade is easily worn, which is a problem. Further, a conductor is formed in the through hole by electroless plating or the like, but this plating process also requires a great deal of time and labor and occupies a large cost ratio. For such a problem, there is a method of molding a substrate with a metal core using a molding material,
Thermoplastic resins mainly used for general molded substrates, such as polyetheretherketone, polyethersulfone, and polyetherimide, have a very high molding temperature of around 300 ° C. and have a problem in dimensional stability. Further, since the melt viscosity is high, the metal core is easily moved and deformed by the molding pressure during molding. In addition, resins with good heat resistance are expensive.
On the other hand, the thermosetting resin can lower the molding temperature and has good dimensional stability. Moreover, the heat resistance is good, but the price is low. On the other hand, there is a method of forming through-holes for through holes in a substrate by using a molding die provided with convex portions, but the positions and the number of through holes are different for each circuit. Therefore, each molding die must be manufactured. It is very expensive. The method of the present invention has been made in view of such circumstances,
A printed wiring board having a metal core, which has excellent heat dissipation and heat resistance and does not require a through-hole forming step.

[0004]

A method of manufacturing a printed wiring board with a metal core according to the present invention is a thermosetting method in which a metal piece for electrically connecting a surface layer circuit and a metal plate having a heat radiation property are inserted. It is characterized by molding with a molding material using a resin. Hereinafter, the present invention will be described in detail. FIG. 1 shows a sectional view of an example in which a metal piece, a metal plate and a metal foil used in the method of the present invention are arranged in a mold. A metal piece 4 for electrically connecting a surface layer circuit and a metal plate 5 for heat dissipation are arranged in a cavity 3 composed of an upper mold 1 and a lower mold 2 so as not to contact each other. At this time, the metal foil 6 for forming the surface layer circuit may be added and arranged. The metal piece is arranged so as to contact the inner surface of the cavity or the metal foil at the contact surface 4a. The number of metal plates for heat dissipation may be one or more. The material of the metal plate may be different or the same, such as metal such as copper, aluminum and iron, alloy such as stainless steel, plated with zinc, tin, nickel and the like. Any material may be used, but a material having a high heat conductivity is preferable in a portion requiring heat dissipation. The shape of the metal plate may be any shape as required, and may be different or the same. Further, a hole for allowing the metal piece for circuit connection to be nested may be provided, but it must be electrically insulated from the metal piece. Regarding the arrangement relationship of the metal plates in the substrate, they may be arranged on a plane, may partially or entirely overlap in the thickness direction, and may be nested. Further, the surfaces of these metal cores can be subjected to degreasing, roughening, treatment with a coupling agent, etc., and the adhesiveness with the resin can be improved. There is no particular limitation on the material of the metal piece, and any electrically conductive material can be used, but due to its electrical conductivity, ease of connection with the surface layer circuit, price, ease of processing, etc. Copper or copper alloys are preferred. Also, its shape is
It may have any shape such as a round or square rod shape, a tubular shape, a plate shape, a box shape or a combination thereof, and may have an uneven surface so as to improve adhesion with a molding material. When such a metal piece is placed in the mold, it is necessary to contact the inner surface of the cavity or the metal foil at at least two places. The reason for this is that the original purpose of the metal piece is to connect the surface layer circuits to each other as in the conventional plated through hole. The molding material does not flow into the contact surface during molding, and a part of the metal piece is exposed. Using this exposed surface, the surface layer circuit and the metal piece are electrically connected by soldering, plating, conductive paint, or the like. It is preferable that such a metal piece is provided with a through hole into which a lead pin or the like of a component mounted on the board is inserted. When the metal piece is used only for the connection of the surface layer circuit, the through hole may not be provided, but in the case of mounting a component such that the lead pin is inserted into the hole opened in the substrate and connected and fixed, Through holes provided in this metal piece can be used.
The through hole may be provided by a method such as drilling or pressing, but a metal piece cut into a suitable length may be used as the metal piece. The conductor to be the surface layer circuit can be formed by electroless plating or the like after molding the substrate, but the plating step is disadvantageous in cost as described above. Therefore, it is preferable to dispose a metal foil, which will become a circuit during molding of the substrate, between the metal piece and the inner surface of the cavity to integrally mold the metal foil. The metal foil is not particularly limited and any electrically conductive material can be used, but it is used for a general printed wiring board because of its electrical conductivity, solderability, circuit formability, price, etc. Suitable copper foil is suitable. A solder coating is preferably formed on the surface of the metal piece that contacts the cavity or the metal foil. The solder coating can protect the exposed surface of the metal piece from the etching solution when forming a circuit on the substrate. Further, in the substrate integrally formed with the metal foil, the exposed surface of the metal piece may be covered with the metal foil and cannot be connected by soldering or the like depending on the circuit pattern, and by interposing solder between them in advance, It can be connected by heating. Such a metal piece is preferably fixed to the heat dissipation metal plate with an electrical insulator. As a result, the efficiency of the work of placing the metal piece in the mold is dramatically improved. That is, it takes a very long time to accurately arrange many metal pieces so as not to contact the metal plate for heat dissipation,
Reduce production efficiency. On the other hand, if the metal piece is fixed to the metal plate in advance, the positioning work becomes unnecessary and the working time can be greatly shortened. The insulator for fixing the metal piece is not particularly limited as long as it can ensure electrical insulation and does not melt or deform during molding. Examples thereof include inorganic materials such as ceramics and mica, thermoplastic or thermosetting resins, and compositions thereof. After placing the metal piece and the metal plate as described above in the molding die, a molding material using a thermosetting resin is injected and cured to obtain a substrate.
As the thermosetting resin of the molding material, any resin such as phenol resin, epoxy resin, polyimide resin, unsaturated polyester resin, and triazine resin may be used, and several kinds thereof may be used in combination. Particularly, a system in which a phenol resin is mixed with an epoxy resin as a curing agent is excellent in heat resistance and electric characteristics. Further, additives such as a curing accelerator that accelerates the curing reaction, a flame retardant auxiliary agent that imparts flame retardancy, a colorant, and a release agent can be appropriately mixed in these resins. By blending various fillers in such a resin system, the thermal conductivity can be improved and the thermal expansion coefficient can be matched with the core material. For example, inorganic materials such as fused silica, crystalline silica, alumina, and silicon nitride, and powders of organic materials such as silicone and Teflon can be used. They may be used alone or in combination of several kinds, but for the purpose of the present invention, the thermal conductivity is Higher is preferable. The particle size of the filler may be any size that does not cause the gate of the molding die to be clogged, and the shape thereof may be any shape. The blending amount of the filler is not particularly limited, but is preferably in the range of 20 to 80% by volume in view of the melt viscosity of the resin composition, the thermal conductivity of the cured product, the thermal expansion coefficient and the like. When the filler is blended, a surface treatment agent typified by a silane coupling agent may be added in order to enhance the adhesiveness with the resin. As a molding method, a general molding material molding method such as casting, transfer molding, injection molding or compression molding can be used, and heating or pressurization may be performed as necessary. Further, as long as the cavity shape of the molding die is moldable, any shape can be used, and if the outer shape of the substrate is the same, it is not necessary to prepare a die for each circuit.

[0005]

In the method of the present invention, the metal piece for electrically connecting the surface layer circuit and the metal plate having heat radiation are inserted and molded with the molding material using the thermosetting resin. It is possible to obtain a printed wiring board with a metal core which is excellent and does not require a through hole forming step. That is, since a metal plate for heat dissipation is inserted in the substrate, excellent heat dissipation can be obtained, and since it is molded with a thermosetting molding material, excellent heat resistance can be obtained. Further, since the metal piece for electrically connecting the surface layer circuits is inserted and molded, it is possible to obtain a printed wiring board with a metal core that does not require a step of forming a through hole such as drilling or plating.

[0006]

The present invention will be described below based on examples.
The invention is not limited to this example.

Example 1 ESCN-195 (Orthocresol novolac type epoxy resin manufactured by Sumitomo Chemical Co., Ltd., trade name): 100 parts by weight HP-800N (phenol novolac resin manufactured by Hitachi Chemical Co., Ltd., trade name): 50 parts by weight Alumina powder: 950 parts by weight Epoxy silane coupling agent: 3 parts by weight Triphenylphosphine: 5 parts by weight Carbon black colorant: 1 part by weight The above compounds were sufficiently kneaded to obtain a thermosetting molding material.
On the other hand, a copper plate having a thickness of 1 mm and having a through hole having a diameter of 2 mm is arranged in a mold having a cavity having a depth of 0.3 mm at both top and bottom, and a copper wire having a diameter of 1 mm having a length of 1. What was cut to 6 mm was placed so as not to contact the copper plate. The above molding material was transferred to this by a transfer press at 175 ° C. for 90 seconds,
The molded product was post-cured at 175 ° C. for 5 hours to obtain a 1.6 mm-thick 100 mm square metal core-containing substrate, which was subjected to electroless copper plating to obtain a metal core-containing copper-clad substrate.

Example 2 Example 1 was repeated except that a copper foil having a thickness of 35 μm was added and arranged between the copper wire and copper plate of Example 1 and the inner surface of the cavity, and that electroless plating was not performed. The same operation was carried out to obtain a 100 mm square copper-clad substrate with a metal core of 1.67 mm.

Example 3 Instead of the copper wire and the copper plate of Example 2, a copper tube having an outer diameter of 1 mm and an inner diameter of 0.8 mm was cut into a length of 1.6 mm, and the copper plate used in Example 2 was epoxy-based. The same operation as in Example 2 was carried out except that the adhesive was fixed so as not to come in contact with the adhesive, and a 100 mm square copper-clad substrate with a metal core of 1.67 mm was obtained.

Comparative Example 1 A dicyandiamide curing epoxy resin varnish having a thickness of 0.
After impregnating a 2 mm glass cloth, it was dried to obtain a prepreg. Eight sheets of this were laminated, the copper foil used in Example 2 was placed on both sides, and heated at 170 ° C. for 90 minutes and pressed to obtain a copper-clad laminate having a thickness of 1.67 mm.

Comparative Example 2 A copper clad substrate containing a metal core was obtained by the same method as in Example 2 except that the copper wire of Example 2 was not used.

Using the substrate obtained as described above,
The thermal conductivity, solder heat resistance, and through hole characteristics were evaluated. The thermal conductivity was measured by using a 100 mm square substrate from which the copper foil was removed and using a thermal conductivity meter (QTMD3: manufactured by Kyoto Electronics Manufacturing Co., Ltd.) by a hot wire method using a flat probe. Solder heat resistance is measured by cutting the board into 25 mm square, 85 ℃,
Humidify for 50 hours in a constant humidity and high temperature tank of 85% RH at 300 ° C.
After floating for 5 minutes in the solder bath, the presence or absence of blisters was visually observed. Regarding the characteristics of the through hole, in Examples 1 to 3, the surface layer circuit was formed, and then the surface layer circuit and the interpolated copper wire were used for soldering. In Comparative Examples 1 and 2, the inner surface was drilled using a drill. The electroless copper plating was used to form the plated through holes, and the connectivity with the surface layer circuit and the insulation with the copper plate as the metal core were evaluated. The through hole of Comparative Example 2 was formed in the through hole opened in the copper plate. The results are shown in Table 1.

[0013]

[Table 1]

As is clear from Table 1, Examples 1 to 3 produced by the method of the present invention had higher thermal conductivity than Comparative Example 1 and had good heat dissipation. Further, in Examples 1 to 3, the drilling and through-hole plating for forming the through-holes were unnecessary. In addition, the insulation with the metal core and the connectivity with the surface layer circuit were good. Furthermore, in Example 3, the component could be mounted by inserting the lead pin of the component into the inserted copper tube.

[0015]

As is apparent from the above description, the method of the present invention is excellent in heat dissipation and heat resistance, and it is possible to obtain a metal core-containing substrate which does not require a through hole forming step. The obtained substrate has no industrial process such as drilling or plating to form a through hole and can significantly reduce the manufacturing cost of a printed wiring board, and thus has high industrial value.

[Brief description of drawings]

FIG. 1 is an example of a cross-sectional view of a metal piece, a metal plate, and a metal foil used in the method of the present invention arranged in a mold.

[Explanation of symbols]

1 ... Upper mold, 2 ... Lower mold, 3 ... Cavity, 4 ... Metal piece, 4
a ... contact surface, 5 ... metal plate, 6 ... metal foil

Claims (5)

[Claims] 1. A molding die is provided with a metal piece that is in contact with the inner surface of the cavity at two or more locations, and a metal plate that is not in electrical contact with the metal piece, and then a molding material using a thermosetting resin is injected. A method for producing a printed wiring board with a metal core, characterized by comprising: 2. The method for producing a printed wiring board with a metal core according to claim 1, wherein a metal foil to be a circuit is arranged between the metal piece and the inner surface of the cavity. 3. The method for producing a printed wiring board with a metal core according to claim 1, wherein a metal piece provided with a through hole for inserting a lead pin or the like of a component mounted on the board is used. .. 4. The method for producing a printed wiring board with a metal core according to claim 1, 2 or 3, wherein the metal piece is previously fixed to the metal plate with an electrical insulator. 5. The printed wiring board with a metal core according to claim 1, wherein a solder coating is formed on an inner surface of the cavity of the metal piece or a portion in contact with the metal foil. Production method.