JPH05299788A - Printed wiring board with cooling device - Google Patents

Abstract

PURPOSE:To obtain a printed wiring board which is capable of forming through holes which are excellent in heat radiation and heat resistance by burying a cooling device, which passes a heating medium, into an insulation layer. CONSTITUTION:A board comprises a conductor 1 which serves as a single or double-sided surface layer circuit, a cooling device 2 through which a heating medium passes and thermosetting resin 3. As for the conductor 1 which serves as a surface circuit, it is acceptable to use a metal foil, which is one-piece formed during the formation of the board or a plated metal formed after the formation of the board. The cooling device 2 incorporates a flow passage 4 where a heating medium flows. It is preferable the device to be made of metals, such as copper, aluminum and iron, or alloy or ceramic. A penetration hole larger than a through hole is provided. The insulation resin filled up in the hole is drilled, thereby enabling the formation of a through hole. It is, therefore, possible to provide excellent heat radiation and heat resistance and through hole formation performance since the insulation resin is a hardened substance of a molding material which uses thermosetting resin.

Description

Detailed Description of the Invention

[0001]

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

To solve such problems, there is a method of molding a substrate with a metal core by using a molding material. However, a thermoplastic resin such as polyresin, which is mainly used for general molding substrates, is used. The molding temperature of ether ether ketone, polyether sulfone, polyether imide, etc. is 3
It is very high at around 00 ° C and has problems in dimensional stability and the like. Further, the resin having good heat resistance is expensive. Further, in a substrate with a metal core, heat generated in a part of the substrate may be transmitted through the metal core and unnecessarily increase the temperature of other parts. Furthermore,
When a component such as a semiconductor element that generates a large amount of heat is mounted, the heat dissipation may be insufficient. The present invention has been made in view of the above circumstances, and provides a printed wiring board having excellent heat dissipation and heat resistance and capable of forming through holes.

[0004]

That is, the present invention provides a printed wiring board having a conductor for forming a circuit on at least one surface of an insulating layer made of a thermosetting resin cured product, and cooling by passing a heating medium through the insulating layer. The present invention relates to a printed wiring board having a built-in cooling device, in which the device is embedded. Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a sectional view of an example of a printed wiring board having the cooling device of the present invention built therein. The substrate of the present invention comprises a conductor 1 which is a surface layer circuit on one side and / or both sides of the substrate, a cooling device 2 through which a heat medium passes, and a thermosetting insulating resin 3.
The conductor forming the surface layer circuit is not particularly limited, and may be a metal foil integrally formed at the time of forming the substrate, or a plated metal formed by electroless plating or the like after forming the substrate.
Although any metal foil may be used depending on the application, a copper foil used for a general printed wiring board is preferable in consideration of solderability, circuit formability, price, and the like. In addition, the surface of the metal foil in contact with the insulating resin can be improved in adhesiveness with the insulating resin by roughening or treating with a coupling agent or an adhesive. The electroless plating may be any one depending on the application, but copper plating used for general printed wiring boards is preferable in consideration of solderability, circuit formability, price and the like. Further, by physically and / or chemically roughening the surface of the insulating resin to be plated, the adhesiveness with the plating metal can be improved.

The cooling device may have any structure as long as it has a flow path 4 for flowing a heat medium therein. The material may be any material such as metal, ceramic, thermoplastic resin, thermosetting resin, etc., but in view of thermal conductivity, heat resistance, workability, price, etc., metal or alloy such as copper, aluminum, iron or Ceramic is preferred. As a specific example of such a cooling device, FIG.
Although the thing shown in (d) can be mentioned, this invention is not limited to this.

FIG. 1A shows a sectional view of an example of a substrate in which a cooling device obtained by bending a tube is inserted. The tube may have any cross-sectional shape such as a circle, an ellipse, a square, or a combination thereof. By providing a space between adjacent pipes, the through hole can be formed by the insulating resin portion filled in the space. An example of a bent tube is shown in FIGS. As shown in FIG. 2B, the net-like joint has a structure in which the tube is not easily deformed when the substrate is molded. FIG. 1B shows a cross-sectional view of an example of a substrate in which a cooling device obtained by processing two plates is inserted. Such a cooling device has a convex portion 6 as shown in FIG.
As shown in FIG. 3 (b), the two plates 5 having the shape of ‘1’ are joined by a method such as welding, brazing, soldering, or adhering the convex portions, and then joined as shown in FIG. It is obtained by removing unnecessary portions of the portion 7. Further, FIG. 1C shows a cross-sectional view of an example of a substrate in which a cooling device obtained by processing three or more plates is inserted. In such a cooling device, for example, a spacer 8 is sandwiched between two plates as shown in FIG. 4 (a) and joined by welding, brazing, soldering, bonding, etc. as shown in FIG. 4 (b). , And is obtained by removing unnecessary portions as shown in FIG. In the method of assembling the cooling device as shown in FIG. 3 or 4, the flow path of the heat medium can be controlled by the shape of the protrusion or the spacer. For example, a serial flow path as shown in FIG. 2 (c), a parallel flow path as shown in FIG. 2 (d), a mesh flow path as shown in FIG. 2 (e), and combinations thereof. There are things like FIG. 1D shows a cross-sectional view of an example of a substrate in which a foamed body having porous or open cells coated with a substance that does not permeate a heat medium is inserted as a cooling device.

One or more such cooling devices can be used for one substrate. The shape of the cooling device may be any shape as required, and may be different or the same. Further, the arrangement relationship of these cooling devices in the substrate may be arranged on a plane, respectively, or part or all of them may overlap in the thickness direction,
It may also be nested. Further, the surfaces of these cooling devices can be subjected to degreasing, roughening, treatment with a coupling agent, etc., and the adhesiveness with the resin can be improved.
It is preferable that the cooling device in the portion where the through hole is formed is provided with a through hole having a diameter larger than that of the through hole.
The through hole can be formed by drilling the insulating resin filled in the through hole. It is preferable that a part of the cooling device is exposed without being covered with the insulating resin. In this exposed portion, components such as a semiconductor element and a resistor that generate a large amount of heat can be directly mounted on the cooling device, and the cooling effect can be significantly improved.

The insulating resin is a cured product of a molding material using a thermosetting resin. The thermosetting resin may be any resin such as phenol resin, epoxy resin, polyimide resin, unsaturated polyester resin, and triazine resin, and may be used in combination of several kinds. 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 cooling device. 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 compounding amount of the filler is not particularly limited, but is 20 to 80% by volume from the melt viscosity of the resin composition, the thermal conductivity of the cured product, the thermal expansion coefficient, and the like.
Is preferred. 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 if necessary, heating,
You may pressurize. The heat medium used in the cooling device may be any liquid and / or gas, and a heat medium including a commonly used refrigerant can be used.

[0011]

The printed wiring board incorporating the cooling device of the present invention has excellent heat dissipation because the cooling device is inserted in the insulating layer. Moreover, since the insulating resin is a cured product of a molding material using a thermosetting resin, excellent heat resistance and through-hole formability are obtained.

[0012]

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 stainless steel tube with an outer diameter of 1.25 mm and an inner diameter of 0.9 mm was bent in a shape as shown in FIG. 2 (a) in a molding die having a cavity with a depth of 0.8 mm and a thickness of 35 μm. And two copper foils of. The above molding material was transferred by a transfer press at 175 ° C. for 90 seconds, and the molded material was post-cured at 175 ° C. for 5 hours to give a thickness of 1.67 mm, 10
A 0 mm square copper clad substrate was obtained.

Example 2 Instead of the stainless steel tube of Example 1, a copper plate having a thickness of 0.1 mm was used, and a cooling device having a thickness of 1 mm obtained by the method shown in FIG. A copper clad substrate having a thickness of 1.67 mm and a size of 100 mm square was obtained in the same manner as in Example 1 except that the through hole was used.

Comparative Example 1 A dicyandiamide curing type 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 and one sheet of each of the copper foils used in Example 1 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 dicyandiamide curing type epoxy resin varnish having a thickness of 0.
After impregnating a 1 mm glass cloth, it was dried to obtain a prepreg. 1 each of this prepreg on both sides of a 1.4 mm thick copper plate
One sheet and each of the copper foils used in Example 1 were placed and molded in the same manner as in Comparative Example 1 to obtain a copper clad laminate with a metal core having a thickness of 1.67 mm.

Comparative Example 3 The same procedure as in Example 1 was performed except that a copper plate having a thickness of 1 mm and a through hole having a diameter of 1.5 mm was used in place of the stainless steel pipe of Example 1, and the thickness was increased. 1.67mm, 100mm
A copper clad substrate with square metal cores was obtained.

Using the substrate obtained as described above,
The thermal resistance, solder heat resistance, and through hole formability were evaluated. For thermal resistance, a 100 mm square substrate etched with a copper foil of 10 mm x 14 mm left on a transistor (type 2SC
2233) is mounted by soldering a flange of a transistor and a copper foil, and this substrate is adhered to an aluminum block at 25 ° C. on the side opposite to the side on which the transistor is mounted. The temperature rise of the flange and the power consumption of the transistor were measured and found. In addition,
In Examples 1 and 2, the measurement was performed in a state where water at 25 ° C. was flown in the cooling device inserted in the substrate without using the aluminum block. Solder heat resistance is measured by cutting the board into 25 mm square pieces, humidifying them in a constant temperature and high temperature bath at 85 ° C and 85% RH for 50 hours, and floating them in a solder bath at 300 ° C for 5 minutes. The presence or absence was visually observed. The evaluation of the through hole formability was performed by electroless copper plating the inner surface of the hole, using a drill to form a plated through hole, and observing the cross section with a microscope. Also, the insulation between the formed plated through hole and the cooling device or the metal core was measured. In addition,
In Example 1, plated through holes were formed between the tubes, and in Example 2 and Comparative Example 3, plated through holes were formed in through holes provided in the cooling device and the copper plate. The results are shown in Table 1.

[0019]

[Table 1]

As is clear from Table 1, Examples 1 and 2
The thermal resistance of Comparative Example 1 was significantly lower than that of Comparative Example 1, and the heat dissipation was extremely good without using an external heat dissipation plate. Further, the formation of the through holes in Examples 1 and 2 was as easy as in Comparative Example 1, and similarly to Comparative Example 3, no voids or unfilling occurred in the through holes, and good insulation with the cooling device was obtained. Met.

[0021]

As is apparent from the above description, the printed wiring board incorporating the cooling device of the present invention has excellent heat resistance and is easy to form through holes, and does not require an external heat dissipation plate or the like. Its industrial value is high because it can obtain excellent heat dissipation.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a printed wiring board incorporating a cooling device according to the present invention.

FIG. 2 is a plan view of a shape of a cooling device and a heat medium passage.

FIG. 3 is a cross-sectional view showing an assembly process of the cooling device.

FIG. 4 is a cross-sectional view showing the assembly process of the cooling device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Conductor, 2 ... Cooling device, 3 ... Insulating resin, 4 ... Heat medium flow path, 5 ... Plate, 6 ... Convex part, 7 ... Joining part, 8 ... Spacer

Claims (3)

[Claims] 1. A printed wiring board having a circuit-forming conductor on at least one side of an insulating layer made of a thermosetting resin cured product, wherein a cooling device for passing a heat medium is embedded in the insulating layer. The printed wiring board. 2. The printed wiring board according to claim 1, wherein the cooling device is provided with a through hole having a diameter larger than a through hole diameter. 3. The printed wiring board according to claim 1, wherein a part of the cooling device is exposed without being covered with a cured product of a thermosetting resin.