JPH0818182A - Circuit board - Google Patents

Abstract

PURPOSE:To obtain a circuit board on which electronic devices can be mounted with high density by enhancing the heat dissipation effect. CONSTITUTION:The circuit board comprises a high thermal conductivity insulating layer 1 containing dielectric inorganic powder having high thermal conductivity, metal foils 2, 4 applied to the surface and rear of the insulating layer 1, and heat dissipation fins 3 fixed tightly at least one of the metal foils 2, 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board suitable for use in equipment requiring heat dissipation such as electronic equipment, electric equipment, communication equipment, and computing equipment.

[0002]

2. Description of the Related Art In recent years, in the field of electronic equipment, there is a trend toward higher density, and how to dissipate the heat generated in high heat-generating components such as ICs, MSIs, LSIs and power transistors,
A major issue is how to mount the semiconductor chips at a high density without affecting the heat.

Conventionally, as a substrate material for a printed wiring board on which the above electronic equipment is mounted, an organic polymer material such as a paper-based phenol resin laminated plate or a glass-based epoxy resin laminated plate, or a ceramic material such as an alumina substrate is used. However, since all of them have low thermal conductivity and insufficient heat dissipation, high heat-generating components such as ICs, MSIs, LSIs and power transistors could not be mounted at high density.

Therefore, a highly heat conductive metal base printed wiring board based on a metal having excellent heat conductivity has come to be used.

As shown in FIG. 4, the high heat conductive metal base printed wiring board has a metal base 7, an insulating layer 8 disposed on the metal base 7, and a copper layer adhered on the insulating layer 8. And foil 9. In order to improve the heat dissipation effect of this highly heat conductive metal base printed wiring board, the heat dissipation fins 3 are fixed to the lower surface of the metal base 7 via the silicone grease 10 with the screws 11.

However, in this high heat conductive metal base printed wiring board, the thickness of the metal base 7 is 1.0 to 3.0 mm in order to radiate the heat of the high heat generating components mounted on the copper foil 9.
It was necessary to use a thick one. Therefore, it has been extremely difficult to reduce the weight of the high thermal conductivity metal-based printed wiring board.

Further, in order to efficiently transfer the heat of the high heat generating component mounted on the copper foil 9 to the metal base 7, the insulating layer 8 is made thin. However, the thickness of the insulating layer 8 corresponds to the capacitor capacity that affects the frequency characteristics, and since the thickness of the insulating layer 8 is inversely proportional to the capacitor capacity,
The capacitor capacity could not be reduced.

Further, since the heat dissipating fins 3 for dissipating the heat of the metal base 7 are provided with a silicon grease 10 or a heat conductive sheet containing silica in silicon resin between the metal base 7 and the like, the adhesion is poor. It was Therefore, in order to increase the adhesion between the metal base 7 and the heat radiation fin 3 and improve the thermal conductivity, the heat radiation fin 3 is fixed to the metal base 7 with a plurality of screws 11.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a circuit board capable of improving the heat dissipation effect and mounting electronic parts at high density. To provide.

[0010]

A circuit board according to claim 1 of the present invention comprises a high thermal conductive insulating layer 1 containing an inorganic powder having a high thermal conductivity and electrical insulating properties, and a high thermal conductive insulating layer 1 It is characterized in that the metal foils 2 and 4 laminated on the front and back and the heat radiation fin 3 are adhered to at least one of the metal foils 2 and 4.

The circuit board according to a second aspect of the present invention is characterized in that the radiation fins 3 and the metal foil 4 are fixed to each other by the solder 5.

A circuit board according to a third aspect of the present invention is characterized by having through holes 6 for conducting the metal foils 2, 4 on the front and back sides of the high thermal conductive insulating layer 1.

[0013]

The circuit board according to the present invention comprises a high thermal conductivity insulating layer 1 containing an inorganic powder having high thermal conductivity and electrical insulation, and metal foils 2, 4 laminated on the front and back of the high thermal conductive insulating layer 1.
And at least one of the metal foils 2 and 4 has a radiation fin 3
Because of the close contact with each other, the heat generated by the metal foil 2 on the surface can be efficiently conducted to the heat radiation fins 3 through the high heat conductive insulating layer 1. Further, the heat radiation fin 3 is soldered to the metal foil 4 with solder 5.
Since it is fixed by using, the heat conduction effect can be enhanced. In addition, the metal foil 2 on the front and back of the high thermal conductive insulation layer 1,
Since the through hole 6 for conducting 4 is provided, the metal foil 2 on the front surface and the metal foil 4 on the back surface can be conducted to form a ground circuit.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view in which a radiation fin 3 is fixed to a circuit board according to the present invention.

Example 1 As shown in FIG. 1, a circuit board according to the present invention comprises a high thermal conductive insulating layer 1 containing an inorganic powder having a high thermal conductivity and electrical insulating properties, and a front and back surface of the high thermal conductive insulating layer 1. On the surface of the metal foil 2, 4
And the heat radiation fins 3 are fixed to the metal foil 4 on the back surface.

The high thermal conductive insulating layer 1 containing the inorganic powder having high thermal conductivity and electrical insulation is a phenol resin, cresol resin, melamine resin, epoxy resin, unsaturated polyester resin, polyimide resin, isocyanate resin, polyurethane. Resin, etc., polybutylene terephthalate resin, polyphenylene sulfide resin, fluororesin, polyphenylene oxide resin, etc., alone or modified,
Used in any of the mixtures. In particular, it is preferable to use a solventless liquid resin because there is no problem such as solvent remaining in the insulating layer unless a solvent is used.

Examples of the inorganic powder contained in the high thermal conductive insulating layer 1 include alumina powder, aluminum nitride powder, boron nitride powder, silicon nitride powder, magnesium oxide powder, silica powder and the like. In the case of aluminum nitride powder, the heat dissipation is good, but since the water resistance is poor, it is preferable that an aluminum oxide powder is formed on the surface to increase the water resistance. Examples of the oxide layer for improving water resistance include silicon oxides and phosphate apatite oxides.

The above inorganic powders may be used alone or in combination of two or more kinds. These powders have a small average particle diameter of 0.1 to 0.9 μm and an average particle diameter of 10 μm. ．
It is preferable to use those having a large diameter of 0 to 30.0 μm in combination, and those having an average diameter of 2.0 to 6.0 μm may be used in combination. This inorganic powder is 50 to 90 wt% and 80 to 8 wt% when the high thermal conductive insulating layer 1 is 100 wt%.
It is preferably in the range of 7% by weight. The high thermal conductive insulating layer 1 can be arranged not only on the coated metal foils 2 and 4, but also in the form of a film, a sheet, a prepreg or the like, and the thickness thereof is preferably 100 to 500 μm.

The metal foils 2 and 4 are made of copper, aluminum, iron,
A single foil of nickel, zinc, or the like, an alloy foil, or a composite foil can be used, and the thickness of the metal foil 4 in contact with the heat radiation fins 3 is 18 to 7 depending on the heat transfer efficiency.
The range of 0 μm is preferable. The method for bonding and integrating the metal foils 2 and 4 and the high thermal conductive insulation layer 1 is not particularly limited as long as they can be integrated such as a press and a roll.

A circuit 2a is formed on the metal foil 2 on the upper surface of the high heat conductive insulating layer 1 by etching or the like, and high heat generating components and the like are mounted thereon.

Further, the metal foil 4 on the lower surface of the high thermal conductive insulating layer 1
The radiation fin 3 is fixed to the. The heat radiation fin 3 is made of aluminum and has an uneven shape and a large surface area in order to improve heat radiation. The method of fixing the heat radiation fin 3 to the metal foil 4 is a method of soldering, but since the solder 5 is not welded to aluminum,
Nickel plating is applied to the surface of the radiating fin 3 that is bonded to the metal foil 4 so that the solder 5 is welded.

It is preferable to use high-temperature melting solder as the solder 5 for fixing the radiating fins 3. When high-temperature melting solder is used, low-temperature melting solder is used when electronic parts are mounted and soldered on the surface of the circuit board. Can be used.

Further, as shown in FIG. 2, the high thermal conductive insulating layer 1
The through-hole 6 is formed in a part of the circuit 2a, and the circuit 2 on the upper surface is formed by the plating applied in the through-hole 6.
It is also preferable to electrically connect a to the circuit 4a on the lower surface.

Next, an embodiment of the method for manufacturing the above circuit board will be described. First, a 35 μm copper foil is coated with an epoxy resin varnish containing alumina powder to a thickness of 400 μm, and then the B-stage is formed to form a high thermal conductive insulating layer. The powder content of the alumina powder is 85% by weight when the high thermal conductive insulating layer is 100% by weight. The alumina powder is used in an amount of 20% by weight having an average particle size of 0.4 μm, 30% by weight having an average particle size of 3.2 μm, and 50% by weight having an average particle size of 15 μm. Then, thickness 35
A copper foil of μm is placed on the high thermal conductive insulation layer 1 and 20 kg /
A circuit board is obtained by heating and pressurizing under the conditions of cm ² , temperature of 160 ° C. and 60 minutes.

The surface of this circuit board is etched to form a circuit. Then, a through hole 6 is formed in a part of this circuit so that the front and back copper foils are electrically connected.

Next, the heat dissipating fins made of aluminum are nickel-plated on the bonding surface with the circuit board,
It is fixed to the circuit board by soldering. The conditions for soldering this heat radiation fin to the circuit board are 280 to 320.
It is preferable to use high-temperature melting solder that melts at 0 ° C. and fix it to the circuit board.

Electronic parts are mounted on the circuit board to which the heat radiation fins 3 are fixed, and soldering is performed by using a low temperature melting solder which melts at 200 to 250 ° C.

The circuit board thus obtained has a heat resistance value of 0.5 ° C./W, which is higher than that of a conventional high heat conductive metal printed wiring board having a heat resistance value of 1.3 ° C./W. The nature is improving. This thermal resistance value is obtained by flowing a collector current through a transistor mounted on a circuit board to obtain a rise temperature per unit collector loss.

The circuit board obtained as described above does not have a metal base and can be made lighter in weight than the conventional high heat conductive metal printed wiring board, and the thickness of the insulating layer is 2 mm.
Since the thickness can be increased, the capacitance of the insulating layer capacitor is reduced, and it is possible to design with low noise.

[0031]

According to the circuit board of the present invention, a high thermal conductivity insulating layer containing a high thermal conductivity and electrically insulating inorganic powder, and a metal foil laminated on the front and back of the high thermal conductivity insulating layer, Since the heat radiation fin is fixed to at least one of the metal foils by using solder, there is no gap between the heat radiation fins and the metal foil, and the heat conduction effect can be improved. Further, the heat of the high heat generating component mounted on the copper foil can be efficiently transmitted to the heat radiation fins through the high heat conductive insulating layer, so that the weight can be reduced. Furthermore, by providing through holes for conducting the metal foils on the front and back of the high thermal conductive insulating layer, the surface circuit and the ground circuit can be easily connected, and the heat conduction efficiency is improved and the surface circuit and the ground circuit are electrically connected. Can be achieved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a circuit board according to an embodiment of the present invention.

FIG. 2 is a sectional view of a circuit board according to another embodiment of the present invention.

FIG. 3 is a cross-sectional view of a conventional high heat conductive metal base printed wiring board metal.

[Explanation of symbols]

 1 High Thermal Conductive Insulation Layer 2 Metal Foil 3 Radiating Fin 4 Metal Foil 5 Solder 6 Through Hole 7 Metal Base 8 Insulation Layer 9 Copper Foil 10 Silicon Grease 11 Pin

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[Procedure amendment]

[Submission date] July 13, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0030

[Correction method] Change

[Correction content]

The circuit board obtained as described above does not have a metal base and can be made lighter in weight and the thickness of the insulating layer can be made thicker than the conventional high heat conductive metal printed wiring board. , The capacitance of the insulating layer capacitor has been reduced, and low noise design has become possible.

Claims (3)

[Claims] 1. A high thermal conductive insulating layer 1 containing an inorganic powder having high thermal conductivity and electrical insulation, and the high thermal conductive insulating layer 1.
And the metal foils 2 and 4 laminated on the front and back of the
A circuit board, characterized in that the heat radiation fin 3 is in close contact with at least one of the above. 2. The circuit board according to claim 1, wherein the heat radiation fin 3 and the metal foil 4 are fixed to each other with solder 5. 3. The metal foils 2, 4 on the front and back of the high thermal conductive insulating layer 1.
3. The circuit board according to claim 1 or 2, further comprising a through hole 6 for conducting the electric field.