JPS6362920B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a metal core printed wiring board.

Conventionally, insulating substrates such as ceramics have been used as substrates for printed wiring circuits, but recently, metal-core printed wiring boards using metal-core substrates have come to be used for the purpose of improving heat dissipation characteristics. . 1st
The figure is a sectional view showing a conventional manufacturing method of such a metal core printed wiring board. First, a metal substrate 10 to be a core is prepared (FIG. 1A), an insulating coating 11 is formed on its surface (FIG. 1B), and a printed wiring circuit 12 is subsequently formed on this insulating coating (FIG. 1C). ).

Because the conventional manufacturing method is as described above, it is extremely difficult to form double-sided circuits, and therefore, even if heat dissipation characteristics are improved, the packaging density cannot be increased accordingly. be. In other words, if a double-sided circuit is to be formed in the conventional example shown in FIG.
It is necessary to form a through hole with high precision in the hole 0 and provide wiring within this through hole to connect the printed wiring circuits on the front side and the back side. Insulation from the metal core is essential, which not only complicates the process but also tends to cause insulation failure at the through-hole portion. Further, in the above-mentioned conventional example, since the circuit forming process is performed on a rigid metal plate that is difficult to transport, it is difficult to employ a manufacturing process using a continuous elongated body, and the manufacturing cost cannot be reduced. Furthermore, in the conventional example described above, since the circuit forming process is performed on the metal core, there is also a drawback that the selection range of the etching method is limited depending on the type of the metal core and the insulation structure.

The present invention has been made in view of the above-mentioned conventional drawbacks, and its object is to provide a method for manufacturing metal-core printed wiring boards, particularly wiring boards for double-sided circuits, at low cost.

The above-mentioned objects of the present invention are achieved by the manufacturing method of the present invention, in which printed wiring lines are first formed on both sides of a flexible insulating film, and then these are bonded onto a metal substrate.

The details of the present invention will be explained below with reference to Examples.

FIG. 2 is a sectional view for explaining one embodiment of the manufacturing method of the present invention.

First, as shown in FIG. 2A, a flexible insulating film 2 is
Prepare 0. As this flexible insulating film, polyethylene, polybutadiene, epoxy-impregnated glass cloth, polyimide, etc. can be used. Polyimide is particularly suitable in terms of heat resistance. The size and thickness of these flexible insulating films can be selected from a very wide range. For example, thin commercial products of about 25 μm are easily available, but such thin films are particularly suitable for reducing thermal resistance. Further, if necessary, these films can be adhered to each other to form a laminated structure. The thickness of these films varies depending on the electrical characteristics of the printed wiring circuit to be formed on it, the required voltage resistance, and the allowable value of thermal resistance in the thickness direction, but is typically 5 μm or more.
Select a range of 60 μm.

Next, as shown in FIG. 2B, through holes 21 are formed at predetermined locations in the flexible insulating film 20 by a method such as pressing.

Subsequently, as shown in FIG. 2C, printed wiring circuits 22 and through-hole circuits 23 are formed on both sides of the flexible insulating film 20. As a method for forming a printed wiring circuit and a through-hole circuit on a flexible insulating film, a method similar to the method for forming a conventional flexible printed circuit (FPC) can be adopted. For example, an etched foil method can be used in which a copper foil is attached to a flexible insulating film such as polyimide, the circuit is printed, and a printed wiring circuit is formed by an etching method.
Alternatively, it is of course possible to employ an additive method or a semi-additive method that has been developed relatively recently. In any of these etching methods, additive methods, and semi-additive methods, conductive treatments such as electroless plating and PVD can also be used together. The material for forming the circuit only needs to be a conductive material, but among these, silver, copper, gold, aluminum, palladium, nickel, tin, lead, an alloy thereof, or a conductive paint can be used alone or in combination. suitable. After forming the printed wiring circuit 22 and the through-hole circuit 23 in this manner, connections are made at predetermined locations 24 by soldering or the like to complete the electrical function of the entire printed wiring circuit. In order to increase production capacity, it is preferable to carry out the above steps A to C by assembly line operations while the flexible insulating film is kept as a continuous long body.

Finally, as shown in FIG.
It is attached onto the metal substrate 30 by using the following steps. At this time, the adhesive 40 closes the through-hole holes.Through-hole plating is mechanically the weakest in printed circuits, so there is a difference in thermal expansion between the flexible printed wiring board and the metal plate, so heat cycles and heat Easily destroyed by impact etc. For this reason, it is preferable to insert resin into the through-hole at the time of lamination so that the parts move together as one. As materials for the metal substrate 30, copper, aluminum, iron, or alloys containing these as main components are inexpensive and easily available, and are suitable in terms of workability and heat dissipation. Note that if an insulating film is previously formed on all or part of the surface of the metal substrate 30 by a method such as screen printing or roll coating before attaching the flexible insulating film 20, the insulation between the circuit and the metal substrate can be improved. You can further enhance your sexuality. Alternatively, instead of forming an insulating film as described above on the metal substrate, an insulating film may be formed on all or part of the printed wiring circuit on the opposite side by a method such as screen printing or roll coating. You can also do it.
When aluminum or an alloy thereof is used as the material for the metal substrate 30, all or part of the insulating film may be formed of an anodic oxide film. As the insulating adhesive 40, appropriate commercial products such as epoxy resin can be used.

Although the embodiment in which a double-sided circuit is formed has been described above, it is clear that a wiring board with a single-sided circuit can also be manufactured by the present invention.

As explained in detail above, the present invention has a structure in which a printed wiring circuit is formed on a flexible insulating film and then this flexible insulating film is attached to a metal substrate. Manufacturing processes can be easily adopted and production capacity can be increased. Furthermore, since the printed wiring circuit is completed before being attached to the metal substrate, a wide range of etching methods can be selected regardless of the type of metal substrate or the insulation structure. Furthermore, the method of the present invention has the advantage that printed wiring boards with double-sided circuits can be easily produced.

[Brief explanation of drawings]

FIG. 1 is a sectional view for explaining a conventional manufacturing method, and FIG. 2 is a sectional view for explaining a process of an embodiment of the present invention. 20...Flexible insulating film, 21...Through hole, 22...Printed wiring circuit, 23...Through hole circuit, 30...Metal substrate, 40...Insulating adhesive.

Claims (1)

[Claims] 1. A printed wiring circuit is formed on both sides of a flexible insulating film by through-hole plating, and then the flexible insulating film is adhered to a metal substrate to seal the through-hole hole. A method for manufacturing a metal core printed wiring board.