JPH0336320B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the production of additive printed wiring boards with good heat dissipation properties at low cost, and furthermore, to improvement of printed wiring boards with metal cores insulated by electrodeposition coating. It is related to.

Today, with the demand for high-density packaging of LSIs, various metal-core heat dissipation boards are being considered to solve the problem of heat generation. There are various methods for insulating the surface of metal substrates, such as powder coating, electrodeposition coating, roll coater coating, and insulating sheet pasting. Electrodeposition coatings are attracting attention.
However, conventional electrodeposition coatings have good film thickness uniformity immediately after electrodeposition, but the problem is that the paint flows when heated and hardened, making the edges extremely thin, and the metal of the conductor and core easily leaks. There were two other major drawbacks: insufficient adhesion between the coating film and the conductive pattern formed by plating. In order to improve these drawbacks, methods have been used to physically stop the edge flow by dispersing large quantities of inorganic pigments and fillers in the paint, but the reliability of the insulation is low, and the surface This was inappropriate because the smoothness was impaired. Furthermore, the usual method of etching with a chromium sulfuric acid mixture to improve the adhesion of plating does not provide sufficient peel strength.

The present invention aims to solve these problems, and its purpose is to provide a print with excellent quality, which can prevent leakage between the conductor and the core metal, and improve the adhesion of the conductor pattern. The purpose of the present invention is to provide a method for manufacturing a wiring board.

The method for manufacturing a printed wiring board of the present invention includes a first electrodeposition coating step for forming a coating film that enables electrical insulation on the surface of a metal substrate, and a second low temperature coating step for removing moisture in the coating film. It is characterized by comprising a drying step, a third electroless plating step for forming a conductor pattern on the coating film from which moisture has been removed, and a fourth heat curing step for curing the coating film.

Embodiments of the present invention will be described below while comparing them with embodiments of the prior art. FIG. 1 illustrates the differences between the conventional method and the present invention. A shows the process of the conventional method,
(A) shows the cross-sectional state immediately after electrodeposition, and the metal core 1 is covered with a substantially uniform coating film 2 over the entire surface. Furthermore, there are many fine grooves in the coating that do not reach the core. (b) is a cross section after heat curing, where the paint on the edges is pulled toward the periphery by surface tension and becomes extremely thin.
If burrs or the like are present, it often results in poor insulation.
Generally, the thickness of the edge portion is less than 10% of that of the flat portion. (c) shows electroless plating applied to the paint film to serve as a conductor. Next, B shows the steps of the present invention, (a) shows the state immediately after electrodeposition, (b) shows the state after electroless plating before curing, and (c) shows the state after heat curing. As described above, according to the present invention,
After the first electrodeposition coating process to form a coating film that enables electrical insulation on the surface of the metal substrate, a second low-temperature drying process is performed to remove moisture from the coating film, and the coating film from which moisture has been removed is A third layer on which a conductor pattern is formed.
After the electroless plating process is performed, a fourth heat curing process is performed to harden the coating film. Compared to conventional technology, where the coating film is uneven, the coating film before curing is held down by the plating film, so it does not flow during the subsequent heat curing process, resulting in a uniform coating thickness. This uniform coating ensures electrical insulation and prevents unnecessary electrical conduction that would otherwise occur if the coating becomes too thin and breaks. It has this effect.

Furthermore, since the surface of the coating film formed during electrodeposition coating is rough, the surface area to be plated is expanded, which also has the effect of improving adhesion.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a metal core electrodeposition coated printed wiring board, in which A shows the conventional method and B shows the method of the present invention in the order of steps. 1 is the core metal, 2
3 indicates electrodeposition paint, and 3 indicates electroless plating that becomes a conductor.

Claims (1)

[Claims] 1. A first electrodeposition coating step for forming a coating film that can provide electrical insulation on the surface of a metal substrate, a second low-temperature drying step for removing moisture from the coating film, and a second low-temperature drying step for removing moisture from the coating film. A method for manufacturing a printed wiring board, comprising a third electroless plating step for forming a conductor pattern on the coating film, and a fourth heat curing step for curing the coating film.