JPS5932916B2 - How to manufacture circuit boards - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a metal core circuit board having a ground circuit.

Circuit boards with metal cores such as iron and aluminum have excellent heat dissipation and thermal conductivity, and are therefore used in the electronics industry for mounting heat-generating electronic components such as high-output transistors.

Iron and aluminum are commonly used as metal core materials.
For example, a method for providing a grounding circuit on a circuit board with an iron core is to provide a hole that penetrates the iron core and the electrical insulation layer on the surface of the iron core, apply chemical copper plating on the iron wall of the hole wall, and then electrolytic copper plating. Chemical copper plating films have been reinforced.

However, when an electronic component ground lead is joined to the wall of the hole by soldering, it has been observed that the chemical copper plating film on the wall of the iron hole often peels off from the iron wall due to the high heat of soldering. . This occurs because the adhesion between the iron and the chemical copper plating film is not sufficient. In addition, when forming a chemical copper plating film directly on an iron wall, iron ions dissolve in the chemical copper plating solution, contaminating the chemical copper plating solution, and hastening the decomposition of the chemical copper plating solution. . SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional method of manufacturing a circuit board with a metal core having a ground circuit, and to provide a method of manufacturing a circuit board with a metal core having a stable ground connection.

That is, in the present invention, in an opening that reaches at least the surface of the metal plate provided in a wiring board made of a metal plate whose surface is coated with an insulating resin, the insulating resin on the surface and the metal surface inside the opening are pretreated with sulfuric acid and chromium. After chemically roughening the surface with a mixed solution with acid, a displacement copper plating film is formed on the metal surface within the opening, and the displacement copper plating film is further reinforced by chemical copper plating and electrolytic copper plating. It is characterized in that another conductive circuit is formed at the same time.

In the present invention, since a displacement copper plating film is formed on the metal surface in advance before performing chemical copper plating, there is no risk of contaminating the chemical copper plating solution in the next step of chemical copper plating. o The displacement copper used in the present invention Preferred composition examples of the plating solution are shown in Table 1. With this composition, a substituted copper plating film with particularly excellent adhesion can be obtained, and the electrical connection and reliability of the ground circuit can be significantly improved. Here, as the wetting agent, an anionic fluorinated hydrocarbon compound can be effectively used.

Embodiments of the present invention will be described below in detail based on the drawings.Through holes 2 and 3 are formed at desired positions of the iron plate 1 by drilling or punching (Fig. 1a).Then, the surface of the iron plate and the through holes are formed. As the electrically insulating resin for forming the epoxy resin layer 4 on the walls of holes 2 and 3, acrylic resin, vinyl chloride resin, ABS resin, etc. can be used in addition to epoxy resin.

Further, as a method for forming the resin layer, an electrodeposition coating method, a fluidized bed dipping method, an electrostatic fluidized bed dipping method, etc. can be used. Here, an epoxy resin layer was formed using the fluidized bed dipping method.
That is, the iron plate 1 is heated at a temperature of 200° C. for about 10 minutes, and immediately immersed in an epoxy resin powder fluidized bed dipping bath (not shown) for about 2 seconds, and the epoxy resin layer 4 is coated on the surface of the iron plate 1 and through holes 2 and 3. The epoxy resin layer 4 was formed on the wall to a thickness of about 200 microns (FIG. 1b) and then heated at 200 DEG C. for about 10 minutes to completely heat cure the epoxy resin layer 4. Next, the epoxy resin layer on the wall of the iron plate 1 in the through hole 3 was removed using a drill (FIG. 1c). In this case, drill through hole 3.
You may use the following method which can obtain the same effect as the method of removing the epoxy resin layer 4 described above. That is, before forming the epoxy resin layer, a metal pin, silicone resin pin, wooden pin, etc. is inserted into the through hole 3 as a hole plug to block the epoxy resin from entering the through hole 3, and the epoxy resin layer is formed. After that, the surface of the epoxy resin layer 4 and the iron wall of the through hole are chemically immersed in a mixed solution of sulfuric acid and chromic acid at a temperature of 70° C. for about 15 minutes. The surface was roughened. Next, a displacement copper plating film 5 of approximately 1 micron was formed on the iron wall of the through hole 3 by immersion in the displacement copper plating solution shown in Table 1 for about 10 minutes (
Figure 1 d). Next, the chemical copper plating film 6 of approximately 5 microns was immersed in a chemical plating catalyst solution consisting of tin chloride, hydrochloric acid, etc. for about 5 minutes, washed with water, and then immersed in a chemical copper plating solution. It was formed on the surface of the resin layer (Fig. 1e). Next, a plating resist film 7 is selectively formed on the chemical copper plating film 6 (FIG. 1f). Next, an electrolytic copper plating film 8 of about 30 microns is deposited using pyrophosphate electrolytic copper plating to reinforce the chemical copper plating film 6 (FIG. 1g).
Next, after dissolving and removing the plating resist film 7 with a methylene chloride solution, the chemical copper plating film on the parts not covered with the pyrophosphate electrolytic copper plating film is removed using a ferrous chloride chemical etching solution, and the iron cored circuit having the grounding circuit 9 is removed. The substrate was manufactured (Figure 1h)
. The circuit board manufactured in this way was heated at a temperature of 230°C for about 30 minutes.
No deterioration in the adhesion between the iron wall and the copper plating film in the roller ground circuit 9 was observed after the heat treatment for 1 minute, demonstrating that the ground circuit had high electrical connection reliability. As described above, the circuit board according to the present invention has high reliability, and the practical value of the present invention is extremely large.Although the above-mentioned embodiment shows the case where the present invention is applied to a through hole containing a metal plate, the present invention The present invention does not necessarily have to be a through hole, and the present invention can also be applied to forming a ground connection when the metal plate is only exposed from the resin coating.

[Brief explanation of the drawing]

Figures 1a to 1h are cross-sectional views of the main parts of the board in the main steps for explaining the method of manufacturing a circuit board with an iron core having a grounding circuit according to the present invention.
・Iron core, 2, 3...through hole, 4...epoxy resin layer, 5...substituted copper plating film, 6...
... Chemical copper plating film, 7 ... Plating resist film, 8 ... Electrolytic copper plating film, 9 ...
・Grounding circuit.

Claims (1)

[Claims] 1. In a wiring board formed by coating a metal plate with an insulating resin, a step of providing an opening reaching at least the surface of the metal plate in a predetermined part of the resin coating, and a step of providing an opening reaching at least the surface of the metal plate in a predetermined part of the resin coating, A method for manufacturing a circuit board, comprising the steps of chemically roughening the surface of the metal plate exposed within the opening, and plating displacement copper on the surface of the metal plate exposed within the opening.