JPS5827679B2 - Method for forming through holes in printed circuit boards - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming through holes in a printed circuit board using an aluminum plate.

Printed circuit boards using aluminum plates, so-called aluminum core printed circuit boards, have good heat dissipation properties and high board strength, and are therefore becoming increasingly important.

To insulate the through-holes for mounting parts on this aluminum core printed circuit board, first drill a hole at a predetermined position on the aluminum plate, then insulate the surface of the aluminum plate with an insulating resin, etc., and at the same time insulate the inside of the hole. Method,
Alternatively, there is a method of drilling a hole after applying insulation treatment to the surface of the aluminum plate, or after forming a conductive film such as copper foil, and then insulating the inside of the hole. It has been difficult to provide insulation with sufficient reliability just by coating such materials.

For this reason, as a highly reliable insulating method within a hole, a through hole forming method shown in FIGS. 1 and 2 through E has been proposed.

A more concrete example of this is as follows.

First, as shown in FIG. 1, an alumite layer 3 is added between the aluminum plate 1 and the copper foil 2 as a conductive film, if necessary, and an electrically insulating layer 4, such as epoxy, phenol, melamine, polyimide, A substrate containing a layer of Teflon resin or the like is prepared, and then, as shown in FIG. 2, a hole 5 is drilled at a desired position using a drill or the like.

After this, an etching solution that does not corrode copper but completely corrodes only aluminum, such as 8 consisting of 10% sulfuric acid and 70% phosphoric acid, is used.
Using a 0.degree. C. solution, the aluminum on the inner wall of the hole 5 is roughened by etching, as shown in FIG. 2B.

The aluminum on the inner wall of the etched banked hole is anodized (electrolytic solution, 25% sulfuric acid, 1.5 AI hours) to form an alumite layer 6 as shown in FIG. By method O, an insulating layer 7, such as a layer made of epoxy, phenol, melamine fluorine resin, etc., is formed on the alumite layer 6, as shown in the second diagram.

After that, the copper foil 2 and the insulating layers 4 and 7 are coated with a plating method that adheres to them at the same time, such as ion blating, chemical copper plating after zincate treatment, chemical nickel plating, etc., and then electrolytic copper plating is applied. As shown in FIG. 2E, a copper through-hole plating layer 8 is obtained, and a layer 9 of solder, copper, gold, etc. is further formed on this layer to form through-holes for attaching components.

According to this method, the insulation inside the hole 5 is performed not only by the insulating layer 7 made of insulating resin but also by the alumite layer 6, which is a good insulator, so that sufficient reliability can be obtained. On the other hand, when etching back the aluminum on the inner wall of the hole, a wet etching solution is used, so the substrate gets wet during this process, so the surface of the substrate must be masked before etching, and the etching solution should be removed after etching. It must be washed and removed and then dried, leading to an increase in the number of manufacturing steps, which is unfavorable in terms of cost.

The present invention has been made in view of the above points, and its purpose is to provide a through-hole forming method for a printed circuit board in which the aluminum on the inner wall surface of the hole is etched back using a dry process, thereby reducing the number of manufacturing steps. It is on offer.

The feature of the present invention is that a small amount of mercury is attached to the exposed aluminum part of the inner wall surface of the hole of the substrate, and the white flocculent aluminum compound produced from this is removed and etched back, which is not necessary in the conventional etching process. The main point is that the masking process, washing process, drying process, etc. that were previously required are no longer necessary.

Hereinafter, one embodiment of the present invention will be explained in detail.
As shown in the figure, first, as shown in FIG. 3, a hole 5 is drilled at a desired position in a substrate having the same structure as the conventional one using a drill or the like, and a small amount of mercury 10 is deposited on the exposed aluminum portion of the inner wall of the hole.

In this attachment process, for example, the hole is filled with mercury, and after attachment,
This can be done by removing the mercury droplets, or by sealing both ends of the hole and sealing a predetermined amount of mercury vapor inside.

Due to this adhesion, the mercury 10 undergoes an aluminization reaction to produce a white flocculent aluminum compound 11 (aluminum amalgam).

Although this reaction depends on the amount of expansion of the inner diameter of the hole 5, it is generally continued until aluminum is reduced by about 30 times the weight of the deposited mercury.

After the reaction is completed, the formed aluminum compound 11 is removed as shown in FIG. 4, and the etch bank on the inner wall surface of the hole 5 is completed.

At this time, the aluminum compound 11 can be easily removed by simply blowing compressed air or the like through the nozzle 12 or the like, since the compound is flocculent and blown away by wind pressure or the like.

Note that this compound removal step is preferably carried out in a closed box equipped with air injection, exhaust, compound recovery equipment, etc. to prevent environmental pollution.

After completing this etchback, insulating layers such as alumite layers, which are good insulators, epoxy, phenol, melamine, fluorine resin, etc., are performed in the same manner as before, and then base plating and electrolytic copper are applied. Perform plating etc.
It forms a through hole for attaching parts.

As is clear from the above description, according to the present invention, when etching back the aluminum on the inner wall surface of the hole in the insulation processing of the through-hole for mounting parts on an aluminum core printed circuit board, it is performed dry using mercury, which is different from the conventional method. The masking process, cleaning process, drying process, etc. that were previously required are no longer required, and it is extremely easy to remove aluminum compounds generated by mercury adhesion, making it possible to simplify the process and significantly reduce manufacturing costs. It is possible to achieve significant reductions.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an example of an aluminum core printed circuit board, FIGS. 2 A to E are longitudinal sectional views of each process showing an example of a conventional through hole forming method, and FIGS. FIG. 3 is a vertical cross-sectional view of a process showing an example of such a through hole forming method. 5... Hole, 10... Mercury, 11... Aluminum compound.

Claims (1)

[Claims] 1. A hole is drilled at a desired position in an aluminum core printed circuit board coated with an insulating layer and copper foil, and mercury is deposited on the exposed aluminum portion of the inner wall of the hole, and flocculent aluminum produced by the mercury is formed. A method for forming through holes in a printed circuit board, characterized by removing a compound and forming an etch bank. 2. The method for forming through-holes in a printed circuit board according to claim 1, wherein the cotton-like aluminum compound is removed by blowing compressed air or the like.