JPS59227186A - Method of producing copper through hole board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for manufacturing copper through-hole substrates.

There are two methods for manufacturing copper through-hole boards: the solder through-hole method and the copper through-hole method.Furthermore, the latter, that is, the copper through-hole method, includes tinting method, hole filling method, solder stripping method, etc. There is.

As described above, various methods for manufacturing copper through-hole substrates have been proposed, but recently it has become common to manufacture copper through-hole substrates by the solder stripping method.

The reason is as follows.

That is, first of all, looking at the solder through hole method, according to this method, solder resist (on the surface of the copper foil of the circuit part (4) located under force) as shown in Fig.
A thick solder layer is formed, but since molten solder is used to attach components to the copper through-hole board, the solder layer is melted during the process, resulting in wrinkles in the solder resist in that area. This causes problems such as the formation of cracks or the tearing of the solder resist, which impairs the appearance of the product and significantly reduces the product value.

Next, in the tinting method of the copper through-hole method, during the etching process to remove unnecessary parts of the copper foil, the resist protecting the inner wall of the through-hole is torn.
There are drawbacks such as etching solution corroding the copper on the inner wall of thistle holes, resulting in so-called "through-hole defects," and the difficulty of manufacturing through-hole boards with high-density wiring. .

Furthermore, in the hole-filling method, the shoulder portion of the through-hole is corroded by the etching solution, which is the so-called "shoulder defect".
In addition, if the ink buried in the through-holes is not removed sufficiently, the ink that remains attached to the inner wall of the through-holes may cause parts to be soldered onto the copper through-hole board. When doing so, there is a drawback that so-called "solder defects" occur.

The solder stripping method is a manufacturing method for copper through-hole boards that eliminates the above-mentioned quality defects, and is therefore commonly used today. It becomes clear that the following aspects are grossly unreasonable.

In other words, according to the same law, circuit parts, round parts and through-holes that have been applied as a resist to the enoting solution are
After etching, the solder layer on the copper foil on the inner wall of the hole is dissolved and removed using a solder stripper, and then the solder layer is removed using a solder stripper.
In the final process after applying the resist, soldering is performed again using a solder leveler machine to ensure that the feet and through holes of the parts are correct when mounting the parts on the copper through-hole board.
Attachment is an essential work process to ensure soldering to the inner wall of the ball and to increase the reliability of the parts.

However, it is extremely unreasonable in terms of the work process to solder the circuit section, round section, and inner walls of through-holes twice, and is a decisive factor that hinders productivity improvement. There is no doubt that it is.

In order to eliminate this drawback, the present inventors have conducted repeated research on resist formation methods using photolithography, and
We have repeatedly considered the soldering process. As a result, the purpose of attaching solder to the through-hole inner walls and round parts by the solder leveler machine is to increase the reliability when attaching components to copper through-hole boards; It can be confirmed that it is only necessary to provide the minimum amount of solder layer on the copper foil surface of the round part, and that it is not necessarily necessary to provide a solder layer on the copper foil surface of the round part because shoulder defects will not occur. Ta.

And here, the two solder processing steps that were attached to the solder stripping method, namely, the solder stripping step after the etching work and the solder stripping step after applying the solder resist.
This led to the devising of a new method for manufacturing copper through-ball boards, which eliminates the need for soldering using a leveler machine.

Therefore, the method for manufacturing a copper through-hole board according to the present invention will be briefly explained with reference to the drawings (FIG. 2).

(1) Perform decopper plating and primary copper plating for a copper through-hole board with copper foil on both sides (FIG. b).

f2) Using a roll coater, apply a negative/positive type photosensitive agent as a photoresist (e.g., product name "g KY Resist", manufactured by KK Yamatoya Shokai) to the surface of the copper foil on both sides of the base material and dry it. (Figure C).

(For example, solder plating is applied to the inner wall K of the through hole K as an etching resist (FIG. d).

(4) Apply negative image film to both sides of the base material, print the image (circuit) according to the procedure of normal photoengraving work (e), and then perform development processing (f) .

(5) Etching and removing unnecessary copper on both sides of the base material (g in the same figure).

(6) Dissolve and remove the photoresist on the surfaces of the circuit portion and round portion using a resist remover (h). This allows the basic printed wiring board to be completed and to proceed to the next finishing steps.

In addition, when producing a copper through-hole board according to the method of the present invention, from the principle of the manufacturing method, shoulder defects will affect product quality and product yield, so this point should be taken into consideration. The following experiments were carried out with emphasis on the results, and the energization shown in Table I was extremely satisfactory.

Example An epoxy glass laminate (NEMA standard G-10) was cut into 250x300% pieces, and one hole each with a diameter of 2.0%, 1.6%, and 0.8% was drilled into it using an NC drill machine. ,000 holes, tinting method, hole filling method, solder stripping method, and the method of the present invention, 5 each of copper through-hole boards were manufactured using an etching machine manufactured by KK Yamatoya Shokai and the product name ``ARCA Etch''. After forming a circuit by etching away the unnecessary copper foil using "S-8-R solution", we observed a part of the shoulder of the through hole with a 10x magnifying glass and a metallurgical microscope, and found that the shoulder was not corroded. The number of through holes causing shoulder defects was counted, and the shoulder defect rate was calculated using the following formula.

Table of numbers for through-holes - ■ Shoulder defect rate In addition, following the conventional practice for copper through-hole boards,
When we conducted an experiment in which a solder layer was formed on the surface of the copper foil of the round part by a conventional electroless solder plating method, we were able to do this easily and reliably.

As is clear from the above detailed explanation, the present invention enables the solder stripping method to be applied without impairing its reliability even in the slightest compared to the solder stripping method, which is currently a highly reliable method. This eliminates the need for the solder stripping process and the soldering process using a solder leveler machine, etc., and its practical effects are truly great.

In the soldering process using a conventional solder leveler machine, the copper through-hole board is immersed in a vertical solder bath, so the solder layer adheres to the inner walls of the through-holes at the top and bottom of the copper through-hole board. In manufacturing high-density printed wiring boards, problems occurred when inserting small parts due to the difference in the thickness of the through-hole and the small diameter of the through-hole at the bottom.However, according to the present invention, the inner wall of the through-hole If the thickness of the solder layer is kept constant, such troubles can be completely avoided.

Furthermore, according to the present invention, it is possible to use a solution-type high-resolution photosensitizer, which makes it possible to increase the wiring density to the limit of the resolution of the photosensitizer, which was considered extremely difficult in the past. A high-density printed wiring board can be manufactured easily and reliably, and components can be attached to the board without any problems as described above.

[Brief explanation of drawings]

Figure 1 (A) is a top view of the circuit section of the printed wiring board and the through-hole formation locations, and Figure 1 (B) is a top view of the printed wiring board circuit section and through hole formation locations, and Figure 1 (B) is the reference numerals in the drawings in Figure 1 (5). Base material, (2)...copper foil,
(3)...Round part, (4)...Circuit part, (5)
... through hole, (6) ... through hole inner wall,
(Force...Solder I resist, (8)...Electroless copper plating layer, chemical copper plating layer, (9)...Unnecessary parts (portions excluding through holes, round parts, and circuit parts)
, (10)...Photoresist, Qυ...Solder plating layer, α...Negative image film. Patent applicant Yamatoya Shokai Co., Ltd.

Claims (2)

[Claims] (1) (A) Forming through holes at predetermined positions on a base material for a copper through hole board that has copper foil on both sides,
This substrate is subjected to electroless plating and primary copper plating according to conventional methods. (b) Apply photoresist to both sides of the substrate except for the inner walls of the through holes formed as described above and dry. (c) Metals (solder, tin, nickel, gold, silver, nickel, etc.) as etching resist on the inner wall of the through hole.
Plating with palladium, etc.). 2) Burn the circuit onto the base material using the usual photo printing method,
Further, development processing is performed. (e) Etching and removing unnecessary portions of the copper foil on the base material surface. (f) Remove the photoresist on the surface of the circuit part and round part. A method for manufacturing a copper through-hole board, comprising the steps (a) to (f) above. (2) After completing the above work step (a), plate the inner wall of the through hole with metal as an etching resist. The method for manufacturing a copper through-hole substrate according to claim 1, which also includes performing the above working step (b)), hereinafter referred to as the above working step).