JPS62598B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for manufacturing printed wiring boards.

Conventionally, in order to manufacture printed wiring boards, a so-called subtractive method has been adopted in which a copper-clad laminate is used as a material and copper foil is selectively etched to form a desired circuit pattern. However, this subtractive method has problems such as pollution caused by discharge of etching solution, reduced pattern accuracy due to side etching, and poor economic efficiency.

For this reason, recent efforts have been made to reduce pollution
In order to improve pattern accuracy, additive methods in which patterns are formed using only chemical plating, and semi-additive methods in which chemical plating and electroplating are used together are attracting attention.

However, the former additive method is not practical because the reliability of through holes is inferior to that of the subtractive method. On the other hand, although the latter semi-additive method improves the reliability of the pattern compared to the additive method, when the underlying chemical plating layer is dissolved and removed with a ferric chloride aqueous solution,
The inner walls of the through holes and the electrolytic copper plating film of the circuit pattern are also etched, and since the inner walls of the through holes drain less easily than the circuit pattern, the degree of etching is 2 to 5 times that of the circuit pattern. As a result, there is a problem in that the thickness between the electroplated film on the inner wall of the through hole and the circuit pattern varies, resulting in poor connectivity, and furthermore, the inner wall of the through hole is easily disconnected, resulting in an unreliable printed wiring board.

On the other hand, as a means of improving the above-mentioned semi-additive method, before dissolving and removing the underlying chemical plating layer, tin plating and solder plating are applied to the electrolytic copper plating film of the through holes and circuit patterns, so that the chemical plating layer can be etched. Etching of the electrolytic copper plating film of through holes and circuit patterns has been prevented. However, this method not only complicates the manufacturing process of the printed wiring board, but also requires new tin solder plating equipment, which has the disadvantage of lowering productivity and increasing production costs.

On the other hand, as a result of extensive research in order to eliminate the above-mentioned drawbacks, the inventors of the present invention formed a solderable passivation layer on the inner wall of the through-hole and the circuit pattern formed by electrolytic copper plating. Accordingly, when removing the chemically plated layer as a base other than the inner wall of the through hole and the circuit pattern by dissolving and removing it with an etching solution, the protective action of the passivation layer prevents etching of the electrolytic copper plating film of the inner wall of the through hole and the circuit pattern. Furthermore, the electrolytic copper plating layer after manufacture can be protected from the outside world with a passivation layer, and even if a portion of the passivation layer above it remains when soldering to the inner wall of the through hole and the circuit pattern, good soldering can be achieved. We have discovered a method for producing an extremely reliable printed wiring board that can be easily attached, has stable solderability over a long period of time, has good connectivity, and has no disconnection on the inner wall of the through hole.

That is, the method of the present invention includes the steps of performing chemical plating treatment on a substrate with chemical plating adhesive having through-hole holes to form a chemical plating layer, and applying a plating resist to the chemical plating layer portion excluding the inner wall of the hole and the desired circuit pattern area. A process of coating a film, a process of performing an electrolytic copper plating process to form an electrolytic copper plating film of a desired thickness on the inner wall of the hole and the circuit pattern area exposed from the plating resist film, and a process of applying solder to the surface of the electrolytic copper plating film. This method is characterized by comprising a step of coating a passivation layer made of a material that can be used, and a step of dissolving and removing the exposed chemical plating layer portion after removing the plating resist film.

Examples of the chemical plating adhesive used in the present invention include those made of acrylonitrile rubber and novolak type or resol type phenolic resin or epoxy resin, and blended with a zirconium compound or silica powder as necessary. I can do it.

Examples of the substrate used in the present invention include an insulating substrate made of epoxy resin or the like, a multilayer substrate having an inner layer plate, and the like.

The chemical plating layer in the present invention is a chemical copper plating layer or a chemical nickel plating layer, and the chemical copper plating layer is particularly useful because it has a low electrical resistance and can make the plating thickness uniform.

The material for the passivating layer used in the present invention does not inhibit solder adhesion during soldering and has excellent dissolution resistance to the etching solution for the chemical plating layer as a base. Examples include compounds or salts thereof.

In addition, in the present invention, by forming the chemical plating layer with a chemical nickel plating layer different from the material of the electrolytic copper plating film and selecting the material of the passivation layer, it is possible to inactivate only the electrolytic copper plating film. After the plating resist film is removed after the electrolytic copper plating process, the passivation layer may be formed with the chemical nickel plating layer exposed.

Next, embodiments of the present invention will be described with reference to FIGS. 1 to 8.

Example First, as shown in FIG. 1, 40 parts by weight of acrylonitrile rubber, 20 parts by weight of resol-type phenolic resin, 20 parts by weight of bisphenol-type epoxy resin, 10 parts by weight of silica gel, and 10 parts by weight of curing agent were placed on an epoxy resin substrate 1 as shown in FIG. A chemical plating adhesive containing a mixed solvent of methyl ethyl ketone and butyl cellosolve was applied using a dip method, air-dried, and then dried at 160° C. for 40 minutes to form an adhesive layer 2 with a thickness of 20 μm. Next, as shown in FIG. 2, a desired portion of this substrate is drilled to form a through hole 3, and then treated with a chromium-sulfuric acid mixture to make it hydrophilic, and activated according to a conventional method. Furthermore, a chemical nickel plating layer 4 was formed on the entire surface of the substrate 1 including the through holes 3 by immersing it in a chemical copper plating solution (as shown in FIG. 3). Thereafter, as shown in FIG. 4, a plating resist film 5 is coated by mask printing on the chemical nickel plating layer 4 excluding the inner wall of the through hole 3 and a predetermined circuit pattern area, and after drying, it is activated with a 15% sulfuric acid solution, and electrolytic copper is applied. A plating process was performed to form an electrolytic copper plating film 6 on the chemical nickel plating layer in the through holes 3 and the circuit pattern area (as shown in FIG. 5).

Next, the substrate after the electrolytic copper plating treatment was treated with an imidazole compound solution (trade name, manufactured by Shikoku Kasei Kogyo Co., Ltd.;
After immersion in Glycoat L) for 5 minutes and washing with water, a solderable passivation layer 7 was coated on the electrolytic copper plating film 6 in the through-hole holes 3 and the circuit pattern area (as shown in FIG. 6). After that, as shown in FIG. 7, after peeling off the plating resist film 5, ammonium persulfate 250
A printed wiring board 1 having through holes 8 and a circuit pattern 9 as shown in FIG.
I got 0.

It was found that in the obtained printed wiring board, the electrolytic copper plating film did not dissolve at all during the etching process, and highly reliable through holes with good connectivity and no disconnection were formed. In addition, after leaving this printed wiring board for one month, we soldered component lead wires to the through holes, and the soldering rate was 95%.
As described above, component connection reliability was also good.

As detailed above, according to the present invention, it is possible to prevent etching of the electrolytic copper plating film on the inner wall of the through hole and the circuit pattern, and furthermore, it is possible to prevent the electrolytic copper plating film after manufacture from being exposed to the outside world without impeding solderability. It is possible to provide an extremely reliable printed wiring board that can be protected, has good connectivity, has no disconnection on the inner wall of the through hole, and has good solderability even after being left unused for a long period of time.

[Brief explanation of the drawing]

1 to 8 are cross-sectional views showing the manufacturing process of a printed wiring board in an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Adhesive layer, 3... Through-hole hole, 4... Chemical nickel plating layer, 5... Plating resist film, 6... Electrolytic copper plating film, 7... Passivation layer, 8... ...Through hole, 9...Circuit pattern, 10...Printed wiring board.

Claims (1)

[Claims] 1. A step of forming a chemical plating layer by performing chemical plating treatment on a chemical plating adhesive-attached substrate having through-hole holes, and a step of coating the chemical plating layer portion with a plating resist film excluding the inner wall of the hole and the desired circuit pattern area. , a step of performing electrolytic copper plating to form an electrolytic copper plating film of a desired thickness on the inner wall of the hole and the circuit pattern area exposed from the plating resist film, and a material that can be soldered to the surface of the electrolytic copper plating film. 1. A method for producing a printed wiring board, comprising the steps of: coating a passivation layer; and removing the plating resist film, then dissolving and removing the exposed chemical plating layer.