JPS5850040B2 - Manufacturing method of printed circuit board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a printed circuit board using a copper foil laminate.

The present invention relates to a method for producing a printed circuit board using a copper foil-clad laminate as a starting material, forming a circuit by etching, and making it conductive by electroless plating in the holes.

In particular, the present invention aims to improve the conductivity reliability and soldering reliability of the in-hole plated film, and further relates to a method for manufacturing a printed circuit board that does not deposit an electroless plated film on the surface of the laminate exposed by etching.

As seen in Japanese Unexamined Patent Publication No. 48-73759, conventional single-sided through-hole and double-sided through-hole printed circuit boards using a copper foil-clad laminate and making the inside of the hole conductive only by electroless copper plating are mainly was manufactured using the process.

Etching-resistant resist ink is printed in the form of a circuit on a copper foil-covered laminate, and the exposed copper foil is etched away using an aqueous solution such as cupric chloride to remove the resist ink.

Next, a plating-resistant resist ink is applied to the surface of the circuit except for the band portion and hardened.

Furthermore, apply alkali-soluble resist ink to the entire surface and make holes in the pad areas.

After depositing palladium, which serves as a catalyst for electroless plating reaction, in the holes and on the entire surface, the alkali-soluble ink is removed.

Next, by performing electroless plating, electroless plating is deposited only on the pad portions and inside the holes, thereby completing a printed circuit board in which the insides of the holes are made conductive.

Generally, a copper plating solution is used as the electroless plating solution in this method.

However, with the above conventional method, it was not possible to increase the thickness of the plating inside the hole to 5 μm or more.

This is because if the plating time exceeds about 60 minutes when electroless copper plating is applied to the inside of the hole and the pad portion, the plating-resistant resist ink applied to the circuit formed by etching will peel off.

The cause of peeling is that when electroless steel plating is applied to the inside of the hole and the band portion, the potential of the plating reaction is transmitted to the circuit under the plating-resistant resist ink, causing a reduction effect on the surface of the circuit.

Therefore, since the plating time is limited and only a plating film with a thickness of about 3 μm is deposited, there may be voids in the plating film inside the hole. There was a problem in that the solder did not rise sufficiently into the through holes, resulting in poor reliability.

Further, in double-sided through-hole printed circuit boards, the plating film inside the holes is thin and brittle, resulting in voids and cranks, and there is a problem in that the plated film inside the holes cannot sufficiently perform the role of providing continuity between the front and back circuits.

As a method for solving the above-mentioned problems, a method for manufacturing a printed board using the following process has been provided.

This is a method in which no resist ink is applied in the aforementioned process.

That is, using a copper foil-clad laminate as a starting material, etching-resistant resist ink is applied in a circuit pattern, the exposed copper foil is etched away, and the etching-resistant resist ink is removed.

Next, after applying alkali-soluble ink to the entire surface, holes are made in the pad area.

After palladium, which serves as a catalyst for electroless plating reaction, is deposited in the holes and on the entire surface, the alkali-soluble ink is removed.

At this stage, palladium remains only inside the hole.

Next, by performing electroless copper plating, an electroless copper plating film is deposited inside the hole and on the circuit formed by etching.

In this method, there is no plating-resistant resist ink, so the above-mentioned problems do not occur, and long-term plating is possible, and a plating film of 10 μm or more can be deposited, making it possible to produce highly reliable printed circuit boards. is obtained.

However, in this method, a plating film is also deposited on the exposed laminate during electroless plating, causing problems such as short circuits.

Generally, in a copper foil-clad laminate, the surface of the copper foil in contact with the laminate is roughened or an oxide film is formed in order to improve the adhesion between the copper foil and the laminating liquid.

When these are laminated, unevenness is formed on the surface of the laminate, and the unevenness remains when the copper foil is removed by etching.

The reason why a plating film is deposited on the surface of the laminate in the above process is due to these irregularities.

In other words, it is thought that the cause of the plating precipitation is the fact that copper particles that are not sufficiently etched remain in the recesses, and the electrical charge of the uneven parts peculiar to electroless copper plating described in Japanese Patent Publication No. 19661/1973. .

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a printed circuit board in which soldering of through-hole portions is highly reliable and continuity is reliable.

The method for manufacturing the printed circuit board of the present invention is as follows (a) to (f)
(a) a step of covering the non-circuit portion of a copper foil-clad laminate having a circuit formed on at least one surface by etching with a plating-resistant resist ink; (b) a step of coating at least the entire surface on the circuit side with an alkali-soluble resist ink; (C) A process of providing through-holes for inserting electronic component lead wires at necessary locations in the circuit; (d) A process of applying a catalyst for electroless copper plating to the entire surface including the inner wall of the through-hole; (e) ) removing the alkali-soluble ink and the electroless copper plating catalyst adhering to the ink using an alkaline solution, and (f) forming a plating film integrally on the inner wall of the through hole and the circuit conductor by electroless copper plating. It is characterized by sequentially including the steps of:

The printed circuit board manufacturing method of the present invention has the following advantages.

That is, since parts other than the circuit are covered with plating-resistant resist ink and the circuit conductors are left exposed, the plating-resistant resist ink on the conductors is not likely to peel off during electroless copper plating and contaminate the plating solution. This makes it possible to apply thick plating inside the through-hole over a long period of time.

In addition, the deposition of plating film on parts other than the circuit is eliminated.
Solve the problem of short circuit or current leak.

Ultimately, soldering has made it possible to produce printed circuit boards with improved reliability and conductive reliability.

Next, a method for manufacturing a printed circuit board according to the present invention will be explained with reference to the drawings.

Figure a = f corresponds to the above steps (a) to (f) and shows the state at the end of each step.

In Figure a, 1 is a circuit conductor, which is formed into a predetermined pattern by etching a copper foil stretched on a laminate 2.

In the step (a), parts other than the circuit are coated with plating-resistant resist ink 3.

In step (b), at least the entire surface on the circuit side is coated with the alkali-soluble ink 4.

In step (e), through-holes 5 for inserting lead wires of electronic components are formed at necessary locations.

In step (d), an electroless copper plating catalyst 6 such as palladium is deposited on the entire surface of the substrate including the inner walls of the through holes.

Then, in step (eJ), the alkali-soluble ink is removed using an alkaline solution.

As a result, only the electroless copper plating catalyst on the alkali-soluble ink is removed, and the catalyst on the inner wall of the through hole remains as it is.

After that, if you perform electroless steel plating using the above substrate,
A printed circuit fluid shown in Figure f is obtained.

In the printed circuit board thus obtained, a sufficiently thick copper plating film 7 is formed on the inner wall of the through hole, and a plating film is also formed on the circuit conductor, and these plating films are formed as one piece.

In the present invention, a double-sided copper foil-clad laminate is used as the copper-clad laminate, circuits are formed on both sides, and the same steps as described above are followed to produce a double-sided through-hole printed circuit board.

In the present invention, the plating-resistant resist ink 3 is provided on the surface other than the circuit by a screen printing method, and then hardened by heating.

Further, the alkali-soluble ink can be applied by coating or screen printing.

The through hole 5 is formed by a drill or a press.

In addition, in the case of having a circuit on only one side, plating-resistant resist ink may be applied to the back side (the side without the circuit) as well.

Thereby, the ink acts as a protective film against the electroless copper plating solution.

Application of a catalyst for electroless copper plating and removal of alkali-soluble ink are performed by a known pretreatment method for electroless copper plating.

That is, after raising the through hole 5, for example, 17% HC
It is immersed in liquid I, then immersed in a catalyst solution of HCI aqueous solution to which tin and palladium have been added, and washed with water.

Then, the alkali-soluble ink is removed with a NaOH solution, and after washing with water, acid treatment is performed for activation, and further washing with water is performed.

Electroless copper plating generally uses sulfuric acid steel as a copper salt, EDTA (ethylenediaminetetraacetic acid) as a complexing agent, formalin as a reducing agent, and sodium hydroxide as a pH adjuster to improve the physical properties of the deposited plated film. Plating is generally carried out at 60 to 80°C using a solution containing the desired additives.

If the process is continued for 3 to 4 hours, a plated film of about 7 to 16 μm will be deposited.

This plating time is suitable for single-sided through-hole printed circuit boards.

That is, if the thickness is at least 7 .mu.m or more, when soldering lead wires of electronic components, sufficient solder will reach inside the through-hole, and a highly reliable product can be obtained.

Moreover, if plating is carried out for 6 to 10 hours, a film of about 20 to 40 μm can be deposited.

This plating time provides sufficient conduction within the through-holes of the double-sided through-hole printed circuit board, resulting in a highly reliable printed circuit board.

Further, since the unevenness on the surface of the laminate exposed by etching is covered with a plating-resistant resist ink, no plating film is deposited on those areas.

The present invention will be specifically described below with reference to Examples.

Example 1 Paper phenol laminate with copper foil on one side (MCL-437F
An etching-resistant resist ink (rosin-modified maleic acid resin ink X-77, manufactured by Taiyo Ink Co., Ltd.) was printed in a circuit shape on the copper foil by a screen printing method.

After air drying, the exposed copper foil was removed by etching with a cupric chloride aqueous solution.

After washing with water, the etching resist ink was removed with an 80-1 l NaOH solution, followed by washing with water.

After drying at 100°C for 15 minutes, using an epoxy plating-resistant resist ink (NTS-30 manufactured by Tokyo Ohka Kogyo Co., Ltd.), screen printing was performed on the exposed surface of the paper phenol laminate other than the circuit. C. for 40 minutes.

The exposed circuit surface was washed with an aqueous copper chloride solution, washed with water and dried, and then an Aluori soluble ink (phenol resin ink B-10 manufactured by Sunf Chemical Co., Ltd.) was first printed on the entire circuit side using a screen printing method.

After air-drying, the other side without the circuit was similarly printed on the entire surface and air-dried.

Then I drilled holes where I needed them.

Next, after being immersed in a 17% HCI solution for 1 minute, it was immersed in a catalyst solution for electroless steel plating for 7 minutes to adhere the catalyst inside the holes and on the entire surface.

After washing for 3 minutes, 20? The alkali-soluble ink was removed using /1 NaOH solution with air stirring, followed by washing with water for 3 minutes.

It was then immersed in 3.5% HCI for 5 minutes for activation and washed with water for 5 minutes.

After that, the thickness of the following composition was applied to electroless copper plating solution at 68℃.
3 [Electroless steel plating solution composition for thick coating] Copper sulfate・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・1M'/l Ethylenediaminetetraacetic acid・・・・・・・・・・・・・・・30
! /l: 37% formalin solution・・・・・・・・・・・・
・・・・・・・・・・・・・・・3 ynl/73 Sodium hydroxide・・・・・・・・・・・・pH 12,5 (20
℃）Amount of polyethylene glycol・・・・・・・・・・・・・・・
...10d/, /2・2' dipyridyl...
・・・・・・・・・・・・・・・・・・・・・20■/l
water························
...An electroless steel plating film of approximately 8 to 10 μm was deposited in the through holes and on the circuit in an amount equal to 11 in total, thereby completing a single-sided through hole printed circuit board.

No plating was deposited on the plating-resistant resist ink provided in areas other than the circuit.

Lead wires of electronic components were inserted into the through holes of this single-sided through-hole printed board, and the boards were floated in a solder bath at 235° C. for 5 seconds.

Observation of the cross section showed that the solder in all through holes was 75% or more, there was no solder flow hole, and there was no peeling of the plating film.

Example 2 Double-sided steel foil paper phenolic laminate (MCL-461F
(manufactured by Hitachi Chemical Co., Ltd.) and the same operations as in Example 1 were carried out to complete a double-sided through-hole printed circuit board.

However, plating was carried out for 9 hours.

A plating film of about 30 μm was deposited inside the through holes and on the circuit conductors.

No plating film was deposited on the plating-resistant resist ink provided on areas other than the front and back circuits.

About this printed circuit board Hot oil (260'C)
As a result of conducting a through-hole reliability test using
It was found that the reliability was high as the increase was only 3% with respect to m#/hole).

In Example 2, the electroless plating time was 9 hours, but no peeling of the plating resist ink occurred.

According to other experiments conducted by the present inventors, it was confirmed that no peeling of the plating resist ink occurred even when electroless plating was performed for more than 12 hours to obtain a plating film thickness of about 40 μm. There is.

Conventional Example In the same manner as in Example 1, a circuit was formed by etching using a paper phenol laminate plated with copper foil on one side.

The same plating-resistant resist ink as in Example 1 was printed on the entire surface of this laminate (on the circuit portion and on the laminate exposed by etching) and cured.

Next, the same alkali-soluble ink was printed on the entire surface and allowed to dry.

Then, a hole was drilled in the pad portion mentioned above.

Thereafter, a catalyst was attached to the inside of the hole and the entire surface in the same manner as in Example 1, and after washing with water, the alkali-soluble ink was removed with NaOH solution.

Next, after washing with water, it was activated, washed with water again, and immersed in the thick electroless copper plating of Example 1 to deposit the plating on the inner wall of the hole.

Observing the plating time at this time and the peeling state of the plating resist ink on the circuit, it is found that after 0.5 hours, the plating resist ink on the circuit conductor has already peeled off (the plating resist ink is partially thick from the circuit). ) After one hour, more than 90% of the plating resist ink on the circuit had peeled off and was floating in the plating.

As a result of continuing plating in this state, the resist ink floating in the plating solution clogged the T cloth of the filter in the plating solution circulation system, the plating solution stopped flowing, and the plating solution began to decompose. Ta.

According to the present invention, after forming a circuit by etching, parts other than the circuit are covered with a plating-resistant resist ink, which eliminates the problem of the ink on the circuit peeling off during plating, which was a problem with the conventional method. Ru.

Therefore, thick plating on through holes and circuit conductors can be performed by electroless plating.

In addition, not only does the plating film not deposit on areas other than the circuit, eliminating problems such as short circuits, but also thick plating can be done inside the through holes over a long period of time, making soldering reliable and conductive. This has the effect of further improving.

[Brief explanation of drawings]

Figures a to f are cross-sectional views showing the state of each manufacturing process of a printed circuit board for explaining the present invention. 1...Copper foil, 2...-laminate, 3...
...Plating-resistant resist ink, 4...Alkali-soluble ink, 5...Through hole, 6...
...Catalyst for electroless copper plating, 7...Copper plating film.

Claims (1)

[Claims] 1. Steps a) to (f) below: (a) Covering the non-circuit portions of a copper foil-clad laminate having a circuit formed on at least one surface by etching with a plating-resistant resist ink; (b) Covering at least the entire surface of the circuit side with alkali-soluble ink; (C) Providing through-holes for inserting electronic component lead wires at necessary locations on the circuit; (d) The entire surface including the inner walls of the through-holes. (e) removing the alkali-soluble ink and the electroless copper plating catalyst adhering to the ink with an alkaline solution; and (f) by electroless copper plating. A method for manufacturing a printed circuit board, comprising the steps of sequentially forming a plating film on the inner wall of a through hole and a circuit conductor.