JPH0851262A - Printed wiring board and its manufacturing method - Google Patents

Abstract

PURPOSE:To enhance a adhesion between a through hole pad part and copper paste in a copper paste through hole, and also set a resistance value of the copper paste through hole to be a stable low value. CONSTITUTION:In a printed wiring board that a front surface wiring circuit pattern 7 formed on a surface of a substrate is connected with a back surface wiring circuit pattern 8 formed on a back surface thereof via a copper paste hole 13 formed by filling a penetrating hole 4 for a through hole formed in the substrate with copper paste 12 to be stiffened, the surface of through hole pad parts 5, 6 of each wiring circuit pattern has been beforehand treated with a solution containing hydrochloric acid before the copper paste 12 is filled in the penetrating hole 4 for a through hole.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board for mounting electronic parts and the like. More specifically, the present invention relates to a printed wiring board having through holes that are made conductive by a copper paste.

[0002]

2. Description of the Related Art Conventionally, in various electronic devices such as television receivers, radio receivers, and cassette tape recorders, copper wiring circuit patterns have been formed on both sides and inner layers of the board in order to mount many electronic parts. The multi-layer printed wiring board formed in the above is often used.

In such a printed wiring board, copper wiring circuit patterns formed on both surfaces of the board are connected to each other by plating a metal such as copper on the inner wall of the through hole for a through hole formed in the board. The plated through holes formed by.

However, the plating process for forming the plated through holes is very complicated and there is a drawback that the cost for forming the through holes increases.

Therefore, in order to reduce the cost of forming a through hole, a silver paste through hole formed by filling a through hole for a through hole formed in a substrate with a silver paste and curing it is used. There is.

However, when the silver paste through hole is used, there is a drawback that the insulation reliability becomes insufficient due to the problem of silver migration. Therefore, there is a problem that it cannot meet the recent demand for higher density of the printed wiring board.

On the other hand, it has been attempted to connect the wiring circuit patterns on both surfaces of the substrate by using copper paste through-holes having a high insulation reliability, which does not substantially cause the problem of migration.

In such a copper paste through hole, first, a through hole for a through hole is formed in a double-sided copper-clad substrate,
Next, the copper foil on both sides is patterned into a wiring circuit pattern having through-hole pad portions, and a copper paste in which copper powder is dispersed in a thermosetting or UV-curing binder resin is applied to the through-holes by a screen printing method or the like. It is formed by filling and curing.

[0009]

However, the conventional copper paste through-hole has a problem that the cured copper paste and the through-hole pad portion of the wiring circuit pattern have insufficient adhesion. Therefore, there is a problem that the hardened copper paste peels off from the through hole pad portion due to vibration or shock. Further, since the contact between the through-hole pad portion and the hardened copper paste becomes unstable, there is a problem that the resistance value of the copper paste through-hole does not become a stable low value.

The present invention solves the problems of the prior art as described above, improves the adhesion between the through-hole pad portion and the copper paste in the copper paste through-hole, and further, the resistance of the copper paste through-hole. The purpose is to make the value stable and low.

[0011]

Means for Solving the Problems The present inventor has found that before filling the through holes of the substrate with copper paste, the surface of the through-hole pad portion is previously acid-treated with a hydrochloric acid-containing solution to form hydrochloric acid traces. The inventors have found that the above object can be achieved and completed the present invention.

That is, according to the present invention, the front surface wiring circuit pattern formed on the front surface of the substrate and the back surface wiring circuit pattern formed on the rear surface are filled with copper paste in through holes for through holes formed in the substrate and cured. In the printed wiring board connected by the copper paste through hole formed by the above, the surface of the through hole pad portion of each wiring circuit pattern, before filling the through hole for the through hole with the copper paste, Provided is a printed wiring board, which has been previously acid-treated.

Further, the present invention is the above-mentioned method for manufacturing a printed wiring board, comprising the step of forming through holes for through holes in a substrate having conductive layers on both sides, and the conductive layers having through hole pad portions. A step of patterning a wiring circuit pattern, a step of acid-treating the surface of the through-hole pad portion with a solution containing hydrochloric acid, and a copper paste is filled in the through holes and cured to make the front side wiring circuit pattern and the back side wiring circuit pattern conductive. Provided is a method for manufacturing a printed wiring board, which is characterized by including steps.

The present invention will be described in detail below with reference to the drawings.

First, a case where a printed wiring board having a basic structure of the present invention is manufactured by using a laminated board having conductive layers formed on both surfaces will be described as an example.

First, as shown in FIG. 1A, the insulating substrate 1
A laminated plate A having conductive layers 2 and 3 formed on both surfaces thereof is prepared. As such an insulating substrate 1, one conventionally used as an insulating substrate for a printed wiring board can be used. Further, copper foil can be used as the conductive layers 2 and 3.

Next, as shown in FIG. 1B, the laminated plate A
Through holes 4 for forming through holes are formed at predetermined positions. In this case, the through hole 4 can be formed with high positional accuracy and hole diameter dimension accuracy by a drill controlled by NC (numerical value).

Subsequently, as shown in FIG. 1C, predetermined wiring circuit patterns 7 and 8 including through-hole pad portions 5 and 6 are formed on the conductive layers 2 and 3 on both surfaces by a subtractive method. .

Next, as shown in FIG. 1D, solder resist layers 9 and 10 are formed on predetermined portions of the wiring circuit patterns 7 and 8 except the through-hole pad portions 5 and 6 by a screen printing method or the like. To do.

Next, the through-hole pad portions 5 and 6 where the solder resist layers 9 and 10 are not formed and other predetermined circuit portions (non-resist wiring circuit pattern portion 11)
And are acid-treated with a hydrochloric acid-containing solution to form hydrochloric acid traces on the surface (FIG. 1 (e)).

As for the hydrochloric acid-containing solution used here, if the hydrochloric acid concentration is too low, the adhesion improving effect is small, and if it is too high, the non-resist wiring circuit pattern 11 and the through-hole pad portions 5 and 6 themselves are greatly damaged. Preferably, a hydrochloric acid having a concentration of 2 to 30% is used.

As a method of acid treatment, the laminated plate of FIG. 1 (e) may be immersed in a hydrochloric acid-containing solution. It can also be carried out using a so-called surface trimming machine.

After the acid treatment, the laminated plate A may be washed with water and dried to remove the hydrochloric acid-containing liquid as needed, or may be dried immediately without washing with water. If the washing with water is omitted, the adhesion between the through hole pad portions 5 and 6 and the copper paste 12 described later can be further improved.

Next, as shown in FIG. 1F, the copper paste 12 is filled in the through holes 4 by a screen printing method or the like. In this case, the filling operation of the copper paste 12 can be performed from one side of the wiring circuit pattern 7 or 8. As a result, the through hole 4 is filled with the copper paste 12, and the copper paste 12 is also laminated on the through hole pad portions 5 and 6 provided above and below the through hole 4.

In this case, as the copper paste that can be used, one that has been conventionally used in a printed wiring board can be used, and one in which copper powder is dispersed in a heat or ultraviolet curable resin can be used. it can.

Next, the copper paste 12 is pre-cured, dried, and finally hardened to obtain a printed wiring board B having a copper paste through hole 13 as shown in FIG. 1 (g).

After this, in order to protect the copper paste through holes 13 from heat during soldering, if necessary,
You may form an overcoat layer which consists of epoxy resins on it. Further, after the symbol is printed, the non-resist wiring circuit pattern 11 is subjected to an acid treatment with sulfuric acid.
It is preferable to remove the traces of hydrochloric acid from. Finally, the outer shape of the printed wiring board may be formed into a desired shape by press working.

Printed wiring board B thus obtained
2, may be laminated with another printed wiring board C via a prepreg 14 or the like to form a laminated wiring board D. In this case, the copper paste through hole 13 becomes a blind via hole.

The laminated wiring board D may be further provided with through holes 15. As this through hole 15,
It may be a plated through hole or a copper paste through hole.

[0030]

In the present invention, the surface of the through-hole pad portion is previously acid-treated with a hydrochloric acid-containing solution before the through-hole of the substrate is filled with the copper paste. Therefore, hydrochloric acid marks are formed on the through hole pad portion. Therefore, it becomes possible to improve the adhesion between the copper paste and the through hole pad portion.

[0031]

The present invention will be described in detail below with reference to the following examples.

Example: 35 μm on both sides of a 1.6 mm thick paper phenolic insulating substrate
An NC drill was used to form 300 through holes having a diameter of 0.8 mm on the double-sided laminated plate on which a thick copper foil was attached.

Next, the copper foils on both sides of this laminate were processed into a wiring circuit pattern by the subtractive method. At this time, through hole pads were simultaneously formed around the openings of the through holes.

Next, the solder resist ink was applied by screen printing to a dry thickness of 20 μm on the entire surface of the laminate except the through hole pads.

Next, this laminated plate was immersed in a 3% hydrochloric acid aqueous solution at room temperature for 10 seconds to subject the surface of the through-hole pad to an acid treatment to form a hydrochloric acid mark on the surface. Then, the laminated plate was pulled up from the hydrochloric acid aqueous solution and immediately air-dried without washing with water.

A copper paste (trade name: TH1259, manufactured by Tatsuta Electric Wire Co., Ltd.) was filled in the through holes of the obtained laminated plate by screen printing.

Next, the laminated plate was placed in a constant temperature oven at 80 ° C. for 120 hours.
It was put in for a minute to pre-cure the copper paste and dried, and then put in a constant temperature oven at 160 ° C. for 30 minutes for main curing. As a result, a printed wiring board having a copper paste through hole as shown in FIG. 1 (g) was obtained.

After that, overcoat ink (MF200-TS9) was applied on the copper paste in the copper paste through hole.
1E, made by Taiyo Ink Co., Ltd.) to form an overcoat layer. Further, after performing symbol printing, hydrochloric acid traces on the surface of the through-hole pad were removed by acid treatment using sulfuric acid. Finally, the outer shape of the printed wiring board was adjusted by pressing.

Comparative Example A printed wiring board was obtained by repeating the example except that the through hole pad was not previously acid-treated with a hydrochloric acid aqueous solution.

(Evaluation) Each of the obtained printed wiring boards of Examples and Comparative Examples was moistened under the conditions of 40 ° C., 90 RH% and 96 hours, and then immersed in a solder bath at 245 ° C. for 5 seconds. . Then, the resistance value of the copper paste through hole of each printed wiring board and the adhesiveness with the tape were measured.

As a result, the resistance value was 38 mΩ / hole in the case of the printed wiring board of the comparative example, but was significantly improved to 26 mΩ / hole in the case of the printed wiring board of the example.

Regarding the adhesion by the tape, in the case of the comparative example, the copper paste was peeled off in the through hole pads of 13% or more of the 300 through holes.
In the case of the example, peeling of the copper paste did not occur.

[0043]

According to the present invention, the adhesion between the through-hole pad portion and the copper paste in the copper paste through-hole can be improved and the resistance value of the copper paste through-hole can be made stable and low. .

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram of a printed wiring board of the present invention.

FIG. 2 is a cross-sectional view of a laminated wiring board using the printed wiring board of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating substrate 2, 3 Conductive layer 4 Through hole 5, 6 Through hole pad part 7, 8 Wiring circuit pattern 9, 10 Solder resist layer 11 Non-resist wiring circuit pattern 12 Copper paste 13 Copper paste through hole 14 Prepreg 15 Through hole A Laminated board B, C Printed wiring board D Laminated wiring board

Claims (6)

[Claims] 1. A front surface wiring circuit pattern formed on a front surface of a substrate and a back surface wiring circuit pattern formed on a rear surface of the substrate,
In a printed wiring board connected by copper paste through holes formed by filling and curing a copper paste in through holes for through holes formed in a board, the through hole pad surface of each wiring circuit pattern, A printed wiring board, which is acid-treated in advance with a hydrochloric acid-containing solution before filling the through-holes for through holes with a copper paste. 2. The printed wiring board according to claim 1, wherein the wiring circuit pattern is formed of copper. 3. A multilayer wiring board containing the printed wiring board according to claim 1. 4. The method for manufacturing a printed wiring board according to claim 1, wherein a through hole for a through hole is formed in a substrate having conductive layers on both sides, and the conductive layer is a wiring circuit pattern having a through hole pad portion. Patterning step, a step of acid-treating the surface of the through-hole pad part with a solution containing hydrochloric acid, and a step of filling the through-hole with a copper paste and curing it to electrically connect the front surface wiring circuit pattern and the back surface wiring circuit pattern. A method of manufacturing a printed wiring board, comprising: 5. The method for producing a printed wiring board according to claim 4, wherein the hydrochloric acid-containing solution has a hydrochloric acid concentration of 2 to 30%. 6. The method according to claim 4, wherein the surface of the through hole pad portion is dried immediately after the acid treatment with the hydrochloric acid-containing solution.