JPS5938759B2 - Manufacturing method for printed circuit boards - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for manufacturing a printed circuit board in which a copper foil circuit and the inner wall of a through hole for inserting a lead wire of an electronic component are electrically connected.

[Background of the invention]

Conventionally, according to Japanese Unexamined Patent Publication No. 56-13794, a circuit was formed on a copper-clad laminate using an etching method, etc., and chemical plating was also applied to the through-holes for inserting lead wires in electronic components to form circuits and through-holes. Electrically connect the inside of the hall,
A method for manufacturing a printed circuit board is provided that improves soldering reliability of electronic components and reliability of conduction between the components and a circuit.

According to this method, it is possible to form a thick chemically plated film on the inner wall of the through hole, thereby improving the soldering reliability and conduction reliability. The present inventors studied ways to further simplify the above method and discovered the present invention.

[Purpose of the invention]

The present invention achieves thick plating on the inner wall of a through hole for inserting a lead wire in an electronic component, thereby ensuring soldering reliability of the electronic component on a printed circuit board and continuity reliability between the component and the circuit. It is an object of the present invention to provide a method for manufacturing a desired printed circuit board using an efficient method.

[Summary of the Invention] The method for manufacturing a printed circuit board of the present invention includes the following steps (a), (b), (c), and (d).
a) A step of treating a substrate having a copper foil circuit formed by etching and a through hole for inserting a lead wire of an electronic component with a chemical plating catalyst liquid to apply a chemical plating catalyst to at least the inner wall of the through hole; b) Removing the catalyst attached to at least the non-circuit part while leaving the catalyst on the inner wall of the through hole; (c) Completely exposing the formed circuit copper foil and removing only the non-circuit part on the surface of the circuit side board. (d) Depositing a chemical plating film on the inner wall of the through-hole and the copper foil circuit by chemical plating treatment to electrically connect the circuit and the inner wall of the through-hole. The method is characterized by including the step of:

According to the present invention, a chemical plating catalyst (hereinafter simply abbreviated as catalyst) is used.

) After treatment with a liquid, only the non-circuit portions are coated with a resist film against chemical plating (hereinafter simply referred to as a resist film).
), it is possible to omit the use of alkali-soluble ink and several accompanying steps found in the conventional method, and it is efficient and can improve productivity. When plating,
Similar to the above conventional method, since only the non-circuit parts are covered with the resist film, the plating film is deposited on both the through-hole inner wall and the circuit part, making it impossible to completely electrically connect the two. can. Moreover, since the resist film does not cover the circuit at all, there is no need to worry about the resist film falling into the plating solution and shortening the life of the plating solution even if the chemical plating process is performed for a long time. It is possible to increase the thickness. In addition, in the case of a thick plating film, there are no pinholes, and there are no defects such as blowholes or insufficient fillets during soldering. Together, these factors improve the soldering reliability of electronic components and the continuity between the component and the circuit. Reliability can be increased. Next, a method for manufacturing a printed circuit board according to the present invention will be explained with reference to the drawings.

In FIG. 1, diagrams A, c, and d are
It corresponds to c) and (d) and shows the state at the end of each step. In FIG. 1a, 1 is a circuit formed of copper foil, which is formed into a predetermined pattern by etching the copper foil pasted on a substrate 2 such as a resin laminate. 3 is a through hole for inserting a lead wire of an electronic component.

In step (a), the catalyst 4 is attached to at least the circuit side surface including the inner wall of the through hole 3 by a method such as immersing the substrate in a catalyst liquid. Next, as shown in FIG. 1c, the non-circuit portion 5 is covered with a resist film 6 in step (c), whereby a chemical plating film is formed only on the inner wall of the through hole 3 and the circuit copper foil 1. In addition, in FIG. c, illustration of the catalyst under the resist film 6 is omitted. In the subsequent step (d), chemical plating is performed to deposit a plating film on the above portion. This results in
The circuit copper foil 1 and the inner wall of the through hole are electrically connected by the plating film 7, thereby improving the continuity reliability and soldering reliability between the electronic component lead wire (not shown) and the circuit copper foil. In the present invention, known catalysts, resist films, chemical plating solutions, and treatment methods thereof can be used.

For example, the method and treatment method described in JP-A-56-13794 can be used. In the present invention, the activation treatment of a catalyst such as palladium chloride, that is, the reduction treatment is the step of coating the resist film (
It may be carried out either before or after c).

According to the research conducted by the present inventors, when the distance between the copper foil circuits is short, that is, when the wiring density is to be increased, the catalyst on the surface other than the inner wall of the through-hole must be
In other words, it has been found that current leakage between circuits can be suppressed by substantially removing the catalyst in non-circuit portions.

The method for manufacturing this printed circuit board includes the above (a) and (b).
), (c) and (d) are performed in sequence. The method of the present invention will be explained using the embodiment shown in FIG.

In Figure 2, Figures (a), (b), (c) and (d
) is the step (a), (b), (c) and (d)
) and shows the status at the end of each process. Here, steps (a), (c) and (d) are the aforementioned steps (a), (
This is exactly the same as steps c) and (d). Therefore, this method includes steps (a), (c), and (d) described above, and includes step (b), which will be specifically explained below, between step a) and step (c). ) is added. At least the catalyst 4 on the non-circuit portion 5 is removed by the step (b) (if the device has a circuit on only one side, it is recommended to also remove the catalyst 4 attached to the side opposite to the circuit). Desirable: This eliminates the problem of current leakage caused by the catalyst and allows higher wiring density.
The catalyst can be easily removed by a mechanical method such as a brush. When using a brush, the catalyst on the copper foil circuit is also removed, but even if the catalyst is not present on the copper foil, there is no problem in depositing the chemically plated film. The intended purpose is achieved even if the catalyst is not necessarily completely removed. As a removal method other than the brush method, for example, there is a method of immersion in a catalyst removal solution. This is the invention of JP-A-53-91381 or JP-A-53-1124, which was invented by some of the inventors.
There is one described in Publication No. 64. For example, ferric chloride or ammonium persulfate is dissolved in dilute hydrochloric acid or the like.
By immersing the substrate in the catalyst removal liquid, the catalyst on the surface of the substrate is substantially removed. Although some of the catalyst adhering to the inner wall of the through-hole may be removed, there is no concern that this will interfere with plating. All of the methods of the present invention detailed above can also be applied to the production of so-called double-sided circuit boards having circuits on both sides of the board. Further, in carrying out the present invention, the inner wall of the through hole may be treated with a surfactant in advance in order to ensure that the catalyst liquid adheres to the inner wall of the through hole.

Furthermore, the same applies to chemical plating treatment, in which the inner wall can be treated with a surfactant to improve its bendability. [Examples of the Invention] The present invention will be described in detail below using specific examples.

Reference example 1 Single-sided copper foil laminate (manufactured by Hitachi Chemical Co., Ltd. MCL-461F
Using a 35 μm thick copper foil), print an etching-resistant ink mainly composed of rosin-modified maleic acid resin in a circuit shape on the copper foil using a screen printing method, and then print the non-circuit portions of the copper foil with a cupric chloride aqueous solution. was removed and washed with water, and then the above ink was removed with an aqueous NaOH solution.

After washing with water and air drying, through holes were drilled in the necessary locations. Next, in the step (a), after being immersed in a 1770 hydrochloric acid aqueous solution for 1 minute, immersed for 10 minutes in a catalyst solution containing liquefied stannous tin, palladium chloride, and hydrochloric acid as the main components, and after washing with water, Activation was performed with a solution containing water, followed by washing with water and drying. Next, in step (c), resist ink (based on epoxy resin) is applied to non-circuit areas.
NTS-30 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) was printed using a screen printing method, and precured for 12"C for 20 minutes. After air drying, the above resist ink was printed on the entire back surface without circuits, and the whole was heated at 150℃. - Cured in 30 minutes. Next, 5% HZS
After treatment with O4 solution and washing with water, as step (d), it is immersed in a chemical copper plating solution with the following composition and plated at 71°C for 4 hours to coat the inner wall of the through hole and the copper foil circuit with approximately 9 to 10
A copper plating film with a thickness of μm was formed to create a single-sided through-hole printed circuit board. Reference Example 2 In Reference Example 1, except that a double-sided copper foil laminated board (MCL-437F 35 μm thick copper foil manufactured by Hitachi Chemical Co., Ltd.) was used as the starting material, and the chemical copper plating time was 10 hours. The work was carried out in the same manner as in Reference Example 1, and a copper plating film of approximately 27 to 30 μm was formed on the inner wall of the through hole and the copper foil circuit, thereby producing a double-sided through hole printed circuit board.

Example 1 In Reference Example 1, before printing the resist ink on the non-circuit portion, a metal roll brush was used in the step (b) to remove the catalyst, i.e., copper, attached to the substrate surface other than the inner wall of the through hole. A step was added to remove most of the catalyst adhering to the foil circuit and non-circuit parts.

The other steps were carried out in the same manner as in Reference Example 1 to produce a single-sided through-hole printed circuit board and a double-sided through-hole printed circuit board. Example 2 In Example 1, in step (b) most of the catalysts attached to the copper foil circuit and non-circuit parts were replaced with ferric chloride 0.1f! , 3770 hydrochloric acid 100d and water 900m
A single-sided through-hole printed circuit board and a double-sided through-hole printed circuit board were prepared in the same manner as in Example 1, except that the method was changed to remove the catalyst attached to areas other than the inner walls of the through holes by immersing them in a catalyst removal solution consisting of T for 15 minutes. A circuit board was created.

Example 3 After the catalyst application and water washing treatment in step (a) of Reference Example 1, the catalyst adhering to the circuit side surface was removed in step (b) using a metal roll brush.

Next, the same process (c) as in Reference Example 1 was carried out, and the catalyst activation process (7) was further carried out to produce a single-sided through-hole printed circuit board. Among the printed circuit boards obtained in Examples 1 to 3 above, the solderability of single-sided through-hole printed circuit boards was investigated.

As a result of floating the board in a solder bath at about 235°C for 5 seconds,
Approximately 75% of the through-holes were filled with solder, and because the plating film was thick, no gas components were blown out from the board, and it was confirmed that there were no solder blowholes. Also, as a result of inserting and soldering lead wires for electronic components, there was no shortage of fillets at all. On the other hand, for double-sided through-hole printed circuit boards, the rate of increase in conduction resistance after heat cycle tests was investigated. [Test conditions] One cycle consisted of immersion in glycerin at 260° C. for 2 to 3 seconds → room temperature/standing for 10 seconds → immersion in trichlene for 2 to 3 seconds, and 20 cycles of this were tested.

As a result, the increase rate of the conduction resistance after the test with respect to the initial value was approximately 470, which was negligible in practical terms. This is because the plating film was thick and cracks occurred in the plating film during the heat cycle test. It means difficult. Next, the insulation resistance after the copper foil circuit (between the lines) was investigated with and without the step (b).

Measurements were made with a copper foil circuit width (wire width) of 0.3 mm and a distance between circuits of 0.3 mm.
7n7! Using the printed circuit board obtained in each of the above examples having a circuit with an L1 circuit length (line length) of 50 mm, measure the insulation resistance between the lines after applying a DC voltage of 500 V between the circuits for 60 seconds. This is what I did. As a result, those of Reference Examples 1 and 2 without step (b) were 2.0×10
11 Ω, but Example 1 to which step (b) was added
The resistance of No. 3 was 4.2×10 12 Ω. [Effects of the Invention] According to the present invention, current leakage caused by catalyst remaining in non-circuit parts is prevented, and high-density wiring becomes possible.

In fact, the secondary effects of reducing the number of man-hours and preventing the resist from falling off can also be obtained.

[Brief explanation of the drawing]

1 and 2 are partial cross-sectional views showing the state of the printed circuit board for each manufacturing process for explaining the present invention. 1: Copper foil circuit, 2: Resin laminate, 3: Through hole, 4
: catalyst, 5; non-circuit portion, 6; resist film, 7: chemically plated film.

Claims (1)

[Scope of Claims] 1. A method for manufacturing a printed circuit board, characterized by sequentially including the following steps. (a) a step of applying a chemical plating catalyst to at least the inner wall of the through hole by treating a substrate having a copper foil circuit formed by etching and a through hole for inserting a lead wire of an electronic component with a chemical plating catalyst liquid; (b) leaving the catalyst on the inner wall of the through hole and removing the catalyst attached to at least the non-circuit portion, (c) completely exposing the formed copper foil circuit, only the surface of the circuit side board exposed by etching (d) Depositing a chemical plating film on the inner wall of the through hole and the copper foil circuit, and electrically connecting the circuit and the inner wall of the through hole. .