JP2712997B2 - Solder resist processing method in manufacturing printed wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a finishing step for manufacturing a printed wiring board having at least two layers of wiring circuits and VIA holes for conducting these wiring circuits.
The present invention relates to a method for treating a solder resist in the manufacture of a printed wiring board in which a solder resist layer is formed on the surface of a printed wiring board.

[0002]

2. Description of the Related Art A printed wiring board is formed by laminating a double-sided printed wiring board in which a wiring circuit made of copper foil, copper plating or the like is formed on both sides of a plate-shaped insulating base material, or three or more wiring circuit layers. There is also a multilayer printed wiring board having a wiring circuit in the inner layer of the printed wiring board. And these printed wiring boards
Via holes for interconnecting a plurality of layers of wiring circuits are formed.

The via holes are formed by forming a through hole in the insulating base material, plating the inner wall of the through hole with a metal plating, and connecting the metal plating to a wiring circuit of each layer to form a wiring circuit of a different layer. These are made conductive to form one circuit.

[0004] During the finishing work in the manufacture of such a printed wiring board, the wiring circuit formed on the surface of the insulating base material is protected, and when the electronic components are mounted, the printed wiring board is soldered. In order to prevent the solder from adhering to the unnecessary parts and short-circuiting of the wiring circuit, a solder resist (hereinafter sometimes abbreviated as SR) layer made of an insulating resin is formed on the surface of the printed wiring board. There are processing steps. In this SR processing step, no SR layer is formed on the terminal portion of the surface of the printed wiring board on which the electronic component of the wiring circuit is mounted.

Conventionally, the above finishing work is performed by the above-mentioned SR processing step and then lightly etching the surface of the wiring circuit exposed from the SR layer to form a wiring circuit for solder coating (hereinafter abbreviated as SC) to be described later. A surface roughening step for cleaning and roughening the surface of the copper to be formed, and then an SR for improving the solderability between the electronic component and the wiring circuit terminal and protecting the wiring circuit exposed from the SR layer. And SC for coating the surface of the wiring circuit exposed from the layer with solder.

After the SC step, there is an inspection step such as an electrical inspection for inspecting the wiring circuit for disconnection or short circuit. In the electrical inspection, a constant voltage is applied between terminals of a wiring circuit of a printed wiring board, and the conduction and insulation state are inspected by a resistance value. At the time of this electrical inspection, by suctioning the printed wiring board, the terminals are brought into close contact with a test probe that applies a voltage to each terminal of the wiring circuit,
Voltage is being applied to the wiring circuit.

During the electrical inspection, if the VIA hole penetrates the printed wiring board, air passes through the VIA hole and sucks the insulating base material, thereby connecting the terminal to the test probe. Since it is difficult to adhere the SR layer, when forming the SR layer on the surface of the insulating substrate,
In the opening on one side of the VIA hole on the surface of the insulating substrate, SR
Is formed to close the VIA hole.

The method of covering the via holes with the SR film in this way is called a tenting method.

[0009]

As described above, when forming an SR layer on an insulating substrate and performing tenting of the SR film on the opening on one side of the VIA hole, the VIA Since the bottom of the SR film is formed in the hole, when cleaning the etchant used in the surface roughening step, the cleaning liquid is applied from one side of the insulating base material to the other side.
You cannot pass through the IA hall. That is, SR
The tenting of the film makes it difficult to clean the etchant entering the via hole.

If a part of the etchant remains in the VIA hole, the metal plating on the inner wall of the VIA hole may be damaged by the etchant, and a conduction failure may occur in the VIA hole.

The present invention has been proposed in view of the above circumstances, and an object of the present invention is to prevent an etching solution from remaining in a VIA hole in the above-described surface roughening step, and to improve the reliability of a printed wiring board. An object of the present invention is to provide a solder resist processing method in the manufacture of a printed wiring board that can improve the performance.

[0012]

According to the present invention, there is provided a method for treating a solder resist in the manufacture of a printed wiring board, comprising the steps of: forming a wiring circuit formed on at least both front and back surfaces of a plate-shaped insulating substrate; And a through hole having a metal plating formed on an inner wall so as to connect the wiring circuits to each other. Forming a solder resist layer on both the front and back surfaces of the insulating substrate on which the circuit and the through hole are formed, and excluding the opening of the through hole and the mounting part of the electronic component of the wiring circuit on the front and back surfaces of the insulating substrate. A resist forming step of forming a solder resist layer, and then a roughening step of etching and roughening a mounting portion of the electronic component of the wiring circuit,
It is a solution to the above-mentioned problem that the method further comprises a closing step of forming a solder resist film in the opening of the through hole and closing the opening after the surface roughening step.

[0013]

According to the above construction, in the resist forming step, the roughening step using an etching solution is performed in a state where the through-hole is not closed by the SR film and the through-hole is not closed. Then, the opening of the through hole is closed by the SR film. Therefore, when cleaning the etchant after etching in the surface roughening step, the cleaning solution can pass through the through-hole, and the etchant can be easily cleaned.

In the closing step, since the through-hole is closed by the SR film, the terminals of the wiring circuit on the surface of the printed wiring board are brought into close contact with the test probe by sucking the printed wiring board during an electrical inspection. At the time, V
No air leaks from the IA holes.

[0015]

An embodiment of the present invention will be described below with reference to the drawings. FIGS. 1 to 3 are views for explaining a solder resist processing method in manufacturing a printed wiring board according to this embodiment. FIGS. 1 and 2 show positions of VIA holes 2 of an insulating base material 1 described later. FIG. 3 is a flowchart of a solder resist processing method.

The printed wiring board is a well-known multi-layer printed wiring board, in which wiring circuits (not shown) are formed in outer layers on both front and back surfaces of a plate-shaped insulating base material 1 and a plate-shaped insulating substrate is formed. A wiring circuit (not shown) is also formed on the inner layer of the insulating base material 1. As shown in FIGS. 1 and 2, the insulating substrate 1 has a large number of VIA holes penetrating the insulating substrate 1 (FIG. 1 and FIG. 2 show one via hole of the insulating substrate 1). 2 is formed by enlarging the hole 2).

The inner wall of the via hole 2 is coated with copper plating 3. The VIA hole 2 connects the copper plating 3 on the inner wall thereof with the wiring circuits in the outer layer and the inner layer, thereby electrically connecting the wiring circuits.

The solder resist treatment of the present embodiment is performed as a finishing step after the formation of the wiring circuit on the insulating base material 1 and the formation of the via hole 2 in the manufacture of the printed wiring board. It is.

Then, as shown in FIG. 3, the solder resist processing method comprises the steps of:
A component forming (hereinafter abbreviated as CM) printing step S2 for printing an abbreviation of an electronic component (not shown) on the SR layer 4 formed in the resist forming step S1. A surface roughening step S3 for roughening the surface of a portion of the wiring circuit on the outer layer of the insulating base material 1 exposed from the SR layer 4 with an etchant, and a wiring circuit roughened in the surface roughening step S3. After the SC step S4 of coating the surface with solder, and after the roughening step S3 and the SC step S4, an SR film 5 is formed in one opening of the VIA hole 2 to form the VIA hole 2 as shown in FIG. It comprises a closing step S5 for closing one of the openings, and an inspection step S6 for performing an inspection such as an electrical inspection of the printed wiring board.

In the resist forming step S1, as shown in FIG. 1, screen printing is performed on both front and back surfaces of the insulating base material 1 by using a well-known liquid photoresist which is a photosensitive resin as an ink. The SR layer 4 is formed, and the SR layer 4 is photosensitive-cured by exposing the portion other than the opening of the VIA hole 2 and the mounting portion of the electronic component on the wiring circuit, and is developed. Therefore, on both the front and back surfaces of the insulating base material 1, the surface except for the terminal (not shown) on which the electronic component of the wiring circuit is mounted and the opening of the VIA hole is covered with
The R layer 4 will be formed.

Subsequently, in the CM printing step S2,
On the surface of the cured SR layer 4, characters, codes, lines, and the like indicating the abbreviations and mounting positions of the electronic components to be mounted on the printed printing board are screen-printed.

In the subsequent roughening step S3, prior to the SC step S4, the surface of the portion of the wiring circuit exposed from the SR layer 4 is soft-etched by contacting the surface with an etchant to form a wiring circuit. Clean copper surface,
This is a step of roughening. That is, only the surface layer of copper is dissolved and removed for the purpose of making the solder easier to coat.

Then, in the surface roughening step S3, after only the copper surface layer is dissolved and removed, the etching solution is washed. At this time, the SR layer 4 is formed in the opening of the VIA hole 2.
Are not formed, so that the VIA hole 2 penetrates and opens as shown in FIG. That is,
The cleaning liquid can pass through the VIA hole 2. Therefore, the etching solution entering the VIA hole 2 can be easily washed out with the cleaning solution.

The SC step S4 performed after the cleaning of the etchant is to coat the surface of the copper exposed from the SR layer 4 with solder by bringing the surface layer of the insulating substrate 1 into contact with molten solder. Also, SC step S
In 4, the insulating substrate 1 is immersed in molten solder,
After the molten solder is brought into contact with the surface of the insulating substrate 1, hot air blowing leveling is performed.

Also in this SC step S4, the VIA hole 2 is in a state of being penetrated and opened, so that the molten solder can flow in the VIA hole 2 and at the time of hot air blowing leveling. Hot air flows into VIA Hall 2
The excess solder in the via hole 2 is blown off, so that the surface of the copper plating 3 on the inner wall of the via hole 2 is uniformly coated with the solder.

When one opening of the via hole 2 is closed by the SR layer as in the prior art, the flow of the molten solder in the via hole 2 is restricted. , There is a possibility that the solder may adhere to the VIA hole 2 as a small lump. Also, VI
Solder adhered in small chunks in the A-hole 2 may come off when electronic components are mounted on the completed printed wiring board. There is a possibility that it may reattach to the terminal of the component and cause a short circuit of the wiring circuit.

However, as described above, in the present embodiment, since the solder can flow in the VIA hole 2 and the hot air can pass through, there is no possibility that a solder lump is generated in the VIA hole 2 and printing is performed. Short circuit of the wiring board can be prevented.

Then, after the SC step S4, the insulating substrate 1
In order to close the opening of the VIA hole 2 on one side of
The SC step S is formed in the opening of the VIA hole 2 of the insulating base material 1.
After that, dot printing using a well-known thermosetting SR as ink is performed to a size substantially the same as the diameter of the VIA hole 2 after the above.
Then, as shown in FIG. 2, an SR film 5 is formed in one opening of the VIA hole. After the dot printing, the SR film 5 for closing the opening of the via hole 2 is cured by baking.

After the above SR processing is performed, an inspection step S6 such as an electrical inspection of the printed wiring board is performed. In the electrical inspection, a test probe (not shown) is brought into close contact with many terminals of the wiring circuit on the surface of the printed wiring board, a constant voltage is applied between the terminals, and the conduction and insulation state of the wiring circuit is determined based on the resistance value. Inspect the wiring circuit for disconnections and short circuits. At this time, the terminals of the wiring circuit are brought into close contact with the test probe by sucking the printed wiring board.
In FIG. 5, since it is closed by the SR film 5, it does not hinder close contact with the test probe due to suction.

As described above, according to the present embodiment, in the roughening step S3 after the SR step S1, the VIA hole 2 is in a state of being penetrated and opened. In addition, the etching solution in the via hole 2 can be easily cleaned, and the etching solution does not remain in the via hole 2. Therefore, VI
It is possible to prevent the copper plating 3 on the inner wall of the VIA hole 2 from being damaged by the etchant remaining in the A hole and the reliability of the printed wiring board from being impaired.

Also, in the SC step S4, since the VIA hole 2 is in a state of being penetrated and opened, the VI
The molten solder in the A-hole 2 can flow freely, and at the time of hot-air blowing leveling, VIA
VIA Hall 2 because you can pass through the hall
No small lump of solder is formed inside, and VI
The surface of the copper plating 3 on the inner wall of the A hole 2 can be uniformly coated with solder. Therefore, when mounting the electronic component, it is possible to prevent the wiring circuit from being short-circuited due to a small mass of solder formed in the VIA hole 2.

The VIA hole 2 is formed in a roughening step S
3. After the SC step S4, the printed circuit board is tented by the dot printing of the SR and closed by the SR film 5, so that when the electrical inspection is performed, the terminals of the wiring circuit of the printed wiring board and the test probe are brought into close contact by suction. Does not interfere with

In this embodiment, when the SR layer 4 is formed, a liquid photoresist is used as the SR,
When tenting the A hole 2 with the SR film 5,
Although a thermosetting type is used as R, other well-known SR may be used for the SR layer 4 or the SR film 5. For example, a well-known ultraviolet curable resist may be used in the closing step S3.

[0034]

As described above in detail, according to the solder resist processing method for manufacturing a printed wiring board of the present invention, the through-hole is not closed when the SR layer is formed, and the resist forming step is not performed. In the subsequent roughening step, the etching liquid can be easily washed,
Since the etching solution does not remain in the through holes, the reliability of the printed wiring board can be improved.

In addition, in the closing step after the roughening step, the through hole is closed, so that there is a problem in that the printed wiring board is sucked and brought into close contact with the test probe during the electrical inspection. There is no.

[Brief description of the drawings]

FIG. 1 is a sectional view of a VIA hole portion of a printed wiring board for describing a solder resist processing method in manufacturing the printed wiring board of the embodiment.

FIG. 2 is a sectional view of a VIA hole portion of the printed wiring board.

FIG. 3 is a flowchart for explaining a solder resist processing method in manufacturing the printed wiring board.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating base material 2 VIA hole (through-hole) 3 Copper plating (metal plating) of VIA hole inner wall 4 Solder resist layer 5 Solder resist film

Claims (1)

(57) [Claims] 1. A wiring circuit formed on at least both front and back surfaces of a plate-shaped insulating base material, and metal plating is formed on an inner wall so as to penetrate the insulating base material and connect the wiring circuits to each other. In a manufacturing process of a printed wiring board having electronic components mounted on the wiring circuit, a solder resist layer is formed on both front and back surfaces of the insulating base material on which the wiring circuit and the through hole are formed. A method of processing a solder resist in the manufacture of a printed wiring board, comprising forming a solder resist layer on both the front and back surfaces of the insulating substrate except for the opening of the through hole and the mounting part of the electronic component of the wiring circuit. A forming step, a surface roughening step for etching and then roughening a mounting portion of the electronic component of the wiring circuit, and a soldering step in the opening of the through hole after the surface roughening step. The solder resist processing method in the manufacture of printed wiring board, characterized by comprising; and a blocking step for blocking to form a resist film.