JPH04363093A - Manufacture of printed board - Google Patents

Abstract

PURPOSE:To cover the pattern with solder uniformly and flatly so as to improve the reliability on connection and the positional accuracy in mounting components, covering the exposed metallic pattern with solder alloy, which has tin and lead for its main ingredients, by electroless plating after forming a wiring pattern. CONSTITUTION:After removal of the pollution and the fat and oil on the surface 1 of a printed wiring board and the oxides on a copper pattern 5, the surface of the copper pattern 5 is etched off using ammonium persulfate aqueous solution so as to expose the clean surface of copper. After removal of the oxides on the surface of the copper with dilute sulfuric acid, it is predipped to wet the printed board 1. Electroless plating is made on the copper foot pad pattern of the board 250mum in pitch and 100mum in width, using electroless plating liquid which has tin, lead, organic sulfuric acid, and thioharnstoff for its main ingredients. Since reaction occurs at the interface between metallic copper and plating liquid with the electroless solder plating and a film 7 is made, the top of the pattern 5 becomes flat without being influenced by the adjacent copper foot pad pattern 5.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a printed circuit board, and more particularly to a method of manufacturing a printed circuit board in which a wiring pattern is coated with solder.

0002

2. Description of the Related Art A conventional method for coating a copper pattern on a printed circuit board with solder will be explained with reference to FIG. 7, using a gas leveler method as an example. First, a printed circuit board 1 that has been patterned and coated with a solder resist is immersed in melted solder 3 in a tank 2 for a predetermined time. Thereafter, as shown in FIG. 7, while the printed circuit board 1 is pulled up from the tank 2, high-temperature, high-pressure gas 4 is blown onto the surface of the printed circuit board 1 to blow off excess solder on the copper pattern, thereby placing it at a desired position on the copper pattern. Cover with solder.

[0003] Next, a multilayer printed circuit board to which the above-mentioned solder coating method is applied includes the following steps: (1) Patterning process of the inner layer conductor plate (2) Surface treatment (blackening treatment) process of the inner layer conductor plate (3) Lamination Press process (4) Through-hole drilling process (
5) Panel copper plating process (6) Multilayer conductor plate patterning process (7) Solder resist and symbol printing process (8) Solder gas leveler process (9) Manufactured through external shape processing process.

0004

[Problems to be Solved by the Invention] In the conventional printed circuit board manufacturing method as described above, it is difficult to uniformly and flatly coat the copper pattern 5 with the solder 6, as shown in FIGS. 8 and 9. In areas where the area of the copper pattern 5 is small and the spacing between the patterns is narrow, the thickness of the solder 6 increases due to the interfacial tension of the solder 6, and the solder 6 tends to short-circuit with each other as shown in A in FIG. Become. Furthermore, if the pressure of the gas 4 used to blow away the solder 6 is increased to prevent short circuits, the thickness of the solder 6 on a pattern with a large area will be insufficient, as shown by B in FIG. This results in poor connection reliability. Furthermore, when determining the component mounting position using an image recognition device, the solder on the recognition pattern has a glossy curved surface, which causes problems such as reflecting the surrounding scene and reducing positioning accuracy. Ta.

This invention was made to solve the above-mentioned problems, and it is possible to coat the solder uniformly and flatly without surface irregularities regardless of the size of the pattern area. Even if there are parts with narrow pattern spacing, there will be no short circuits, and the connection reliability of components is high.Furthermore, the recognition rate of image recognition equipment when mounting components is improved.
The purpose of the present invention is to obtain a method for manufacturing a printed circuit board that can improve the positional accuracy of components.

[0006]

[Means for solving the problem] Claim 1 of this invention
The method of manufacturing a printed circuit board according to claim 2 is such that after forming a wiring pattern, the wiring pattern is coated with a solder alloy mainly composed of tin and lead by electroless plating. The manufacturing method of the board is as follows: After forming the wiring pattern, a solder resist is applied to a part of the wiring pattern, and the remaining exposed part is coated with a solder alloy mainly composed of tin and lead by electroless solder plating. Further, the method for manufacturing a printed circuit board according to claim 3 further includes tin (0.1 mol/l), lead (0.
．． 01 mol/l), organic sulfonic acid (0.2 mol/l)
, an electroless solder plating solution containing thiourea (2 mol/l) as a main component is used.

[0007]

In the present invention, the solder coated on the exposed metal pattern is formed by electroless plating to have a flat and uniform thickness.

[0008]

【Example】

Example 1. Hereinafter, a process in a method for manufacturing a printed circuit board according to Example 1 of the present invention will be described. Process (1) Patterning process of inner layer conductor plate (2) Surface treatment process of inner layer conductor plate (3) Lamination press process (4) Through hole drilling process (
5) Panel copper plating process (6) Multilayer conductor plate patterning (pattern plating method or tenting method) Process (7) Solder resist and symbol printing process (8) Electroless solder plating process (9)
) Outline processing A printed wiring board is formed by coating the copper pattern with solder by electroless plating through the manufacturing process described above. Note that processes (8) and (9) are the same even if they are replaced.

Next, the detailed process of electroless solder plating in process (8) will be explained with reference to FIG. Process (8-1) Degreasing (acidic) Removes dirt, oil and fat on the surface of the printed wiring board, and oxides on the copper pattern. Process (8-2) Soft etching (ammonium persulfate aqueous solution) The surface of the copper pattern is removed by etching of 0.5 to 2 μm to expose a clean copper surface. Process (8-3) Pickling (dilute sulfuric acid) Removes oxides from the copper surface. Process (8-4) Before the pre-dip plating main bath, the printed circuit board is wetted with a solution with the same pH and concentration of additives as the main bath to stabilize plating precipitation and prevent impurities from entering the main bath. Prevents contamination and extends the life of the plating solution.

Process (8-5) Electroless solder plating (acidic) First, tin (0.1 mol/l), lead (0.01 mol/l)
), organic sulfonic acid (0.2 mol/l), thiourea (2
Using an electroless solder plating solution whose main component is mol/l), the plating temperature is 70°C, and the plating time is 15 minutes.
Electroless solder plating was performed on a copper foot pad pattern of a substrate with m pitch and width of 100 μm. FIG. 3 shows the state of the solder film coated on the copper foot pad pattern in this way, and FIG. 4 shows the thickness and tin composition ratio of this solder film. In addition, when using an electroless solder plating solution with the above components, a solder film with an arbitrary plating thickness can be formed on the copper foot pad pattern by adjusting the plating time, as shown in Figure 5. Can be done.

[0011] In electroless solder plating, a reaction occurs at the metal copper/plating solution interface and a film is formed, so that the solder film is formed without being affected by the adjacent copper foot pad pattern. Furthermore, since the reaction occurs only at the metallic copper/plating solution interface, the original shape of the copper footpad pattern is maintained even if the solder film is deposited, and the top of the copper footpad pattern 5 remains flat as shown in Figure 2. It is. In this way, according to this embodiment, a highly accurate and flat solder film 7 can be formed even on copper foot pads with a fine pitch.

FIG. 6 shows that the foot pad pattern coated with solder according to the above embodiment is coated with I by a pulse heating method.
An example in which soldering was performed by heating a C package at 270° C. for 5 seconds is shown. When the peel strength of the soldered part was measured, the leads of the IC package were broken without the soldered part peeling off, and a good soldered part was obtained. As described above, according to this embodiment, it is possible to form a solder film on the fine pitch foot pad pattern of a printed circuit board with the thickness controlled with high precision, making it easy to solder a fine pitch IC package. be able to. Process (8-6) Solder surface activation (acidic) Removes dirt oxides from the solder surface.

Example 2. In Example 1 above, solder resist is applied to a part of the wiring pattern, and the remaining exposed parts are coated with solder alloy by electroless plating. A similar effect can be obtained by covering the solder alloy with plating.

Example 3. The solder coated on the copper pattern may contain 1% or less antimony.

Example 4. The degreasing in process (8-1) in Example 1 above may be alkaline.

Example 5. The soft etching of process (8-2) in Example 1 above includes sodium persulfate,
A liquid whose main components are potassium persulfate, sulfuric acid + hydrogen peroxide, or ammonium persulfate + sulfuric acid may be used.

Example 6. The pickling in process (8-3) in Example 1 above may be performed using an organic acid, hydrochloric acid, or nitric acid.

Example 7. The formation of the copper pattern in process (1) in Example 1 may be performed by a full additive method or a part additive method.

It should be noted that it is not mandatory to use all of the electroless solder plating processes (8-1) to (8-6), and printed circuit boards can be printed on one or both sides. It goes without saying that the present invention can be applied to multilayer substrates of four or more layers, ceramic substrates, injection molded substrates, curved substrates, glass substrates, and the like.

[0020]

As described above, according to the present invention, after forming a wiring pattern or after forming a wiring pattern and applying a solder resist, tin and lead are mainly applied to the exposed metal pattern by electroless plating. Since the solder alloy that is the component is coated, the solder can be applied uniformly over the pattern regardless of the pattern dimensions or pattern spacing.
Moreover, it can be coated flatly. Moreover, this has the effect of improving connection reliability and positional accuracy during component mounting.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing a detailed process of electroless solder plating as a main process in a printed circuit board manufacturing method according to a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view showing the state of a solder film formed by electroless solder plating in FIG. 1;

FIG. 3 is a diagram showing an example of the solder film in FIG.
A) is a photograph showing the surface condition of the solder film on the board, (
B) is an enlarged photograph of a part of the solder film.

FIG. 4 is a characteristic diagram showing the thickness and tin composition ratio of the solder film in FIG. 3;

5 is a characteristic diagram showing the relationship between plating time and plating thickness in the electroless solder plating process shown in FIG. 1. FIG.

FIG. 6 is a diagram showing an example of an IC package soldered onto the solder film shown in FIG. 3, where (A) is a photograph showing the state of the soldered part, and (B) is an enlarged view of a part of the soldered part. This is a photo shown.

FIG. 7 is a diagram for explaining the procedure for coating solder on a printed circuit board using a conventional gas leveler method.

FIG. 8 is a schematic cross-sectional view showing an example of the state of a solder film formed by a conventional method.

FIG. 9 is a schematic cross-sectional view showing another example of the state of a solder film formed by a conventional method.

[Explanation of symbols]

1 Board 5 Copper pattern 7 Solder film

Claims (3)

[Claims] 1. A method for manufacturing a printed circuit board, characterized in that after forming a wiring pattern, the wiring pattern is coated with a solder alloy containing tin and lead as main components by electroless plating. [Claim 2] After the wiring pattern is formed, a solder resist is applied to a part of the wiring pattern, and the remaining exposed part is coated with a solder alloy mainly composed of tin and lead by electroless plating. A method for manufacturing a printed circuit board, characterized by: Claim 3: Tin (0.1 mol/l), lead (0.0
1 mol/l), organic sulfonic acid (0.2 mol/l), and thiourea (2 mol/l) as main components. 2. The method for manufacturing a printed circuit board according to any one of 2.