JPH08139438A - Solder coating method - Google Patents

Abstract

PURPOSE: To easily coat each land of a wiring board with uniform solder quantity without irregularity, by heating and fusing solder supplied to each of the apertures of a resist layer, and coating each of the lands. CONSTITUTION: Lands 3 are arranged on the pattern surface 2A of a board 2 constituting a wiring board 1. Photo solder resist is stuck on the pattern surface 2A of the board 2, so as to cover the whole part of the neighboring lands 3 as the solder coating objects. Thus a resist layer 4 is formed on the pattern surface 2A of the board 2. After the resist layer 4 on each of the lands 3 is exposed to light and cured in a specified pattern, the wiring board 1 is dipped in alkaline solution, and uncrosslinked photo solder resist of the resist layer 4 is eliminated. Thereby an aperture 4A is formed in the resist layer so as to expose each of the lands 3.

Description

Detailed Description of the Invention

[0001]

[Table of Contents] The present invention will be described in the following order. Field of Industrial Application Conventional Technology Problems to be Solved by the Invention Means for Solving the Problems (FIGS. 1 to 4) Actions (FIGS. 1 to 4) Embodiments (FIGS. 1 to 4) Effects of the Invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder coating method, and is suitable for application to, for example, a solder coating method of coating (solder coating) a land of a wiring board for flip chip mounting with solder.

[0003]

2. Description of the Related Art Conventionally, as a method of solder-coating each land of a wiring board for flip-chip mounting, a method of dipping the wiring board in molten solder (hereinafter referred to as an immersion method) or soldering on the land is used. There is a method of performing mask vapor deposition (hereinafter referred to as vapor deposition method), a method of performing wet plating (hereinafter referred to as plating method), and the like.

[0004]

However, when the dipping method is applied as a means for solder-coating the land of the wiring board, the thickness of the solder layer (solder coat) formed on each land is about 10 [μm]. There is a problem that the film thickness is low and that the film thickness is likely to vary greatly depending on each land.
This is because when the substrate is immersed in the molten solder, the molten solder itself also serves as a heating source, and the amount of solder supplied to each land is almost infinite compared to the size of the land. This is because it is unavoidable that the amount of solder attached to each land changes due to a slight change in condition when pulling up the wiring board from the above.

On the other hand, in the vapor deposition method, there is a problem that forming a thick solder layer on each land of the wiring board becomes extremely expensive, and in the plating method, a conductive land for flowing electricity to each land of the wiring board. Therefore, there is a problem that the mounting density of the wiring board is reduced.

The present invention has been made in consideration of the above points, and is intended to propose a solder coating method capable of coating each land of a wiring board easily and with a uniform solder amount without variation. is there.

[0007]

In order to solve such a problem, in the present invention, one or a plurality of lands (3) formed on one surface (2A) of a substrate (2) are coated with solder (30), respectively. In the solder coating method, a first step of forming a resist layer (4) on one surface (2A) of the substrate (2) so as to avoid each land (3) and cover each land (3), and each land ( 3) A second step of supplying a uniform amount of solder (10) to each opening (4A) of the exposed resist layer (4) and each opening (4A) of the resist layer (4). By heating and melting the solder (10) respectively supplied to
A third step of coating each land (3) with the solder (10) supplied to the corresponding opening (4A) of the resist layer (4) is provided.

Further, in the present invention, in the first step, a photo solder resist layer made of a photo solder resist is formed on one surface (2A) of the substrate (2) so as to cover the entire area including each land (3). In the fourth step, the photo solder resist layer is exposed to light in a predetermined pattern and then developed to form openings (4) in the photo solder resist layer.
And the fifth step of forming A).

Further, in the present invention, the second step is
A step of embedding a solder paste (10) obtained by uniformly mixing solder particles having a small particle diameter in the flux into each opening (4A) of the resist layer (4) was included.

Further, in the present invention, the wiring board (1) in which each land (3) is formed on one surface (2A) of the board (2) is a wiring board for flip chip mounting.

[0011]

The resist layer (4) is formed on the one surface (2A) of the substrate (2) so as to avoid the land (3) formed on the one surface (2A) of the substrate (2) and cover each land (3). A uniform amount of solder (10) is supplied to each opening (4A) of the resist layer (4) formed and exposed to each land (3), and the solder supplied to each opening (4A). (1
0) is melted by heating so that each land (3) is coated with the solder (10) supplied to the corresponding opening (4A) of the resist layer (4). Each land (3) on the substrate (2) can be solder-coated with a uniform thickness without the need for land or vapor deposition process, and thus each land (3) of the wiring board (1) can be simply and easily formed. Further, it is possible to realize a solder coating method capable of coating with a uniform amount of solder without variation.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

1 to 4 show an example of a process of solder-coating each land of a wiring board for flip-chip mounting using the present invention. First, as shown in FIG. 1, the wiring board 1 is constructed. The lands 3 made of a copper material or the like are juxtaposed on the pattern surface 2A of the substrate 2 with a predetermined pitch (for example, 0.15 [mm]), and the lands 3 of the adjacent solder coating targets are covered with the lands 3. A photo solder resist containing an acrylic resin and an epoxy resin as main components is applied on the pattern surface 2A so as to have a film thickness of, for example, about 30 [μm] to form the resist layer 4 on the pattern surface 2A of the substrate 2. Form. Then, after the resist layer 4 on each land 3 is exposed and cured in a predetermined pattern, the wiring board 1 is dipped in an alkaline solution to remove the uncrosslinked photo solder resist of the resist layer 4, thereby removing each land. A 100 [μm] square opening (hereinafter, referred to as a window) 4A is formed in the resist layer 4 so that 3 is exposed.

Next, as shown in FIGS. 2 and 3, a solder paste 10 made by mixing solder powder into the flux.
Is dropped on the resist layer 4 of the wiring board 1, and then the squeegee 11 is moved on the resist layer 4 so that the solder paste 10 rolls on the resist layer 4, so that each window 4A of the resist layer 4 is moved. The solder paste 10 is embedded. In this case, as the solder powder of the solder paste 10, a spherical powder having a particle size of 10 [μm] or less is used so that the solder particles can be uniformly embedded in each window 4A of the resist layer 4, and the flux As the material, a resin-based viscous flux or a water-soluble viscous flux having good detergency is used. Also squeegee 11
As the material, a hard metal material is used.

Subsequently, the solder paste 10 embedded in each window 4A of the resist layer 4 is heated and melted. In this case, heating the solder paste 10 is performed in an inert gas such as N ₂ (nitrogen) or Ar (argon) so that good solderability can be obtained without promoting surface oxidation of the solder particles. Try to do it. After that, when a resin system is used as the flux of the solder paste 10, it is washed with an organic solvent after this, and when a water-soluble flux is used as the flux, it is washed with water.

As a result, as shown in FIG. 4, the wiring board 1
Each of the lands 3 can be coated (solder coated) with the solder 30 having a predetermined thickness. According to an actual experiment, a solder coat having a thickness of about 20 [μm] could be formed on each land 3 of the wiring board 1 by the above-mentioned solder coat method.

In the above structure, in this solder coating method, the resist layer 4 made of hardened photo solder resist is formed on the pattern surface 2A of the substrate 2 while avoiding the corresponding lands 3 formed on the substrate 2. After embedding the solder paste 10 composed of solder particles having a predetermined diameter and flux in each window 4A of the resist layer 4, each solder paste 10 in each window 4A is embedded.
After being melted by heating, the flux is washed off as needed to form a solder coat on each corresponding land 3 of the wiring board 1. In this case, in this solder coating method, in order to uniformly embed the solder particles in each window 4A of the resist layer 4, the solder powder forming the solder paste has a spherical shape with a particle diameter of 10 [μm] or less. Therefore, since the amount of solder supplied into each window 4A of the resist layer 4 is substantially uniform, each land 3 can be solder-coated with a uniform thickness.

Further, in the above-mentioned solder coating method, it is not necessary to provide the conductive land unlike the plating method, so that
Since it can be performed without lowering the mounting density of the wiring board 1 and a process such as vapor deposition is not necessary, each land 3 of the wiring board 1 can be coated with a large film thickness at a low cost. Therefore, it is possible to provide the wiring board 1 for flip-chip mounting having a high added value at a low cost.

According to the above configuration, the board 2 of the wiring board 1
The resist layer 4 is formed on the pattern surface 2A of the substrate 2 while avoiding the corresponding lands 3 formed above, and each window 4A of the resist layer 4 is formed by exposing each land 3.
After embedding a solder paste 10 composed of solder particles having a predetermined diameter and a flux into each of the
The solder paste 10 in A is heated and melted, and then the flux is washed away to form solder coats on the corresponding lands 3 of the wiring board 1, thereby stabilizing each land 3 of the wiring board 1. Solder coating can be performed with a uniform thickness and thus the wiring board 1
It is possible to realize a solder coating method capable of easily coating each land 3 with a uniform amount of solder without variation.

In the above embodiment, the wiring board 1
The case where the lands 3 are arranged in parallel with the 0.15 [mm] pitch using the copper material on the substrate 2 has been described, but the present invention is not limited to this, and as a material for the lands formed on the substrate 2, Other materials may be used, or the land may be formed by other pitches.

Further, in the above-mentioned embodiment, the case where the present invention is applied to the wiring board 1 for flip-chip mounting is described, but the present invention is not limited to this, and each land of various other wiring boards. It is suitable when applied on the top with solder.

Further, in the above embodiment, as a method of forming the resist layer 4 on the pattern surface 2A of the substrate 2 while avoiding the corresponding lands 3 formed on the substrate 2 of the wiring substrate 1, the substrate 2 In the case where the photo solder resist is attached to the pattern surface 2A of 3 .about.30 .mu.m thick, and the photo solder resist is exposed and cured and developed in a predetermined pattern to form the resist layer 4 having the window 4A. , But
The present invention is not limited to this, and various other methods can be applied as a method of forming the resist layer 4 on the pattern surface 2A of the substrate 2 while avoiding the corresponding lands 3 formed on the substrate 2.

Further, in the above-described embodiment, the resist layer 4 formed on the substrate 2 of the wiring substrate 1 has 100 [μm] square windows 4 centered on each land 3 of the wiring substrate 1.
Although the case where A is provided has been described, the present invention is not limited to this, and the size of the window 4A may be other than this. Incidentally, by adjusting the size of the window 4A, the solder 3 attached to each copper land 3 of the wiring board 1 is attached.
The thickness of 0 (that is, the thickness of the solder coat) can be adjusted.

Further, in the above-mentioned embodiment, the case where the resist layer 4 formed on the substrate 2 of the wiring board 1 is formed by sticking a photo solder resist mainly containing acrylic resin and epoxy resin However, the present invention is not limited to this, and the point is that the wiring board 1
If the resist layer 4 can be formed on the pattern surface 2A of the substrate 2 while avoiding the corresponding lands 3 formed on the substrate 2, the other method of forming the resist layer 4 will be described. Can also be applied. in this case,
For example, a dry film may be used instead of the photo solder resist, and the dry film may be removed after the copper lands 3 of the wiring board 1 are solder-coated.

Further, in the above-mentioned embodiment, the case where each corresponding land 3 of the substrate 2 of the wiring substrate 1 is solder-coated by the steps of FIGS. 1 to 4 has been described. Not limited to this, for example, when it is desired to increase the film thickness, the steps of FIGS. 2 to 4 may be repeated after the above-described solder coating step is completed. Incidentally, when the steps of FIGS. 2 to 4 are performed again after the steps of FIGS. 1 to 4 are completed, the film thickness of the solder coat formed on each land 3 is about 30.
It has been confirmed by experiments that the thickness can be increased to [μm].

[0026]

As described above, according to the present invention, a resist layer is formed on one surface of a substrate so as to cover each land area while avoiding each land formed on one surface of a substrate that constitutes a wiring board, A uniform amount of solder is supplied to each opening of the resist layer in which the lands are exposed, and the solder supplied to each of the openings is heated and melted to form each land in the corresponding opening of the resist layer. By coating with the solder supplied to the parts, each land on the substrate can be solder-coated with a uniform thickness without the need for conductive lands and the process of vapor deposition. It is possible to realize a solder coating method capable of easily coating each land with a uniform amount of solder without variation.

[Brief description of drawings]

FIG. 1 is a schematic perspective view for explaining a process of a solder coating method according to an embodiment.

FIG. 2 is a cross-sectional view for explaining a process of a solder coating method according to an example.

FIG. 3 is a cross-sectional view for explaining the steps of the solder coating method according to the example.

FIG. 4 is a cross-sectional view for explaining the steps of the solder coating method according to the example.

[Explanation of symbols]

1 ... Wiring board, 2 ... Board, 2A ... Pattern surface, 3
... Copper land, 4 ... Resist layer, 4A ... Wind,
10 ... Solder paste, 30 ... Solder.

Claims (4)

[Claims] 1. A solder coating method for coating a single or a plurality of lands formed on one surface of a substrate with solder, wherein a resist layer is formed on the one surface of the substrate so as to avoid the lands and cover the lands. And a second step of supplying a uniform amount of solder to each opening of the resist layer in which each of the lands is exposed, and each of the openings of the resist layer. A third step of coating each of the lands with the solder supplied to the corresponding opening of the resist layer by heating and melting each of the supplied solders. Solder coating method. 2. The first step comprises a fourth step of forming a photo solder resist layer of a photo solder resist on the one surface of the substrate so as to cover the entire area including each land, and the photo step. The solder coating method according to claim 1, further comprising a fifth step of forming each of the openings in the photo solder resist layer by developing the solder resist layer after exposing the solder resist layer in a predetermined pattern. . 3. The second step includes a step of embedding a solder paste obtained by uniformly mixing solder particles having a small particle diameter in a flux into the openings of the resist layer. Item 3. The solder coating method according to Item 1. 4. The wiring board in which each of the lands is formed on the one surface of the board is a wiring board for flip chip mounting, according to claim 1, 2, or 3. Solder coating method.