JPH06140747A - Method for forming solder land on printed-wiring board - Google Patents

Abstract

PURPOSE:To avoid the blotting when a land part of the title printed-wiring board is printed with a solder land. CONSTITUTION:During the forming step of a round solder land 2 by printing process on an electronic part connecting land 1 provided on a substrate, the shape of the solder land 2 is divided for two time printing steps in the directions of P and Q so that the solder land 2 causing no blotting at all during the printing steps in the two directions of P and Q may be formed by performing the printing step using a mask wherein the print relief parts of A, B, C, D and D, E, F, G are formed in the blotting parts during respective printing steps for relieving the A, B, C, D parts during the printing step in the P direction while D, E, F, G parts during the printing step in the Q direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a solder land on a printed wiring board.

[0002]

2. Description of the Related Art A large number of lands for connecting electronic components are provided in a printed wiring circuit on a substrate of a printed wiring board, and the connecting lands have a round shape, as shown in FIG. Ellipse, square, rhombus, deformed land 3
There are various things such as 1-36. And their shape is decided at the time of designing the printed wiring board,
The shape of the solder mask for the connection land is CA
Filmed by D or artwork.

When the solder land is formed by a photographic method, the film having the solder mask formed thereon is used, and the surface of the photoresist provided on the printed wiring board is subjected to the steps of exposure and development so that the solder resist is formed. To form the shape of the solder land.

In the case of the printing method, after the film pattern is transferred to the screen plate making, the solder land is formed by printing with a solder resist ink on the printed wiring board using the screen plate making.

[0005]

However, with the miniaturization of the wiring pattern, the shape of the connection land is also reduced, and the boundary line (plane) between the land portion and the solder resist portion.
In the present situation that the size of the solder land is close to the unit of 1/100 mm, a slight misalignment occurs when the shape of the solder land is printed on the printed wiring board using the screen plate making in the method of forming the solder land. , Or
Copper foil thickness (normally 35
μ) causes a phenomenon in which the solder resist ink bleeds to the land portion, and this bleeding is a major cause of defective soldering.

That is, when a solder land shape is formed by a solder resist by a printing method, bleeding and blurring of the resist ink are incidental and it is very difficult to prevent the occurrence. As a countermeasure, it is necessary to regularly clean the screen (wiping the plate).

However, the reason why bleeding occurs will be described below with reference to FIGS. 6 to 12.

First, in the screen printing method, an ink is formed by selectively covering a gauze 21 which is knitted with Tetoron or stainless steel thread on a mouth-shaped frame called a plate frame 20 with a mask called an emulsion 24. The place where 22 is desired to be printed is distinguished from the place where it is not desired to be printed. In practice, the entire surface is first coated with an emulsion, and the film is exposed and developed to selectively form a mask.
(Figure 1) (Figure 2)

Next, an ink (viscosity about mayonnaise) 22 is placed on it, and a squeegee 23 of urethane resin type is used. Ink 22 is applied on the plate 10. (Figure 7) (Figure 8)

At this time, since the squeegee 23 runs on the plate making with a very large printing pressure, the gauze 21 is also printed with a slight distortion in the running direction of the squeegee 23, and the error appears as a deviation. Regarding the error, of course,
It is included in the calculation due to the positional relationship between the plate-making and the printed wiring board 10 below.

However, as described above, the gauze 21 itself is formed by knitting with a thread such as Tetron. The force acts on the contraction side immediately before running the squeegee 23, and the force on the stretch side immediately after running. .

Further, at the time of printing the solder resist after forming the conductive pattern, as shown in FIG. 7, there is already unevenness due to the copper foil 4 having a thickness of 35 μm, and when printing the vicinity of the land 4 together with the expansion and contraction of the gauze 21 described above. The expansion and contraction of the gauze 21 is further increased.

In reality, the amount of expansion and contraction is very slight, but when the squeegee 23 is stroked with dozens or hundreds of sheets, the ink 22 on the plate is below the emulsion edge of the plate. Side (printed circuit board side). (Figure 8)

When the printed wiring board 10 after printing is viewed, it gradually appears as bleeding as shown in FIG. 9, and when it further proceeds, bleeding is applied to the land 4 as shown in FIG.

It is also conceivable that the misalignment of the land 4 and the solder resist layer 6 may cause a misalignment 26, resulting in a misalignment 26. When the land edge comes into contact with the resist (FIG. 11), Bleeding is more likely to occur due to the step between the emulsion and the copper foil (Fig. 12).

As described above, in the screen printing method, the bleeding 25 always occurs due to its principle, and the soldering failure due to the phenomenon still frequently occurs even now, and it is a future problem. But also.

Therefore, the present invention has been made in view of these problems, and a method for forming a solder land in a printed wiring board capable of preventing the occurrence of a bleeding phenomenon due to solder resist printing and eliminating defective soldering. For the purpose of providing.

[0018]

In order to achieve the above object, a method for forming solder lands in a printed wiring board according to the present invention comprises a step of forming solder lands on a land provided on a substrate by a printing method. It is characterized in that the shape of the solder land is divided and the solder land is formed by printing each of the divided shapes.

[0019]

According to the method of forming solder lands in the printed wiring board of the present invention, the occurrence of the bleeding phenomenon due to the solder resist printing can be prevented.

[0020]

EXAMPLE 1 In this example, as shown in FIG. 4, a method of forming a concentric solder land 2 on a round land 1 by a screen printing method will be described.

Conventionally, when the concentric solder lands 2 are formed on the round lands 1 by the screen printing method,
As described above, since the squeegee is formed by one-time traveling, the problem that the bleeding phenomenon occurs in the traveling direction of the squeegee is a problem.

Therefore, in the present embodiment, first, as shown in FIG. 1, in order to avoid the range of bleeding that occurs when the squeegee is run in the P direction, from the solder land 2 inner diameter 3 to avoid the bleeding. A mask having print relief portions A, B, C and D is formed on the outer side, and the mask is used to prevent the resist from being printed on the relief portions.

Next, for the same surface of the printed wiring board,
The squeegee 23 is run in the Q direction, which is the direction perpendicular to the P direction. In this case, as in the case described above, as shown in FIG.
A mask provided with E, F, and G is formed so that the resist is not printed on that portion.

When the respective prints in which the squeegee 23 is run in the P and Q directions are combined, the print runout portions A,
B, C, D and D, E, F, G have a positional relationship as shown in FIG.

That is, the A. B.
The C and D parts are printed when printing in the Q direction, and the D, E, F, and G parts that are missed when printing in the Q direction are printed when printing in the P direction. Since the shape of the solder land 2 is completed while avoiding the bleeding phenomenon, bleeding does not occur inside the inner circumference 3 of the solder land 2.

The solder land forming method of the present invention can be applied to lands having various shapes shown in FIG.

[0027]

According to the present invention, it is possible to prevent the bleeding from occurring on the round lands during the screen printing of the solder lands.

[Brief description of drawings]

FIG. 1 is a diagram showing a print escape portion of a solder land in printing in a P direction.

FIG. 2 is a diagram showing a print escape portion of a solder land in printing in the Q direction.

FIG. 3 is a composite view of a solder land printing relief portion in printing in P and Q directions.

FIG. 4 is a view in which a round solder land is formed on a land.

FIG. 5 is a view showing various conventional land shapes.

FIG. 6 is an explanatory diagram of a conventional method.

FIG. 7 is an explanatory diagram of a conventional method.

FIG. 8 is an explanatory diagram of a conventional method.

FIG. 9 is an explanatory diagram of a conventional method.

FIG. 10 is an explanatory diagram of a conventional method.

FIG. 11 is an explanatory diagram of a conventional method.

FIG. 12 is an explanatory diagram of a conventional method.

[Explanation of symbols]

 1 Round land 2 Solder land 3 Inner circumference of solder land

Claims (1)

[Claims] 1. A solder land is formed by dividing a shape of the solder land in a step of forming a solder land on a land provided on a substrate by a printing method, and printing each divided shape. Method for forming solder land in printed wiring board characterized in that