JP3381950B2 - Solder land forming method for flat package - Google Patents

Description

Description: 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. 2. Description of the Related Art A large number of lands for connecting electronic components are provided in a wiring circuit of a printed wiring board. The lands for connection are round or elliptical as shown in FIG. form,
There are various types such as lands 31 to 36 having a square shape, a rhombus shape, and a deformed shape. The shape of the solder mask is determined at the time of designing the printed wiring board, and the shape of the solder mask for the connection land is formed by CAD or artwork. When the solder land is formed by a photographic method, the surface of the photoresist applied to the printed wiring board is exposed and developed by using the film on which the solder mask is formed, and then developed by using the solder resist. The shape of the land is formed. In the case of the printing method, the pattern of the film is transferred onto a screen plate, and then printed on a printed wiring board with solder resist ink using the screen plate to form a solder land. However, with the miniaturization of the wiring pattern, the shape of the connection land is also reduced, and the boundary (surface) between the land portion and the solder resist portion is reduced.
In the current situation where the size of the solder land is close to the unit of 1/100 mm, when the shape of the solder land is printed on a printed wiring board using a screen plate making method, there is a slight misalignment. Or
Copper foil thickness of land part in printed wiring part (normally 35
Due to the gap with μ), a phenomenon occurs in which the solder resist ink bleeds into the lands, and this slight misalignment or bleeding is one of the major causes of poor soldering. That is, when a solder land shape is formed with a solder resist by a printing method, the bleeding or blurring of the resist ink is an attached matter, and it is very difficult to prevent the occurrence. As a countermeasure, it is necessary to periodically clean the screen (wipe the screen). [0007] The reason why bleeding occurs will be described below with reference to FIGS. 7 to 13. First, the screen printing method is to selectively coat a mouth-shaped frame called a plate frame 60 with a gauze 61 woven with a tetron or a stainless steel thread with a mask called an emulsion 64 to thereby form an ink. 62 is distinguished from a place where printing is desired and a place where printing is not desired. In practice, first, the entire surface is coated with the emulsion 64, and the film is exposed and developed to selectively form a mask. Next, an ink (viscosity of the order of mayonnaise) 62 is placed on the squeegee, and a squeegee 63 made of urethane resin is used. The ink 62 is applied on the plate 50 (FIGS. 8 and 9). At this time, since the squeegee 63 travels on the plate making with a very large printing pressure, the gauze 61 is also printed with very slight distortion in the traveling direction of the squeegee 63, and the error appears as a deviation. Regarding the error, of course,
The calculation is based on the positional relationship between the plate making and the printed wiring board 50 below. However, as described above, the gauze 61 itself is formed by knitting with a thread such as tetron, and a force acts on the contraction side immediately before traveling of the squeegee 63, and a force acts on the extension side immediately after traveling. . Also, at the time of printing the solder resist after the formation of the conductive pattern, as shown in FIG. 8, there are already irregularities due to the copper foil 44 having a thickness of 35 μm. The expansion and contraction of the gauze 61 is further increased. In reality, the amount of expansion and contraction is very small. However, when the squeegee 63 is stroked for tens or hundreds of sheets, the ink 62 on the plate-making plate becomes lower than the edge of the emulsion edge of the plate-making plate. Side (printed circuit board side) (FIG. 9). When the printed wiring board 50 after printing is viewed, it gradually appears as shown in FIG. 10, and when the printed wiring board 50 is further advanced, the blur is applied to the land 44 as shown in FIG. The land 44 and the solder resist layer 46
It is also conceivable that the misalignment of the printing results in a misalignment 66, resulting in a misalignment 66. When the land edge comes into contact with the resist edge (FIG. 12), more blurring occurs due to the step between the plate making emulsion and the copper foil. This easily occurs (FIG. 13). As described above, in the screen printing method, the bleeding 65 always occurs due to the principle thereof, and even in the present situation, soldering failure due to the phenomenon frequently occurs. But also. Accordingly, the present invention has been made in view of these problems, and a method of forming a solder land on a printed wiring board, which can prevent the occurrence of bleeding due to solder resist printing and eliminate soldering defects. The purpose is to provide. In order to achieve the above object, a method for forming a solder land on a printed wiring board according to the present invention is to form a flat package connection land provided on a substrate by a printing method. In the step of forming a solder land, the shape of the land is divided, a portion where bleeding is generated for each of the divided land shapes is removed, and printing is performed from a direction perpendicular to each other to form a solder land without bleeding. It is characterized by the following. According to the method for forming a solder land for a flat package of the present invention, a solder land having a correct shape can be formed while preventing the occurrence of bleeding due to solder resist printing. 1 to 5 show an embodiment of a method for forming a solder land for a flat package according to the present invention. FIG. 1 is a view of a solder land for a flat package, and FIGS.
FIG. 3 is a diagram showing a printing process by enlarging a part of FIG. As shown in FIG. 5, the flat package 30 used in this embodiment is an electronic component in which a plurality of leads 31 are provided close to each other on four sides, and as shown in FIG. Each of the connecting lands 1 to 28 corresponding to the plurality of leads 31 has a rectangular shape, and the lands 1 to 28 are arranged in four directions while approaching each other. However, when the solder lands 29 are formed on the connection lands 1 to 28 by the screen printing method, the lands are formed by running the squeegee once in the conventional method. As described above, bleeding occurs in the running direction of the squeegee, which causes soldering failure. Therefore, in the solder land forming method of the present embodiment, first, as shown in FIG. 2, a squeegee (not shown) is used to prevent bleeding from occurring on the lands 1 to 28 as in the prior art. A mask provided with a print escape portion is formed to avoid portions 1a and 15a indicated by A, B, C, D and H, I, J, K as a range in which bleeding occurs when the vehicle is driven in the X direction. A mask is used to prevent the resist from being printed on the escape portion. Next, on the same surface of the printed wiring board,
As shown in FIG. 3, the squeegee is caused to travel in the Y direction perpendicular to the X direction. In this case, in the same manner as described above, the print relief portions D,
1b and 15 denoted by E, F, G and K, L, M, N
A mask provided with b is formed so that the resist is not printed on the mask. When the respective printing processes when the squeegee is run from the X and Y directions are combined, the positional relationship between the print escape portions 1a, 1b, 15a, and 15b is as shown in FIG. That is, the print escape portions 1a, 1 during X-direction printing
5a is printed at the time of printing in the Y direction, and the printing relief portions 1b and 15b at the time of printing in the Y direction are printed at the time of printing in the X direction, so that the bleeding phenomenon at the time of printing in each of the X and Y directions is avoided. Solder lands can be formed. In the manner described above, as shown in FIG.
By escaping 14a and 15a to 28a and shading 1b to 14b and 15 to 28b during printing in the Y direction,
It is possible to form a correctly shaped solder land without bleeding by avoiding all bleeding portions. According to the present invention, when screen printing of a solder land, printing is performed in two directions while avoiding the occurrence of bleeding, so that bleeding does not occur on the land for a flat package. , And an accurate solder land shape can be formed. Accordingly, it is possible to prevent soldering failure and to increase the reliability of connection of the electronic component to the land.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing a relief portion of printing bleed of a solder land for a flat package of the present invention. FIG. 2 is a partially enlarged view of FIG. 1 showing a printing process in the X direction. FIG. 3 is an enlarged view of FIG. 1 showing a printing process in a Y direction. FIG. 4 is a diagram illustrating a state in which a printing process in the X and Y directions is combined by enlarging a part of FIG. 1; FIG. 5 is a view showing the shape of a flat package. FIG. 6 is a diagram showing various conventional land shapes. FIG. 7 is an explanatory diagram of a conventional method. FIG. 8 is an explanatory view of a conventional method. FIG. 9 is an explanatory diagram of a conventional method. FIG. 10 is an explanatory view of a conventional method. FIG. 11 is an explanatory view of a conventional method. FIG. 12 is an explanatory diagram of a conventional method. FIG. 13 is an explanatory diagram of a conventional method. [Description of Signs] 1, 2 Land for connection 29 Solder land 30 Flat package 31 Lead

────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Kazuo Sato 1106 Fujikubo, Miyoshi-cho, Iruma-gun, Saitama Japan CMK Co., Ltd. (56) References: Japanese Patent Publication No. 55-2758 (JP, B2) Japanese Patent Publication No. 58-58 56999 (JP, B2) (58) Field surveyed (Int. Cl. ⁷ , DB name) H05K 3/28 H05K 3/34

Claims (1)

(57) [Claim 1] In a step of forming a solder land on a connection land for a flat package provided on a substrate by a printing method, the shape of the land is divided, and each of the divided land is divided. Forming a solder land free from bleeding by printing from a right angle direction for each shape of the solder package.