JPH0222889A - Method for printing cream solder - Google Patents

Abstract

PURPOSE:To realize printing of cream solder which can cope with a fine wiring pattern by extending the cream solder in two directions inclined by prescribed angles by using a squeegee. CONSTITUTION:A squeegee is constituted of a main body section 22 with a projecting handle 21 and a blade 23 held by the section 22. It is preferable to use an elastic material, such as rubber, etc., which can easily deform by elasticity as the materiel for forming the blade 23 which is directly brought into contact of cream solder. At the time of printing of the cream solder, the squeegee is moved in the 45 deg. direction against the outer frame of a screen mask 3 after the cream solder is put on the mask 3 so that the solder can be extended. Therefore, the solder can be extruded against transversal through holes 1 and longitudinal through holes 2 under almost the same conditions and the adhering quantity of the solder to the wiring pattern is uniformized. Thus excellent flow soldering can be performed.

Description

[Detailed Description of the Invention] Summary Regarding a method of printing cream solder on wiring patterns of printed wiring boards, the purpose of this invention is to provide a method of printing cream solder that can be applied to fine wiring patterns, and to Cream solder is placed on a screen mask in which a long horizontal hole is formed on one side and a long vertical hole is formed on the other side, and the cream solder is spread with a squeegee to form the horizontal hole and the vertical hole. A method for printing cream solder that is applied onto a wiring pattern of a printed wiring board through a through hole, wherein the cream solder is spread by the squeegee at an angle of about 45 degrees with respect to the two directions. do.

INDUSTRIAL APPLICATION FIELD The present invention relates to a method of printing cream solder onto a wiring pattern of a printed wiring board.

In the field of electronic device manufacturing, electronic circuits are constructed by mounting electronic components such as integrated circuits, resistors, and capacitors on printed wiring boards on which wiring patterns are formed, and then soldering the electronic components and wiring patterns. That's what I do. Recently, in order to automate the mounting or soldering of electronic components or to increase the mounting density, surface mount technology, which performs soldering using a reflow method, has come into widespread use. . The reflow method prints cream solder on the wiring pattern, adheres the chip component (component without lead wires) on top of it, and then melts the cream solder in a heating furnace to connect the chip component and the wiring pattern. electrical connection and mechanical fixation. When carrying out this reflow one-type method, there is a need for a cream solder printing method that can sufficiently cope with the trend of increasingly finer wiring patterns in recent years.

Prior art FIG. 6 is an explanatory diagram of a beam flow one-type system. 31 is a wiring pattern formed on the printed wiring board 32 (a);
First, cream solder 33 is printed on this wiring pattern 31 (b). Here, cream solder is a mixture of powdered solder and highly viscous flux to form a cream. Next, the chip component 34 is pressed against the printed wiring board 32 so that its solder layer portion 35 contacts the cream solder 33, and the chip component 34 is temporarily fixed (C). In this state, the whole is heated in a heating furnace, so that the cream solder 33 and the solder layer portion 35 are melted together, and a soldered portion 35' is formed (d).

FIG. 7 is a diagram for explaining a conventional method of printing cream solder onto a wiring pattern. As shown in FIG. 3A, a screen mask 4 has through-holes 41 formed therein corresponding to portions of the wiring pattern 31 to which cream solder is to be attached.
2 is held parallel to the printed wiring board 32 at an appropriate distance, cream solder 43 is placed on the screen mask 42, and the cream solder 43 is spread with a squeegee 44, as shown in FIG. As shown, through hole 4
The cream solder 43 is attached to the wiring pattern 31 through the wire 1.

Problems to be Solved by the Invention FIG. 8 is a plan view of a screen mask used for, for example, a QFP (Quad, flat package) type IC. A plurality of horizontal through-holes 1 and a plurality of vertical through-holes 2 which are long in the horizontal direction as shown in the figure are mixed and formed in the screen mask 3 in correspondence with the electrode parts provided on all sides. .

When printing cream solder using such a screen mask, there is no problem if the size of the through holes is relatively large, but if the through holes are small (for example, the distance between the through holes is 0.35 m +
n), if the conventional method is to spread the cream solder horizontally or vertically in the figure, the cream solder will adhere to the wiring pattern in the horizontal through hole 1 and the vertical through hole 2. There was a problem that the amount of Specifically, when the cream solder is spread in the vertical direction in the figure so that an appropriate amount of cream solder is printed through the horizontal hole 1, a pot of cream solder is printed through the vertical hole 2. Run short. On the other hand, if the amount of cream solder is changed so that an appropriate amount of cream solder is printed through the vertical through-holes 2, the amount of cream solder printed through the horizontal through-holes 1 becomes excessive, resulting in a gap between the wiring patterns. There is a risk of short circuit.

In order to solve this problem, a method may be proposed in which cream solder is spread twice in the horizontal and vertical directions; , the work becomes complicated. .

The present invention was created in view of such technical problems, and an object of the present invention is to provide a cream solder printing method that can also be applied to minute wiring patterns.

Means to solve problems FIG. 1 is a diagram showing the principle of the present invention.

In this printing method, cream solder is placed on a screen mask 3 in which a long horizontal hole 1 is formed in one of two directions orthogonal to each other and a long vertical hole 2 is formed in the other direction. In a method of printing cream solder, the solder is spread with a squeegee 4 to be deposited on the wiring pattern of a printed wiring board through the horizontal through-holes 1 and the vertical through-holes 2. The spreading is performed at an angle of about 45° with respect to the above two directions.

Function According to the method of the present invention, the cream solder is spread at an angle of approximately 45 degrees with respect to both the direction in which the horizontal through-holes extend and the direction in which the vertical through-holes extend. Cream solder is inserted into the vertical through holes under almost the same conditions, so that the amount of cream solder that adheres to the wiring pattern is uniform.

Example Embodiments of the present invention will be described below based on the drawings.

FIG. 2 is a plan view of a screen mask device that can be used to implement the present invention, and FIG.
FIG. 2 is a cross-sectional view taken along line II. This device has horizontal through hole 1
A screen mask 3 in which vertical through holes 2 are formed is stretched over an outer frame 12 with a resin film 11 interposed therebetween.

The illustrated horizontal through hole 1 and vertical through hole 2 are for an IC, but the horizontal through hole 1 and vertical through hole 2 are for through holes for other surface mount components such as chip resistors and chip capacitors. Since these holes are not formed obliquely to the surface, these holes can be classified as horizontal or vertical. In addition, in FIG. 3, the two-dot chain line indicated by P indicates the surface on which the upper surface of the wiring pattern of the printed wiring board is located.

FIG. 4 is a perspective view of a squeegee that can be used to implement the present invention. This squeegee includes a blade 23 held between a main body portion 22 from which a handle 21 projects. The material of the blade 23 that directly contacts the cream solder is preferably an elastic body such as rubber that can be easily elastically deformed. Blade 23 made of elastic material
This is because when the blade 23 passes over the through-hole, the blade 23 is partially elastically deformed and enters the through-hole, thereby making it possible to extrude the cream solder well.

When printing cream solder, cream solder (not shown) is placed on the screen mask 3 in FIG. 2, and the cream solder is spread by moving a squeegee in a direction of 45 degrees with respect to the outer frame. By doing this, the cream solder is extruded under almost the same conditions for the horizontal through hole 1 and the vertical through hole 2, so the amount of cream solder adhered to the wiring pattern is uniform, and good flow soldering is possible. become.

FIG. 5 is a plan view of a screen mask device showing another embodiment of the present invention. In this example, a screen mask 3 in which horizontal through holes 1 and vertical through holes 2 are formed is stretched on an outer frame 12'' with a resin film 11'' interposed therebetween at an angle of 45 degrees.

According to this device, uniform printing can be performed by moving the squeegee in parallel to the outer frame 12'', so it is suitable for automating the movement of the squeegee.

Effects of the Invention As detailed above, according to the method of the present invention, it is possible to obtain a constant amount of cream solder adhesion regardless of the extending direction of the through holes formed in the screen mask. This has the effect of making it possible to respond adequately.

[Brief explanation of the drawing]

Fig. 1 is a principle diagram of the present invention, Fig. 2 is a plan view of a screen mask device showing an embodiment of the invention, Fig. 3 is a sectional view taken along the line III-I in Fig. 2, and Fig. 4 is a plan view of a screen mask device showing an embodiment of the present invention. FIG. 5 is a plan view of a screen mask device showing another embodiment of the present invention; FIG. 6 is an explanatory diagram of a beam flow one type; FIG. 7 is an illustration of cream solder. An explanatory diagram of a conventional printing method. FIG. 8 is an explanatory diagram of problems in the conventional technique. 1...Horizontal through-hole, 2...Vertical through-hole, 3...Souffreen mask, 4...Squeegee.

Claims (1)

[Claims] A screen mask (3) in which a long horizontal hole (1) in one of two directions orthogonal to each other and a long vertical hole (2) in the other direction are formed. Cream solder is placed on the printed wiring board, and the cream solder is spread with a squeegee (4) so that it adheres to the wiring pattern of the printed wiring board through the horizontal through holes (1) and the vertical through holes (2). In the solder printing method, the cream solder is spread using the squeegee (4) described above.
A method for printing cream solder, characterized in that printing is performed at an angle of about 45 degrees with respect to the direction.