JPH09207313A - Height retaining mechanism for metal mask for cream solder printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent movement of a metal mask and missed print due to resilience when a plate is released, by providing a stay to retain a metal mask at a constant height when the metal mask and a printed circuit board are released after cream solder printing. SOLUTION: Both ends of height retaining stays 14, 14 are fixed to both inside walls of a frame printer body 15. A pair of parallel grooves 12, 12 which exist on the surface of the clamping stage 10 and engages with the stays 14 in the topmost position of the clamping stage is provided by indentation. Therefore, after cream solder printing, when plate release is made by moving the clamping stage 10 joined with the metal mask 1 downward by a lifting table 11, the metal part 4 contacts the top of the stay 14, and is restrained from moving downward. As a result, the metal part 4 is prevented from moving by the adhesiveness of the cream solder, and from sagging in the moving direction of a printed circuit board 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a plate separating mechanism in cream solder printing used for surface mounting of electronic parts.

[0002]

2. Description of the Related Art As one of the methods for electrically connecting electronic components to a wiring board, cream solder is printed on an electrode pad on the wiring board, and then the electrodes of the surface mounting electronic component are connected to electrode pads. There is a reflow-type connection method in which the solder paste is mounted on the top and then the cream solder is melted and cured. FIG.
The relationship between the metal mask and the wiring board in the printing process is shown. In the figure, a metal mask 1 includes a metal portion 4 disposed inside a lower portion of a frame 2 via a tension portion 3.
And a plurality of openings 5 formed in a predetermined pattern by etching or the like for filling the metal part 4 with cream solder. Through the openings 5 of the metal part 4, the wiring pad 7 on the wiring board 6 is provided. The cream solder 8 is transferred.

[0003]

However, in this printing method, as the electronic components are made narrower in pitch and smaller in size, the openings 5 formed in the metal portion 4 are miniaturized, and the wiring pad 7 is formed. Cream solder 8 transferred on top
However, it does not transfer according to the shape of the opening 5, and as shown in an enlarged view in a part of FIG. 4, a print defect 9 in which the center portions on both sides are thin is likely to occur with respect to the regular pattern shape shown by the broken line.
FIG. 5 is a configuration diagram of a printing process showing a state where a conventional metal mask and a wiring board are separated from each other, which is a cause of the printing defect.
In the cream solder printing process, after printing the cream solder,
In the process of moving the clamp stage 10 on which the wiring board 6 is placed from the printing metal mask 1 downward by the wiring board clamp stage lift 11 to separate the plate, the adhesive force of the cream solder 8 and the deterioration of the tension part 3 As a result, the metal portion 4 and the tension portion 3 follow the direction in which the wiring board 6 separates, as shown by the arrow in the figure, and after a certain repulsive force is generated in the tension portion 3, the metal portion 4 and the tension portion 3 move upward. It jumps up in the direction, causing cream solder printing defects. FIG. 6 is a diagram showing in more detail the behavior of the cream solder 8 when the plate is separated.

First, as shown in (a), at the time of printing, the cream solder 8 is filled in the opening 5 of the metal mask 3 and is in contact with the wiring pad 7. Then (b)
As shown in FIG. 4, when the wiring board 6 starts to separate from the metal portion 4, the adhesive force of the cream solder 8 and the deterioration of the tension portion 3 cause the metal portion 4 to follow the moving direction of the wiring board 7. 8 is still filled in the opening 5. Thereafter, as shown in (c), the repulsive elasticity of the tension part 3 causes the metal part 2 to jump up to the side opposite to the moving direction of the wiring board 6, and this jumping causes some of the cream solder to adhere to the inner wall of the opening 5. As a result, the solder printing defect 9 described above occurs,
The printing defect 9 causes defects generally called bridge, unsoldered, and lucon when mounting electronic components for surface mounting and solder melting and hardening in the subsequent steps. Therefore, various cream solder printing methods have been proposed in order to prevent the above-mentioned defects. However, as the surface mounting electronic components become smaller and the pitch becomes narrower, the conventional printing method does not always provide sufficient effects. I couldn't do it. An object of the present invention is to improve the above-mentioned cream solder printing defect by adding a simple structure.

[0005]

In order to achieve the above object, according to the present invention, after the cream solder printing in the cream solder printing process, when the metal mask and the wiring board are separated from each other, the height of the metal mask is kept constant. By providing a stay for holding the plate, it is possible to prevent printing defects due to movement of the metal mask side and repulsive elasticity when the plate is separated.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. 1 and 2 show an apparatus provided with a mask height holding mechanism according to the present invention. Since the present embodiment is the same as the conventional one except for the main part of the present invention, the same parts are designated by the same reference numerals, and only new portions or newly added portions will be described by using different reference numerals. In the figure, as in the conventional case, a metal mask 1 has a metal portion 4 disposed inside a lower portion of a frame 2 via a tension portion 3 and a plurality of openings formed for filling the metal portion 4 with cream solder. And the wiring pad 7 on the wiring board 6 through the opening 5 of the metal portion 4.
The cream solder 8 is transferred. Also,
In addition to this, the clamp stage 1 on which the wiring board 6 is placed
On the surface of 0, a pair of parallel grooves 12 are engraved on both sides of the installation position of the wiring board 6, and at the highest position of the clamp stage 10, as shown in FIG. The height holding stays 14 are engaged with each other, and the clamp stage 1
0 and the surface of the wiring board 6 are flush with each other. Both ends of each holding stay 14 have a frame-shaped printing machine body 1 that surrounds the metal mask 1, the clamp stage 10, and the lifting table 11 as a whole.
It is being fixed to both inner side walls of 5 which oppose. Therefore, by providing the height holding stay 14, the clamp stage 10 joined to the metal mask 1 after the cream solder printing is performed.
When the plate is moved downward by the elevating table 11 to separate the plate, the metal portion 4 contacts the upper surface of the holding stay 14 and the downward movement is suppressed, so that the cream solder 8
There is no movement of the metal part 2 due to the adhesive force of the metal part 4, and slack in the moving direction of the metal part 4 due to deterioration of the tension part 3 is suppressed, and the metal part 4 and the tension part 3 always maintain the same height. It becomes possible to do.

FIG. 3 shows a metal mask height holding stay 11.
When the height of the metal mask is kept constant,
It is a figure which shows the behavior of the cream solder 5. First, as shown in (a), at the time of printing, the opening 5 of the metal portion 4 is filled with the cream solder 8 and is in contact with the wiring pad 7. Then, as shown in (b), when the wiring board 6 starts to separate from the metal portion 4, the adhesive force of the cream solder 8 and the deterioration of the tension portion 3 cause the metal portion 4 to follow the moving direction of the wiring board 7. However, the metal portion 4 is held at a constant height by the holding stay 11, and the cream solder 8 is completely padded to the pad of the wiring board 6 depending on the shape and thickness of the opening 5, as shown in (c). It is transferred onto the plate 6 and the cream solder 6 can be printed in a stable state.
As described above, it is possible to eliminate the soldering defects generally called bridge, unsoldered, and loucon, which are caused by the conventional printing process. It is needless to say that the present invention is not necessarily applicable to a printing machine in which the wiring board clamp stage elevating table is movable as in the embodiment, but is similarly applicable to a printing machine in which a metal mask is movable. In this case, the height holding stay may be moved along the moving direction of the metal mask.

[0008]

Since the present invention is constructed as described above, it is possible to prevent defects due to the movement of the metal mask side and repulsion elasticity when the plate is separated, thereby preventing cream solder printing defects. It has a remarkable effect.

[Brief description of drawings]

FIG. 1 is a perspective view of an apparatus according to the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

3 (a) to 3 (c) are detailed explanatory views showing a cream solder transfer state according to the present invention.

FIG. 4 is a perspective view showing a relationship between a conventional metal mask and a wiring board.

FIG. 5 is a cross-sectional view showing a conventional cream solder transfer situation.

6A to 6C are detailed explanatory views showing a cream solder transfer state.

[Explanation of symbols]

 1 Metal Mask 2 Frame 3 Tension Part 4 Metal Part 5 Opening 6 Wiring Board 7 Wiring Pad 8 Cream Solder 10 Clamp Stage 11 Lifting Table 14 Height Holding Stay 15 Printer Main Body

Claims (1)

[Claims] 1. A cream solder printing machine for performing cream solder printing on a wiring board using a metal mask having an opening of a predetermined pattern for printing, wherein after the cream solder printing, the wiring board and the metal mask are A height holding mechanism for a metal mask for cream solder printing, comprising a stay for holding the metal mask at a constant height when separated.