JPH06334320A - Mounting method for electronic component - Google Patents

Abstract

(57) [Summary] [Object] To provide a mounting method of an electronic component capable of eliminating the occurrence of a bridge defect that short-circuits between the adjacent lead terminals 5 when mounting the electronic component 4 having the lead terminal 5. [Structure] The cream solder to be printed on the copper pad 2 of the printed wiring board 1 is divided into a wide portion 3a and a narrow portion 3b, and the cream solder 3 on the adjacent copper pads 2 is divided.
It was arranged so that a and 3b were located alternately. Therefore, the space between the adjacent cream solders 3a and 3b becomes large, and the occurrence of solder bridges is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface mounting method for electronic parts on a printed wiring board by reflow soldering, and more particularly to a mounting method for electronic parts having a small lead terminal pitch.

[0002]

2. Description of the Related Art Generally, as surface mounting of electronic components, cream solder is printed on a copper pad on a printed wiring board so that the lead terminals of the electronic component face the cream solder on the copper pad. After mounting, it is mounted by reflow heating.

In such a mounting method, FIG. 4 is a cross-sectional view of an essential part showing a conventional mounting method, FIG. 5 is a plan view showing a printed wiring board, and FIGS. 6 (A) and 6 (B) are electronic drawings. It is a top view which shows a component, In these figures, 1 is a printed wiring board,
Reference numeral 2 is a copper pad formed by etching a copper foil on the printed wiring board 1, 3 is cream solder printed on the copper pad 2 by metal mask printing, and 4 is opposed to the cream solder 3 on the copper pad 2. 5 is a plurality of lead terminals protruding from the electronic component 4 at a predetermined interval, and 6 is a solder connection portion at the tip of the lead terminal 5.

FIG. 7 is a plan view showing a mounted state of an electronic component by a conventional mounting method, and FIGS. 8A to 8D are views for explaining a mechanism of a solder bridge defect occurrence in the conventional mounting method. FIG. 9 is a perspective view of a solder bridge defect occurrence location. In these drawings, 7 is a solder bridge formed by bridging between the copper pads 2 by reflow heating, and 8 is a lead terminal 5 and a copper pad by reflow heating. 2 is a solder fillet having a substantially triangular cross section.

Next, the operation will be described. 8, when the electronic component 4 is mounted, the solder connection portion 6 is placed on the paste-like cream solder 3 as shown in FIG. 8A.
Are placed so as to face each other, and a part of the solder connection portion 6 is sunk into the cream solder 3 due to the weight of the electronic component 4 or the mounting pressure of the component mounting machine.

When this is reflow-heated, FIG.
The paste-like cream solder 3 as shown in (B) begins to soften and melt, and the solder connection portion 6 further sinks into the cream solder 3 due to the weight of the electronic component 4. When the reflow heating is further performed, the cream solder 3 melted instantly is attracted to the periphery of the solder connection portion 6 due to the surface tension of the cream solder 3 within a short time within 1 second.
At this time, most of the connection portions 6 are separately provided with the cream solder 3
However, since the cream solder 3 receives a vertical pressure due to its own weight of the electronic component 4 and the gap between the adjacent cream solders 3 is small, the adjacent cream solders 3 as shown in FIG. Are bridged to form a solder bridge 7.

[0007]

Since the conventional mounting method is configured as described above, when mounting an electronic component having a narrow lead terminal pitch, a solder bridge defect between lead terminals or between copper pads is caused. Occurred frequently, and it took a lot of time to modify and fix it. Further, when mounting an extremely narrow electronic component, there is a problem that the solder bridge cannot be repaired and corrected.

The present invention has been made to solve the above problems, and an object thereof is to obtain a mounting method in which solder bridge defects are less likely to occur.

[0009]

SUMMARY OF THE INVENTION In an electronic component mounting apparatus according to the present invention, cream solder provided on a copper pad to which one lead terminal of the electronic component is connected is divided into two in a direction along the lead terminal. To form a wide width portion and a narrow width portion, and the wide width portion and the narrow width portion of the cream solder on adjacent copper pads are alternately arranged. Is.

[0010]

According to the electronic component mounting method of the present invention, the cream solder on each copper pad is divided into two in the direction along the lead terminals, and the cream solder on the adjacent copper pads has a wide portion. Since they are alternately arranged in the narrow width portion, the gap between the adjacent cream solders becomes large, so that the solder bridge hardly occurs.

[0011]

EXAMPLES Example 1. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view of a printed wiring board corresponding to the lower left part of the printed wiring board of FIG. 5, and FIGS. 2A to 2D are views sequentially showing the behavior of cream solder in the reflow heating process of this embodiment. is there. 1 and 2, 3a and 3b are cream solders obtained by dividing the cream solder on the copper pad 2 into two in the direction along the lead terminals 5.
3a has a wide width and 3b has a narrow width.
The cream solders 3a and 3b on the adjacent copper pads 2 are
The wide ones and the narrow ones are arranged alternately.

Next, the operation will be described. Since the connection process by reflow heating is the same as the conventional example, only different points will be described. In FIG. 1, since the cream solders 3a and 3b adjacent to each other have the wide cream solder 3a and the narrow cream solder 3b alternately arranged,
The gap between the cream solders 3a and 3b becomes wider.

In addition, in FIG. 2, FIG.
In (A) and FIG. 2 (B) when the cream solder is melted,
Although the cream solders 3a and 3b are in a separated state, when reflow heating continues, wetting progresses, and the cream solder 3a and the cream solder 3b are fused and integrated by surface tension as shown in FIG. The normal reflow soldering of the shape as shown in FIG. 2D can be performed, and if the sum of the solder amounts of the cream solder 3a and the cream solder 3b is set to an optimum amount, the solder joint strength is sufficient and good mounting is performed. be able to.

Example 2. In the above embodiment, the cream solders 3a and 3b are divided into two in the direction along the lead terminals. However, as shown in FIG. 3, the cream solder 3a having a wide width and the cream solder 3b having a narrow width are connected to each other. Also, the same effect can be obtained.

[0015]

As described above, according to the present invention, the cream solder on the copper pad is provided with the wide portion and the narrow portion, and the cream solder on the adjacent copper pad is provided with the wide portion and the narrow portion. Since and are arranged alternately, the gap between the cream solders is increased, and the effect of reducing the occurrence of solder bridge defects can be obtained.

[Brief description of drawings]

FIG. 1 is a plan view of a printed wiring board showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram sequentially showing the behavior of the cream solder in the reflow heating process of this example.

FIG. 3 is a plan view of a printed wiring board showing another embodiment of the present invention.

FIG. 4 is a side sectional view showing a soldered portion by a mounting method of a conventional example.

FIG. 5 is a plan view showing a conventional printed wiring board.

FIG. 6 is a plan view showing an electronic component.

7A and 7B are a plan view and a side view showing a mounted state of a conventional electronic component.

FIG. 8 is a diagram for explaining a mechanism of solder bridge generation in a conventional example.

FIG. 9 is a perspective view of a solder bridge portion that frequently occurs in a conventional example.

[Explanation of symbols]

 1 Printed wiring board 2 Copper pad 3a Cream solder (wide part) 3b Cream solder (narrow part) 4 Electronic component 5 Lead terminal 6 Solder connection part

Claims (1)

[Claims] 1. An electronic component, which has a plurality of lead terminals protruding from an electronic component at regular intervals from each other, and is formed so that the lead terminals have a connecting portion, faces the lead terminal of a printed wiring board. Printed sticky cream solder on the pad part at room temperature, bonded the lead wire connection part to this cream solder, and then heated,
In a method of mounting an electronic component by reflow soldering, in which an electronic part is mounted on a printed wiring board by cooling thereafter, a wide part and a narrow part are provided in the cream solder to be printed on the pad, and they are adjacent to each other. A method of mounting an electronic component, comprising using a printed wiring board in which cream solder on a pad is formed such that a wide portion and a narrow portion are alternately arranged.