JPH0666067U - Solder pad - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce the occurrence of solder bridges 7 when the QFP 4 is mounted on the printed circuit board 1. [Structure] As a shape of the solder pad 2 for mounting the QFP 4, lead terminals 5 of the QFP 4 for mounting both ends in the longitudinal direction are formed.
The width of the solder pad 2 is wider than that of the lead pad 5, and the widthwise middle portion of the solder pad 2 is narrower than that of the lead terminal 5. With this configuration, the intermediate portions of the solder pads 2 where solder bridges 7 are likely to occur are arranged apart from each other, and the occurrence of solder bridges 7 is reduced.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a shape of a solder pad formed on a printed board for mounting an electronic component having a plurality of external lead terminals such as a QFP (Quat Flat Package).

[0002]

[Prior art]

 A solder reflow method is known as a method for surface-mounting an electronic component having a plurality of external lead terminals, for example, a QFP as shown in FIG. 5, on a printed board. This solder reflow method is widely used because it has high reliability in soldering with a fine pitch and has features such as easy handling. An example of this solder reflow method is as follows.

First, cream solder is printed by a screen printing method on a solder pad continuous with a circuit pattern formed on a printed circuit board. Next, the external lead terminals of the QFP are mounted on a solder pad on which cream solder is printed. Also, other electronic components are mounted at predetermined positions on the printed circuit board. Then, the printed circuit board on which the QFP and other electronic components are mounted is put in a solder reflow furnace to melt the cream solder and solder the lead terminal to the solder pad.

The solder pad as described above is generally formed as a rectangular area larger than a joint surface of the lead terminal of the QFP to be mounted as shown in FIG. 3, which is in contact with the solder pad. .

[0005]

[Problems to be solved by the device]

 By the way, in the solder reflow process when mounting the QFP on the printed circuit board, as shown in FIG. 4, the molten solder on the solder pad 2 overflows from the area of the solder pad 2 and reaches the adjacent solder pad 2. The so-called solder bridge 7 may be caused. In this solder bridge 7, the adjacent lead terminals of the QFP electrically short-circuit with each other, and the QFP circuit operation is not properly performed, which is extremely inconvenient.

Therefore, an object of the present invention is to reduce the occurrence of solder bridges when mounting electronic components.

[0007]

[Means for Solving the Problems]

 Therefore, in this invention, in a solder pad on a printed circuit board mounting a surface mount type electronic component having a plurality of external lead terminals, both ends in the longitudinal direction of the solder pad are made wider than the middle portion of the solder pad. Is characterized by.

[0008]

[Action]

 By making the shape of the solder pads into a shape in which the middle portion thereof is constricted, it becomes possible to increase the distance between the middle portions of adjacent solder pads where solder bridges are likely to occur. Further, since the area of the solder pad is smaller than that of the conventional solder pad, the amount of cream solder to be printed is small, and the molten solder is less likely to overflow from the solder pad area.

[0009]

【Example】

 Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a plan view showing a solder pad of the present invention, and FIG. 2 is a plan view showing a state in which a QFP is mounted on the solder pad of the present invention. FIG. 6 is a plan view showing another embodiment in which QFP is mounted on the solder pad of the present invention.

As shown in FIG. 1, a solder pad 2 is formed on a printed circuit board 1 so as to be continuous with a circuit pattern 3. The solder pads 2 are formed at intervals that match the intervals of the arrangement of the lead terminals 5 of the QFP 4. The shape of the solder pad 2 is such that both ends in the longitudinal direction of the solder pad 2 are wider than the width of the lead terminal 5 of the QFP 4 to be mounted, and the middle portion of the solder pad 2 is wider than the width of the lead terminal 5 of the QFP 4. Formed narrowly. Further, the narrow portion of the solder pad 2 is formed shorter than the portion of the lead terminal 5 of the QFP 4 that contacts the solder pad 2.

Cream solder 6 is printed on the solder pad 2 by a screen printing method. Then, as shown in FIG. 2, the QFP 4 is mounted on the solder pad 2. At this time, QFP4 contacts both ends in the longitudinal direction of the portion of the QFP4 lead terminal 5 contacting the solder pad 2 with the wide portion of the solder pad 2, and the longitudinal middle portion of the lead terminal 5 of QFP4. The solder pad 2 was mounted so as to come into contact with the narrow portion of the solder pad 2. At the same time, other electronic components are mounted on the same printed circuit board 1 at predetermined positions. Then, the printed circuit board 1 on which the QFP 4 and other electronic parts are mounted is inserted into a solder reflow furnace, the printed cream solder 6 is melted, and the lead terminal 5 of the QFP 4 is joined to the solder pad 2.

It is conceivable that the melted cream solder 6 overflows from a predetermined area of the solder pad 2 during the solder reflow process, but in the present invention, the middle portion of the solder pad 2 is narrowed to form a constricted portion. Since the solder pads 2 are provided, the adjacent solder pads 2 are arranged apart from each other in the constricted portion. Therefore, even when the melted solder overflows from the solder pad 2, the solder rarely reaches the adjacent solder pad 2, so that the solder bridge is less likely to occur.

In the above embodiments, the width of the lead terminal of the QFP for mounting both ends of the solder pad in the longitudinal direction is wider, and the middle portion of the solder pad is narrower than the width of the lead terminal. However, as shown in FIG. 6, even if the narrow portion of the intermediate portion of the solder pad 2 is formed wider than the width of the lead terminal 5 of the QFP 4 to be mounted, the purpose of this idea can be achieved. can do.

In the above embodiments, the QFP has been described as an example of the electronic component mounted on the printed circuit board. However, the present invention is not limited to the above embodiments, and the PLCC (Plastic Leaded Chip Carrier) is not limited to the above embodiments. ) And SOP (Small Outline Package), etc., is also effective when mounting electronic components with multiple lead terminals.

[0015]

[Effect of device]

 According to this invention, since the middle portion of the solder pad is narrowed and the constricted portion is provided, the adjacent solder pads are separated from each other in the constricted portion. Therefore, even if the solder overflows from the solder pad, the solder rarely reaches the adjacent solder pad, so that the solder bridge is less likely to occur.

Further, since the solder pad of the present invention has a smaller area than the conventional solder pad, the amount of cream solder to be printed and applied to the solder pad is reduced, and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a plan view showing a solder pad of the present invention.

FIG. 2 is a plan view showing a state in which QFP is mounted on the solder pad of the present invention.

FIG. 3 is a plan view showing a conventional solder pad.

FIG. 4 is a view showing a state in which a solder bridge is raised by a conventional solder pad.

FIG. 5 is a perspective view showing a QFP used in the present invention.

FIG. 6 is a plan view showing another embodiment in which the QFP is mounted on the solder pad of the present invention.

[Explanation of symbols]

 1 Printed Circuit Board 2 Solder Pad 3 Circuit Pattern 4 QFP (Electronic Component) 5 Lead Terminal 6 Cream Solder 7 Solder Bridge

Claims (1)

[Scope of utility model registration request] 1. In a solder pad on a printed circuit board for mounting a surface mount type electronic component having a plurality of external lead terminals, both longitudinal ends of the solder pad are wider than an intermediate portion of the solder pad. Solder pad characterized by.