JPH06169153A - Printed wiring board - Google Patents

Abstract

PURPOSE:Not only to prevent a semiconductor package from falling off from a wiring board due to external shocks or oscillations but also to restrain solder bridges from being produced on the wiring board even if solder increases in amount. CONSTITUTION:An electronic component mounting pad 3b located at the outermost end of a pad row is set larger in dimensions in both a lateral and a longitudinal direction than the other electronic component mounting pads 3a. Therefore, the pad 3b is larger than the pad 3a in area, and when an SOP 4 is mounted, cream solder applied onto the pad 3b increases in amount, so that a lead 5 is firmly connected to the pad 3b. Even if solder is much applied onto the pad 3b, as the pad 3b is large in area, solder is restrained from flowing out of it, and consequently a solder bridge is hardly produced between the adjacent pads 3a and 3b at the time of reflow.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board, and more particularly to a printed wiring board having pads for mounting surface mounting electronic components.

[0002]

2. Description of the Related Art As electronic equipment becomes smaller and more sophisticated, SO
P (Small Outline Package), QFP
Surface mounting of semiconductor packages such as (quad flat packages) on printed wiring boards is progressing. In this printed wiring board, for example, as shown in FIG. 5, a plurality of component mounting pads (hereinafter, simply referred to as pads) 21 are formed in parallel on the surface of an insulating substrate 20 at equal intervals. Wiring portions 22 are connected to the pads 21, respectively, and the pads 21 and the wiring portions 22 form a part of a conductor circuit. When the semiconductor package is mounted on the printed wiring board, each pad 21
After applying the cream solder, the leads 24 of the semiconductor package (in this case, SOP) 23 are applied as shown in FIG.
Are positioned on the pad 21 and soldered by reflow soldering.

[0003]

In recent years, as the density of printed wiring boards has been increased, the pitch of leads of a semiconductor package has become narrower, the distance between adjacent pads 21 has become narrower, and the area of the pads 21 has become smaller. Tends to become. When the area of the pad 21 is small, the pad 21 and the substrate 2
There is a problem that the bonding strength between the lead 24 and the pad 21 is weakened as the adhesive strength with 0 is reduced and the amount of applied solder is reduced. Therefore, after the semiconductor package 23 is mounted, the leads 2 are exposed to external shock or vibration.
4 and the connection between the pad 21 and the
May be peeled off from the substrate 20 and the semiconductor package 23 may be detached.

It is conceivable to increase the amount of cream solder in order to strengthen the connection between the lead 24 and the pad 21, but if the amount of solder is increased, the solder will flow out of the pad 21 during reflow and the adjacent pad There is a problem that a solder bridge occurs between the two.

Further, when the electronic component is mounted on the printed wiring board, the electronic component may be displaced so as to rotate about its center. In this case, the deviation amount of the outermost lead of the electronic component becomes larger than the deviation amounts of the other leads, and there is a problem that the connection reliability between the outermost lead and the outermost pad is lowered.

The present invention has been made in view of the above problems, and an object thereof is to prevent the semiconductor package from being detached from the wiring board due to external impact or vibration and to increase the solder amount by increasing the solder bridge. It is an object of the present invention to provide a printed wiring board capable of preventing the occurrence of the above-mentioned problem and further improving the reliability of mounting electronic components.

[0007]

In order to solve the above problems, in the present invention, a pad row is constituted by a plurality of electronic component mounting pads for mounting electronic components, and the pad row of the plurality of electronic component mounting pads is formed. Among them, the arrangement direction dimension of the electronic component mounting pads located at the end of the pad row and the dimension in the direction orthogonal to the arrangement direction are respectively larger than the dimensions of the other electronic component mounting pads in the pad row in the respective directions. I made it bigger.

[0008]

In the present invention, the dimension of the electronic component mounting pad located at the end of the pad row and the dimension in the direction orthogonal to the array direction are set to the respective directions of other electronic component mounting pads in the pad row. By making each larger than
The area of the pad at the end is increased, and the adhesive strength between the pad and the base material is improved. In addition, the amount of cream solder applied to the pad when mounting the electronic component can be increased, and the connection between the lead and the pad can be strengthened. As a result, it is possible to reliably prevent the electronic component from coming off from the printed wiring board.

Further, even if a large amount of solder is applied to the electronic component mounting pad located at the outermost end, it does not protrude due to its large area, and a solder bridge does not occur between adjacent pads during reflow. . Further, when the electronic component is mounted such that the electronic component is rotated and displaced, the lead shift amount increases. However, since the area of the pad at the end corresponding to the lead is large, the pad and the lead Is securely connected.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIG.
It will be described with reference to FIG. As shown in FIGS. 1 and 2A, a plurality of pads 3 are formed on an insulating substrate 2 that constitutes the printed wiring board 1. The pads 3 are arranged in parallel in two rows with four pads in one row. Arrangement dimension (width) of the two pads 3a located inside each row and dimension (length) in the direction orthogonal to the arrangement direction
Two pads 3b located on the outer side, that is, at the outermost end
Are formed so that the respective dimensions become larger. That is, the pad 3a has a certain width (about 0.7 mm) and a length (about 1.5 mm) necessary for connecting the lead 5 of the SOP 4 as an electronic component mounted on the printed wiring board 1. There is. The pad 3b has a width (about 1.0 mm) and a length (about 2.0 m) larger than the width and length of the pad 3a.
m). Wiring portions 6 are connected to the pads 3a and 3b, respectively, and form a part of a conductor circuit.

When the SOP 4 is mounted on the printed wiring board 1, as shown in FIGS. 2 (a) and 2 (b),
The cream solder 7 is applied on the pads 3a and 3b, and the leads 5 of the SOP 4 are positioned and placed thereon. At this time, since the width and length of the pad 3b are larger than that of the pad 3a, the area thereof is also larger. Therefore, the pad 3b
The amount of the solder 7 applied to is also large. Subsequently, the solder 7 is melted by reflow soldering to connect the lead 5 and the pads 3a and 3b. At this time, the pad 3b
Since a large amount of solder 7 is applied to the lead 5, the lead 5 and the pad 3b are firmly fixed to each other. Further, since the area of the pad 3b is large, the adhesive force between the pad 3b and the insulating substrate 2 is also increased.
As a result, it is possible to prevent the SOP 4 from separating from the printed wiring board 1 due to external impact or vibration.

Even if the amount of the solder 7 applied to the pad 3b is large, the area of the pad 3b is large so that it does not protrude, and a solder bridge is generated between the adjacent pad 3a by the melted solder 7 during reflow. Can be prevented.

Further, when the SOP 4 is mounted, even if the SOP 4 itself shifts so as to rotate about its center, the pad 3
Since the area of b is large, both pads 3b and the outermost leads 5 are reliably connected. Therefore, the reliability of electronic component mounting can be improved.

Further, since the area of the pad 3b is large, it is possible to easily perform the displacement check with the pad when positioning the lead 5 and the displacement check of the lead 5 after mounting as compared with the narrow pad 3a. .

The present invention is not limited to the above-mentioned embodiments, and a part of the constitution may be modified within the scope of the present invention. (1) In the above embodiment, the mounting pad 3a for the SOP4,
3b, as shown in FIG. 3, as shown in FIG. 3, the pads 3 are arranged in four rows corresponding to the four-way leads 5 such as the QFP8.
You may form a, 3b. In this case, eight pads 3b having a large area are formed. (2) As shown in FIG. 4, in the printed wiring board 1 in which the pads 3a and 3b are also arranged in a zigzag pattern corresponding to the semiconductor package 9 having zigzag leads, the pad located at the end of the pad row. The size of 3b may be increased.

[0016]

As described in detail above, according to the present invention,
By arranging the dimension of the pad located at the extreme end of the pad row and the dimension in the direction orthogonal to the array direction to be larger than the dimensions of other electronic component mounting pads in the pad row,
The leads and pads are firmly fixed to prevent the semiconductor package from coming off from the wiring board due to external impact or vibration, and even if the amount of solder applied to the pad located at the outermost end increases, Since the area is large, the solder does not squeeze out, the occurrence of solder bridges can be prevented, and further, the reliability of electronic component mounting can be improved, which is an excellent effect.

[Brief description of drawings]

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

2A and 2B also show a printed wiring board on which an SOP is mounted, FIG. 2A is a schematic partial plan view, and FIG. 2B is a schematic partial sectional view.

FIG. 3 is a schematic partial plan view showing a printed wiring board on which a QFP of another embodiment is mounted.

FIG. 4 is a schematic partial plan view showing a printed wiring board on which a staggered semiconductor package of another embodiment is mounted.

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

FIG. 6 is also a schematic partial plan view showing a printed wiring board on which an SOP is mounted.

[Explanation of symbols]

1 ... Printed wiring board, 3a, 3b ... Pad, 4 ... SOP as an electronic component.

Claims (1)

[Claims] 1. A pad row is composed of a plurality of electronic component mounting pads for mounting electronic components, and among the plurality of electronic component mounting pads, the electronic component mounting pad located at the end of the pad row. A printed wiring board, wherein the dimension of the pads in the array direction and the dimension in the direction orthogonal to the array direction are made larger than the dimensions of other electronic component mounting pads in the pad row in the respective directions.