JPH04176190A - Printed wiring board provided with flat package pad - Google Patents

Abstract

PURPOSE:To obtain a printed wiring board where a flat package can be easily and surely corrected in position when it gets out of position by a method wherein at least a set of pads which are located point-symmetrical about the center of a printed wiring board are formed larger than other sets of pads in area, and the adjacent pads are arranged equal in pitch. CONSTITUTION:Pads 11 arranged on the opposed sides of a printed wiring board 10 are equal to each other in number and size and provided point- symmetrical about the center C of a flat package 20 accurately mounted on the printed wiring board 10. A large pad 12 is arranged on each of the sides of the square printed wiring board 10 and located at the front end of each side when the board 10 is rotated clockwise around the center C. The adjacent pads are arranged equal in pitch.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a printed wiring board, and particularly to a printed wiring board having pads for mounting a flat package.

(Prior art) A flat package is a package in which a semiconductor element is wrapped in a resin or the like and has external connection terminals protruding outward from the semiconductor element.
It has an appearance as shown in the figure. After positioning each external connection terminal of this flat package with respect to each pad of the printed wiring board,
Each external connection terminal and pad are connected by solder. Therefore, this type of flat package has the advantage that it can be connected by soldering as soon as it is positioned on the surface of a printed wiring board, and is a package type that has been increasingly used in recent years.

However, in order to mount such a flat package on a printed wiring board, it is necessary to position it on the printed wiring board, but as with recent flat packages, the number of external connection terminals has increased. As it increases and the distance between them becomes narrower,
This positioning is not so easy and misalignment is likely to occur. It is true that positioning can be performed with high accuracy of ±0.05 mm by employing optical recognition technology that is currently being developed, but such positioning equipment is quite expensive and cannot be easily achieved. It's not something that can be implemented.

For this reason, various studies have been made to see if the positioning of the flat package with respect to the printed wiring board can be handled by the structure of the flat package itself or by the printed wiring board. For example, JP-A-59-1
As proposed in JP-A No. 17139, JP-A-60-210858, JP-A-60-12746, etc., positioning pins or protrusions provided on the bottom of the flat package, external connection terminals (leads), etc. It has been considered that the unit itself can be used as a positioning bin for the printed wiring board to position it for the printed wiring board, but this method requires corresponding processing not only on the flat package side but also on the printed wiring board side. Moreover, the accuracy itself cannot be improved sufficiently. Also, JP-A-61-1609
It has been proposed to provide grooves for positioning flat package terminals on the board body side, as in the "printed wiring board" shown in Publication No. 92, but this is only for positioning on the printed wiring board side. Since this method requires the formation of grooves, it is not only undesirable in printed wiring boards that aim to be more compact, but also is considered to be inferior in accuracy.

Therefore, the inventors have conducted various studies on how to create a structure that can correct the misalignment of the flat package with respect to the printed circuit board with a simple configuration.
They realized that the ``self-alignment effect'' can be effectively used in printed wiring boards that mount flat packages that are becoming larger and have more pins. "
The "self-alignment effect" is also referred to as self-position correction, and the misalignment between the external connection terminals on the package side and the pads on the printed wiring board side is corrected by the surface tension of the molten solder. It is a phenomenon. This "self-alignment effect" appears more effectively when a constant solder exists.

A study of the "self-alignment effect" on printed wiring in recent years shows the following. For example, as shown in FIG. 7, each pad (1
1) to each connection terminal (21) of the flat package (20).
), and each pad (11
) are of equal size, each connection terminal (21) is connected to each bat (1) as shown in Figure 5 = 8.
1) Place the pad (11) on the printed wiring board (lO) so that it is on top, and apply cream paste to the pad (11).
Even if you print a pattern and reflow it, you can connect the flat package (20) to the printed wiring board (10) and the second pad (J).
11) Sufficient movement (movement including rotation and translation)
It is difficult to generate enough force to cause this, that is, the ``self-alignment effect.'' Of course, surface tension is generated in the reflowed solder between each pad (11) and the connection terminal (21), but this surface tension is small due to the small amount of solder. This generally makes it impossible to move the flat package (20) to a predetermined position.

Under these circumstances, the inventors focused on this "self-alignment effect," and found that even if flat packages increase in number of pins, the number of butts on a printed wiring board increases and the spacing between them narrows. - We completed the present invention with the confidence that this "self-alignment effect" can be fully demonstrated even if the

(Problems to be Solved by the Invention) The present invention has been made based on the above-mentioned circumstances, and an object to be solved by the present invention is to facilitate correction of misalignment of a printed wiring board of a flat package.

An object of the present invention is to make it extremely easy to correct any misalignment of the flat package by slightly changing the shape of the pad to which the external connection terminal of the flat package is to be connected by solder. It is an object of the present invention to provide a printed wiring board which can be reliably manufactured and has a simple structure.

(Means for Solving the Problems) In order to solve the second problem, the means adopted by the present invention are explained with reference numerals used in the embodiments. A plurality of pads (11) to which terminals (21) are connected by molten solder
) in a printed wiring board (]0) having pads (
11) in the center (C) of the flat package (20).
), and
The area of at least one set of pads (12) which is point symmetrical with respect to the center (C) among these pads (11) is made larger than that of the other sets, and each of the adjacent bats (11) ) is a printed wiring board (10)j characterized in that the pitches of the wiring boards (10) and (10) are made equal.

(Operation of the invention) The printed wiring board (1) according to the present invention configured as described above
0) by soldering will be described below.

First, in order to mount the flat package (20) on this printed wiring board (10), the large pad (12
) on each connection terminal (21) on each parallel plate (11) including
The flat package (20) is placed so that the flat package (20) is positioned, but there may be a positional shift during this placement. Each bunt (1) including the large pad (12)
This is because when the pre-printed solder in 1) is reflowed, the "self-alignment effect", which is the positional misalignment correcting effect due to the surface tension of the molten solder, is fully exerted as shown below.

Flat package (20) printed wiring board (10)
When the solder is reflowed after placing it on the pad, each pad (11) including the large pad (12) and each connection terminal (
21) The solder located in between melts and creates surface tension. Although the surface tensions generated in each are very small, they are combined as follows, and the flat package (20) is rotated, translated, or a combination of these movements, that is, moved to an accurate position. It is placed in

-9= First, each pad (11) including the large basso F (12) is
Since they are arranged in pairs at points symmetrical positions with respect to the center (C) of the flat package (20), the surface tension generated in each pad (11) including the large pad (12) will affect the flat package (20). It works most efficiently as a moment with respect to the center (C) of . Moreover, since each pad (11) including the large pad (12) is located at a point symmetrical position with respect to the center (C) of the flat package (20), the moment forces generated here are all in the same direction. This also allows the surface tension of each solder to work most efficiently toward the center (C) of the flat package (20).

In addition, in this printed wiring board (10), the large pad (12) is formed at a point symmetrical position with respect to the center (C) of the flat package (20). The amount of solder printed on the pad (11) in advance can be larger than that of other pads (11). Therefore, the surface tension caused by the molten solder in each of these dog bags F' (12) can be made larger. Moreover, these large pads (12) are available in flat packages (
Since they are arranged point-symmetrically with respect to the center (C) of the flat package (20), the moment force due to the surface tension generated in each of these dog pads (12) is applied to the flat package (20).
) can be most efficiently exerted at the center (C).

Furthermore, in this printed wiring board (10), the pitches of the pads (11) including the large pads (12) adjacent to each other are made equal, so that the pitches of the connection terminals (21) are made equal. Flat package (2
0) without changing the configuration, and the surface tension caused by the molten solder in each pad (11,) (12) can be efficiently concentrated.

When the flat package (20) is rotated to the specified position by each surface tension as described above, the large pad (
The surface tension in each pad (11) including 12) is stable, that is, the center of the flat package (20) (
Since the moment force is no longer applied to C), the flat package (20) stops at an accurate position relative to the printed wiring board (lO), that is, the "self-alignment effect" is reliably exhibited. Therefore, even if the pads (II) (12) of the flat package (20) or printed wiring board (10) are slightly misaligned, by reflowing the printed solder, other devices can Even if you do not use the above, the positional deviation can be reliably corrected.

(Example) Next, the printed wiring board (10) of the present invention that exhibits the above-mentioned effects will be described with respect to each example shown in the drawings.

FIG. 1 shows a partial plan view of a printed wiring board (10), and a large number of pads (11) are arranged on each side of a square on an insulating substrate that constitutes this printed wiring board (10). It is. The number of pads (11) on opposite sides of this square is the same and the same size, and moreover, the flat package (20 ) center (C
) Each bat (11) is arranged at a point symmetrical position with respect to the point corresponding to the point. Of course, although not shown, predetermined conductor circuits are connected to each of these pads (11) and the large pad (12) described below.

In addition, in this printed wiring board (10), one large pad (12) is arranged on each side of the aforementioned square, and each dog pad (12) is centered on the center (C). If you rotate it clockwise, it will be located at the front end of each side. This is to maximize the distance from the center (C) of the large pad (12), and as a result, the moment force generated on this large pad (12) relative to the center (C) of the flat package (20) This is to maximize.

In this embodiment, the area of each thick pad (12) is approximately twice that of the pad (11), and the large bat (12)
) and each pad (11), the amount of solder on this large pad (12) can be varied l'
It is made to be approximately twice that of (11). In this manner, by arranging each dog pad (12) at the end of each side of the square, there is an effect that the area can be increased without adversely affecting other pads (11) such as short circuits due to bridges.

Furthermore, the bats (11) including the large bats (12) lined up on each side are arranged so that the pitches of adjacent ones are equal, and the pitches on each side are also equal. That's how it is. This is because it is common to form the connection terminals (21) of the flat package (20) with equal pitches, so that this general flat package (20) can be mounted as is = 14 = is.

Although FIG. 3 shows another embodiment of the printed wiring board (10), the embodiment shown in FIG.
(12) are made up of two sets of four pieces in total, but the printed wiring board (10) of FIG. 3 shows a case of one set of two pieces in total. In this case, the above-mentioned "self-alignment effect J" will occur on the printed wiring board (10
), but it is advantageous when forming another conductor circuit near each vertex of the square mentioned above.

Note that in the above embodiment, Q F P (Quad Fl,
Although the present invention is directed to a type of flat package (20) with leads extending in four directions, which is called an at package, the present invention is limited to this type of package.
It goes without saying that the present invention can also be applied to a type of package with leads extending in two directions, called a line package.

(Effects of the Invention) As described in detail below, in the present invention, as exemplified in each of the above embodiments, each connection terminal (21) of a flat package (20) has a plurality of connections connected by molten solder. pad (11
), the printed wiring board (10) has a pad (
11) in the center (C) of the flat package (20).
), and
The area of at least one set of bats (12) that is point symmetrical with respect to the center (C) of these pads (11) is larger than that of the other sets, and each pad (11) adjacent to each other is ), and by slightly changing the shape of the pads to which the external connection terminals of the flat package should be connected by solder, even if the flat package has positional scratches, It is possible to provide a printed wiring board with a simple structure that allows the correction to be made extremely easily and reliably.

[Brief explanation of the drawing]

Fig. 1 is a partially enlarged plan view of a printed wiring board according to the present invention, Fig. 2 is a plan view when a flat package is mounted on this printed wiring board, and Fig. 3 shows another embodiment of the printed wiring board. A partially enlarged plan view, FIG. 4 is a plan view when a flat package is mounted on this, FIGS. 5 and 6 are perspective views each showing a general flat package, and FIG. 7 is a conventional printed wiring board. FIG. 8 is a plan view of a flat package mounted thereon. Explanation of symbols 10...Printed wiring board, 11...Pad, 12.
・・Large pad, 20・・Flat package, 21・・
Connection terminal, C...center. Above = 17 = to O C'Q r-1 r+ + r'' -墾

Claims (1)

[Claims] In a printed wiring board having a plurality of pads to which each connection terminal of a flat package is connected by molten solder, all of the pads are positioned point-symmetrically with respect to the center of the flat package. and the area of at least one set of pads that is point symmetrical with respect to the center is larger than that of the other sets, and the pitches of adjacent pads are equal. A printed wiring board characterized by: