JPH05315519A - Semiconductor element - Google Patents

Abstract

PURPOSE:To prevent the short circuit between lead wires by fused solder, and to improve junction strength by a method wherein the tip of the lead wires of a semiconductor element, having a plurality of lead wires, is formed into a tapered shape. CONSTITUTION:A GFP 1, with a plurality of lead wires, has a tapered part 3 in which the thickness of the tip 2 of a lead wire, which comes in contact with a circuit substrate, is thinned off. The solder, which is fused and adhered on the tip 2 of the lead wire, is adhered and bonded covering the tip of the lead wire. Accordingly, the bonding strength can be increased twice or more when compared with the lead wire bonded by solder on the outer circumference. Also, as the tip of the lead wire can be covered by a small quantity of solder, the quantity of solder cream can be reduced to obtain the same strength, and the defective short circuit generating between leads, which is called a bridge, can be decreased remarkably.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead wire tip shape of a surface mounting semiconductor element having a plurality of lead wires mounted on a circuit board of an electronic device or the like.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional surface mount semiconductor device having a plurality of lead wires. FIG. 4 shows an example of the QFP 1, which has a uniform thickness from the lead wire tip 2 to the root. The QFP1 is set on a solder cream applied to the land portion on the circuit board by printing or the like by a mounter or the like, and the lead wire and the solder on the circuit board are heat-bonded in a reflow furnace. The solder joint portion of the lead wire tip 2 after heating is an arc-shaped solder fillet 4 as shown in FIG.

[0003]

However, in the above-mentioned prior art, short-circuit defects due to solder between the lead wires called bridges may occur or may occur due to variations in the amount of applied solder cream or variations in the amount of heat applied. If the coating amount of the solder cream is reduced as a whole in order to reduce the amount, there is a problem that the manufacturing yield is poor such as insufficient strength and defects. Further, automation of appearance inspection of circuit board mounting is progressing. For example, in the method of illuminating the solder fillet portion at the tip of the lead wire and determining good or defective by the reflected light, the conventional method in which the fillet shape is likely to vary Therefore, it is very difficult to improve the detection accuracy, and there is a problem that the inspection cost increases. In the future, even in surface board mounting, it is expected that the density will become higher and higher, the pitch between lead wires will be minimized, and the number of parts will increase, resulting in higher defective costs due to poor soldering and higher inspection costs . Therefore, development of a semiconductor device that solves these problems is desired. Therefore, the present invention solves such a problem, and the purpose thereof is to easily change the shape of the lead wire tip of the semiconductor element, suppress solder bridge defects, secure the bonding strength, and easily perform the appearance inspection and the inspection cost. It is an object to provide a semiconductor element that can be reduced.

[0004]

The semiconductor device of the present invention comprises:
In a semiconductor element having a plurality of lead wires, the tip of the lead wire of the semiconductor element that contacts the circuit board is tapered and thin. Further, it is characterized in that the tip of the lead wire is pre-coated with solder.

[0005]

(Embodiment 1) Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. As shown in FIG. 1, in a QFP 1 having a plurality of lead wires, a lead wire tip 2 in contact with a circuit board has a tapered portion 3 such that the tip thickness becomes thin. This element is mounted on a solder cream previously screen-printed on a land of a circuit board or a solder previously coated by another method, and is heat-bonded by a reflow furnace or the like to fill the solder fillet 4.
The shape of is shown in FIG. As shown in FIG. 2, the solder melted and fixed at the tip 2 of the lead wire is fixedly joined to cover the tip of the lead wire. Therefore, the bonding strength can be more than doubled as compared with the case where the outer circumference of the lead wire is fixed with solder. Also,
Since the tip of the lead wire can be covered with a little solder,
Even if the same strength is obtained, the amount of solder cream can be reduced, and a short circuit between leads called a bridge can be extremely reduced. This becomes more effective as the density becomes higher and the pitch between the lead wires becomes narrower. In this way, by tapering the tip of the lead wire, the yield in mounting is greatly improved. In addition, when the appearance inspection is automatically performed after the circuit board is raised, when the solder fillet is illuminated and the quality of the light is determined by the reflected light, or when the solder fillet is scanned with a laser beam, the quality is determined by the shape. In this case, the erroneous determination rate of quality is high due to the variation of the solder fillet, and it is very difficult to start up to a practical level. However, by tapering the tip of the lead wire, the quality judgment standard can be simplified, so that the automatic appearance inspection becomes very simple. This quality criterion may be, for example, the presence or absence of a change in the taper angle when the center of the taper portion at the tip of the lead wire is scanned with laser light. If the connection between the lead wire tip and the solder is good, the taper angle changes because the tip of the lead wire is covered with the solder, and in this case, it may be determined as a good product. vice versa,
If the wetness of the solder is bad or the lead wire floats, the taper portion at the tip of the lead wire has no solder, the angle is constant and there is no change, so it can be determined as defective. The size of the taper angle 5 at the tip of the lead wire may be arbitrarily set according to each semiconductor element. To obtain the above effect, the taper angle 5 may be about 45 degrees or less, but if possible, 30 The best is around. Further, it is preferable that the height 6 of the tip of the lead wire is as small as possible, and if it is too large, the desired effect cannot be obtained.

[0006] This method of tapering the tip of the lead wire of the semiconductor element is performed by a pressing die at the time of cutting in a pressing step in which the semiconductor element is separated from a lead frame which is usually used, and at the same time, the shape of the tip of the lead wire is formed. Need only be changed to a shape that allows the tip of the lead wire to be crushed after cutting.

(Example 2) As the density becomes higher and higher in the future, the conventional solder supply by solder cream printing to a circuit board cannot meet the quality requirement. Therefore, in the present embodiment, as shown in FIG. 3, the lead wire tip 2 of the semiconductor element having a plurality of lead wires and the tip of the lead wire 2 being tapered is provided with the precoat solder 7. ing. On any land on the circuit board,
This element is mounted, and a heating tool is pressed to melt the precoated solder, and the element is fixedly bonded to the circuit board. At this time, the melted solder smoothly flows through the taper portion at the tip of the lead wire to cover and fix the tip portion of the lead. For the conventional semiconductor element with the lead wire tip pre-coated with solder, if the same method is used, the solder will flow around the lead wire and the solder will not cover the lead wire tip, only the fillet part around the lead wire. Since it is fixed, it is necessary to secure a sufficient amount of solder precoat in order to secure the strength, but in the case of this embodiment, even if the amount of precoat solder is reduced compared to the conventional case, the strength is improved. Can be secured, the time required for pre-coating the solder can be shortened, and the cost can be reduced in mass production. this,
For pre-coating solder on the tip of the lead wire,
For example, electrical solder plating or spray application of molten solder may be used.

[0008]

According to the present invention, the tip of the lead wire of the semiconductor element having a plurality of lead wires is tapered, so that when the semiconductor element is fixed to the circuit board, a short circuit is caused by the molten solder between the lead wires. This has the effect of preventing the above, and improving the yield and quality at the time of high-density surface mounting. Further, in the automation of the appearance inspection of the surface mounting board, the inspection can be easily performed in a short time, so that the cost for mounting the circuit board can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a partial perspective view of a semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a partial cross-sectional view showing a solder fillet shape according to the first embodiment of the present invention.

FIG. 3 is a partial cross-sectional view of a tip of a lead wire of a semiconductor device according to a second embodiment of the present invention.

FIG. 4 is a partial perspective view of a conventional semiconductor device.

FIG. 5 is a partial sectional view showing a conventional solder fillet shape.

[Explanation of symbols]

 1 QFP (semiconductor element) 2 Lead wire tip 3 Tapered part 4 Solder fillet 5 Taper angle 6 Lead wire tip height 7 Precoat solder

Claims (2)

[Claims] 1. A semiconductor element having a plurality of lead wires, wherein a tip of a lead wire of the semiconductor element that abuts a circuit board is tapered and thinned. 2. The semiconductor element according to claim 1, wherein the tip of the lead wire is pre-coated with solder.