JPH0555424A - Tie bar removing method for lead frame - Google Patents

Abstract

PURPOSE:To easily remove a tie bar without adhering dross (melted ingot). CONSTITUTION:In order to previously remove a sharp protrusion predicted to remain after cutting by a beam spot 6 at a boundary between a tie bar and a lead, a cutout 1a and a release hole 1 are formed. Thus, adherence of dross remaining by quenching is eliminated, and a relatively flat tie bar residue 7a is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of removing a tie bar in a lead frame in which a semiconductor element is mounted on an island portion of a lead frame, the semiconductor element is resin-sealed, and then a laser beam is projected onto the tie bar of the lead frame to remove the semiconductor element. Hereinafter referred to simply as a tie bar removal method).

[0002]

2. Description of the Related Art A lead is connected to a pad which is an input / output terminal of a semiconductor element with a thin metal wire, and then a semiconductor device is assembled by sealing the periphery of the semiconductor element with a resin to form a resin outer body. In addition, as a finishing process, the resin was removed by flashing and unnecessary tie bar portions were cut off to complete the process.

FIGS. 3A to 3C are partial plan views of the lead frame exposed from the resin shell for explaining an example of a conventional tie bar removing method. In this type of semiconductor device, it was always necessary to finish after sealing with resin. One of them is to remove the tie bar portion 3 shown in FIG. This method has been performed by irradiating a laser beam. That is, as shown in FIG. 3B, the laser beam is applied to a position where the spot 6 of the laser beam completely covers the tie bar portion 3 and is slightly overlapped,
The tie bar portion 3 was removed so as to melt and break.

[0004]

In the above-mentioned conventional tie bar removing method, when the tie bar portion is removed by the laser beam, the portion not irradiated with the laser beam draws an arc as shown in FIG. 3 (c). As I have seen, the tie bar occurs as the remaining 7. Further, in the process of melting the tie bar remainder 7 so that the concentric circle shape spreads outward from the center of the laser beam spot 6, the lead frame material adheres to the cut portion as dross 9 which is unmelted residue. However, the dross 9 at both ends of the arc shape after melting often becomes a lump, and the size thereof is more than the thickness of the lead frame. It is not easy to remove the molten mass called the dross, and when mechanically attempting to remove it, there is a problem that the fragile lead portion is damaged and the product becomes defective.

An object of the present invention is to provide a tie bar removing method for easily removing the tie bar without generating dross in order to solve such a problem.

[0006]

According to a first method of removing a tie bar in a lead frame of the present invention, a semiconductor element mounted on the lead frame is resin-sealed, and then a resin outer shell formed by resin molding is used. In a tie bar removing method in a lead frame for projecting and removing a laser beam on a tie bar that crosses and connects a plurality of protruding leads at a right angle, preliminarily cutting out the remaining part that is cut by the circular spot of the laser beam. It has a feature.

The tie bar removing method in the second lead frame is characterized in that the plate thickness at the boundary between the lead and the tie bar is previously thinned by etching.

[0008]

The present invention will be described below with reference to the drawings. 1A to 1C are partial plan views of a lead frame exposed from a resin shell for explaining an embodiment of a tie bar removing method of the present invention. This tie bar removal method is
As shown in FIG. 1A, the notch 1a and the escape hole 1 are formed in advance at the boundary between the tie bar portion 3 and the inner lead portion 2a and the outer lead portion 2, which are the lead portions, before being removed. This means that no sharp protrusions should be left on the tie bar 7a after melting with the laser beam.
It is to eliminate the part that is cooled quickly. That is, it is to prevent the portion which is irradiated with the laser beam and heated and melted from solidifying by cooling.

Next, the tie bar removing method will be described in detail by following the procedure. First, as shown in FIG. 1A, the notch 1a is formed in the outer lead portion 2, the tie bar portion 3, the inner lead portion 2a and the corner portion of the tie bar portion before resin sealing, and the tie bar portion 3 and the lead portion are formed. That is, an escape hole is formed in a portion where the beam spots 6 of the laser applied to the boundary of the cross section intersect. The number of escape holes is determined according to the number of times the laser beam is emitted. That is, it is necessary not to leave a sharp protruding portion left by two irradiations.
For example, in the case of three times, it is to form two escape holes. Next, as shown in FIG. 1B, a laser beam spot 6 is projected to make a hole corresponding to the spot. As a result, as shown in FIG. 1 (c), the tie bar residue 7a has a smoother cross section, and the molten mass does not adhere to the fusing part.

2 (a) to 2 (c) are partial plan views of the lead frame exposed from the resin shell for explaining another embodiment of the tie bar removing method of the present invention. In this tie bar removing method, the plate thickness of the tie bar portion 3 at the boundary between the tie bar portion and the lead portion is reduced as shown in FIG. is there.
Specifically, the etching portion 8 thinned by etching
Is formed.

By providing the etching portion 8 which is thinned in advance by etching in this way, when the tie bar portion 3 is irradiated with the laser spot 6 so as to overlap twice, the thickness of the etching portion 8 of the tie bar portion 3 is reduced. Since it is thin, melting by laser progresses earlier than the center of the tie bar portion 3, so that the etched portion 8 is melted first and the molten mass adheres to the central portion side and is cut off.
Then, as shown in FIG. 2 (c), the remaining tie bar 7b has a flat cross section and no dross occurs. In the case of this embodiment, there is an advantage that in the case of the above-mentioned embodiment, this cross section becomes smoother and the finishing process of the subsequent process is unnecessary.

[0012]

As described above, according to the tie bar removing method of the present invention, when the tie bar portion is irradiated with the laser beam to remove the tie bar portion, a sharp protrusion protruding from the cut portion left uncut by the laser beam irradiation. By forming the hole and the notch for cutting out in advance, there is an effect that the dross that solidifies due to rapid cooling does not occur and the tie bar portion can be easily removed.

In the second tie bar removing method, the plate thickness of the boundary portion between the tie bar portion and the lead portion is made thinner than other regions in advance,
The same effect can be obtained because the laser beam can accelerate the fusing faster and the tie bar portion can be cut off without generating dross.

[Brief description of drawings]

FIG. 1 is a partial plan view of a lead frame exposed from a resin shell for explaining an embodiment of a tie bar removing method of the present invention.

FIG. 2 is a partial plan view of a lead frame exposed from a resin shell for explaining an embodiment of a tie bar removing method of the present invention.

FIG. 3 is a partial plan view of a lead frame exposed from a resin outer body for explaining an example of a conventional tie bar removing method.

[Explanation of symbols]

 1 Escape Hole 1a Notch 2 Outer Lead Part 2a Inner Lead Part 3 Tie Bar Part 4 Resin Dam Part 5 Resin Outer Body 6 Beam Spot 7, 7a, 7b Remaining Tie Bar 8 Etching Part

Claims (2)

[Claims] 1. A semiconductor device mounted on a lead frame is resin-sealed, and then a laser beam is applied to a tie bar for connecting a plurality of leads projecting from a resin outer body molded by resin sealing at right angles. A method for removing tie bars in a lead frame for projecting and removing, wherein a portion remaining after being cut off by the circular spot of the laser beam is cut out in advance. 2. A tie bar removing method for a lead frame, wherein a plate thickness of a boundary portion between the lead and the tie bar is previously thinned by etching.