JPH0992763A - Punching process method for lead frame - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of a burrs at flattening process even when cracks and burrs of plating occur at a punched end surface part of a lead frame for a transistor. SOLUTION: A lead frame material with plating is punched into a specified form. When a part of a punched end surface part 4 of the punched lead frame is flattened, flattening process of chamfer is performed in advance for forming a chamfer 11. The flattening process for raising adhesion-property of the mold resin is performed on the punched end surface part 4 after the chamfer flattening process, for forming a flattening 5. By this, occurrence of burrs on the edge of the flatting 5 due to the teared plating 7 is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for punching a lead frame, and more particularly to a technique for processing an end face portion after punching.

[0002]

2. Description of the Related Art In a lead frame, for example, a power transistor lead frame (particularly TO-220, TO-3P type), as shown in FIG. 2, a part of the extraction end surface portion 4, for example, a header portion on which a transistor chip is mounted is mounted. In many cases, the flat end 5 is formed on the header end face 2 of No. 1 and the screw hole 3 for mounting the transistor in order to improve the biting property of the mold resin. Conventionally, this flattening process has been performed directly after punching a lead frame for a transistor. The surface of the base material 6 of the lead frame is usually plated.

[0003]

A lead frame material for a transistor having a plated surface is punched out to manufacture a lead frame for a transistor. When the flattening process is performed directly after punching as in the conventional case, It was easy for problems such as

As shown in FIG. 1 (a), minute burrs 8 are generated in the material after punching, but since the material is largely deformed in the vicinity of the burrs 8, cracks 9 are formed in the plating 7 on the surface. Is easy to enter. The crack 9 is particularly noticeable in a hard plated material such as nickel. Since the burr 8 portion is weak in strength, if the punched end face portion 4 is directly flattened thereafter, the plating 7 is torn and a whisker burr 10 is generated as shown in FIG.

The whisker 10 is a very dangerous defect because if it falls off during the mounting process or the like, it will lead to a short circuit in the electric circuit and cause a malfunction of the control system in the final product.
However, in the manufacturing process of the lead frame, it is very difficult to eliminate the plating cracks 9 and burrs 8 that may cause whiskers.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a lead frame punching method capable of suppressing the occurrence of whiskers even when cracks and burrs of plating occur. It is in.

[0007]

According to the method of punching a lead frame of the present invention, a plated lead frame material is punched into a predetermined shape, and an end face portion of the punched lead frame is subjected to chamfering crushing.

Further, the lead frame stamping method of the present invention is such that a plated lead frame material is stamped into a predetermined shape, and the end face portion of the stamped lead frame is flattened, and chamfering is performed. The flattening process for improving the biting property of the mold resin is performed on the end face portion subjected to the chamfering process.

In these cases, the beveling can be effectively eliminated by setting the angle for chamfering crushing to 10 ° ≦ θ ≦ 60 °.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. As in the past, TO-22
The lead frame material for power transistors, such as 0 and TO-3P type, is punched into a predetermined shape to form a lead frame material for power transistors. Then, Figure 1
As shown in (a), minute burrs 8 are generated in the material after punching, but since the material is largely deformed in the vicinity of the burrs 8, cracks 9 are easily formed in the plating 7 on the surface. As described above.

The burrs that occur during flattening are
The cause is that the plating 7 having the cracks 9 is placed on the burr 8 where the strength is weak. Therefore, in the present embodiment, after punching and before flattening processing, as shown in FIG. 1B, the chamfering processing of square chamfering is performed on the burrs to form the square chamfering 11. . Burrs 8 and cracks 9 are formed by such a corner surface cutting process.
The plated plating 12 is embedded in the base material 6 to eliminate a portion having weak strength, and to prevent the plating from breaking due to the flattening process thereafter.

Therefore, even if the flattened 5 is formed by flattening the end face portion that has been subjected to the flattening process of the corner surface, as shown in FIG. can get. In fact, at present, the occurrence of whiskers due to the scraping of the corner has not been found.

As described above, when the flattening process is applied to the punched end face portion of the plated lead frame for a transistor, the punched end face portion is subjected to the square face squashing process in advance, so that the occurrence of whiskers can be effectively prevented. .

Particularly, according to the present invention, as shown in FIG. 2, in the header portion 1 of the lead frame for power transistor, C
This is effective when flattening the header end face 2 and the screw hole portion 3 in a material obtained by nickel-plating the base material 6 of the u alloy.

By the way, the angle θ of the crushing process of the chamfer
Has a lower limit of 10 ° from the viewpoint of embedding the plating with burrs 8 and cracks 9 in the base material 6, and if the angle is too tight, the burrs 8 will be scraped off.
The upper limit is 0 °.

[0016] In addition, since the plating mustaches may be generated only by the punching, the square face shaving process is effective even for the punched end face portion which is not flattened. Further, the present invention is not limited to the lead frame for transistors, and may be any lead frame that is plated, and may be applied to, for example, an IC lead frame.

[0017]

According to the invention as set forth in claim 1, since the punched end face is subjected to a crushing process for chamfering, it is possible to eliminate the whisker even when the plating mustache is generated only by punching. It can prevent short circuit due to beard.

According to the second aspect of the present invention, when the flattening process is performed after the punching, the chamfering process is performed in advance on the punched end face portion, so that cracks and burrs of plating occur on the punched end face portion. However, it is possible to effectively prevent the occurrence of plating burrs.

According to the invention described in claim 3, since the angle of the chamfering crushing process is 10 ° ≦ θ ≦ 60 °, the burr can be embedded in the base material without scraping.

[Brief description of drawings]

FIG. 1 is a process diagram showing an embodiment of a lead frame punching method of the present invention, in which (a) is a sectional view of a material showing the vicinity of a burr after punching, and (b) a chamfering process of a burr part. FIG. 3C is a cross-sectional view of the material subjected to the flattening process, and FIG.

FIG. 2 is a perspective view of a typical lead frame for power transistor, which is common to the embodiment of the present invention and the conventional example.

FIG. 3 is a cross-sectional view of a material showing a state of occurrence of whiskers after performing a flattening process of a conventional example.

[Explanation of symbols]

 4 End face 5 Flattened 6 Base metal 7 Plating 8 Burr 9 Crack 11 Chamfering 12 Cracked plating

Claims (3)

[Claims] 1. A method for punching a lead frame, wherein a lead frame material with plating is punched into a predetermined shape, and the end surface of the punched lead frame is chamfered. 2. A lead frame material with plating is punched into a predetermined shape, and the flattened portion of the punched lead frame is chamfered, and the chamfered end surface is subjected to chamfering. A lead frame punching method that performs flattening to improve the biteability of the mold resin. 3. The angle of chamfering crushing is 10 ° ≦ θ ≦
The lead frame punching method according to claim 1, wherein the lead frame is 60 °.