JPH0538909U - Lead frame coining end face shape - Google Patents

Abstract

(57) [Summary] [Purpose] When the lead frame 1 is manufactured by pressing, the tip of the inner lead is crushed by a flat-head coining punch for the purpose of expanding the flat part to facilitate wire bonding. Try not to go up. [Structure] When the coining boundary line of the tip of the inner lead formed by the coining punch angle is symmetrical with respect to the center line of the inner lead and intersects at an angle θ of 40 ° to 50 °, the stress directions of the boundary lines are mutually different. Since they intersect at about 90 °, they are offset by the action of the reaction force, and the feature is that the splash is prevented.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a coining end face shape of a lead frame for preventing the inner lead tip from jumping up and increasing the dimensional accuracy in the plate thickness direction when coining the inner lead tip of a lead frame used in a semiconductor device. Is.

[0002]

[Prior Art]

 2. Description of the Related Art Conventionally, when a lead frame 1 as shown in FIG. 2 is manufactured by press working, a punching material is intermittently supplied to a progressive die and sequentially punched into a predetermined shape. Then, in a step close to the final step, the tip of the inner lead 2 is crushed with a flat head coining punch for the purpose of expanding the flat portion so that the cross-sectional shape can be easily wire-bonded, so-called coining It has been attempted to secure a flat portion having a size capable of ding.

However, in the case of such coining, as shown in FIG. 3, stress concentration acts on the boundary line 4 crushed by the flat-head coining punch having straight corners serving as the boundary line of the coining. As a result, the inner lead tip portion B was struck up in the direction M opposite to the crushed direction L with the crushed boundary line A as a fulcrum.

Since the wire bonding process is performed by applying heat to the inner lead 2 from the heater block, if the tip of the inner lead bounces up, the contact area of the inner lead to the heater block becomes smaller, and the heat conduction decreases. However, a situation occurs in which wire bonding becomes impossible.

In order to prevent the tip of the inner lead from jumping up, a notch C ′ as shown in FIG. 4 is provided at the corner of the conventional flat-head coining punch head. As shown, the so-called slope C is left to prevent splashing, or the coining is divided into two steps, and the tapping is first made wider than the required area and then pressed again to the required area, or as shown in FIG. A groove D is provided in advance on the coining boundary line of the tip of the inner lead formed by the punch corners for the purpose of stress division, and a means for relaxing the stress concentration of coining is taken.

[0006]

[Problems to be solved by the device]

 However, with the above-mentioned splash-up preventing means, the coining depth may become deep due to fluctuations in die stroke that occur during work. As a result, the distortion increases and the effect decreases. Therefore, it was unsatisfactory for practical use because it took extra time to adjust this.

[0007] Therefore, an object of the present invention is to solve the above-mentioned problems and to obtain a means capable of preventing the rebound when coining the inner lead tip end portion of the lead frame.

[0008]

[Means for Solving the Problems]

 According to the present invention, when coining punching the inner lead tip of the lead frame, the coining boundary generated by the coining punch on the inner lead tip is symmetrical with respect to the center line of the inner lead and is 40 ° to 50 °. The shape is such that they intersect at an angle θ.

[0009]

[Action]

 With the above-described shape, the boundary lines become two, and the reaction directions intersect with each other at 80 to 100 °, and the reaction forces cancel each other, so that there is no splashing. It is possible to obtain a lead frame with inner leads that have been coined with good dimensional accuracy in the plate thickness direction.

[0010]

EXAMPLE A lead alloy 1 having 40 inner leads 2 having a tip width of 0.28 mm as shown in FIG. 2 was punched out and manufactured by using 42 alloy material having a thickness of 0.25 mm. Using a coining punch, coining the tip of the inner lead 2 so that the coining end face is symmetrical with respect to the center line of the inner lead 2 as shown in FIG. Was applied.

In this way, the boundary line A becomes two, and the stress directions intersect each other at 90 °, so that they are canceled by the action of the reaction force. Therefore, as shown in FIG. 1, there is no rebound. It is possible to obtain a lead frame having a coined inner lead with good dimensional accuracy in the plate thickness direction.

It should be noted that the closer the intersection angle θ between the coining boundary line A and the center line of the inner lead is to 45 °, the greater the action of the reaction force and the greater the effect.

This is because if the stresses created by the two coining boundary lines A intersect with each other at 90 °, the component forces cancel each other out, and the component offsetting effect diminishes by the amount deviated from 90 °.

When the crossing angle of the coining boundary line with the center line of the inner lead is 40 ° or less, the flat portion for bonding becomes narrow, and the meaning of coining becomes meaningless. On the contrary, when the crossing angle is 50 ° or more, the canceling component force becomes small and there is no effect.

As a comparative example, as shown in FIG. 4, a coining punch having a notch at a corner portion of the coining punch is used to perform coining on the tip end of the inner lead so that the coining boundary line has a so-called slope shape. As a result, as shown in FIG. 3, the surface was a raised surface having an angle of 2 ° 30 'with respect to the surface of the blank material.

[0016]

[Effect of the device]

 As described above, according to the present invention, when the tip of the inner lead is crushed, stress concentration acts on the corner of the flat-head coining punch, and the tip of the inner lead is crushed by the boundary line crushed by the corner. Taking advantage of the fact that it pops up in the direction opposite to the crushed direction, it intersects with the center line at an angle θ of 40 ° to 50 ° so that this angle becomes symmetrical with the center line of the inner lead. Since the coining is performed by using a coining punch with a coining shape devised so as to cancel out, the inner lead can be prevented from jumping up and a coined surface almost parallel to the punched material surface can be obtained. The dimensional accuracy in the thickness direction of the coined portion of the lead tip can be improved. Therefore, remarkable effects such as improvement in wire bondability and yield are recognized.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a coining end surface shape of a lead frame according to the present invention.

FIG. 2 is an overall plan view showing a lead frame of the present invention.

FIG. 3 is a perspective view showing a jump of a tip portion of an inner lead according to a conventional example.

FIG. 4 is a perspective view showing an example of a notch provided in a corner portion of a head of a flat head coining punch.

FIG. 5 is a perspective view showing an example of an inner lead tip portion coined by a coining punch having a notch at a corner portion of the head.

FIG. 6 is a perspective view showing an embodiment in which a groove is provided in the coining portion for the purpose of dividing the rising stress.

[Explanation of symbols]

 1 Lead frame 2 Inner lead A Boundary line B Inner lead tip C Slope D Groove

Claims (1)

[Scope of utility model registration request] 1. When coining punching the inner lead tip of a lead frame, the coining boundary line of the coining produced on the tip of the inner lead is symmetrical with respect to the center line of the inner lead and is 40 ° to 50 °.
The coining end face shape of the lead frame, characterized in that they intersect at an angle θ.