JP2555075Y2 - Coining punch for coining lead frames - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION The present invention is intended to prevent swelling of the inner lead tip when coining the inner lead tip of a lead frame used in a semiconductor device and to increase the dimensional accuracy in the thickness direction. The present invention relates to a coining punch for coining a lead frame.

[0002]

2. Description of the Related Art Conventionally, when a lead frame 1 as shown in FIG. 2 is manufactured by press working, a blank material is intermittently supplied to a progressive die, and punched sequentially to form a predetermined shape. Then, in a process close to the final process, a process of crushing the tip of the inner lead 2 with a flat-head coining punch for the purpose of expanding a flat portion so that the cross-sectional shape is easy to wire-bond, that is, wire bonding is performed by so-called coining. Attempts have been made to ensure flats of the possible dimensions.

However, when such coining is performed, as shown in FIG. 3, stress concentration acts on a boundary 4 crushed by a flat-head coining punch having a straight corner which becomes a boundary of coining. As a result, the crushed boundary line A was used as a fulcrum, and the inner lead tip B jumped in the direction M opposite to the direction L in which the inner lead tip B was crushed.

[0004] Since wire bonding is performed by applying heat from the heater block to the inner lead 2, if the tip of the inner lead is raised, the contact area of the inner lead with the heater block is reduced and heat conduction is reduced. However, a situation arises in which wire bonding becomes impossible.

[0005] In order to prevent the tip of the inner lead from rising, a conventional flat-head coining punch has a
If a notch C 'as shown in FIG. 4 is provided and coining is performed, as shown in FIG. 5, a so-called slope C is left to prevent the spring from rising, or the coining is divided into two steps. After tapping wider than the area, press again to the required area, or, as shown in FIG. 6, place a groove D in advance on the coining boundary line of the tip of the inner lead formed by the corner of the coining punch for the purpose of separating stress. Means are provided to alleviate the stress concentration of coining.

[0006]

However, in the above-described spring-up preventing means, the depth of coining may be increased due to the fluctuation of the die stroke generated during the operation. As a result, distortion increases and the effect decreases. Therefore, it is unsatisfactory in practical use, for example, it takes extra time to adjust this.

Therefore, the present invention solves the above problems,
An object of the present invention is to provide a coining punch for coining a lead frame, which is provided with a means for preventing the spring from rising when coining the tip of the inner lead of the lead frame.

[0008]

In order to achieve the above object, the present invention provides a coining punch used for coining the tip of an inner lead of a lead frame.
A boundary line of coining whose end surface is formed on the tip of the inner lead is formed symmetrically with respect to the center axis in the width direction of the inner lead, and is formed in a tapered V-shape so as to cross the axis at an angle θ of 40 ° to 50 °. And a coining punch for coining the lead frame.

[0009]

According to the above-mentioned shape, the boundary line becomes two, and the stress directions are 80 to 1 with respect to each other.
Since they intersect at 00 ° and cancel each other due to the action of the reaction force, it is possible to obtain a lead frame having inner leads which are not bumped and are subjected to coining with good dimensional accuracy in the thickness direction.

[0010]

EXAMPLE A lead frame 1 having 40 inner leads 2 having a tip width of 0.28 mm as shown in FIG. 2 was punched out of a 42 alloy material having a thickness of 0.25 mm, and manufactured by punching. 1 is the inner lead 2
Is formed symmetrically with respect to the center axis of the inner lead 2 in the width direction of the inner lead 2 and is formed in a tapered V-shape so as to intersect the center axis of the bracket at an angle θ of 45 °. The tip of the inner lead was coined using a coining punch.

In this way, the boundary line A becomes two, and the stress directions cross each other at 90 ° and cancel each other out due to the reaction force. Therefore, as shown in FIG. Thus, it is possible to obtain a lead frame having inner leads that have been subjected to coining with good dimensional accuracy in the thickness direction.

The closer the intersection angle θ between the coining boundary line A and the axis of the center of the inner lead in the width direction to 45 °, the greater the effect of the reaction force and the greater the effect.

This is because if the stresses generated by the two coining boundary lines A cross each other at 90 °, the component forces cancel each other out, and 90 °
This is because the component offsetting effect is reduced by the amount deviated from the range.

When the intersection angle of the coining boundary line with the center axis in the inner lead width direction is 40 ° or less, the flat portion for bonding becomes narrow, and the meaning of coining is lost. On the other hand, when the crossing angle is 50 ° or more, the component force to be canceled out 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 of the coining punch is used to perform coining at the tip of the inner lead so that a so-called slope is formed at the coining boundary. As a result, as shown in FIG.
The surface was raised with an angle of 30 '.

[0016]

As described above, according to the present invention, when the tip of the inner lead is crushed, stress concentrates on the corner of the flat-head coining punch, and the inner line is formed with the boundary line crushed by the corner as a fulcrum. Utilizing the fact that the tip of the lead rises in the direction opposite to the direction in which the lead is crushed, the end face is symmetric with respect to the center axis in the width direction of the inner lead, and is 40 ° away from the center axis. The shape is devised so as to cancel out the direction of the stress by using a tapered V-shaped coining punch so as to intersect at an angle θ of ゜ 50 °. It is possible to make a coined surface almost parallel to the punched material surface, and it is possible to increase the dimensional accuracy in the thickness direction of the coined part at the tip of the inner lead . Therefore, remarkable effects such as improvement in wire bonding property and yield are recognized.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of a coining end face shape of a lead frame of the present invention.

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

FIG. 3 is a perspective view showing a conventional example in which a leading end of an inner lead rises.

FIG. 4 is a perspective view showing an embodiment of a notch provided at a corner of the head of a flat-head coining punch.

FIG. 5 is a perspective view showing one embodiment of an inner lead tip portion coined by a coining punch provided with a cutout at a corner of the head.

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

[Explanation of symbols]

 1 Lead frame 2 Inner lead A Boundary line B Tip of inner lead C Slope D Groove

Claims (1)

(57) [Scope of request for utility model registration] In a coining punch used for coining a leading end portion of an inner lead of a lead frame, a boundary surface of the coining generated on the leading end of the inner lead is symmetrical with respect to an axis at a center in a width direction of the inner lead. A coining punch for coining a lead frame, wherein the coining punch is formed in a tapered V-shape so as to cross the axis at an angle θ of 40 ° to 50 °.