1. Field of the Invention:
This invention relates generally to lead frames which are used to constitute various electronic components such as IC's or LSI's, and more particulary to such a lead frame having a pin holding structure which serves to prevent undesirable deformation of the lead pins during transport of the lead frame or during assembly thereof into an electronic component. The invention also relates to a pin holding method for a lead frame.
2. Description of the Prior Art:
As is well known in the art, lead frames are manufactured by photoetching or press-working a thin metallic strip into a predetermined form to have a longitudinally spaced islands and a plurality of lead pins associated with each island. The metallic strip is usually made of Fe-Ni based alloy, copper, or copper based alloy.
Due to recent demand for further integration or sophistication of semiconductor devices, lead frames to be incorporated in such devices are required to have a very small thickness with its lead pins slenderized and densely arranged. Therefore, the lead pins are becoming increasingly liable to deformation during transport of the lead frame and/or during assembly thereof into an IC, particularly during chip bonding and wire bonding. Such deformation of the lead pins results in poor quality and low yield.
In order to eliminate the above problem, it has been proposed to apply a heat-resistant adhesive tape onto the inner lead pins of a lead frame, so that the inner lead pins are prevented from deformation and resultant shorting. More specifically, the tape consists of a polyimide film coated at one side with an acrylic adhesive. Such adhesive tape is available under the tradename "PYRALUX" from Du Pont Company.
In use, a blank adhesive tape which is originally wide is punched by a die into a segment of suitable shape and dimensions depending on the particular type of lead frame being processed. The tape segment is then transferred onto a specified surface portion of the lead frame, and the taped lead frame is subjected to heat and pressure to maximize adhesion of the tape.
The above pin holding tape, however, has a disadvantage that it necessitates the use of a costly punching die which is designed to suit a particular type (length, width, configuration, etc.) of lead frame and which must be replaced in a time-taking operation by a differetly designed die to suit another type of lead frame. After punching, the tape produces a substantial residual portion, resulting in economical problem in view of the expensive materials of which the tape is made. Further, the tape has a possibility of coming off relatively easily from the lead frame surface.