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PEDESTAL ENCAPSULATION CURE FOR TAB ASSEMBLIES

IP.com Disclosure Number: IPCOM000006424D
Original Publication Date: 1992-May-01
Included in the Prior Art Database: 2002-Jan-02
Document File: 2 page(s) / 89K

Publishing Venue

Motorola

Related People

Peter J. Cole: AUTHOR

Abstract

A process for encapsulation cure overcomes problems encountered when TAB tin plated leadframes are heated. The encapsulation cure process is performed on TAB units after the die has been bonded to the tape (inner lead bonding-ILB); and consists of baking the parts in an oven for a specified time(s)/temper- ature(s). The primary problem is that the curing process consumes the free tin in a copper/tin intermetallic, which greatly reduces the solderability of the part for future outer lead bonding (OLB) by the customer. This problem cannot be addressed by the addition of tin before the curing process due to negative effects on the ILB process, and the potential for "whisker" formation.

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M MOTOROLA INC. Technical Developments Volume15 May 1992

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PEDESTAL ENCAPSULATION CURE FOR TAB ASSEMBLIES

by Peter J. Cole

  A process for encapsulation cure overcomes problems encountered when TAB tin plated leadframes are heated. The encapsulation cure process is performed on TAB units after the die has been bonded to the tape (inner lead bonding-ILB); and consists of baking the parts in an oven for a specified time(s)/temper- ature(s). The primary problem is that the curing process consumes the free tin in a copper/tin intermetallic, which greatly reduces the solderability of the part for future outer lead bonding (OLB) by the customer. This problem cannot be addressed by the addition of tin before the curing process due to negative effects on the ILB process, and the potential for "whisker" formation.

  Experiments have been successfully conducted in which an encapsulated TAB units were placed on a heated pedestal; curing the epoxy with minimal impact on the free tin of the leadframe. This approach not only pre- serves the amount of free tin, it also provides a faster and more controllable cure than an oven.

  Figure 1 shows two views of a TAB assembly: TOP-to illustrate the structure of a TAB unit; and SIDE to show how the die and heated pedestal interface.

  After application of the encapsulant, the die (4) is place on the heated pedestal (5) and the heat is conducted through the silicon to the encapsulant. Since the heat transfer is made by direct contact with the...