Flip Chip Assembly with No Flow Underfills

Category: Flip Chip and Die Placement
Post Date: July 19, 2004
Author(s): Pericles A. Kondos and Peter Borgesen, Surface Mount Laboratory, Universal Instruments

Description
Reflow encapsulants or flux underfills have appeared in recent years as an alternative to capillary flow underfills, offering several cost and throughput advantages. The present work addresses issues related to the use of these in cost-efficient flip chip assembly. Numerous materials from several manufacturers were considered. Voids in the encapsulant are a potential problem. These can originate during dispense, die placement, or reflow but can be eliminated through proper materials selection, board preparation, dispense parameters and reflow conditions. Electrical continuity was achievable by optimizing assembly parameters and reflow profile. Optimized assemblies performed quite well in thermal cycling tests.

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