SMTA International Conference Proceedings


Authors: Stephen C. Busch and Daniel Baldwin, Ph.D.
Company: Georgia Institute of Tech.
Date Published: 9/25/2005   Conference: SMTA International

Abstract: Wafer-level flip chip assemblies are vulnerable to misalignment during underfill liquification and die collapse. In order to better understand the physical phenomena governing the collapse of wafer-level flip chip die, a theoretical and experimental investigation is undertaken. The major forces acting on wafer-level flip chip die during underfill wetting have been identified and represented mathematically. Surface tension forces have been found to dominate the system.

Wafer-level underfill fillet formation is considered and explained in detail, with the evolution of fillet profiles being studied theoretically and experimentally. The constraints on fillet shape at various points in the collapse of wafer-level flip chip die have been identified. Mechanisms for die misalignment are identified, and experimental samples are fabricated and observed during collapse with video imaging. Having verified a cause for wafer-level flip chip misalignment, recommendations are made to reduce or eliminate the defect.

Key words: Wafer Level Packaging, Wafer Applied Underfill, Flip Chip, Underfill, Flip Chip Processing

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