SMTA International Conference Proceedings


Authors: Steve Hackett, Ph.D.
Company: 3M Company
Date Published: 9/22/2002   Conference: SMTA International

Abstract: Capillary underfills have been used to extend the life of flip chip devices for many years. The capillary underfills currently used for flip chip packaging exhibit shortcomings that may limit their use in more demanding applications. The tighter pitch and narrower gap that are anticipated for future flip chip packages will require improvements in the flow properties of capillary underfill materials.

Fillers that are now typically incorporated at high levels to decrease the thermal expansion coefficient of underfills will be too large to fit into the narrow-gap, tighter-pitch packages. Additionally, these fillers have a tendency to settle, providing a bond with a non-uniform thermal expansion coefficient. In this paper, a new class of materials containing nanosilica filler will be described.

Due to the reduced size of the nanosilica filler versus conventional filler, several important capillary underfill processing features are improved. The material properties and processing characteristics of these materials will be discussed. In addition, the use of these materials as no-flow underfills will be described.

Key words: flip chip, nanosilica filler, no-flow.

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