Author: G. Lehmann Company: The State Univ. of New York Date Published: 9/10/1996
Surface Mount International
Abstract: In direct chip attach technology, thermal stresses that arise during temperature fluctuations are compensated for by underfilling chips with epoxy encapsulant. The encapsulant are filled with particles (generally silica) to better match the coefficient of thermal expansion of the encapsulant to the solder intercomects. However, these fillers have strong effects on the flow of the encapsulant, particularly in regions of small stand off heights. In order to better facilitate the design and manufacture of faster flowing, lower voiding encapsulant, the basic mechanisms that affect the flow of encapsulant are investigated. The flow process of particulate-filled liquids of different particle concentrations are studied for various parallel plate separations. Comparisons of experimentally obtained and semi-emperical flow models are provided. Keywords: Direct-chip-attachment, underfill, encapsulant, flow processes.