Hysol FP4581 and Hysol FP4583 are liquid epoxy encapsulants for use as underfills for flip-chip devices. FP4581 is a high-purity, liquid epoxy encapsulant formulated specifically for the requirements of high-lead, bumped large die flip-chip packages. Low CTE properties, improved toughness; forms rigid, low stress seal that dissipates stress on solder joints and extends thermal cycling performance. Ideal for flip-chip devices that require improved crack and fracture resistance. Compatible with most no-clean flux systems. Contains fillers less than or equal to 2 µm in diameter and has been formulated for use with overmolded components in high-lead and Pb-free applications. Amine-based underfill systems are said to offer excellent adhesion to SiN and polyimide. Both are designed to deliver lower stress with the combination of thermal mechanical characteristics to prevent delamination, bump fatigue and UBM failure. 

Henkel Corp., www.henkel.com/electronics