New developments in single pass reflow encapsulant for flip chip application

This paper introduces a series of single pass reflow encapsulants that requires no post curing after solder bump reflow. Acting as a flux and an encapsulant, this product performs two functions. First, the material activates the solder bump and metallic bond pad during solder reflow to establish the interconnection between the die and substrate. Second, while this material is being cured, it forms a mechanical bond between the surface of the die and substrate. This product allows processing normal surface mount component packages concurrently with flip chip, CSPs or BGAs under the standard surface mount reflow profile. Such a process eliminates capillary underfilling and curing time. The product's solderability is robust and high yield; the parts are reliable after thermal shock testing. We have employed DSC, TMA, DMA and shear test techniques to investigate the properties of the material. These properties include influence of filler loading level, curing reflow profile, percentage cure, glass transition temperature (Tg), coefficient of thermal expansion (CTE), modulus and die shear adhesion.