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The transfer molding process used to encapsulate semiconductor devices suffers from significant
problems due to the high operating temperatures and high pressures required to fill the mold. These aspects of the current process can lead to incomplete mold filling, thermal stresses, and displacement of the fine wires that provide electrical interconnection between the silicon chip and the Ieadframe. In this contribution, we discuss an encapsulation process based upon a low viscosity, epoxy novolac-based vinyl ester resin that cures rapidly upon exposure to UV light. For these photopolymerizable liquid encapsulants (PLE5), we have characterized the viscosity, flexural strength and modulus, coefficient of thermal expansion, glass transition temperature, initiation scheme, and illumination time for systems containing 70.0-74.0 wt% fused silica. The results indicate that a photocurable encapsulant containing 74.0 wt.% fused silica is very promising for microelectronic encapsulation. These liquid encapsulants cure (to an ejectable hardness) in less than two minutes for an initiating light intensity of 2002 and exhibit appropriate values for the thermal and mechanical properties listed above.
