This paper discusses an innovative technique for rapid cure of polymeric encapsulants such as underfills used in direct chip attach devices using variable frequency microwaves (VFM). VFM processing reduces the cure time for underfill encapsulants to 10 min or less, as compared to 30 or more minutes when using convection oven methods. We report here the results of our investigations measuring key material attributes of VFM and conventionally cured underfill encapsulant samples, and we also have characterized voiding and delamination characteristics of flip-chip with underfill test structures. Finally, particle settling in the flip-chip with underfill test structures has been characterized. Our results show that the VFM technique produces underfill attributes that are comparable to conventionally cured samples.