The objective of this research is to improve the fundamental understanding of a capillary flow process, that is a key step in the manufacture of electronic systems, and the effective delivery of these process fundamentals through the development of software based flow process tool. The flow process arises in the manufacture of direct-chip-attachment packaged electronics. Here a solder bump array provides the I/O interconnection between a chip and substrate.
The process goal is to rapidly flow an "underfill" material, which is a mixture of silica particles suspended in an epoxy, into the passage formed by the chip, substrate and solder bump surfaces. A laboratory study on the capillary flow of dense suspensions in small flow passages will be conducted. Motion of the mixture-air interface will be tracked and correlated with a number of parameters including the chip-to-substrate standoff (10~100 microns); the mixture rheology; the wetting surfaces (both chemical inhomogeneity and patterned surface topology are typical of the electronics application); and, solder bump geometric pattern. Rheological measurements will be conducted for both commercial underfill materials and model suspensions. Flow modeling will be conducted at two distinct levels: (1) to understand the underlying mechanisms; and, (2) to develop cost-effective calculation strategies for implementation in the flow process tool.
