Masters Abstracts (1996)

FOSBERRY, JENNIFER
(August 1996), Tessera Inc., San Jose, CA

Email: jenfos@tessera.com

An Investigation of the Physical Properties and Flow Behavior of Encapsulant Materials for Direct Chip Attach Applications

As the electronics packaging industry moves toward components with increased numbers of I/Os (input/outputs), the component pitch is greatly reduced. This has led to the development of alternate assemblies, such as direct chip attach (DCA). While there are many benefits to this technology, thermal mismatch between the solder joints and the substrates (chip and solder mask) require an additional encapsulation step using a silica particle filled polymer liquid. Currently, a complete understanding of the encapsulant materials used in this process step does not exist. Study of these materials, particularly the flow behaviors is necessary to further the development of DCA assembly processes.

A simple capillary flow model was developed and parameters of this model were considered with flow experiments. Physical properties (i.e. contact angles and liquid surface tensions) were measured and determined to be within a small range and therefore did not drastically alter the flow rate. It was determined that application parameters such as standoff, preheat temperatures, and surfaces (both surface morphology and condition) led to much different flow behaviors for encapsulants. Through this research, the need for a rapid screening experiment was identified and an efficient, effective procedure was developed and used. Through many flow experiments, some general tendencies have been identified.

This research shows that the flow behaviors of the materials are more complex than described by the simple capillary flow models. It also shows that the flow behaviors of these materials vary drastically and should be tested before they are applied to individual applications. Full understanding of the parameters of a DCA assembly would be required, along with a full understanding of the material flow, before an individual encapsulation process can be developed.