Materials Research Project
Hygroscopic Swelling: For many years, moisture induced swelling in plastic encapsulant in microelectronic package was ignored. Recently, new techniques of swelling measurements revealed that swelling coefficient is comparable to the coefficient of thermal expansion (CTE), and therefore, swelling mismatches between adjacent components in plastic encapsulated microelectronics must be considered in the design and reliability analysis. We were one of the pioneers to measure and present swelling coefficients of common plastic encapsulants (epoxy molding compounds) using a modified thermo-mechanical analyzer (TMA).
Moisture Diffusion Modeling: Moisture in plastic encapsulated electronics (PEMs) can lead to variety of reliability problems including popcorning (cracking during solder reflow), delamination and corrosion. Modeling moisture diffusion allows us to better understand and predict the diffusion process, and more effectively mitigate it. Moisture diffusion can be either Fickian or non-Fickian. We have found through experimental observations of moisture sensor placed inside the PEM that in many cases, Fickian model is sufficient to predict moisture content at the interface of encapsulant and passivated chip.
Lead-Free Nanomaterials for Electronics: In electronics manufacturing, lower solder reflow temperature is desirable to prevent manufacturing problems such as popcorning, delamination and warpage. On the other hand, during operation, especially in high temperature application such as aerospace and military electronics, the solder joint must withstand high temperatures and maintain high reliability. This poses a converse set of goals, namely, low manufacturing melting point and high operation melting point, which cannot be achieved with bulk solder joint materials. Alloy nanoparticles offer a unique combination of low and high melting temperature. We have shown that AuSn nanoparticles have significantly reduced melting temperature for manufacturing. As the particles melt and form solder joint, they can recover the high bulk AuSn melting point making them suitable for high temperature and high reliability electronic applications.