An improved methodology for determining temperature dependent moduli of underfill encapsulants

Finite element analyses (FEAs) have been widely used to preventively predict the reliability issues of flip-chip (FC) packages. The validity of the simulation results strongly depends on the inputs of the involved material properties, For FC packages Young's modulus-temperature relationship is a critical material property in predicting of the package reliability during -55 degrees C to 125 degrees C thermal cycling, Traditional tensile tests can obtain the modulus at-selected temperatures, but it is tedious, expensive, and unable to accurately predict the Young's modulus-temperature relationship within a wide temperature range. Thus, this paper is targeted,to provide a simple but relatively accurate methodology to obtain the Young's modulus-temperature relationship. In this paper, three commercial silica filled underfill materials were studied, A simple specimen (based on ASTM D638M) preparation method was established using a Teflon mold. A dynamic-mechanical analyzer (DMA) was used to obtain the stress-strain relationship under controlled force mode, storage and loss modulus under multi-frequency mode, and stress relaxation under stress relaxation mode, A simple viscoelastic model was used and an empirical methodology for obtaining Young's modulus-temperature relationship was established.