A simple evaluation methodology of Young´s modulus-temperature relationship for the underfill encapsulants

FEA computer simulation has been widely used to 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 the package reliability during -55°C to 125°C thermal cycling. Traditional tensile tests can obtain the modulus at selected temperatures, but it is tedious, expensive, and cannot accurately predict the Young´s modulus-temperature relationship within a wide temperature range. Thus, this paper is targeted to provide a simple but 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 then proposed and an empirical methodology in obtaining the Young´s modulus-temperature relationship was established