Effects of Thermal Cycling on Material Properties of Nonconductive Pastes (NCPs) and the Relationship Between Material Properties and Warpage Behavior During Thermal Cycling

In this paper, the effects of thermal cycling on material properties such as coefficient of thermal expansion (CTE), modulus, and glass transition temperature (T_g) of nonconductive pastes (NCPs) for flip chip applications were investigated. Using a thermomechanical analyzer, the dimensional changes of NCPs and an underfill material were measured. The dimensional changes of all materials during the first cycle rapidly increased near T_g. However, the rapid increase of dimensional change near T_g was not observed during the second and third cycles. Furthermore, using a dynamic mechanical analyzer, the modulus and T_g were measured. The modulus in the first cycle was smaller than that in the second cycle for all materials. After the first cycle, the modulus curves followed the second cycle curve. Next, the warpage behavior of the flip chip assemblies was observed using the Twyman-Green interferometry method to investigate how material property changes affect warpage behavior during thermal cycling (T/C) and it was found that the warpage of the flip chip assembly decreased after the first cycle. However, after the first cycle, the amount of warpage was constant for the following five cycles. As a result, it was verified that the material properties of NCPs and the underfill material change after the first thermal cycle, and the material property changes are closely related to the warpage hysteresis behavior during T/C. Finally, warpage hysteresis was understood as shear strain.