Experimental Characterization of Monotonic and Fatigue Delamination of Novel Underfill Materials

No-flow underfill materials reduce assembly processing steps and can potentially be used in fine-pitch flip chip on organic board assemblies. Such no-flow underfills, when filled with nano-scale fillers, can significantly enhance the solder bump reliability, if the underfills do not prematurely delaminate or crack. Therefore, it is necessary to understand the risk of underfill delamination during assembly and during further thermal excursions. In this paper, the interface between silicon nitride $(SiN)$ passivation and a nano-filled underfill (NFU) material is characterized under monotonic as well as thermo-mechanical fatigue loading, and fracture parameters have been obtained from such experimental characterization. The passivation-underfill interfacial delamination propagation under monotonic loading has been studied through a fixtureless residual stress induced decohesion (RSID) test. The propagation of interfacial delamination under thermo-mechanical fatigue loading has been studied using sandwiched assemblies and a model for delamination propagation has been developed. The characterization results obtained from this work can be used to assess the delamination propagation in flip-chip assemblies. Though the methods presented in this paper have been applied to nano-filled, no-flow underfill materials, their application is not limited to such materials or material interfaces.