Paul F. Bodenweber

Measurements of interfacial strengths in underfilled flip-chip electronic packages using Wedge Delamination Method (WDM)

In this work, a new wedge delamination technique for measurement of interfacial fracture strength is presented. This method can be implemented to assess the interfacial fracture behavior of underfill and silicon in flip-chip packages. Our method offers substantial advantages over traditional interfacial test methods which can be difficult to implement on brittle materials like silicon die. The efficacy of our method for interfacial strength measurements on multiple underfill-silicon interfaces will be shown in this work. A numerical framework for crack kinking at the silicon-underfill interface will also be presented. And finally, results from WDM experiments conducted at room temperature and corresponding numerical analysis will be used to compare the relative fracture strength between underfill and silicon at the flat-face and sidewall of a silicon die.

Modeling and experimental study of thin bond line thermal interface material failure

Thermal delivery has become an even tougher a challenge with the increasing levels of integration, which drives the demand for low bond line thicknesses of the thermal interface materials (TIM) in electronic packages. The low elongation property of thin bond line thermal interface in turn leads to significant complications for reliable electronic packaging. Package encapsulation needs to be carefully designed to handle the thermal expansion mismatch driven stress engendered during the bond and assembly (BA) process and in field operation. In this paper, special attention is paid to the material characterization of the thin bond line thermal interface. As the thickness of TIM is comparable to its filler particle size, the mechanical behavior of the TIM cannot be described by the material properties determined with traditional testing techniques using bulk specimens. To fill this gap, testing coupons are built with the dimensions of field application. A testing technique developed for characterizing the TIM will be discussed. The material properties obtained will be implemented into the commercial finite element codes ABAQUS through its cohesive zone model. Thermo-mechanical modeling to predict the propagation of TIM delamination and model verification will be presented. The impact of TIM tearing on other risks associated with electronics encapsulation will be discussed.