Microcontact Spring Reliability: Design Against Interfacial Fracture

The microcontact spring technology, based on stress-engineered thin film strips, is a potential solution to the International Electronics Manufacturing Initiative (iNEMI) forecasted flip chip die-to-package interconnect requirements. Preventing interfacial fracture due to monotonic loading during fabrication of these springs is one primary issue to ensure its reliability. This work applies a combined analytical and experimental framework to examine the interfacial integrity of microcontact springs, which are a form of thin film cantilevered plates. An analytical model, based on nonlinear plate theory, is discussed and validated for its use as a tool for predicting structural reliability in thin film cantilevers (i.e., microcontact springs). Further application of the plate theory is used to understand design guidelines of the microcontact spring to minimize delamination and to understand the impact of bifurcation of curvature on delamination. Finally, experimental interfacial fracture toughness data, based on the results of a modified decohesion test (MDT), are discussed and applied to create a design map for microcontact spring fabrication. Although this work is being applied to the application of microcontact springs, most of the trends are generic to any intrinsically stressed film plate.