Thin wafer probe breaking strength testing using microforce tester

A probe (needle) card is conventionally used in wafer-level test to check defects in Integrated Circuit. A stable contact resistance must achieve when each probe contacting with bonding pad. Mechanical contact using excessive probe force will cause over sizing scrubbing mark that may lead to damage of die pad as well as breaking of silicon chip for thin wafer. This damage of thin wafer can adversely influence the quality of the following assembly process and more costs by reducing bond and assembly yield. To support probe shape design and realize the relationship between the testing condition and the thin wafer strength, specialized experimental methods and tools must be developed to carry out thin wafer breaking strain/stress. In this paper, newly developed Three-Point-Bending test were set up and carried out to measure the force-displacement relation of various wafer thickness (100 μm - 25 μm). The results from the testing then coupled with finite element analysis to reverse finding the breaking stress/strain as a function of wafer thickness. The result, from this research can support the engineer to design better probe geometry shape and choose wafer testing conditions.