A Comparison of Biaxial Bending Strength of Thin Silicon Dies in the BoR and PoEF Tests

Abstract

This paper aims to demonstrate the biaxial bending strength test on thin silicon dies using the classic ball-on-ring (BoR) test, and discuss it in detail by comparing those results with the newly-proposed point load on elastic foundation (PoEF) test. The geometric linear and nonlinear solutions to the BoR test are reviewed and also provided with theoretical and numerical formulations, respectively. Three different thicknesses (t = 42 μm, 57 μm and 82 μm) of the thin silicon dies (with a size of 10 mm × 10 mm) are tested in the BoR test, and their bending strengths, load-displacement curves and failure modes are presented and thoroughly discussed with a comparison of the published data from the PoEF test. It is found that, for the bending strengths of 57 μm and 82 μm-thick dies, the data from both the BoR and PoEF tests are very consistent, but not for 42 μm-thick dies with a relatively lower value in the BoR test. This lower strength value in the BoR test is attributed to the more pronounced local buckling effect than the PoEF test. Based on that, it can concluded that the PoEF test is better and more reliable than the conventional BoR as for testing the ultra-thin silicon dies, even though both tests are identical for the regularly thin dies.