Experimental Evaluations of the Strength of Silicon Die by 3-Point-Bend Versus Ball-on-Ring Tests

Abstract

Silicon wafers and dies are made of single crystalline material in semiconductor applications which must withstand high stresses within electronic packages. The apparent mechanical strength of single-crystalline Si depends on process induced defects. Mechanical bending tests are the simplest way to obtain the strength of Si dies and wafers and have been used for many years throughout the industry. Some of the bending tests, such as the 3-point-bend (3PB) test, provide a convoluted contribution from both the defects on die surface (caused by backgrinding and mishandling) and defects on die edges (caused by sawing or dicing). However, the ball-on-ring (BOR) test provides a way to single out the contribution of backside grinding defects to the die strength. This paper compares the results of both 3PB and BOR tests on a number of backgrinding and dicing processes. The die strength of the 3PB test is consistently less than that of the BOR test due to the fact that the edge defects are under tension for 3PB tests but not for BOR. It is demonstrated that the BOR test is a good method for backgrinding process optimization. Due to the intrinsic scattering nature of the strength data, a Weibull-based probabilistic mechanics approach is the method of choice to present the data.