An Experimental and Numerical Investigation Into Wafer Probing Parameters Based on Thin Wafer Breaking Strength

Abstract

Mechanical contact caused using excessive probe force produces an oversized scrubbing mark that may result in damage to the die pad and the silicon chip breaking for thin wafer. Therefore, investigating the relationship between the wafer thickness and the limited breaking stress of the wafer, and applying this relationship as a basis for establishing suitable design rules for a multilayer needle layout are crucial. In this paper, two experimental techniques, three-point-bending test and ball-on-ring, were setup and carried out to measure the forcedisplacement relation of various wafer thicknesses (100-25 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. In addition, experimental setup with a single tungsten needle probe contact with Al pad were employed to investigate the relations between the overdrive, beam length, and scrub mark length. A 3-D computational probing simulation model was developed and verified against the experimental data. The model is then used to examine the effects of the beam length, overdrive distance (OD), and shooting angle on the maximum stress induced within the wafer. Finally, a four-layer probe card needle shape design has been demonstrated as a practical application example; it is shown that for a wafer thickness of 25 µm and an OD of 60 µm, the allowable shooting angles of a four-layer needle probe card are as follows: 1500 µm and 0°-4°(Layer 1); 2100 µm and 0°-9°(Layer 2); 3500 µm and 0°-15°(Layer 3); and 4000 µm and 0°-15°(Layer 4).Index Terms-Finite-element method (FEM), thin wafer strength, wafer probing test. . His current research interests include multiscale computational methods, electronic packaging failure modes analysis, microforce testing methods, and structural design in precision machines.Zi-Hau Chen received the B.S. degree from Chung Hua University, Hsinchu, Taiwan, in 2008. He is currently pursuing the Ph.D. degree with the His current research interests include finiteelement simulation, mechanical modeling for electronic package and precision machine tools, and microforce testing methods. Chi-MinChang received the B.S. degree from Cheng Kung University, Tainan, Taiwan, in 2003, and the Ph.D. degree in mechanical engineering from National Chung Cheng University, Chiayi, Taiwan, in 2011.His current research interests include TIM evaluation, miniature specimen testing methods, and epoxy probe card geometry analysis and design layout using experimental, finite-element, and mechanical methods.