Characterization of Silicon Die Strength with Different Die Backside Unevenness Location

Abstract

Development of mircoelectronic packages are always moving towards smaller and thinner. This is in conjunction of consumers need for mobile and wearable electronic gadgets. In order to achieve this, beside improvements in packaging technologies silicon die had to be smaller and thinner too. However thinner packages increase the challenges of package stress and thinner silicon chip becomes more susceptible to process related weakness especially at the front-end processes. Silicon die strength is an important parameter to ensure the packing reliability under stringent conditions. The strength of silicon wafer is heavily influenced by the die thickness and wafer the backside surface preparation prior to metal deposition. Stresses induced in the silicon die throughout the process of wafer processing, packaging and die assembly. Small flaws such as small micro cracks or uneveness can occur during backside processes causing the strength of the Silicon die to decrease and cause failure at early stage of packaging process or even reliability concern. This paper investigated the effect of die strength to the surface morphology using 3 point bending test and 3D Laser Measuring Microscope. The die strength was characterized using 3 point bending test while surface morphology was characterized using 3D Laser Measuring Microscope. The evaluation was performed with silicon die singulated from wafers of unevenness at wafer backside. The silicon die was then categorized into 4 different types by unevenness location, 1) unevenness through complete die in x-direction, 2) unevenness through complete die in y-direction 3) unevenness at the middle of die, 4) unevenness at the edge of die. Silicon die strength of 4 different type of location of unevenness was being measured using 3 point bending test. The result showed that the depth of unevenness was not the main factor of low die strength. Unevenness location at the die is the main factor of low die strength. Die strength with unevenness at the edge of die having the lowest strength.