In this study, a three point bending test is used to determine how the susceptivity of large chips to brittle fracture correlates with chip thickness and backend process quality. Four sets of wafer backend processes, including the commonly used mechanical grinding, were used in this experimental work. In the mechanical grinding process, chip strength was more significantly influenced by the geometry of the machine mark than by the depth of the scratched groove. This experimental result indicates that a limitation exists in the enhancement of the mechanical stability of Si chips by the control of chip thickness because cracks in chips have a tendency to seek out deep scratches rather than typical flaws. Therefore, the mechanical instability associated with increasing chip size should be compensated for by optimization of the backlap process.