New equivalent stress describes the dicing caused anisotropic breaking strength of silicon dies

Due to increased demands, reliability has become an important part of the research and development on electronics, in the last years. An important reliability factor is failure due to chip fracture. In several scientific papers three types of chip fracture are described: vertical cracks, horizontal cracks and mixed cracks. Till now, all approaches to explain the relations of these crack types have based on the deterministic fracture mechanics. But especially for statistical process control, it is better to use a probabilistic fracture mechanic based on the Weibull distribution. In the present work damages caused by the dicing were analyzed by means of SEM-pictures. A special type of crack was found. Such cracks have a preferred orientation which is parallel to the dicing feet direction. The influence of those cracks on the breaking strength of silicon chips was investigated. The results showed a kind of dicing caused anisotropic breaking strength. This means the fracture relevant die strength depends on the local orientation of the stresses which acts on the chips. To detail this phenomenon a new equivalent stress was develop, which offers to directly compare stresses by means of theirs impact to fracture.