Determination of LED die strength

LED (Light Emitting Diode), converting the electron current into the light through the p-n junction of semiconductor diodes, has recently gained popularity worldwide. The high-power LEDs are found in a number of applications to high-volume consumer markets, such as illumination, signaling, screen backlights, automotives and so on. In these applications, the high-power LED packages would be subjected to mechanical, thermal, and environmental loadings during manufacturing processes and services. The strength of LED dies, cut from wafers, has to be determined for the design need in order to assure good reliability of the packages in manufacturing and service. The objective of this study is to determine high-power LED die strength with size of 1 times 1 times 0.1 mm by point-load test (PLT) and line-load test (LLT) associated with a plate-on-elastic-foundation configuration. The finite element analysis and the related stress formulation are used to correlate the failure force of the tests to die strength. It is found that the good consistency of the strength data (~1.3 GPa) with a minor scatter from both the point- and line-load tests is for the specimens failed on chip surfaces, but not for the ones (-1.2 GPa and -0.6 GPa, respectively) failed on the ground surfaces. The inconsistency of strength data from both tests for failure on ground surfaces is found due to edge chipping, observed by scanning electron microscopy. As a result, it can be confirmed that the LED die strength has been successfully determined by these feasible and reliable test methods.