Evaluating Process Yield for LED Assembly under Undetected Process Parameter Change

Abstract The technology of light emitting diode (LED) assembly has become more popular due to the high demand for LED backlight modules, which can provide desirable characteristics such as a wide color gamut, a high dimming ratio, a long lifetime, and high power efficiency. For LED assembly processes, the distance between LEDs is one of the key parameters because the uniformity of an LED backlight module can be affected by it. In order to obtain good optical performance of an LED backlight module, the process yield of the parameter needs to be controlled well. Conventionally, process yields of LED assembly processes are evaluated using typical capability index methods under the essential assumption that the processes are stable. However, some inevitable process parameter changes regarding the distance between LEDs might exist on the shop floor. In order to evaluate the process yield more accurately, this paper presents an accommodated capability index method for process yield evaluation under undetected process parameter changes. For illustration purposes, an application is presented.