Reliability assessment of contact wires in LED-devices using in situ X-ray computed tomography and thermo-mechanical simulations

The demand for high performance white light LED devices for general illumination systems increases continuously. However, high illumination performance also implies higher thermo-mechanical stresses on the LED device and could lead to changes in quality parameters of the device like color stability, efficiency and of course a decrease in lifetime. This paper investigates the thermo-mechanical interaction of wire bonds with the surrounding embedding compound. A new method using X-ray computed tomography (XCT) in combination with a heating/cooling stage is applied to investigate the temperature-dependent displacement of wire bonds embedded in a phosphor converted (pc) material. The displacement of the wire within the device due to an increase of temperature from room temperature (RT) to 150°C is measured by using a nominal-actual comparison procedure. Finite element (FE) based simulations are performed in order to determine the thermo-mechanical behavior of this micro-assembled LED system subjected to different temperature profiles. The results obtained from the in situ XCT experiments and simulations are compared to each other and it is shown that there is a significant correspondence.