An Innovative Way to Improve the Reliability of Gold Wire in Lighting Emitting Diodes (LEDs)

As the most promising candidate for the realization of high-efficiency light sources for general lighting, the high power lighting emitting diodes (LEDs) still have reliability issues that hinder the large scale application of LED devices, Nowadays, the reliability is becoming an essential barrier for LED devices to substitute the traditional light sources, Before it is applied into mass production, many kinds of experiments under harsh conditions should be done to predict its reliability, Among those factors affecting LED's reliability, fractures in the gold wire cannot be underestimated, Gold wire is often used for providing an electrical interconnection with outside power, while after some typical package reliability tests, such as the thermal cycling and thermal shock tests [3], there are fractures at two critical zones, the second bond and neck of the first bond, It is confirmed that the failure is mainly caused by the coefficient of thermal expansion (CTE) mismatch between gold and other materials and the large deformation of the silicone enclosing the gold wire. Many approaches have been tried to enhance the reliability of gold wire, few of them have studied whether the wire loops have influences on the reliability of LEDs, In this paper, reliability of both traditional wire loops and innovative wire loops are evaluated by transient thermo-mechanical finite element modeling (FEM) under thermal shock loadings. The Von Mises stress at the neck of first bond zone and the second bond zone are examined, which indicate the Von Mises stress at the neck of the first bond zone of the innovative wire loops is lower than the stress at the traditional wire loops. However, the stress at the second bond zone almost keeps the same. Then, a cooper ring is applied around the silicone lens, and finite element modeling results show that the cooper ring can reduce the stress at the second bond zone remarkably by suppressing the deformation of the lens near the second bond zone, and the higher the cooper ring is, the lower the stress at the second bond is. Finally, an optimal copper height is present by optical simulation. These efforts are helpful for design of high reliability high power LEDs.