Fatigue behavior of Au, Cu and PCC fine wire bond connections for power LED applications

Abstract

One of the main reliability issues in power LED devices is the bond wire connection due to wire neck breakage. Time consuming thermal cycling or thermal shock tests are the standard testing methods to evaluate this lifetime. Furthermore numerical or simulation methods are used as a convenient and fast substitution, but accurate reliability and lifetime material models are difficult to obtain. For this purpose, a mechanical fatigue testing system was designed to induce mechanical stresses to the critical region of the bond wire connection above the ballbond to expedite fatigue cracks at this bottleneck. The purpose is to induce similar fatigue failure mode as during thermal tests. The experimental investigations are carried out on Au, Cu and Pd-coated Cu bonding wires with a diameter of 25 μm using low and high frequency excitation. The obtained lifetime of the wire bond ranges from 100 - 1 000 000 cycles. The proposed testing method provides material lifetime data in a very short period of time with minimal sample preparation. Finite element simulations were conducted to quantify the stresses at the wire neck which allows a comparison to conventional testing methods, operation conditions fatigue test comparisons, material models and design evaluations of fine wire bond reliability in LED and microelectronic packages.