LED flip-chip assembly with electroplated AuSn alloy

InGaN based high brightness (HB)-LED chips have been fabricated and bonded to substrates that were coated with electroplated Au/Sn/Au solder. The assemblies yielded a forward voltage of 5.6 V and an optical output power of 42 mW when tested at 1,000 mA bias. The electroluminescence distribution was mapped with a CCD camera to determine the current spreading into the p-contact region. Computational fluid dynamics (CFD) was used to check the effect of non-uniform current spreading on the thermal resistance of the assemblies. We show that a good knowledge of the non-uniform heat generation is required to obtain accurate modelling results. The bond strength of the AuSn solder joints exceeded the norm, when shear tested according to MIL-STD-883E (method 2019.5).