Effect of (Ni, Au)3Sn4 growth on the thermal resistance of Au-20 wt% Sn solder/ENIG joint in flip-chip LED packages

In this study, the effect of growth of intermetallic compound (IMC) layer between Au-Sn solder and electroless Ni/immersion Au (ENIG) on the thermal resistance of a flip-chip (FC) light emitting diode (LED) package was investigated. Two IMC layers were formed at the interface of FC LED package, including Au5Sn and (Ni,Au)3Sn4 that were identified using a transmission electron microscopy (TEM). A thermal aging test was carried out at 200 °C for 1000 h to observe IMCs growth. After 1000 h, the (Ni,Au)3Sn4 thickness increased to about 1.5 µm and the thermal resistance of the FC LED package increased by 3.5 times compared to the initial thermal resistance of 2 K/W. As the (Ni,Au)3Sn4 grew, a calculation of thermal resistance also increased comparing to the initial aging test, thus, the growth of (Ni,Au)3Sn4 layer can be effective factor on the increase of thermal resistances of FC LED package.