Effect of (Ni, Au)(3)Sn-4 growth on the thermal resistance of Au-20 wt% Sn solder/ENIG joint in flip-chip LED packages

Abstract

In this study, the effect of growth of intermetallic compound (IMC) layer between Au-20 wt% 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)(3)Sn-4 that were identified using a transmission electron microscopy. A thermal aging test was carried out at 200 degrees C for 1000 h to observe IMCs growth. After 1000 h, the (Ni, Au)(3)Sn-4 thickness increased to about 1.5 mu m and the thermal resistance of the FC LED package increased by 3.5 times compared to the initial thermal resistance of 2 K W-1. As the (Ni, Au)(3)Sn-4 grew, a calculation of thermal resistance also increased comparing to the initial aging test, thus, the growth of (Ni, Au)(3)Sn-4 layer can be effective factor on the increase of thermal resistances of FC LED package.