Effect of protection atmosphere's temperature on morphology of Au-Sn IMCs in laser reflowed micro-solder joints

Abstract

Formation of AuSn x IMCs in laser reflowed solder joints protected by N 2 atmosphere at room temperature, 60℃, 100℃ and 130℃ was investigated respectively. The solder balls were Sn-2.0Ag-0.75Cu-3.0Bi, and 120μm in diameter. The surface finish of one pad in the solder joints was 4.0μmAu/0.1μmNiFe/0.01μmTa, the other pad was made of Cu plated with 3.0μm thickness of Au. The laser reflow time was within 10ms. AuSn 4 IMCs and Au-riched phases formed at the interfaces of solder and pads, the AuSn 4 was needle-like in morphology in the solder joints protected by N 2 atmosphere at room temperature. As the temperature of N 2 atmosphere was increased to higher than 100 ℃, almost all of the Auriched phases disappeared, more needle-like AuSn 4 IMCs formed at the interface, and orientation of the IMCs changed obviously as compared with that in the solder joints protected by N 2 atmosphere at room temperature. The results indicated that the temperature of protection atmosphere would affect the Au-Sn interfacial reaction in the solder joints fabricated by laser reflow process evidently, even the reflow time was shorter than 10ms. Therefore, by regulating the temperature of protection atmosphere, we may control the morphology of Au-Sn IMCs in the laser reflowed micro-solder joints, and achieve solder joints with good properties.