TEM Observation of Interfacial Reaction Layers Formed Between Pb(Lead)-Free Sn-3.5Ag Solder and ENIG Plated Cu Substrate

摘要

The interfacial reaction between eutectic Sn-3.5Ag solder and ENIG substrate during reflow was investigated. During the reflow, the topmost Au layer dissolved into the molten solder, and the reaction layers of Ni_3Sn_4/Ni-Sn-P/Ni_3P formed between Sn-Ag solder and Ni-P plating layer. After the reflow at 255°C for 3 min, most of Ni_3Sn_4 intermetallic compound (IMC) spalled off the substrate. The formation of thick Ni_3P and Ni-Sn-P layers was related to the direct reaction between solder and Ni-Sn-P layer by the IMC spalling.