Intermetallic Compound Formation in Sn-Co-Cu, Sn-Ag-Cu and Eutectic Sn-Cu Solder Joints on Electroless Ni(P) Immersion Au Surface Finish After Reflow Soldering

Journal article, 2006

The interfacial reactions between Sn-0.4Co-0.7Cu eutectic alloy and immersion Au/electroless Ni(P)/Cu substrate were investigated after reflow soldering at 260 °C for 2 min. Common Sn-4.0Ag-0.5Cu and eutectic Sn-0.7Cu solders were used as reference. Two types of intermetallic compounds (IMC) were found in the solder matrix of the Sn-0.4Co-0.7Cu alloy, namely coarser CoSn 2 and finer Cu 6 Sn 5 particles, while only one ternary (Cu, Ni) 6 Sn 5 interfacial compound was detected between the solder alloy and the electroless nickel and immersion gold (ENIG) coated substrate. The same trend was also observed for the Sn-Ag-Cu and Sn-Cu solder joints. Compared with the CoSn 2 particles found in the Sn-Co-Cu solder and the Ag 3 Sn particles found in the Sn-Ag-Cu solder, the Cu 6 Sn 5 particles found in both solder systems exhibited finer structure and more uniform distribution. It was noted that the thickness of the interfacial IMCs for the Sn-Co-Cu, Sn-Ag-Cu and Sn-Cu alloys was 3.5 μm, 4.3 μm and 4.1 μm, respectively, as a result of longer reflow time above the alloy's melting temperature since the Sn-Ag-Cu solder alloy has the lowest melting point. © 2006 Elsevier B.V. All rights reserved.