Interfacial Reaction And Reliability In Lead-free Electronics Packaging

With the impending lead-free transition, various materials are being introduced into lead-free electronics package. The interfacial reactions become more complex, which have important effects on the reliability of lead-free interconnections. The interfacial reactions and reliability of lead-free solder joints are systematically investigated in this thesis.The liquid and solid-state reactions between SnAgCu solder and Cu-based lead frame alloys were investigated. The effects of trace additive elements in Cu-based alloys on the formation and growth of intermetallic compounds (IMCs) were studied. The results revealed that (Cu,Ni)₆Sn₅ ternary IMCs formed with the use of Ni-containing Cu-based alloy. The morphology of (Cu,Ni)₆Sn₅ IMCs became more planar compared to typical scallop type Cu₆Sn₅ in other Cu-based alloys. Cu3Sn phase was inhibited by the nickel but accelerated by tin additive in the alloy.The liquid and solid-state reactions in real solder joints were investigated. A coupling effect between the two interfaces was observed when different surface finishes were employed at the two sides in real solder joints. The metal atoms tend to diffuse to the opposite interface and joined in the interfacial reaction, resulting in the formation of ternary IMCs. The morphology, composition and thickness of IMCs were affected by materials at both interfaces. The consumption of metallization was also greatly influenced by the coupling effect. In a sandwich structure of Cu/SnAgCu/Ni, the consumption of Cu was very much enhanced while the consumption of nickel layer was greatly reduced by the coupling effect. The findings are valuable to the design and assessment for the reliability of solder joints.The reliability of lead-free interconnections between TSOP (with FeNi 42 alloy terminations) and PCB with different finishes (OSP, ENIG) were investigated under board level drop test and temperature cycling. Under drop test, the interconnections with ENIG finishes on PCB outperformed the OSP counterpart. Three-times reflow showed positive effect while high temperature aging showed negative effect on the solder joint lifetime. While under temperature cycling, the interconnections with OSP finishes revealed a better...