Phase identification on the intermetallic compound formed between eutectic SnIn solder and single crystalline Cu substrate

• Reflowing at 160 °C Cu(In,Sn)2 and Cu2(In,Sn) were formed on single crystalline Cu.
• Large Cu(In,Sn)2 grain has tetragonal crystal structure with chunk-type morphology.
• Cu(In,Sn)2 layer is prone of spalling into solder in liquid soldering process.
• Cu2(In,Sn) is made up of fine and coarse sublayers with hexagonal crystal structure.
• Fine Cu2(In,Sn) grain has granular morphology and coarse one is elongated.

The intermetallic compound (IMC) formed between eutectic SnIn solder and single crystalline Cu substrate during reflow and solid-state aging was investigated precisely utilizing electron microscope. Two kinds of crystal structures with different morphologies were identified, which are Cu(In,Sn)2 at the solder side and the Cu2(In,Sn) at the Cu substrate side. The Cu(In,Sn)2 layer with chunk-type morphology suffered spalling easily during slightly increased liquid soldering at 160 °C, and Cu2(In,Sn) was in the form of duplex structure with coarse-grain and fine-grain sublayers. During solid-state aging at 60 °C, the morphology of fine-grain Cu2(In,Sn) kept granule-type, while that of the coarse-grain Cu2(In,Sn) was substrate-dependent with elongated morphology.

Two kinds of intermetallic compounds were formed in three sublayers during interfacial reaction between eutectic SnIn solder and single crystalline Cu substrate, which are Cu(In,Sn)2 layer with tetragonal crystal structure at solder side, coarse-grain Cu2(In,Sn) sublayer and fine-grain Cu2(In,Sn) sublayer with hexagonal crystal structure at Cu side.Figure optionsDownload as PowerPoint slide