| Summary: | 碩士 === 國立中興大學 === 化學工程學系所 === 101 === The trend of electronic products development is toward lighter, thinner, smaller, multi-fuctional, and lower cost with advanced technology. When the volume continuously shrinks, the solder joints in electronic products must have better reliability. In recent years, due to the environmental concerns, not only the packaging industry but the academic institutes aggressively search for other lead-free solders to substitute the conventional eutectic SnPb solder. However, the disadvantage of lead-free solders is the more Sn content, so it will cause excessive intermetallic compound growth and consume the under bump metallurgy at a faster rate. The interfacial reactions between pure tin and electroplated copper substrates fabricated using different formulas were investigated in this thesis.
PCS, PCSV, and PC represented the three different electroplated Cu substrates, respectively. The grain size of PCS was the largest and PC was the smallest. The results showed that PCS and PCSV formed prism Cu6Sn5 after reflow for 90s and the Cu6Sn5 grains would align regularly in air-cooling condition. The morphology of Cu6Sn5 tranformed to scallop after reflow for 600s. The PC-formed Cu6Sn5 didn’t presented specific texture and there were many voids existing on the Cu6Sn5 surface. In the icewater-cooling condition, the Cu6Sn5 phase formed on the three substrates had finer grains and didn’t present specific texture. In the reflow process, the IMC thickness didn’t have significant differences for the three cases. In addition, the reaction orders of three cases were about 0.33, indicating that the kinetics of IMC growth belonged to grain boundary diffusion.
The Cu6Sn5 and Cu3Sn phases were formed at the Cu/Sn interface at 150, 170, 200°C. The Cu6Sn5 grains became bigger with aging time and increasing reaction temperature. The IMC formed by PCS and PCSV could grow more stablely. However, because the Cu3Sn formed by PC would produce many Kirkendall voids, these voids would restrain the Cu diffusion and then induced secondary IMC formation. At 150°C, this mechanism wasn’t obvious but it could be observed complexed and multi-layered IMC structure after aging for 600 hrs at 170°C. The multi-layered IMC structure also could be found after aging at 200°C for 72 hrs. The mechanism of Kirkendall-voids- induced secondary IMC formation would form large IMCs and had bad influence on the solder joints reliability.
|
|---|
