| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系 === 103 === Gold wire bonding is one of the oldest and most mature process due to its high yields and low processing costs. However, Kirkendall effect in Au/Al interface has been an important issue in gold wire bonding process. With slower IMC layer growth and cheaper cost, copper wires have recently been reckoned as a candidate. However, the oxidation and strong mechanical property shortened the applications. In addition to copper wires, silver wires have the best electric and thermal conductivity, but they have problem in their humidity corrosion, electrolyte migration phenomena and Kirkendall effect.
In this study, we focused on Ag/Al and Ag-Au/Al intermetallic compounds (IMCs) analysis using Ag-3Pd and Ag-8Au-3Pd wires. SEM, EDS and EBSD techniques were applied to characterize the IMC layers at the bonded interfaces, the chemical composition and structures analysis of IMCs after HTST and HAST reliability aging tests.
The IMC average thicknesses was measured 1.6 μm in Ag-3Pd wires and 2.52 μm in Ag-8Au-3Pd wires after HTST 2000 hours. We can clearly determine the tendency of IMC growth in Ag-3Pd and Ag-8Au-3Pd wires respectively. The kinetics parameter n, no matter in HTST or HAST, were calculated to be 0.093 and 0.123, which were diffusion controlled reactions in Ag-8Au-3Pd wires; 0.604 and 0.642, which were diffusion-reaction mixed mechanism in Ag-3Pd wires. We found cracks formed in Ag-8Au-3Pd wires after HTST 500 hours earlier than those in Ag-3Pd wires after HTST 1000 hours.
Based on what we observed in IMC thicknesses evolution and cracks formation, by comparing the differences between silver alloy and copper wires, thicker IMCs were found in silver alloy wires, which will provide better bondabilities. At last, we found Ag-3Pd wires to be the best wire materials of all.
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