| Summary: | 博士 === 國立中山大學 === 材料與光電科學學系研究所 === 104 === For lower cost considerations, copper wire bonding has been applied in IC packaging in recent years. In this study, the intermetallics(IMCs) formed, growth and crack development were examined to evaluate the reliability of several copper wires with/ without wire surface coatings.In this study, the reliability tests include HTST, PCT, and TCT. The wire types are the 0.7 mil 4N copper wires, the Palladium coated-Copper (Pd-Cu) wires, and Au-Pd-plated copper wires. And there are three substrate types with the aluminum pad thickness of 1.6/2.8/4 micrometer. For the HTST test samples, two aging temperatures, 175℃and 205℃ were applied and the aging periods from 150 hrs to 2000 hrs. The microstructure of micro joints are cross-sectioned and examined under an electron microprobe to verified the formed intermetallic phases for the samples tested in various aging periods. The samples under PCT and TCT tests are examined for the corrosion and crack formation behavior. The formation of IMCs, Cu9Al4, CuAl and CuAl2, which are main compounds formed in copper wire bonding micro joints. The Al-rich phase (CuAl2) has high priority, and the second phase(Cu9Al4) appear on the interface near the copper wire side. After long period aging, the Cu-rich phase(Cu9Al4) expected to form when Al pad be consumed. However, in the thicker Al pad cases, the Cu9Al4 phase will be replace by the first phase(CuAl2) finally. The results also show that, the kirkendall voids accumulate and form cracks in the bonding micro joint, and therefore make the micro joint fail. The intermetallic formation sequences of different wire types are shown for a comparison.The second part of study is about Ag wire bonding process. Ag wire has good electric conductivity, thermal conductivity, high current withstand capacity, and easy to store. However, compared to Au-Al wire bonding system, it is not enough to understand Ag-Al-Au phase diagram and the intermetallic formation of Ag-alloy wire bonding. This study of Ag wire can provide more information about diffusion paths and phase identification of Ag-Al-Au ternary system in the lower temperature.
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