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Cu wire package reliability failure mechanism and factors including molding compounds
Keywords: Cu wire reliability, Failure mechanism, Molding compounds
Cu wire is drastically replacing Au wire due to surge of Au price. However, Cu wire package has poorer humidity reliability than Au wire package. Crack and corrosion were the root causes for open failure. We used chemical model simulation to predict what kinds of IMC could be created after wire bonding, then which IMC could be corroded more easily during HAST. Desorption energy was used to estimate reactivity between specified Cu/Al IMC and chlorine ion. The simulation suggested that the formation of Cu rich and Cu poor Cu/Al IMCs and the Cu rich IMC was estimated to be corroded by chlorine ion. Furthermore, chemical model simulation for Pd coated Cu wire would be done to explore the effect of Pd existence and distribution of Pd in Cu/Al IMC. We explored the factors of humidity reliability failure for Cu wire packages. As a result, extracted chlorine ion from molding compounds turned to be major factor while pH of extracted water turned to be minor factor through Bias HAST. Some customers defined spec range of 20ppm or below for chlorine ion and 5 to 7 for pH. However, based on our chemical model simulation results, higher pH than 7 could give us further better HAST performance. We try to define appropriate spec range for chlorine ion and pH to pass reliability through bias HAST evaluation. We also discuss impact of other factors such as wire bonding strength, bias, reliability condition and other materials. In addition, we used this chemical model simulation technique to develop superior Cu wire compatible molding compounds with new ion trapper. Bias HAST results with the newly developed material would be discussed.
Hidenori Abe, Engineering manager
Hitachi Chemical Co., Ltd.
Cupertino, CA

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