Effects of Substrate Metallization on Solder/Under-Bump Metallization Interfacial Reactions in Flip-Chip Packages during Multiple Reflow Cycles

摘要

The effects of various elements of substrate metallization, namely, Au, Ni, and P, on the solder/under-bump metallization (UBM), (Al/Ni(V)/Cu) interfacial reactions in flip-chip packages during multiple reflow processes were systematically investigated. It was found that Au and P had negligible effects on the liquid-solid interfacial reactions. However, Ni in the substrate metallization greatly accelerated the interfacial reactions at chip side and degraded the thermal stability of the UBM through formation of a (Cu, Ni)_6Sn_5 ternary compound at the solder/UBM interface. This phenomenon can be explained in terms of enhanced grain-boundary grooving on (Cu, Ni)_6Sn_5 in the molten solder during the reflow process. This could eventually cause the rapid spalling of an intermetallic compound (IMC) from the solder/UBM interface and early failure of the packages. Our results showed that formation of multicomponent intermetallics, such as (Cu,Ni)_6Sn_5 or (Ni,Cu)_3Snd_4, at the solder/UBM inter-face is detrimental to the solder-joint reliability.