| Summary: | 碩士 === 國立高雄第一科技大學 === 機械與自動化工程所 === 95 === The aim of this paper is to investigate the electromigration effect on lead-free solder joints under conditions of different temperature and current density. Samples were combined with 99.3Sn-0.7Cu/96.5Sn-3Ag-0.5Cu composite flip-chip solder bump and Ti/Ni(V)/Cu under bump metallurgy. Substrate pad metallization were chosen as Au/Ni/Cu or Cu samples were tested at three different current densities, 5kA/cm2, 10kA/cm2and 15kA/cm2, and three temperature 150℃、160℃、125℃ to understand the electromigration reliability and IMC reactions conditions.
It is found that, characteristic life of samples with SOP pad were longer than that of with NiAu pad under conditions of 10kA/cm2-160℃. However, with conditions of 5kA/cm2-150℃, 10kA/cm2-150℃, and 15kA/cm2-125℃, characteristic life of samples with NiAu pad were longer than that of SOP pad.
For the failure mechanism, electromigration-induced UBM and IMC dissolution caused by current density was been addressed as main reason that resulted in voids formed in these interfaces and leaded to final failure.
As for the interface interaction, current density would only affect the thickness of IMC, but not influence the phase compositions. Co-existence of two phase IMC was also observed after long term aging test. Cu6Sn5 and Cu3Sn were identified at interfaces of the samples combined with SOP pad substrate and would accumulate at anode by electron flow. Nevertheless, (Cu,Ni)6Sn5 and Ni3Sn4 were formed for samples with NiAu pad at chip and substrate side, respectively. As test went on, (Cu,Ni)6Sn5 IMC would accumulate at anode caused by electron flow, but Ni3Sn4 rarely migrated with electron flow.
Keywords: flip-chip packaging, lead-free solder, joint, electromigration, solder bump, imtermetallic compound, IMC, exposure, under bump metallization, UBM, current crowding, pad, characteristic life, reliability.
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