Effect of Electromigration-Induced Joule Heating on the Reliability of Sn-Ag Microbump with Different UBM Structures

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Journal of Electronic Materials

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The effect of current stress-induced Joule heating on two different under-bump metallization (UBM) structures in Sn-Ag microbumps was investigated with current stressing at 150°C and a current density of 5 &!thinsp;× 104 A/cm2. Both Ni UBM and Cu UBM configuration microbump structures underwent extensive electromigration (EM) testing, with results revealing a longer lifetime with the Cu UBM configuration than the Ni UBM structure. The observed EM failure mechanism in the Ni UBM configuration was identified as a void formation within the bump interconnected Al trace and not due to damage accumulation inside the microbump structure. The intermetallic compound developed inside the microbump was formed and maintained its stability throughout the current stressing period. To identify the main driving force of damage accumulation in the Al trace, the current density and temperature distributions in the Sn-Ag microbumps were analyzed numerically via the finite element method. The simulation results showed higher Joule heating with the Ni UBM than the Cu UBM microbump configuration, along with the bump geometrical contribution of add-on higher Joule heating in the Ni UBM microbump structure.


2020 The Minerals, Metals & Materials Society



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