Role of (111) nanotwinned Cu on dissolution behavior and interfacial reaction in micro-scale nanotwinned Cu/Sn/Ni interconnects

The liquid-solid (L-S) interfacial reaction of the micro-scale Cu/Sn (100 μm)/Ni type interconnect was investigated with (111) nanotwinned Cu (nt-Cu) acting as under bump metallization (UBM) instead of common polycrystalline Cu, and the shear strength and the electric resistance of micro-scale interconnects after soldering reaction for various times were also studied. The dissolution rate of (111) nt-Cu UBM (0.06 μm/min) during the soldering reaction at 250 oC was only one third of that of polycrystalline Cu UBM (0.18 μm/min), and the growth of interfacial IMCs in nt-Cu/Sn/Ni interconnects was effectively suppressed. The growth mechanism on interfacial IMCs in the Cu/Sn/Ni type interconnect was explained by the concentration gradient control (CGC) interfacial reaction model. Even after soldering reaction for 60 min, the shear strength of the Cu/Sn/Ni type interconnect dropped by only 12.3 % if nt-Cu acts as UBMs, compared to 28.1 % if common polycrystalline Cu acts as UBMs; the electric resistance of the Cu/Sn/Ni interconnect increased only 3.3 % if nt-Cu acts as UBMs, compared to 20.3 % if common polycrystalline Cu acts as UBMs. This study will provide the experimental basis and theoretical guidance for the application of newly developed (111) nanotwinned Cu UBMs in advanced packaging and the design of micro-scale interconnects.