Suppressing Ni–Sn–P growth in SnAgCu/Ni–P solder joints

The interfacial morphologies for SnAgCu/Ni–P with various phosphorous contents were investigated by electron microscopy. The initial formation of the phosphorous-rich phase in Ni–P under-bump metallizations (UBMs) was dependent on phosphorous content, i.e., Ni3P for Ni–7 wt.%P UBM and Ni12P5 for Ni–13 wt.%P UBM. Different NixPy phases significantly affected the subsequent Ni–Sn–P formation. The growth of Ni–Sn–P could be thus controlled by altering the phosphorous content of the Ni–P UBMs. Therefore, an approach to suppress Ni–Sn–P formation is proposed.