Study on short time interfacial reactions between Sn-3.0Ag-0.5Cu solder balls and ENEPIG pads

摘要

Short time interfacial reactions between Sn-3Ag-0.5Cu solder balls and ENEPIG pads at 250 °C were investigated. Transitions in morphology and type of the interfacial intermetallic compounds (IMCs) with reaction time were revealed. It was found that the transition rate of the interfacial IMCs in smaller solder joints was faster than that of larger ones. For 200 µm solder joint, dodecahedron type (Cu,Ni)6Sn5 grains together with brick type (Ni,Cu)3Sn4 particles first formed at the interface. Then (Ni,Cu)3Sn4 grew up rapidly with (Cu,Ni)6Sn5 particles submerged and even disappeared in the weed shape (Ni,Cu)3Sn4. For 300 µm solder joint, hexagonal prism (Cu,Ni)6Sn5 particles with pointed tips firstly formed at the interface. Then the particles quickly transformed to polyhedron type IMC within the following few seconds. Thereafter, with the interfacial reaction kept going, (Ni,Cu)3Sn4 needles grew up from the interspaces of (Cu,Ni)6Sn5 particles. It is convinced that the change of Cu concentration in the solder balls is the main reason causing the IMCs transformations.