Skip to Main Content
The failure mechanisms of Ni/Sn3.0Ag0.5Cu/ENEPIG flip chip solder joint were investigated during EM at 150°C under a current density of 1×104 A/cm2. In as-soldered state, (Cu,Ni)6Sn5 IMCs formed at the both Ni/solder and electroless Ni-P/solder interfaces, and the spalled (Cu0.58Ni0.42)6Sn5 was observed in the solder at the chip side. After aging for 600 h, the interfacial IMCs at the both Ni/solder and electroless Ni-P/solder interfaces transformed from the initial (Cu,Ni)6Sn5 into (Ni, Cu)3Sn4. The composition of spalled IMC was nearly unchanged. In the solder, (Au,Pd,Ni)Sn4 phases coarsened during aging. During EM, the failure mechanisms could be classified to two types. When electrons flowed from the chip to the PCB, at the chip side (the cathode) the current crowding effect induced the serious localized dissolutions of interfacial Cu-Ni-Sn IMC, Ni UBM and Cu trace at the electron-entry corner. The solder joint would fail due to that the complete dissolution of Cu trace induced an open circuit at the electron-entry point. While when electrons flowed from the PCB to the chip, at the PCB side (the cathode) EM induced the consumption of electroless Ni-P to form Ni3P and Ni2SnP. After the complete consumption of electroless Ni-P, the poor attachment between Ni3P and Cu pad induced a crack across the cathode interface, and then the failure of the solder joint occurred. Furthermore, during EM (Au,Pd,Ni)Sn4 phase tended to deposit at the anode interface and in the solder near the anode interface.