Shear Performance and Accelerated Reliability of 6 × 4 mm2 FOWLP Solder Joints Using an ENIG PCB Electrode

Abstract

As the packaging density of wafer-level package becomes higher, the packaging process for fan-out packaged devices have been extremely needed. The soldering reliability of board-level device is very important. The Fan-out Wafer Level Package (FOWLP) usually packaged by flip-chip techniques on Cu electrodes and PCB substrates. In this study, we designed a new PCB based on the 6 $\text{x}4\text{m}\text{m}^{2}$ FOWLP test vehicle with ENIG surface fmish. After optimizing from 21 bonding parameters (temperature, holding time and shear strength), the best bonding parameter was achieved at $260^{\circ}\text{C}10\text{s}$. It can be found that the ENIG pads were dissolved in solder joints higher than $270^{\circ}\text{C}10\text{s}$, which makes the pads break away from the PCB and causes the soldier joint failure, making the mechanical properties of the joints very poor. With the long duration under high temperature, the molten Sn bypassed the Ni layer, flowed into the bottom of the pad and reacted with Cu, resulting into the volume shrinkage of the soldier joints and breaking the pad from the PCB.