Wire sweep characterization of multi-tier palladium-copper (Pd-Cu) wire bonding on LQFP package using low alpha green mold compound

Abstract

Controlling wire sweep is critical in transfer molding process as excessive results in shorting of wires, which in turn cause electrical failure. Therefore, understanding the effects of various factors on wire sweep is crucial to ensure processability and high yield for Pd-Cu wire production. In this study, wire sweep characterization carried out on Low Quad Flat Package (LQFP) package subject to various wire location, mold flow direction, wire length, wire pitch and wire angle. Fractional factorial design of experiment (DOE) is performed using 4 factors and 3 center points to identify key molding parameters which influence wire sweep. Wire sweep performance is also investigated under various mold cavity temperature, die thickness and wire loop height. Wire location is found to be the most significant factor that affects wire sweep percentage. A positive correlation is found for the wire length and wire sweep percentage. The prediction profiles show that longer transfer time improves wire sweep performance. Optimum mold parameters are identified using JMP statistical analysis software in order to improve the wire sweep performance. It is also noteworthy that a thicker 11 mils die gives better wire sweep performance compared to a 7 mils die. A mold cavity temperature of 175°C gives lower wire sweep percentage compared to 165 °C and 185°C. In conclusion, the wire located at segment F of corner 4 (mold gate at corner 1) experiences the worst wire sweep due to longer wire length and mold compound turning effect. Optimum compound fluidity, lower wire loop height and optimized molding parameters are determined to be the essential factors that improve wire sweep performance during mold encapsulation process.