A novel no-flow flux underfill material for advanced flip chip packaging

A novel no-flow underfill material for advanced flip chip and CSP packaging has been successfully developed. This new material is based on a non-anhydride resin system and therefore it does not have the chemical sensitizing concern. Unlike the short pot life of most anhydride systems this new material exhibited excellent pot life. The viscosity of the material did not increase over 48 hours at room temperature. During the assembly process, the material demonstrated that it fluxed the solder bumps, formed a nice fillet, and was fully cured during a single reflow exposure. Production efficiency is therefore significantly increased. In addition, the assembled packages using this novel no-flow underfill material also achieved high interconnect yield. In this paper, we present the curing kinetics study and material properties of this novel no-flow material. The influence of fluxing agents on curing kinetics of this system is discussed. Material properties such as glass transition temperature (Tg), modulus, and viscosity were systematically characterized. Differential scanning calorimetry (DSC) dynamic-mechanical analysis (DMA), and rheometry were used for this study. In addition, promising assembly trial results, using small flip chips (PB8) and CSPs (TV46), are reported. Finally, the effects of the formulations and reflow profile on voiding and yield are also discussed.