High performance no flow underfills for low-cost flip-chip applications

Underfill encapsulant is critical to the reliability of the flip-chip solder joint interconnects. No-flow underfill encapsulant is one type of underfill encapsulants and is increasingly becoming attractive to production engineers due to the simplification of the no-flow underfilling process. To develop the no-flow underfill materials suitable for no-flow underfilling process of flip-chip solder joint interconnects, we have studied and developed several catalysts for no-flow underfill formulations. These catalysts were reacted with epoxy resins (cycloaliphatic type epoxy), crosslinkers or hardeners, and other additives, such as adhesion promoters, silica fillers, self-fluxing agents, and surfactants, to form the low-cost high performance underfills. The effects of concentration of hardeners and catalysts as well as other factors on the curing profile and physical properties of the cured formulations were studied. The kinetics and reaction heat of the curing reactions of these formulations were investigated by differential scanning calorimeter (DSC). Glass transition temperature (Tg) and thermal coefficient of expansion (TCE) of these cured resins were investigated by thermo-mechanical analyzer (TMA). Cured formulations were measured by dynamic-mechanical analyzer (DMA). Additionally, the comparison results of our successful generic underfills with the current state-of-the-art commercial no-flow underfills are reported here.