Development of no-flow underfill materials for lead-free solder bumped flip-chip applications

No-flow underfill process in flip chip assembly has become a promising tech nology toward a smaller, faster and more cost-efficient packaging technolog y. The current available no-flow underfill materials are mainly designed fo r eutectic tin-lead (Sn/Pb) solders. With the advance of lead-free intercon nection due to the environmental concerns, a new no-flow underfill chemistr y needs to be developed for lead-free solder bumped flip-chip applications. Many epoxy resin/hexahydro-4-methyl phthalic anhydride (HMPA)/metal acetyl acetonate material systems have been screened in terms of their curing beha vior. Some potential base formulations with curing peak temperatures higher than 200 degreesC (based on differential scanning calorimetry at a heating rate of 5 degreesC/min) are selected for further study. The proper fluxing agents are developed and the effects of fluxing agents on the curing behav ior and cured material properties of the potential base formulations are st udied using differential scanning calorimetry (DSC), thermomechanical analy zer (TMA), dynamic-mechanical analyzer (DMA), thermogravimetric analyzer (T GA), and rheometer. Fluxing capability of the developed no-flow formulation s is evaluated using the wetting test of lead-free solder balls on a copper board. The developed no-flow underfill formulations show sufficient fluxin g capability and good potential for lead-free solder bumped flip-chip appli cations.