Development of no-flow underfill for lead-free bumped flip-chip assemblies

No-flow underfill process in flip-chip assembly has become a promising tech nology towards a smaller, faster and more cost-efficient packaging technolo gy. The current available no-flow underfill materials are mainly designed f or eutectic Sn-Pb solders. This paper presents a new no-flow underfill for lead-free solder bumped flip-chip assemblies. Many epoxy resin/HMPA/metal a cetylacetonate material systems have been screened in terms of their curing kinetics. Some potential base formulations with curing peak temperatures h igher than 200 degreesC are selected for further study. The proper fluxing agents are developed and the effects of fluxing agents on the curing kineti cs and cured material properties of the potential base formulations are stu died using differential scanning calorimetry (DSC), thermo-mechanical analy zer (TMA), dynamic-mechanical analyzer (DMA), thermogravimetric analyzer (T GA), and rheometer. The results show that the addition of flux significantl y reduced the curing temperature and limits the potential of many formulati ons for application in lead-free bumped flip chip assembles. Fluxing capabi lity of several no-flow formulations is evaluated using the wetting test of lead-free solder balls on a copper board. The feasibility of developed no- flow underfill is demonstrated using a lead-free bumped flip-chip package, which shows 100% yield in interconnection after the solder reflow.