In recent years, no-flow underfill technology has been drawingmore attention due to its potential advantages over conventionalunderfill technology, and several no-flow underfill materials have beendeveloped and reported. However, most of these materials are notsuitable for lead-free solder applications that usually have highermelting temperatures than the eutectic solder. Due to the increasingenvironmental concern, the demand for friendly lead-free solders hasbecome an apparent trend. This paper demonstrated the study on two newformulas of no-flow underfill developed for lead-free solders withmelting point around 220° C. As compared to the G25, a no-flowunderfill material developed in our research group, which uses a solidmetal chelate curing catalyst to match the reflow profile of eutecticsolder (melting point 187° C), these novel formulas employ a liquidcuring catalyst thus provides ease in preparation of the no-flowunderfill materials and more choices in combining fluxing agents. Inthis study, the curing kinetics, glass transition temperature (Tg), thermal expansion coefficient (TCE), storage modulus (E') andloss modulus (E'') of these materials were studied with differentialscanning calorimetry (DSC), thermo-mechanical analysis (TMA), anddynamic-mechanical analysis (DMA), respectively. The pot-life in termsof viscosity of these materials was characterized with a stressrheometer. The adhesive strength of the material on the surface ofsilicon chip was studied with a die-shear instrument. The influences offluxing agents on the materials curing kinetics were studied with DSC.The materials compatibility to the solder penetration and wetting oncopper clad during solder reflow was investigated with both eutectic andno-lead solders on copper laminated FR-4 organic boards and heated in areflow oven
展开▼
