Recent advances in the development of no-flow underfill encapsulants-a practical approach towards the actual manufacturing application

No-flow underfill technology has been proven to have potential advantages over the conventional underfill technology, and a no-flow underfill material (called G25) has been developed and reported in our prior papers. In this paper, two modified no-flow underfill materials are studied. Compared to the G25 no-flow underfill material, these two materials can be fully post-cured at the temperature below 170°C. These two materials also exhibit lower coefficient of thermal expansion (CTE), lower moisture absorption, better adhesion, and more fluxing stability. In this study, a differential scanning calorimetry (DSC) is used to study the curing kinetics and glass transition temperature (DSC Tg) of the two materials. Thermo-mechanical analyzer (TMA) is used to investigate the heat distortion temperature (TMA Tg) and the coefficient of thermal expansion (CTE). Dynamic-mechanical analyzer (DMA) is used to measure the storage modulus (E\´) and loss modulus (E") within the temperature range from 25°C to 250°C and then estimate the cross-linking density (p) of the cured material system. Rheometer is used to investigate the material viscosity. Die shear testing is conducted to investigate the adhesive strength between the cured underfill material and polyimide passivation layer. Surface mount technology (SMT) reflow oven, quartz chips and copper laminated FR4 substrates are used to in-situ test the processability of the two materials. Scanning electron microscopy (SEM) is used to observe the integrity of the reflowed solder interconnects. A potential approach toward the production application of no-flow underfill material is then proposed