Development of no-flow underfill for board level assembly

In this paper, no-flow underfill formulations are developed to provide reworkability, high impact resistance, and good reliability for board level components. The designed underfill materials are characterized with a differential scanning calorimeter (DSC), thermal mechanical analyzer (TMA), and dynamic mechanical analyzer (DMA). The potential reworkability of the underfills is evaluated using a die shear test at elevated temperature. The 3-point bending test and the DMA frequency sweep indicate that the developed materials have high fracture toughness and good damping properties. CSP components are assembled on a board using a no-flow underfill process and a high interconnect yield is achieved. Reworkability of the underfills is demonstrated. Reliability of the components is evaluated in air-to-air thermal shock (AATS). The developed formulations have potential high reliability for board level components.