Novel fast cure and reworkable underfill materials

A series of novel underfill materials has been developed. These non-epoxy, thermoplastic-based materials satisfy all the basic requirements for underfill materials: fast flow, fast cure, and reworkable. In addition, these new materials show high modulus, low thermal expansion coefficient, and glass transition temperature (T_g ) comparable to epoxies. The new materials exhibit excellent flow behavior, taking only 10 seconds for a quarter inch full array die. Fast cure can be achieved within 5 minutes at 150°C. Another distinct feature of these underfill materials is the reworkability. With current commercial epoxy-based underfills, reworking is impractical due to the high crosslinking density. Rework of these underfills was achieved by thermal removal of the malfunctioned die, followed by solvent cleaning of the residue. Laboratory work demonstrated that the chip removal and underfill cleanup process can be completed within 5 minutes