High reliability non-flow underfill material with filler loading

The non-flow underfill (NUF) process is an important technology that can be used to reduce the cost of flip chip package assembly. NUF reduces the oxide layer on metal (e.g. bump or pad) and encapsulates the package during bump connection processes such as the reflow process. Generally, in order to achieve higher reliability, filler must be formulated into the underfill material. In the case of NUF, it is difficult to load filler because the filler might become sandwiched between the bump and the substrate, hindering connection. However, we have developed a new NUF system which can connect between bump and substrate according to optimize fine filler distribution and wettability of material, even with much higher filler content formulation. In this paper, we will outline this new filler loaded NUF system, which offers higher connection reliability and thermal cycle reliability.