Tsutomu Nishioka

Solid type cavity fill and under fill materials for new IC packaging applications

IC packaging methods are diversified drastically today, because of the requirement for the package to perform the IC characteristics itself. The majority of encapsulating material in the IC packaging market is transfer molding. However, the transfer molding method is hard to apply to some new applications such as flip chip, cavity fill type PPGA (plastic pin grid arrays), BGA (ball grid arrays), and tape carrier packages. Liquid type resins are mainly used for these new applications in the current market. However, there are several serious disadvantages to using liquid type resins. The problems are poor processability and reliability. Under these circumstances, we focused on the improvement of the two disadvantages for liquid resin applications on flip chip and cavity fill type PPGA and BGA. Our newly developed materials are solid compounds at room temperature. These compounds are designed based on the study of reliability and processability. The base resin systems are selected by moisture performance and fluidity characteristics.

New analytical study for popcorn phenomenon

Package crack during mounting on the printed circuits is a major concern in package design and material development by engineers. This package crack (the so-called popcorn phenomenon) is caused by evaporation and expansion of absorbed moisture in the package at the temperature of reflow soldering for mounting on printed circuits. This package crack has been assumed to start from delamination between the encapsulant and the leadframe. But a new crack mode was found starting from the delamination of the silver paste. In order to evaluate this new crack mode, the following items were investigated: (1) the mechanism of package cracking, (2) stress, generated during the soldering process, and (3) the design of physical properties of a molding compound that has resistance of the new crack mode. Using these studies the authors developed a new molding compound that has excellent resistance to the new crack mode.<<ETX>>

Multi layer film adhesive for IC packaging applications

The adhesives have important functions in the recent IC packaging. The packages are more complex because of the trend of IC integration. For example, high thermal conductive adhesives are used for high power ULSIs. Stress insulating adhesives are used between two materials which have big difference in thermal expansion coefficient such as between metal heat sink and ceramics. From the general technical standpoint, in almost all cases, thermal conductivity and stress insulation are trade-off factors. Additionally, the adhesion strength and processability are also discussed as important functions. To develop materials which have high performance such as stress insulation with good thermal conductivity, multi layer functional film adhesives have been studied. The multilayer structure has made it possible to get high thermal conductive and low stress characteristics simultaneously with high adhesion.