Abstract
The development of PKG-substrates with lower coefficients of thermal expansion (CTE) is desired, since the warpage introduced by the difference between the coefficients of the substrates and that of the silicon chips is a serious obstacle in the practical application of FC-PKG technology. Simulation and experimental studies were conducted in the present study in order to reduce the CTE-values of the PKG-substrates by using nanosilica particles. The FEM simulation revealed that the reduction of the CTE of the substrates was important to suppress the warpage. 25 nm-diameter nanosilica induced deteriorations in the properties of the substrates; i.e., a reduction in Tg and an increase in CTE. A thermo-gravimetrical study showed incomplete cross-linking due to inhibition by the acidic protons from the unreacted free silanol groups on the nanosilica surface. Curing at higher temperatures and for longer duration led to an increase in Tg and a reduction of α2. Finally, by employing a newly developed polyimide with lower CTE and higher silica content of 45 vol%, we succeeded in preparing a PKG-substrate with a 5 ppm/K lower CTE compared to the conventional one.
