Characterization of Substrate Materials for System-in-a-Package Applications

System-in-a-Package (SiP) aims to integrate the entire system functions within a system-level package containing multiple ICs and other components interconnected in a high-density substrate. A structure based on the SiP concept is proposed in this paper. Based on this SiP structure, four substrate candidates, namely FR4, liquid crystal polymer (LCP), teflon (PTFE) and low temperature co-fired ceramic (LTCC) were compared by assessing and measuring their mechanical reliability, electrical performance and environmental influence. First, to evaluate long-term reliability, the 3D finite element method (FEM) was used to calculate the stress distribution and warpage of the whole package. Both three-point bending and cooling in the manufacturing process were taken into consideration. The LCP has a coefficient of thermal expansion (CTE) close to that of the silicon chip, and a Young’s module close to that of FR4, which gave the best reliability in both bending and cooling situations. Next, the dielectric constants and the loss tangent for the four substrates were evaluated in the electrical performance investigation. The LCP has a low relative dielectric constant and a low dissipation factor for the frequency range 1 GHz to 35 GHz, making it a good substrate for high frequency applications. An environmental assessment included several environmental impact categories; this assessment indicated that LCP is the most environmentally acceptable substrate.