Ultra low CTE (1.8 ppm/°C) core material for next generation thin CSP

Abstract

Along with the advancement in miniaturizing of mobile devices, typified by smart phones and tablet PCs, the semiconductor PKG substrate installed in these devices is demanded to be thinner and higher in density. As one of the most innovative solutions, the PoP (package on package) technology, which has the three-dimensional construction, has been expanding rapidly in recent years. However, the thinner PKG such as PoP tends to warp at the assembly process and cause the decrease in the connection reliability. Therefore ultra low CTE (coefficient of thermal expansion) core materials have been needed as a key solution for the reduction of the warpage for PoP. Recently, we have developed new ultra low CTE core material named E-770G for next generation thin CSP, applying new resin systems, featuring low shrinkage and low residual stress. In particular, E-770G has achieved ultra low CTE of 1.8 ppm/°C which leads to significant reduction of the warpage. Furthermore, it has low dissipation factor at high frequencies (Df: 0.005 at 1 GHz). So it's also applicable to high speed PKG applications. Confirming the warpage property, we evaluated the warpage behavior of the bottom PKG before/after assembly process. E-770G showed the much lower warpage than the conventional ultra low CTE core material.