New Concept Paste Material for Improving PoP SMT Yield in Mobile Products

Tadashi Maeda & Kazuo Ishibashi, Panasonic Factory Solutions Co., Ltd.

Recently, PoP (Package on Package) technology is emerging as an alternative solution to SiP especially for ASIC+memory applications since it has advantage of easier testing and sourcing. Typically PoP has FBGA format and is board-assembled by normal SMT process. Bottom package (ASIC usually) is placed on a paste-printed motherboard as usual, then top package (memory) is flux/paste-dipped and placed on top of bottom package, followed by one-time reflow. PoP top and bottom package may have different warpage amount/direction during reflow due to CTE mismatch and asymmetric package structure, which may cause large "relative" warpage between top and bottom package thus could lead to open joint. Controlling warpage by optimizing design/material set is challenging especially when top and bottom device come from different suppliers. New dipping paste material "STAMP (Soldering Technology Assisted by Metalliferous Paste)" was developed to address the open joint problem above. The paste consists of metal flakes uniformly dispersed in flux. The metal flake alloy is selected to have higher melting point than package solder ball, and the melting timing delay is effective to fill and bridge a gap between molten solder ball and ball pad. PoP stacking yield and BLR results will be presented at the workshop.

Tadashi Maeda is the material development engineer of R&D center for Panasonic Factory Solutions. He has currently focused on 3D packaging process. He received the B.E. and M.E. degrees in applied chemistry from Kyusyu University of Japan in 1993.

Kazuo Ishibashi joined Nokia Japan in 1999 and now works as Research Specialist in Technology Platforms. He has been focusing mainly on 3D packaging for cell phone application. He obtained B.E. and M.E. degrees in applied physics from Waseda University, Tokyo and began his career at Digital Equipment Corporation Japan in 1983 where he engaged in magnetic recording material development. He subsequently joined AMP Technology Japan in 1992 and worked on anisotropic conductive material as Technology Manager.