Grounding design for low-cost ball grid array package with high shielding effectiveness

This paper presents grounding design for shielded packages to obtain high shielding effectiveness at low cost. Shielded packages are required for high-speed LSIs in mobile handsets and should have not only shield layers with high conductivity but also ground pattern arrangement on interposers. While arranging a ground area on an interposer is indispensable for high shielding effectiveness, a large ground area increases the number of wiring layers and raises the cost. Therefore, investigation of the relationship between the grounding design and the shielding effectiveness is important. In the present work, several kinds of fine-pitch ball grid array (FBGA) packages were designed and fabricated. Each package is different in terms of the design of the contacts between shield layers and ground patterns on the interposer. The grounding design, especially the maximum distance between the contacts, affects the magnetic shielding effectiveness (MSE).