Advanced reliability study of TSV interposers and interconnects for the 28nm technology FPGA

TSV interposer has emerged as a good solution to provide high wiring density interconnections, improved electrical performance due to shorter interconnection from the die to substrate, and minimized CTE mismatch between the chip and copper filled TSV interposer, resulting in high reliability micro bumps and more reliable low-k chip. Furthermore, for an interposer that does not contain any active device, already established process technology could be applied, TSV pitch could be coarser and a thicker interposer could be used. This paper presents the development of TSV interposer technology for a high-performance 28nm logic die that is mounted on a large silicon interposer with Cu through silicon via. A representative silicon interposer test chip with thousands of micro-bumps at 45um pitch has been fabricated. The silicon interposer is 100um thick, and is mounted on a 42.5mm×42.5mm substrate through 180um pitch C4 bumps. TSV fabrication process steps and assembly process of the large logic die mounted on the TSV interposer with lead-free micro-bumps have been optimized as well as assembly of the component on the organic substrate. 3D thermal-mechanical modeling and simulation for the packaged device with TSV interposer have been performed. The samples have been subjected to thermal cycling, electro-migration and moisture sensitivity tests. Effect of TSV interposer on the stress of the die, low-k layers and fatigue life of micro bumps and C4 bumps have been investigated. Several DOEs have been performed to optimize design and material selection in order to maximize yield and reliability. Finally, Si interposer seemed to be a low-risk 3D path to have a reliable package with acceptable warpage/coplanarity, passing 1000TCB without any crack, delamination or void being detected in low-k, TSV, micro bumps and C4 bumps.