Bed of Nails—100- $mu$m-Pitch Wafer-Level Interconnections Process

The rapid advances in integrated chip (IC) design and fabrication continue to challenge electronic packaging technology, in terms of fine pitch, high performance, low cost, and reliability. Demand for higher input/output (I/O) count per IC chip increases as the IC chip fabrication technology is continuously moving towards nano ICs with feature size less than 90 nm. As micro systems continue to move towards high speed and microminiaturization technologies, stringent electrical and mechanical properties are required. To meet the above requirements, chip-to-substrate interconnection technologies with less than 100-mum pitch are required. Currently, the coefficient of thermal expansion (CTE) mismatch between the Si chip and the substrate serves as the biggest bottleneck issue in conventional chip to substrate interconnections technology, which becomes even more critical as the pitch of the interconnects is reduces. Further, the assembly yield of such fine-pitch interconnections also serves as one of the biggest challenges. Bed-of-nails (BoN) interconnects show great potential in meeting some of these requirements for next-generation packaging. In the present study, BoN interconnects prepared by a novel process called copper column wafer-level packaging is presented. The BoN interconnect technology is being developed to meet fine pitch of 100 mum and high-density interconnections. These BoN interconnects are demonstrated by designing a test chip of 10times10mm²size with 3338 I/Os and fabricated using an optimized process. The board-level reliability tests performed under temperature cycling in the range of -40degC to 125degC show promising results.