10μm Pitch Bumping of Singulated Die Using a Temporary Metal-Embedded Chip Assembly Process

This paper presents a novel process for fine-pitch bumping of singulated multi-project wafer (MPW) die. The MPW chips are integrated onto a silicon interposer using a variation of HRL’s Metal Embedded Chip Assembly (MECA) technology, wherein thin electroplated copper is used as the temporary embedding material. Chip placement misalignment is assessed and corrected for during subsequent lithography steps, allowing us to achieve die bumping down to 10μm pitch. The chips are finally released from the interposer and are ready for flip-chip packaging. In this effort, 1mm x1mm 10μm pitch I/O test die were fabricated. The chips were bumped using different fabrication processes (liftoff, plating, and metal etching) to demonstrate the versatility of the Temporary MECA (T-MECA) approach. The bumped die were released from the reconstructed wafer and bonded onto a test interposer using Au-Au thermo-compression. A pad-to-pad resistance of 90mΩ and bonding yield of >95% were extracted from DC measurements of daisy chain structures.