Assembly of silicon onto FR4-based organic substrates using flip-chip process continues to pose substantial thermomechanical challenges largely due to the disparate coefficients of thermal expansion (CTEs) of silicon and substrate.… Click to show full abstract
Assembly of silicon onto FR4-based organic substrates using flip-chip process continues to pose substantial thermomechanical challenges largely due to the disparate coefficients of thermal expansion (CTEs) of silicon and substrate. In flip-chip packaging, this CTE mismatch causes mechanical stresses in the chip-to-substrate interconnection bumps and the mechanically fragile interlayer dielectric (ILD) within the chip, leading to fracture and delamination. A novel process called pressure-compensated chip attach (PCCA) is presented, where the silicon chip is attached to the substrate by reflowing the solder bumps while maintaining the chip and substrate in a controlled hydrostatic pressure environment. Experiments show that the new PCCA process reduced the silicon test-chip warpage by 40% and eliminated ILD cracking.
               
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