Fabrication and Thermo-Mechanical Characterization of Fine Pitch All-Copper Interconnect

Abstract

The thermal cycling and effect of misalignment of all-copper, chip-to-substrate bonding was evaluated. Electroplated copper pillars on the chip and board were joined using an optimized electroless deposition process after alignment. The width of the copper lines were 50, 25 and 15 μm The joints were robust and void-free. The mechanical strength and electrical continuity of the bonded copper pillars were assessed before and after thermal cycling. The mechanical strength of these joints was substantially higher than typical solder fracture strength. Finite element medeling was used to analyze the effect of (i) misalignment and (ii) underfill on the mechanics of the assembled parts.