Evolution mechanism of interconnect interface and shear properties of 64.8Sn35.2Pb microbump during flip chip bonding

• Flip chip bonding parameters significantly influence the microstructure and shear properties of 64.8Sn35.2Pb microbumps. • The dominant IMC at the interconnect interface is (Ni, Cu)3Sn4, with nanoscale (Cu, Ni)6Sn5 precipitates exhibiting specific orientation relationships. • A maximum shear force of 77.3 gf is achieved at 250 °C with parameter V1, attributed to dense IMCs and a crack-free interface. • Fracture modes include solder fracture and mixed fracture; high thermal stress in thick IMC layers initiates cracks that propagate along α/β phase boundaries.