Formation mechanism and mechanical properties of compliant interconnects incorporating Cu nanowire arrays for heterogeneous integration

• Well-controlled preparation of NWs arrays as micro-bumps via templated DC electroplating. • NWs exhibited uniform orientation, high aspect ratio, and moderate density. • Formation of robust nanowired interconnects by thermal compression bonding of Sn NWs. • These interconnects feature superior mechanical compliance and consistent performance. • Nanowired compliant interconnects offer a promising option for heterogeneous integration. The conventional solder interconnects in heterogeneous integration face serious reliability issues resulting from thermally induced fatigue and premature brittle fracture. This study presents Cu nanowired compliant interconnects to solve these issues. Free-standing Cu nanowire (NW) arrays with uniform orientation were fabricated by templated direct-current electroplating. The current densities were revealed to dominate the crystal orientations, growth rate, and height uniformity of the nanowires (NWs). The underlying mechanisms were thoroughly elucidated. Various techniques were proposed to obtain their identical height and perpendicularity, which can benefit interconnect bonding and performance. The prepared Cu NW arrays with (100) crystallographic orientation were bonded to form reliable compliant interconnects by melting Sn NWs under thermo-compression bonding. These interconnects exhibited super-high mechanical compliance, characterized by a low Young's modulus of 5.6 MPa and shear modulus values of 0.28 MPa, along with excellent shear strength of 30 MPa. The electrical conductivity was measured to be 1.35 × 10⁷ S m⁻¹, and the thermal conductivity was evaluated to be significantly high. Bending fatigue tests over 2000 cycles demonstrated their excellent resistance to mechanical fatigue. The proposed nanowired compliant interconnects are expected to serve as promising candidates for heterogeneous integration.