Interconnect diameter effects on the thermo-mechanical reliability of sandwich-structured Cu–Cu bonded stacked dies

The thermo-mechanical reliability of sandwich-structured Cu–Cu bonded stacked dies is strongly governed by interconnect geometry, yet the influence of diameter remains insufficiently resolved under cyclic thermal loading. This study establishes a validated thermo-mechanical framework to examine how Cu–Cu interconnect diameter controls global curvature, stress localization, irreversible energy dissipation, and fatigue resistance in a bonded layered assembly subjected to JEDEC JESD22-A104D thermal cycling. A sequentially coupled transient thermo-mechanical model incorporating orthotropic silicon elasticity and temperature-dependent copper viscoplasticity was developed and experimentally validated during the heating stage, with less than 2% deviation in peak warpage. Across a diameter range of 10 to 18 μm, increasing diameter progressively reduced the positive deformation peak from 0.62043 to 0.55574 μm and extended the predicted fatigue life from 1.29 × 10 6 to 3.97 × 10 6 cycles. The local reliability response, however, was non-monotonic: the lowest maximum tensile stress and stabilized irreversibility occurred at 14 μm, whereas the lowest peak plastic work rate and the most mechanically balanced overall response emerged at 16 μm. These findings reveal a transition from distributed thermo-mechanical accommodation to increasingly edge-dominated inelasticity, establishing interconnect diameter as a governing energetic design variable in thermally cycled sandwich-structured Cu–Cu bonded assemblies.