Thermally Induced Creep and Viscoelastic Behavior of Copper Micropillar Arrays

Copper micropillar arrays integrated in microchannel structures promise superior heat dissipation, yet their long-term reliability can be limited by creep deformation under thermomechanical constraints. Here, we fabricate Cu micropillar arrays (∼50 µm in diameter and ∼300 µm in height) via electrodeposition within through-glass vias (TGVs) and elucidate how heat treatment tailors creep, viscoelastic response, and deformation mechanisms. Nanoindentation creep combined with EBSD and TEM reveals the transition: 200°C promotes grain-boundary-mediated deformation with the largest creep displacement (101 nm) and the smallest activation volume (0.64 nm³), whereas 300°C increases dislocation density and produces dislocation pile-ups/networks that pin grain boundaries, reducing creep displacement to 42 nm, raising the stress exponent to 3.76, and the activation volume recovers to 1.49 nm³. Viscoelasticity is quantified with a generalized Kelvin model and retardation spectrum analysis, which shows suppressed relaxation activity after 300°C treatment. Thermal tests on arrays with varying pitch indicate that 70 µm spacing yields the most pronounced monitored-surface temperature rise (46.5°C) under identical heating, implying enhanced effective heat transport through the micropillar network. These results establish a microstructure-mechanism-property framework to guide the design of Cu micropillar arrays that balance manufacturability, creep reliability, and thermal performance for microscale liquid-cooling.