Thermal-Mechanical Analysis of Electroplated Copper for IC Packaging

This paper examines the temperature-dependent mechanical properties of an electroplated copper film. The stress in a 3μm thick copper film electroplated on a 775μm thick silicon substrate was measured using a custom-built setup based on a laser optical method. The thermal cycling covered a temperature range from room temperature to 420°C, revealing that the films exhibit stress relaxation at elevated temperatures and significant strain hardening during thermal cycling. Continuum plasticity analyses indicate that the experimentally measured stress-temperature response can only be represented with a combined isotropic-kinematic hardening model. The parameters of the model were identified by minimizing the difference between the experimental results and a Finite Element model, which successfully predicts the stress-temperature hysteresis observed during thermal cycling. The research also delves into the effects of thermal cycling on the mechanical characteristics of electroplated copper. The reduction in hardness observed post-thermal cycling which may suggest grain growth as reported in literature. Despite this Young's modulus value of the copper film under investigation remained unchanged after thermal cycling.