Novel test and validation methods for packaging stress assessment in elastomeric materials

Elastomeric materials are widely used in electronic packaging, yet the thermal mismatch with packaged components can induce significant stress and cause device failure. While linear-elastic models are commonly used for stress analysis, their accuracy is critically limited by unreliable material parameters, especially the near-incompressible Poisson’s ratio, and the lack of direct experimental stress validation under representative constraints. To overcome these limitations, this study develops an accurate, self-consistent, and comprehensive analytical framework within the linear-elastic constitutive model by introducing two key methodological advances. This framework has been experimentally validated and demonstrates high precision. First, to obtain reliable inputs, a novel bulk modulus testing device based on passive-confining pressure loading is proposed. It achieves high-resolution characterization of near-incompressible elastomers, determining Poisson’s ratios for four different silicones, yielding values between 0.49975 and 0.49997 with a resolution on the order of 10 -4 to 10 -5 , which significantly surpasses the conventional methods. Second, for direct model validation, a novel strong-constraint structure is designed. It provides quantifiable and adjustable constraints, enabling packaging stress to be derived and experimentally validated under two different constraint levels. This capability is not available in standard test setups. The experimentally measured stresses validate the finite element model built with the newly characterized parameters. Finally, a sensitivity analysis using the validated model identifies the critical parameters governing packaging stress. This work demonstrates that within the established linear-elastic framework, the accuracy of packaging stress analysis can be significantly enhanced through high-resolution material characterization and the designed packaging stress testing methodology.