Numerical Parametric Study of the Thermomechanical Effect of Encapsulation on a Welded Beam Lead Component

Abstract

Encapsulation of components and assemblies has become widespread in the design of electronic products, providing protection from the environment and enhancing reliability. In this thesis, computational simulations are used to parametrically investigate the thermomechanical role played by the encapsulant when a beam-lead component is welded to slender copper busbars, encapsulated in a polymeric encapsulant, and subjected to temperature cycling. The parametric studies are conducted in two phases, using simplified two-dimensional finite element models.

In the first phase, a parametric design space is generated to systematically vary the encapsulant's thermomechanical properties, namely the Young's modulus and Coefficient of Thermal Expansion. A gull wing geometry is introduced into the lead of the component as a stress relief feature. In this case, a ramp thermal loading profile is used to understand the physics of this design and to provide relative comparisons between different combinations of the encapsulant's material properties within the design space. Response surface models are generated over the design space.

In the second phase, a Taguchi Design of Experiments (DOE) approach, based on orthogonal arrays, is used to analyze the effects of multiple design parameters under cyclic thermal loading. This includes encapsulant properties (a subset of the properties investigated in the first phase), encapsulant dimensions, lead geometry and dimensions, and busbar dimensions. Lead geometry is considered with and without stress relief features. The loading used in this phase is three temperature cycles between -40oC and 90oC. The primary areas of concern (response variables) in both studies are the component lead and interconnect regions. Deformation and stress states in these critical regions are compared. Main factor effects and selected parameter interactions are computed in accordance with the Taguchi orthogonal arrays, to understand the dominant parameters and parameter interactions for cyclic thermomechanical stresses in this encapsulated assembly.