Reliability investigations on conductive adhesive joints with emphasis on the mechanics of the conduction mechanism

The isotropic conductive adhesive (ICA) mounting technology is of growing interest, but reliability concerns are still preventing its broad application. Reports on environmental testing results are related to both high temperature storage and thermal cycling. Additionally, the influence of moisture has been investigated for both pressure cooker test and humidity storage with exposure times up to several weeks. In an ICA, the conductive particles are embedded in a polymeric matrix material, where they can form conductive paths. This mechanical part of the conductive mechanism was studied in more detail using a finite element (FE-) model, because only a little information is available on this subject. A joint of a chip resistor on an organic board was selected for the model. The conductive adhesive is not treated as a homogeneous material, but split into the polymeric matrix material and idealized conductive particles. A temperature dependent viscoelastic constitutive description has been used to model the epoxy behavior. Additionally, moisture diffusion analyzes of the adhesive joints were conducted. The contacting pressure of the particles is shown to depend on cure shrinkage, temperature changes, and moisture swelling effects