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 i nterest, but reliability concerns are still preventing its broad applicatio n. Reports on environmental testing results are related to both high temper ature storage and thermal cycling, Additionally, the influence of moisture has been investigated for both pressure cooker test and humidity storage wi th 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 mor e detail using a finite element :(FE-) model, because only little informati on is available on this subject, A joint of a chip resistor on an organic b oard was selected for the model. The conductive adhesive is not treated as a homogeneous material, but split into the polymeric matrix material and id ealized conductive particles. A temperature dependent viscoelastic constitu tive description has been used to model the epoxy behavior. Additionally, m oisture diffusion analyzes of the adhesive joints were conducted. The conta cting pressure of the particles is shown to depend on cure shrinkage, tempe rature changes, and moisture swelling effects.