Effects of conformal coating on anisotropically conductive adhesive joints; a medical perspective

Purpose - The purpose of this paper is to study epoxy and parylene C-coated samples. These coatings are used to protect the electronic devices from harsh environments. The effect of these conformal coatings on electronics reliability is considered.Design methodology approach - Epoxy coating is applied using dip coating and parylene C is applied with the vapour deposition polymerisation method. Test chip used is joined using flip-chip technology and an anisotropically conductive adhesive. Reliability of the test samples is evaluated in a constant humidity test, where test conditions are 85°C and 85%RH. The test lasts 4,000 h. Failure analysis is carried out by cross-sectioning failed samples and using scanning electron microscopy for closer analysis.Findings - The results show variation in the reliability of adhesive joints with different conformal coating materials. Failure analysis highlights explicit failure mechanisms. Adhesion testing is also carried out on the test samples after constant humidity testing. The results of these reliability tests indicate clearly that parylene C is a more reliable choice of conformal coating than epoxy.Originality value - The paper shows the influence of certain conformal coatings on the reliability of adhesive flip-chip joints. In medical applications, reliability plays an important role.