Corrosion protection of anisotropically conductive adhesive joined flip chips

Corrosion is a common cause of failure in electronic devices. Conformal coatings may be used to prevent corrosion of electronics packages. Water and contaminants are thus not in direct contact with the package surface, which may improve resistance to corrosion. However, it is important to study the effects of corrosion on both coating materials and on the electronics itself. The protection method and the level of protection can then be selected.This study presents a salt spray test of anisotropically conductive adhesive joined flip chip components on FR-4 substrate, where half of the test samples were parylene C coated. A dramatic difference was seen between these two test lots. Parylene C proved to be an excellent barrier against salt spray. The test lots without conformal coating suffered severe corrosion, and were thus considerably less reliable. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) revealed the reasons for the failures in the non-coated test samples. The main reason was found to be severe corrosion of the nickel layer. There were no failures among the parylene C coated test samples during the 3000 h test. Moisture absorption of the FR-4 substrate material is also studied in this paper. Both plain FR-4 and parylene C coated FR-4 materials were studied. These tests were performed both at room temperature and in boiling water.