Effect of Sacrificial Anodic Fillers on Contact Resistance Stability of Electrically Conductive Adhesives onto Lead-Free Alloy Surfaces

摘要

Electrically conductive adhesive (ECA) is a promising alternative for the toxic lead-based soldering materials for electronics interconnects. However, its unstable electrical conductivity has long been a haunting problem. The galvanic corrosion has been identified as the major mechanism responsible for this conductivity decay at the ECA/pad interface. Applying a more active metal or alloy on a dissimilar metal couple in electrically contact can protect the comparably active metal from galvanic corrosion. Using sacrificial metals in ECA has been recently studied and demonstrated to be an effective method to protect the metal surfaces from corrosion. In this study, powders of aluminum, magnesium, zinc and two alloys were used in ECA as the sacrificial metals and applied on five typical and lead-free pad/lead surface finishes (tin/lead, copper, nickel/gold, tin/silver, and tin/silver/copper). The electrode potential measurement of these metals, alloys, and ECAs were conducted, and reliabilities of bulk resistivity and contact resistance of EGA/metal surface pairs with respect to 85°C/85%RH aging were studied. After 500 hours of aging, the two alloys added significantly suppressed the increase of the contact resistance on all tested metal surfaces with the Alloy 1 being the better one. The Al and Mg, added ECA and Zn and Al added ECA also showed obvious positive effects on slowing down the contact resistance increase. The order of reliability of contact resistance was found in coincidence with the order of electrode potential data of all metal, alloys and ECAs.