Preventing Aging of Electrically Conductive Adhesives on Metal Substrate Using Graphene-Based Barrier
Paper i proceeding, 2016
Electrically conductive adhesives (ECAs) seem to be a promising substitute to traditional metal-based solders, because of them being environmentally friendly materials requiring much lower processing temperatures, and offering a much finer pitch. However, a critical problem related to the use of ECAs is that the contact resistance to the metal pad tends to increase significantly during aging tests due to galvanic corrosion, particularly in 85oC/85% relative humidity (RH) atmospheres. In this respect the reported impermeability of graphene, a property prohibiting most molecules including water vapor from penetrating the film, has made graphene a major candidate as an anti-corrosion barrier material. The use of graphene as an anti-corrosion barrier material on steel and other metals has already been reported in literature. In this paper, the use of graphene-based barriers between the ECA and the copper pads on a printed circuit board for alleviating the galvanic corrosion problem is reported.
A PCB test board was designed for monitoring the effects of introducing the graphene-based barrier on the contact resistance between ECA and copper while exposing the board to a 500 hour aging test in 85℃/85% RH. For samples without graphene-based barriers it was found that the contact resistance increased rapidly during the first 200 hours of the aging test, while the contact resistance for samples with the graphene-based barriers remained stable. For these samples with graphene-based barriers, the contact resistance showed a much smaller decay during the aging test than for those samples without graphene-based barriers. These findings indicate that graphene-based barriers could be a solution for improving the reliability of electrically conductive adhesives, especially in harsh 85oC/85% RH environment conditions.