An overview and evaluation of anisotropically conductive adhesive films for fine pitch electronic assembly

Anisotropically conductive adhesive films (ACAFs), which provide electrical as well as mechanical interconnections for fine pitch applications, are discussed. The conductivity of ACAF materials is only in the Z-direction (perpendicular to the plane of the board), and electrical isolation is maintained in the X-Y plane. Currently, at least 15 ACAF materials are commercially available. The authors have developed a methodology for evaluating these materials for their mechanical and electrical properties and interconnection use in the 8 to 15-mil pitch range. In addition they characterized the materials according to their physical properties and cure characteristics. They detail the findings with a comparison of physical form to assembly/cure and final electrical properties. Data from scanning electron microscopy, thermal analysis of the ACAFs, and cure and assembly studies on mixed substrate test vehicles are included. Information on initial electrical testing and long-term reliability testing is given