Conductive adhesives for SMT and potential applications

Environmental issues have as ever-increasing influence on the selection of materials and processes in electronic manufacturing. This paper discusses the use of conductive adhesives as a replacement for solder on SMT-printed circuit boards. As a result of a world-wide market survey, a number of conductive adhesives have been selected. The key issue of this paper has been to uncover the market for adhesive types and their composition, as well as the technical investigation of the influence of component termination and printed-circuit surface types on adhesive bonding stability. Four different types of adhesives on two different metal surfaces are compared with conventional solder technology. Each adhesive has been applied to the PCB´s by either screen printing or dispensing according to the manufacturer´s recommendation, followed by curing. All PCB´s went through thermal and humidity cycling followed by electrical measurements of resistance; all variants have been adhesion tested. All adhesive variants have been microsectioned for metallurgical and microstructure examination. Energy Dispersive Analysis of X-ray (EDAX) of the metal particles in the adhesive has been carried out and documented. Rework of conductive joints is briefly addressed. Finally, aspects of occupational health are discussed concerning work with adhesive types. Work with epoxy-based adhesives has been brought into special focus