Optimization of the Soldering Process with ECAs in Electronic Equipment: Characterization Measurement and Experimental Design

With the introduction of the European Directives restrictions of hazardous substances, electrically conductive adhesives (ECAs) have received great attention in the field of electronics as a possible replacement of the traditional tin-lead soldering technology. So, in this new context, the analysis and the characterization of these alternative materials represent a fundamental topic, above all, from the industrial point of view. Nevertheless, studies on ECAs have rarely been reported in the literature, but more recently research has started to focus on this specific topic. After a comparative assessment concerning soldering materials, this paper focuses attention on their characterization through measurement in order to verify the electrical behavior of the isotropic silver conductive adhesive. In addition, since the soldering process is affected by a large number of variables such as the thickness of the conductive adhesive film, radial velocity, and curing temperature, the optimal selection of the factors is carried out through experimental design theory and the dual-response approach by means of generalized linear models. In this paper, the experimental and comparative studies on soldering made up of epoxy adhesives are carried out, in particular, the adhesives constituted by metallic particles (silver), normally in the form of flakes, in a polymer matrix are considered. The novelty of the kind of adhesive considered is the Ag filler loadings of 50-65% by volume. At these loadings, the materials achieve the percolation threshold and are electrically conductive in all directions after the materials are cured. Two different types of conductive adhesives, characterized by different chemical structures and compositions, are experimented and tested. Then, since the lead-free soldering process is characterized by several critical factors, a statistical approach is used to optimize this process. Experimental results obtained by testing samples with ECA materials prove the validity of this paper. The value of this paper is in the application of a statistical approach to these adhesive materials in order to achieve the optimization of the soldering process with a small number of treatment combinations, satisfying at the same time the stringent requirements and achieving robust electrical interconnections.