Desenvolvimento de adesivos eletricamente condutivos na fixação de componentes eletrônicos em montagens de superfície (SMT)

Abstract

For many years the most commonly used metal alloy as solder was the Pb-Sn alloy, a malleable material with a low melting temperature. With the European Directive 2002/95/CE (as known as RoHS Directive), the suspension of the use of hazardous substances such as lead is approved. It is necessary to replace the Pb-Sn solder alloy with new materials and the most used of these are the alloys of the SAC family (metal alloy composed by Sn-Ag-Cu). This alloy melts at temperatures above 210°C, which can damage the electronic components, that are becoming smaller and with more functions. The possibility of using electrically conductive adhesives arises. These are mostly formulated using silver particles and other good conducting metals such as gold and nickel, dispersed in a polymer matrix. In this way, there is economy of metals, compared to the use of solder pastes. This work proposes three formulations for electrically conductive adhesives, obtained from an epoxy resin with butadiene with different types of conductive fillers: carbon nanotubes and silver with different morphologies. All the materials were characterized as their physical, morphological and electrical characteristics through MEV, electrical resistance measurement by the 4-point probes method, thermal shock and aging. Electrical resistance of each material and the contact resistance were tested and compared with commercial adhesives and the reference SAC305 alloy solder. It was identified that the adhesives demonstrated resilience in relation to the contact with the PCI even after successive aging cycles at 85°C with 85% RH or thermal shock tests. Electrical resistance measured on the adhesive formulated using silver nanosheets is very close to the values obtained with the commercial reference, in the order of 10-4 cm. It was also the only material that presented less than 20% variation of electrical contact resistance after thermal shock, proving its good performance against the other formulations of this work.