The company's Rachel Gordon, Technology Analyst, says that materials are needed to replace the estimated 50,000 metric tons of tin-lead solder currently used each year, but there are no "drop-in" replacements for eutectic tin-lead solder. $1.2 billion of electrically conductive adhesives (ECAs) are already selling each year, and they are becoming increasingly common to replace solders in a variety of functions, applications and industries.
ECAs consist of a polymeric resin (such as an epoxy, or a silicone) that provides physical and mechanical properties such as adhesion, mechanical strength and impact strength, and a metal filler (such as silver, gold or nickel) that conducts electricity. In order to reduce the volume of filler used, increase the electrical conductivity, and decrease the finest possible pitch width, there is research into using nanoparticle fillers including silver nanowires, silver nanoparticles, nickel nanoparticles and carbon nanotubes.
Obviously in all these materials, the electrical conductivity is of primary importance. However, the thermal conductivity must also be high enough so that components do not overheat. The thermal conductivity of isotropic conductive paste (ICP) is approximately 20 W/m.K, compared to 60 W/m.K for lead solders. Adhesion to the mating surfaces must be good enough that there will not be adhesive failure, and the tensile strength must be high enough to avoid cohesive failure, even under bending and flexing conditions. The viscosity must be low enough for easy dispensing, but high enough after curing to avoid pump out and dry out. In some applications, the operating temperature will be important and, whereas solders can operate up to 270ºC, ECAs are limited to around 200ºC. It must be non-toxic, because there is no point replacing lead with another equally toxic material.
Lead solder melts at 215ºC, whereas isotropic conductive paste can be cured as low as 110ºC. This opens up possibilities for using plastic substrates to allow a new generation of flexible electronics. In order to use PET