Lead-free Soldering Paste

<strong>Background</strong><br>

Metal pieces can be joined together by melting a metal or an alloy with a lower melting temperature than the metal pieces. Since 2006 the use of lead in electrical and electronic products is prohibited in the European Union. Therefore lead-free soldering pastes with low melting points are required. Nanoparticles have been proposed for the use in solder pastes as they have lower melting points than their bulk counterparts.<br><br> <strong>Technology</strong><br> According to legal requirements and the trend to use nanoparticle scientists at the Technische Universität Berlin now developed a method to obtain compact sintered silver layers as joining materials at low temperatures without applying pressure. Therefore a metal-organic silver complex is used that can generate silver nanoparticles during heat treatment below 200 °C. The complex offers the features to form a molten metal-like silver phase in which silver particles in the nanometer and submicron size range, respectively, are completely miscible. The connecting silver layer is stable up to a temperature of ~ 961°C, what is the melting point of bulk silver. In contrast to current state of the art soldering paste this one contains nearly no organic ingredients, as they mostly lead to holes or bubbles with in the bonding layer. First experiments were carried out with copper specimens and achieved pressureless copper-to-copper silver joints at low temperatures. <br><br> <b>Benefits:</b><br> <ul> <li>Melting temperature below 200°C</li> <li>Metal joints with high strength</li> <li>Compact and homogeneous silver layers </li> <li>Formation of a molten metal-like silver phase is beneficial for joining</li> <li>Joining at atmospheric pressure</li> <li>Formation of nanoparticles allows low temperature sintering</li> </ul><br> <strong>IP Rights</strong><br> German patent application (04/2012) <br> <br> <strong>Origin</strong><br> Technische Universität Berlin

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