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New Thick Film Conductor Pastes on AlN for Pb-Free Solder
Keywords: conductor paste, AlN, Pb-free solder
In recent years the claim for elimination of hazardous materials, including lead, cadmium, mercury and hexavalent chromium from electronic devices was strengthened (RoHS). Furthermore in industrial production the change of lead soldering (63Sn 35,5Pb 1,5Ag) to lead-free soldering (95,5Sn 3,8Ag 0,7Cu) has begun and the demand of a compatible paste system growth. The major challenge of Pb-free soldering is the solder leach resistance of the conductor layer at the higher temperature of 255 °C. The aim of the investigations at IKTS was the development of new conductor pastes for AlN, which can be used for lead-free soldering and shows good film characteristics. To characterize the correlations between film properties and paste alloy components, microscopy, FESEM and wire peel test were used and solder leach resistance was determined. The solder leach resistance was not only quantified by dipping the sample in solder, but also qualified by the exact measurement of the soldered area compared to the beginning area. Starting point of the investigations was a conductor paste for AlN with Ag : Pd ratio of 3:1. By gradually substitution of Pd by Pt a paste series was produced between the both points Ag : Pd = 3:1 and Ag : Pt = 3:1. It could be found, that the replacement of Pd by Pt induced a better solder leach resistance and adhesive strength. With a second paste series the influence of the components of inorganic binder was determined. Wire peel tests showed an improved adhesive strength, as well for the initial as for the aged state. Furthermore the solder leach resistance was improved too with this new inorganic binder. Summary conductor pastes for AlN with good adhesion and high leach resistance were developed. Because of the results of a mixed Ag, Pd, Pt alloy, pastes can be offered with an optimal cost-effectiveness.
Melanie Hentsche, Scientist
Fraunhofer Institute for Ceramic Technologies and Systems
Dresden 01277,
Germany


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