Lead-free solder paste for electronic systems A European consortium was established to replace conventional tin/lead alloy soldered assemblies with a lead-free equivalent. A lead-free solder paste was developed and tested before becoming a standard product. Industrial Technologies © Shutterstock Europe needs to develop high density, environmentally friendly interconnection technology in order to compete successfully with products from America and Asia. The development of lead-free solder by the IMECAT project will enable European manufacturers to perform in domestic and foreign markets following a ban on lead in solder. The IMECAT project developed lead-free solder paste for ecologically sound assembly technology of electronic systems. The consortium comprised nine partners from five different Member States including W. C. Heraeus GmbH & Co. KG an expert in the electronic development and commercialisation of interconnection materials. The Heraeus team developed a standard solder paste using a 'type 3' powder with a tin/silver/copper alloy suspended in a flux medium. Different factors were investigated including soldering quality, solder printing, and resistance to corrosion. Soldering quality was maximised using wetting performance and solder balling tests which were carried out in both air and nitrogen. Solder balling can create short circuits thereby affecting reliability, particularly when devices become reduced in size. Different factors affecting printing behaviour were also investigated, including fine pitch capability, stencil life and cold and hot slump. Slump, the collapse of the applied solder due to gravity, is particularly undesirable as it causes spread of the material beyond the area where it was initially deposited. At the end of the testing process the developed paste was compared with two other products already found on the open market. The paste is now a standard product and is also commercially available. The researchers also developed a lead-free paste for the wafer bumping process using 'type 6' solder powder which has the smallest particles specified according to national and international standards. The team tested four different lead-free alloys, the most suitable of which was SnAg4Cu0.5 which formed the basis for a novel product that is available for all manufacturers and interested consumers.
