Two New Lead-free Solder Alloys: Ag-Sn-Bi and Cu-In-Zn

Lead and Lead containing compounds are among the top chemicals posing a great threat to the environment and to human life. Consequently the use and disposal of lead containing materials is of great concern. Therefore it is necessary to eliminate lead in solder joints because the disposal of great amounts of electronic equipment (mobile phones, computers, TV-sets and so on) in landfills can cause lead to leach out and contaminate the underground water and subsequently find its way into the human body. For this reason the European Union plans to ban all lead containing material by the year 2007. Lead-tin solders have been extensively used in the elctronic industry as a primary method for interconnecting electronic components. New technological developments require new Lead free solders with a wide variety of new and improved properties. In this proposed research we want to investigate two ternary alloys, silver-tin-bismuth and indium-copper-zinc (Ag-Sn-Bi and Cu-In-Zn), which will be used in certain applications as new lead-free solder material. The thermodynamic properties will be measured with electromotive forte and calorimetric measurements. The oxidation behavior will be investigated with a thermo-gravitybalance and the phase diagram will be determined with Differential Thermal Analysis (DTA], Xray measurements and microprobe analysis. A theoretical approach will be taken to calculate the surface tension and the viskosity of the liquid alloys from the obtained thermodynamic data. The importance of this type of research is demonstrated by the establishment of a new LOST project by the EU. My colleague Prof. Ipser and myself proposed a COST-Action an Lead-free solders. COST 531 was approved and got started an March 11,2002. For the moment scientists of 15 countries will participate.

Lead was an essential component in all soft solders which were used in the electric and electronic industry. Because of its high toxicity lead has been banned by the EU since July 2006 in all lead containing solders with a low melting point. For this reason in 2003 my colleague Herbert Ipser and myself started a European COST project for the development of lead free solders. COST projects of the EU are research projects in which at least five EU countries and research institutions of these countries must take part. The necessity of such research projects was shown that more than 15 countries decided to take part in it with over 40 research institutions. My research group should determine the thermodynamic properties of different alloys which could be possible be used as a lead-free solder material. From the thermodynamic data the phase diagram, wetting and other physical properties could be calculated. To determine the thermodynamic properties we used several different methods: Emf-measurements: The electromotive force between two electrodes, one electrode is the pure metal and the other one is an alloy was measured. From the obtained current the thermodynamic data can be calculated. Calorimetric measurements: here the heat is measured which occurs at the dissolution of alloys. The third method was the DSC measurements (Differential Scanning Calorimetry). With this method the heat change is determined. The main criteria for alloys to be used as solder material are: Melting point around 200C, good electrical and thermal conductivity, metals must be cheap and in ample supply on the world market, and must be environmental safe. The systems which were investigated in my group fulfil these criteria and one system Al-Sn-Zn is already used by a Japanese company and a certain composition is patent as solder material. During our research we investigated the following systems: Cu-In-Zn, Al-Sn-Zn, Ag-Bi-Sn, Cu-Sn-Zn, Ag-Bi-Sn, Ag-Au-Sn and Bi-In-Zn. Our results at some systems were used to calculate different properties.