A European Research Action on lead-free soldering has been initiated in 2002 under the COST Program of the European Union. Its goal is the establishment of a database that contains the relevant knowledge on possible lead-free solder materials and to provide the expertise for selecting particular materials for specific soldering purposes. By March 2004, 20 European countries have signed the corresponding Memorandum of Understanding, in addition, two Canadian research organizations have been accepted as non-European partners.
The Action is structured into four Working Groups: WG 1 is responsible for experimental data on phase equilibria and thermochemical properties of possible lead-free solder materials and systems of relevance for joints with various substrates. WG 2 carries out the theoretical modeling of the corresponding phase diagrams. WG 3/4 investigates physical and chemical properties of candidate alloys, and WG 5/6 is responsible for reliability as well as for processing and packaging issues. Currently nine Group Projects are active involving scientists from 38 participating research institutions in 15 European countries. A tenth Group Project is in the status of preparation.
WG 1 and WG 2, in close cooperation, have identified nine quaternary systems as the immediate goal for a thermodynamic database; they comprise five possible ternary solder alloys together with relevant substrate materials: Ag-Cu-Sn + Au, Ni, Pd; Ag-Bi-Sn + Ni; Bi-Sn-Zn + Au, Cu, Pd; In-Sn-Zn + Pd. This means that all binary and ternary subsystems have to be described in a consistent way to build up, at the end, the corresponding quaternary alloy systems. For this purpose COST 531 has signed an agreement with SGTE to ensure a fruitful cooperation and an optimum mutual benefit.
In our laboratory in Vienna we are currently working on the
ternary systems Ag-In-Pd and
In-Pd-Sn in order to understand the interaction of Sn-Ag-In solders with Pd
substrates, and on the various combinations of ternary systems that are necessary
for a description of the interaction of Sn-Ag-Cu solders with Ni substrates.
This research comprises experimental phase diagram investigations and
thermodynamic measurements, and the results are being used as input data for a
CALPHAD optimization of the corresponding alloy systems by our Czech partners
within Group Project 4.