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Development of a lead-free solder paste

The RoHs directive 2002/95/EC and the WEEE directive 2002/96/EC have been enforced in the EU. Therefore lead will be banned in many applications after July 1, 2006. Lead free solder pastes will become a new standard in the electronic industry at least after this date. The development of such lead free solder pastes was done in the IMECAT project. For standard application a solder paste was developed by using exclusively type 3 powder. The alloy used in most cases was SnAg4Cu0.5. The flux was optimised in different aspects: soldering quality, printing and slump behaviour, corrosion resistance, stability and colour of flux residues.

Soldering quality was optimized by means of wetting performance and solder balling results. These tests were conducted under different conditions: 2 different profiles in air and in nitrogen. Printing behaviour was tested in most cases with an EKRA printer type X5 and a special test layout (Heraeus Benchmarker II). Important items were fine pitch capability, stencil life (viscosity change during continuous printing), cold and hot slump and print-after-wait performance. It is planned to make this paste a standard product. At the end the developed product

Called F640) was benchmarked and compared with 2 different products which are already available on the market. The developed paste is made a standard product now and it is available on the open market: F640SA40C5-89M30. For wafer bumping application a lead free solder paste was developed by using exclusively type 6 solder powder. This is the finest powder specified so far in national and international standards. 4 different lead free alloys were tested: Sn96.5Ag3.5, SnAg4Cu0.5, Sn99.3Cu0.7 and SnAg3.4Bi4.8. The most promising product is based on SnAg4Cu0.5 alloy. It is made a standard product now and it is available on the open market: F510SA40C5-89S6.

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63450 HANAU
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