SMTA International Conference Proceedings


Authors: Anders Åström
Company: Linde Gas Division
Date Published: 9/21/2003   Conference: SMTA International

Abstract: By 1 July 2006, a large segment of the European electronics industry will be obligated by law to replace any solder or metallisation containing lead (Pb). However, many companies around the world have already started to manufacture lead-free assemblies in response to customer demands.

In this study, the effect on solder spreading by changing the reflow time, or the time above solder liquidus temperature, was investigated. Further, the effects of changing the super-heat were also studied. By conducting the tests in air and nitrogen atmospheres, it was possible to observe how the soldering environment and the tested process settings affected the result. In addition, assembled printed circuit boards were soldered both in nitrogen and air.

At the end of this paper, the observed results and the practical consequences they might have are discussed. It was demonstrated that solder pastes from different suppliers performed differently under the same conditions but all of them benefited from a nitrogen atmosphere. It was also shown that spreading was better in a nitrogen atmosphere even if the super-heat was limited to 3°C above liquidus temperature. Further, it was also shown that under the existing conditions, the time above liquidus temperature could be reduced by about 16%, resulting in the same solder-spread for the nitrogen process, as when soldering was performed in an air atmosphere with the reflow profile recommended by the paste supplier.

Finally, for all components tested, both with lead-free and lead containing metallisations, wetting was considerably improved when the atmosphere was switched from air to nitrogen.

Key words: nitrogen soldering, wetting, super-heat, lead-free solder.

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