SMTA International Conference Proceedings


Authors: Mathias Nowottnick, Wolfgang Scheel, Uwe Pape, Rolf Diehm, Joachim Wiese, Wolfgang Kempe, Marcel Mallah, Manfred Suppa, Peter Fink
Company: University Rostock
Date Published: 9/24/2006   Conference: SMTA International

Abstract: This paper is showing results from a joint research project “MICROFLOW”, funded by the German Department for Education and Research (BMBF). Usual simultaneous reflow soldering processes like convection soldering or vapor phase soldering were optimized in the past for a minimum of temperature difference between small and large or heavy components on electronic assemblies. Especially the increasing demands for polymer electronics, for electrical-optical assemblies or high temperature electronics require are further development of soldering processes. Such a process should allow a direct heating of the solder joints up to soldering temperature and have to save all other components at the same time. Today this is possible only by application of sequential working selective soldering processes like hot bar soldering or laser soldering. But for a cost effective industrial application it is necessary to realize a selective and as well simultaneous soldering process, which is indeed not available at present. The wanted selective heating method for an effective simultaneous process is possible in principle by using of electromagnetic fields, when the energy is penetrating the assembly and is launching heat in certain regions, depending on specific material characteristics. Electromagnetic fields in the microwave frequency region are able to treat various sizes and shapes of assemblies with large capacity and with a high throughput. Indeed it is possible to heat conventional solder pastes only very slowly and with a high microwave power density. It is possible to increase the launched heat considerable by mixing of additional materials, so called suszeptors, into the solder paste, which are absorbing microwave power with a high efficiency. A fundamental task for a save microwave application was to guarantee the operators safety and to ensure the electromagnetic compatibility of printed circuit boards, integrated circuits and other components as well. This was possible by means of minimizing of volumetric microwave power, optimizing microwave frequency and above all the ensuring of field homogeneity. Key words: soldering, microwave heating, flux

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