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Proceedings Paper

Investigation of electroless tin deposition from acidic thiourea-type bath
Author(s): A. Araźna; J. Bieliński
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Paper Abstract

The constant tendency of miniaturization in electronic products and developments in surface assembly techniques creates requirement to prepare new techniques and processes also in the range of metallic coatings. An additional factor which influences the evolution of preservatives coatings technology is the necessity to adapt Polish law to European directive. From 1st July 2006 there will be an obligatory RoHS directive banning applying lead in electronics. Electroless tin deposition is one of an alternative for Sn/Pb lead free preservative films on copper surface in PCB technology. Electroless deposition of tin coatings on copper can be made in two ways: from an alkaline bath - the process disproportionation of Sn(II) compounds and from acidic bath contain complex compound such as thiourea - the displacement of copper by tin in Sn(II). Alkaline baths are not used in printed circuit board technology because it has destructive influence on resists. Besides acidic baths complex compounds contain additional stability solution composition which modify structure of obtained tin film. Quality and thickness tin layer are fundamental parameters which determine its protective character. The research test were done in thiourea-type electroless tin bath. The influence of different parameters on n rate of tin deposition and thickness of Sn coating were determined: temperature of the bath, Sn(II)-salt, thiourea and HCl concentration. Tin layers were depositioned on electrolytical copper foil. The thickness of Sn coating was determined by coulometry in 2M HCl. The rate deposition process depends mainly on the thiourea and HCl concentrations in solution. The temperature is also a very important parameter. The thickness of tin layer grows when the temperature increase. Although above 70°C appear undesirable thiourea decomposition. The results of the investigation show that further investigations are necessary for this solution.

Paper Details

Date Published: 12 October 2006
PDF: 4 pages
Proc. SPIE 6347, Photonics Applications in Astronomy, Communications, Industry, and High-Energy Physics Experiments 2006, 63471W (12 October 2006); doi: 10.1117/12.714555
Show Author Affiliations
A. Araźna, Instytut Tele i Radiotechniczny (Poland)
J. Bieliński, Warsaw Univ. of Technology (Poland)


Published in SPIE Proceedings Vol. 6347:
Photonics Applications in Astronomy, Communications, Industry, and High-Energy Physics Experiments 2006

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