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40 SMT Magazine • April 2015 it remained low for incomplete cleaning of no- clean solder pastes. Conclusion The purpose of the paper was to highlight the differences between water-soluble and no- clean solder pastes in order to guide users in their choice. To achieve this goal, six lead-free solder pastes were extensively studied, three being wa- ter-soluble and three being no-clean. In the first part of the paper, water-soluble pastes generally yielded results below the no-clean pastes with a significant sensitivity to temperature and hu- midity, a tendency to slump during preheat and a narrower printing window. It was concluded that the WS pastes had to be stored, handled and used with more caution before reflow compared to no-clean pastes. In the second part of the paper, regarding wetting properties, WS pastes rank generally better, especially for oxidized substrates. As far as cleanability is concerned, of course only water-soluble pastes can be cleaned with water only whereas no-clean pastes need detergent to achieve a complete removal of their residues. However, in case of poor cleaning, as the amount of ionic species usually found in WS residues is high (presence of ionic surfactants es - pecially), the risk of corrosion is very high: This is the major drawback of such pastes. The use of water-soluble pastes generally takes place in high-reliability assembly as medi- cal, military or aerospace fields where close attention is paid to the quality of substrates, components, where reflow is done in inert at- mosphere (nitrogen, vapor phase or under vac- uum ovens) and where cleaning is compulsory for the majority of the products. The use of ag- gressive chemistry may not be necessary when using such equipments. Moreover, the risk of tombstoning is increased. In such fields, in case of new solder paste evaluation, it is useful to also consider the option of no-clean solder pastes in comparison with water-soluble sol- der pastes and even to think about review the whole cleaning process. This paper can then be used as a guide to study the critical aspects of these two types of solder pastes. SMT acknowledgments Originally published in the IPC APEX EXPO 2014 proceedings. The authors would like to thank Richard Anisko and Aurélie Ducoulombier. references 1. E. Guéné, S. Teh, Reliability Assessment of No-clean and Water-soluble Solder Pastes, Part I, IPC APEX EXPO 2013. Figure 11: Poor/good cleaning under CSP (after removal): (left) Paste B/poor; (right) Paste B/good. emmanuelle guéné is electronics applications manager with inventec performance chemicals in bry sur Marne, france. Steven Teh is Asia applications manager with Inventec in Selangor, Malaysia. rEliaBiliTy aSSESSMENT OF NO-ClEaN aND WaTEr-SOluBlE SOlDEr paSTES, parT ii continues FeAture