Evaluation of the Corrosion and Reliability Aspects of Printed Circuit Boards Flow Soldered Using ‘No Clean’ Fluxes

‘No clean’ fluxes (NCFs) have been in existence for a few years now. The initial claimed advantages of these fluxes were that post flow soldering cleaning would not be required, therefore a substantial cost‐reduction could be obtained in terms of no cleaning plant or cleaning solvent being necessary, and a consequent reduction in floor space requirements. Latterly, the restrictions to be placed on the manufacture of CFCs (the major flux cleaning solvent) via the Montreal Protocol have given these NCFs a much higher level of prominence. The advantages claimed for NCFs are very attractive; however, the fluxes represent a considerable technology shift from the conventional high solids rosin type fluxes which have been successfully used for many years. Probably the most important questions to be raised when considering their use are: ‘Will any remaining residue be corrosive and will the long‐term reliability of the printed circuit boards be affected?’ This paper sets out to address the following issues: (a) A definition of corrosion and long‐term reliability and what it means in practical terms, (b) an understanding of the basic formulation of NCFs and (c) evaluation and selection of test methods to establish confidence that corrosion and reduction in long‐term reliability, as described in (a), will not occur.