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Non‐corrosive rosin fluxes have historically been used for telephone communications assemblies because they provide a measure of reliability even if the flux is not totally removed from the assembly. While cleaning is not always necessary from a reliability standpoint, testing issues, product appearance, operating performance and customer requirements must also be considered when making the decision whether or not to clean. As the electronics industry packages more and more functionality on less and less real estate, soldering yields need to increase in order for the assembly process to remain profitable. This requires not only attention to the product's design for manufacturing but it may also require aggressive fluxes to be used in the assembly process. When aggressive fluxes are employed, the necessity for cleaning is greatly increased. The particular combination of flux and cleaning option depends on product design, process capabilities, end point requirements, and environmental considerations. Pending restrictions on the production and use of chlorofluorocarbons (CFCs), and the potential for tighter controls on chlorinated solvents and aqueous detergent effluents, are certain to add to the cost of standard processes. For these reasons alternative cleaning processes have been explored. The evaluation and subsequent use of water soluble flux with ‘water only’ cleaning, terpene cleaning of rosin flux residues, low solids flux ‘no‐clean’ wave soldering and ‘no‐clean’ assembly using reflowed rosin based solder pastes within AT&T are reviewed. A user's assessment of aqueous and semi‐aqueous cleaning is presented which indicates that there are acceptable alternatives to CFCs.

This paper outlines the composition of water soluble fluxes for the electronics industry and their methods of use when wave soldering and reflowing tinned coatings and solder pastes. Process optimisation is facilitated by the Taguchi method. Three types of cleaning machinery are evoked, with varying results. It is shown that the energy/time relationship is important to ensure adequate cleaning quality. A number of fallacious arguments are debunked. Methods of water purification and the problems of effluent treatment for all sizes of installation are addressed. Doubt is expressed as to the viability of closed‐circuit water recycling except for the largest installations or where exceptional conditions prevail. It is shown that water soluble fluxes and their subsequent aqueous removal are unlikely to make any significant contribution to the Greenhouse Effect. The overall cost of their use is substantially similar to that of rosin fluxes with CFC‐113 azeotropes at 1986 prices. Cleanliness control under production and laboratory conditions is discussed with reference to both ionic contamination testing, including its use for SMDs, and SIR analysis, especially at low voltages, including non‐destructive production SIR testing. Reliability of the assembled circuits is shown to be at least as good as that with more traditional soldering and cleaning methods, frequently better, and this is the case even for military and aerospace applications. The paper concludes that, now that quality water soluble solder pastes are available, this method is most likely to become the workhorse for the majority of electronics applications.

The threat posed to the environment by CFC cleaning processes for printed circuit boards has led to an investigation of possible alternatives. In a preselection procedure, surprising results were obtained using propylene glycol ethers (PGE), solvents for the paint industry. In this study these ethers are compared with five other groups of cleaners, which can be divided into four water‐based classes: weak acid, neutral, weak and strong alkaline, and water miscible organic solvent cleaners which are non halogen‐containing and biodegradable. The cleaning power of PGE and other cleaners is tested on fluxes for wave and reflow soldering. Comparative results for the different groups are given, combined with surface insulation resistance measurements. Good results can be obtained using alkaline or solvent cleaners. However, it appears that the cleaning results depend heavily on the type of flux used and the choice of a matching cleaning process.

With the advent of the Montreal Protocol, the removal of flux residues from printed circuit assemblies using solvents based on CFC‐113 is no longer an acceptable option. An alternative range of cleaning technologies is being developed and marketed for this purpose, and the aim of this work was to study the efficiency of a variety of these alternative cleaning regimes after IR reflow soldering. The results indicated that: (i) all the cleaning regimes were capable of removing flux and flux residues after standard IR reflow soldering; (ii) as the level of flux contamination under the components increased, the ability of the cleaning regimes to clean the boards decreased; (iii) the cleaning regimes had varying problems in removing the flux residues after the non‐standard (overheat) IR profile processing; (iv) when additional flux is introduced under the components (i.e., non‐standard IR reflow), the delay between soldering and cleaning becomes important; and (v) the cleaning regimes exhibited a wide variation in their ability to clean under components with small stand‐off heights.

This paper summarises briefly all the substitutive techniques for CFC‐113 and 1,1,1 ‐trichloroethane blend cleaning, including the use of ‘no‐clean’ and controlled atmosphere soldering, with emphasis on high‐reliability applications. Each technique is discussed with regard to its influence on the final reliability of the assembly under normal and abnormal storage and working conditions. Reliability is determined by numerous other parameters which are frequently ignored, such as the component layout for best cleaning quality. The requirements of conformal coating are also frequently given scant attention. In practical terms, this paper may help those selecting a substitutive soldering/cleaning process to choose one which will meet their quality requirements at minimum cost.

The efficiency of cleaning of flux residues after various periods of ageing was assessed by measuring the ionic contamination removed in an Ionograph 500 SMD. The flux residues were removed from bare boards, and boards with through hole and surface mount components. The effect of different ageing temperature was also investigated. The work has shown that there is a maximum time interval following assembly during which cleaning should be carried out. The ionic contamination of aged assemblies with through hole and surface mount components were cleaned with varying efficiencies. The surface mount components were more difficult to clean. The use of brushing and scrubbing proved particularly beneficial for the through hole components. A proprietary cleaner proved more effective than the generic alternatives considered.

‘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.

In August 1987, the EPA held a conference in Washington DC with consultants and users from the electronics industry to determine the feasibility of practical cleaning alternatives to reduce emissions of chlorofluorocarbon solvents which are considered to be a major contributor to the ozone problem in the stratosphere the world over. This paper presents a short resume of these goals and how they will affect cleaning in the electronics industry. Electronic design and packaging are the first steps in the soldering and cleaning processes. Selection of components compatible with alternative cleaning methods as well as process changes to permit low solids fluxes in some cases where cleaning can be eliminated will be discussed. ‘High containment’ in‐line solvent cleaning systems which reduce emissions are likely to become the new standard for the industry. Machines will become longer in order to include internal drying stages, instead of allowing a board with residual solvent trapped under components to evaporate after it leaves the machine prior to electronic test. Alternative solvents will become available. Designers of components and assemblies will respecify their designs to permit water cleaning, even for surface mount assemblies.

The contamination on SMT assemblies caused by a number of flux/cleaning variation has been investigated, with several analysis methods used to quantify the contamination. The results from analysis of test printed circuit boards (PCBs) using anion separation, conductivity, ionic contamination measurement, visual and SEM inspection, microsections and surface insulation resistance (SIR) methods were compared. The best cleaning result was observed with the combination of water soluble (WS) solder cream and water cleaning. The best measurement method for cleanliness of PCBs was considered to be SIR measurement. For WS fluxes, the iconic contamination test offers effective measurement of the amount of residues left on the PCBs.

This paper is an examination of residues on printed wiring boards and printed wiring assemblies. Sources of residues are illustrated and the effects of various residues are discussed. Case studies are presented for bare board cleanliness issues, water soluble flux and aqueous cleaning processes, and low solids flux (no‐clean) processes, with and without cleaning. The case studies reflect lessons learned in various process troubleshooting efforts. Residues in this paper were characterized using advanced ion chromatography procedures. In addition, some data on surface insulation resistance (SIR) are presented.