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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.

The demise of the CFC‐113/alcohol azeotropic solvent for de‐fluxing circuit assemblies after soldering has led, in recent years, to the electronics assembly industry being offered other cleaning technologies, some new and some new to this industry. In terms of uptake, one of the most successful will be semi‐aqueous cleaning involving the use of an organic solvent of low volatility to dissolve the contamination followed by an aqueous rinsing process. Two families of solvent have evolved based on natural products (terpenes) and synthetic hydrocarbon chemicals. This paper reviews the possible semi‐aqueous processes and the development of the solvents that has taken place. The cleaning performance is considered as well as the potential for effluent control and fully closed‐loop systems.

The effects of ultrasonic agitation on electronic components during PCB cleaning has long been the subject of controversy. This paper summarises the results of a series of studies into these effects for a range of components using CFC, aqueous and semi‐aqueous cleaning media. The variations with exposure time and power density under various ultrasonic stress conditions (loose, mounted on PCBs, or on purpose‐built test boards) are discussed. The results are encouraging and suggest that there is a large margin of safety when employing currently accepted regimes of operation and good quality components. However, the strong dependence of the damage accumulation on power density emphasises the need to specify and tightly control the power density used.

The options for eliminating CFC‐113 as a solvent for cleaning flux residues from soldered circuit assemblies, or minimising the need to clean, are now clear: diluted CFC solvent blends, new HCFC solvents, alcohols, water plus saponifier, water with water‐soluble flux, semi‐aqueous solvents, ‘no‐clean’ fluxes and controlled atmosphere soldering. This paper summarises the advantages and the limitations of each option and presents a methodology (first suggested by Northern Telecom) for ranking the options in a way that is specific to the requirements of the user. Both the cost and the technical feasibility of the implementation of each option are considered to provide a quantitative measure that can form the basis for the decision making ‘which option best fits my requirements and my resources?’

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.

Electronics exhibitions are the same the world over, very tiring affairs. If your stand is busy, time flies; if not, the strain is more noticeable.

‘Fluxing and Cleaning in Electronics Soldering’ The Grosvenor Hotel, London, 22 February 1989. ‘To clean or not to clean?’ ‘Aqueous or solvent cleaning?’ ‘What is the future for CFCs and other chlorinated solvents?’ The electronics assembly industry is ringing with such questions that make the cleaning of electronic assemblies the key issue for 1989—an issue that urgently requires answers that have the stamp of authority based on fact rather than speculation. This BABS seminar was therefore very timely and attracted a large audience to listen to eight presentations from speakers representing the cleaning equipment manufacturers, flux manufacturers, MoD quality assurance, and users' experience, as well as background on solvents in the environment.

This paper gives a general survey of the methods of contamination control related to assembled printed circuits. Particular emphasis is given to those aspects of the subject which are currently in a state of change because of environmental difficulties, notably those due to the curtailment of use of chlorofluorocarbon solvents.