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102 SMT Magazine • January 2017 by Eddie Groves, SELECTIVE SOLDERING ACADEMY, and Jonathan Wol, PILLARHOUSE USA INC. While often overlooked, the flux chosen for the selective soldering process has a great im- pact on solder joint quality, long term reliabil- ity and overall selective soldering performance. This article outlines the critical factors of com- monly available selective soldering fluxes and how they impact the soldering quality, reliabil- ity and equipment performance. Fluxes essentially fall into three basic cate- gories or flux types: • Low-solids/no-clean fluxes • Rosin fluxes (full/high-solids rosins) • Water soluble fluxes When discussing fluxes for the selective sol- dering process, we are generally referring to low-solids/no-clean fluxes, and it is the most commonly used flux type in selective soldering. If a company is using a full rosin or water soluble flux in their selective soldering process, they are usually mandated to use them by their customer, or industry, and are usually produc- ing a legacy product with a legacy reliability standard. From a flux performance standpoint, both of these flux types solder very well, and there is little to evaluate. But most companies using selective soldering avoid them because of the need to install expensive cleaning processes as well. After all, one of the benefits of selective soldering is the ability to selectively flux so that cleaning can be eliminated. NOTE: If you are required to use a rosin or water soluble flux in your selective soldering process, then you should consult with your equipment manufacturer to make certain you have the appropriate options or materials for handling these types of fluxes. Low-solids/no-clean fluxes breakdown into a few other categories: • Alcohol-based, rosin or resin containing • Alcohol-based, rosin or resin free • Water-based, rosin or resin free (VOC-free); rare occasions will contain rosin or resin In this category, there are a variety of man- ufacturers and many more flux choices. So how do you decide? Even if your customers, corpo- rate management, or your available manufac- turing processes dictate the flux you use, it is Choosing the Correct Flux – Advantages/ Disadvantages ARTICLE

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