![]() ![]() It’s not (always) possible to tick all the boxes at the same time, but modern fluxes can get close. Be easily soluble in commonly available, cheap, and safe solvents (ideally water).Non-hygroscopic, to avoid dendritic growth - a phenomenon where a voltage present between two conductors induce migration of metal ions, usually through a hygroscopic medium that has absorbed moisture.Leave only thin residues, easily pierced by in-circuit test probes.Leave only transparent and non-reflective residues (to enable optical inspections).When cooled to ambient temperature, soldering flux should: ![]() Dissolves the oxides if they’re transformed into metal salts.Reacts with or removes the metal oxides.Have you ever tried the experiment where you float a paperclip on water due to surface tension, then add a drop of soap and the paperclip sinks instantly? Similarly, a flux can break the surface tension between the solder and the metal surface, improving the wetting. Protects the surface from further oxidation, especially necessary as the surface is going to be heated during the soldering process and would oxidize quickly.The ideal soldering flux does all of the following when heated. ![]() Air is the foaming agent for Italian meringue.Įnsuring surface preparation is the job of the flux. ✟oaming agents, or blowing agents, are used to create foams such as polyurethane and vinyl foams. For the joint to be successful, all surfaces involved must be clear of metallic oxides and other surface contamination. Soldering is the joining of metal surfaces with each other using a low-melting alloy as the proverbial “glue”, without melting the base metals. These solvents have now been replaced by water-based detergents containing surfactants (not unlike dish-soap) and saponifying agents, a change that required reformulating most fluxes to make them more easily washable. As I’m sure all but the youngest readers are aware, CFCs were found to have devastating effects on the atmospheric ozone layer. These compounds are incredibly effective solvents and are cheap to manufacturer - one of the many reasons they were used in countless applications, from hairspray to refrigerant systems to foaming agents¹. In the early 90s, the mainstream practice in the industry was to remove the flux residues after fabrication, usually through the use of Chlorofluorocarbons (CFCs) and methyl chloroform (now known mainly as 1,1,1-trichloroethane). It has been used for millennia to increase frictions (for example in violin bows), as glue, binding agents, or varnish. Rosin is a resin obtained by heating and/or distilling of naturally-occurring resins, such as those produced by pines and other conifer trees. Up to the 70s, most fluxes were rosin-based. ![]() The customer, however, will likely want to take into consideration future reliability, corrosion resistance, environmental impacts, and compatibility with successive treatments, such as conformal coating. The EMS house wants the cheapest and easiest to use base materials, with the highest yields possible. HistoryĬhoosing the right kind of flux is something where the interests of the electronics manufacturing services (EMS) house and of the customer (that’s you) can experience a divergence of values. In this article, we’ll discuss fluxes - what they are, what they are made of (yes, there is going to be a lot of chemistry, don’t be scared), how they should be used, and in what direction the industry is going. Unless connectors, conductive adhesive, wire-bonding, or zebra-tape are used, in the modern electronics industry it’s always necessary to use some kind of flux during the soldering process to create an electric connection. The truth of the matter is, when studied in-depth, PCB fabrication is an extremely complex technological topic that deserves recognition as the most fundamental part of PCB engineering. As engineers, we sometimes sit high on our pillowy chairs, looking at the nitty and gritty of the industry - such as the fabrication of the PCB - with a bit of nonchalance. ![]()
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