What is the difference between “soft soldering” and “silver soldering”?
Although both expressions use the word “soldering,” the terms “soft soldering” and “silver soldering” mean two different types of metal joining. “Soft soldering” refers to a process of metal joining that uses Tin-based alloys as the metal being used to join the two pieces of metal. “Silver soldering,” on the other hand, refers to a process whereby two pieces of metal are joined using a Silver-based alloy. Tin-based alloys melt at a lower temperature than Silver-based alloys; therefore, soft soldering requires lower heating temperatures than does silver soldering. These days, many people simply refer to soft soldering as “soldering” and silver soldering as “brazing,” which reduces the confusion of using the word “soldering” in both terms. It should be noted that it is not uncommon for Tin-based solders to contain Silver. However, the amount of silver added is relatively small compared to the amount of Tin present in such solders. One thing that both soft soldering (or soldering) and silver soldering (or brazing) have in common is they both need flux! However, since the alloys and temperatures are substantially different in each process, it stands to reason that you need to choose the right flux for each process. A soldering flux won’t do you any good for a brazing application, and a brazing flux is not going to help if you’re soldering a Tin-based alloy.
What’s the difference between a No-Clean Flux and a Water-Soluble Flux?
A No-Clean flux is typically a soldering flux used in electronics applications whose residues do not need to be cleaned off after soldering. This means that the flux is strong enough to facilitate the soldering at hand, but mild enough that its residues won’t cause damage to the components or printed circuit board (PCB) if left on after soldering and not cleaned off. In order to be accurately labeled as a No-Clean, a flux needs to undergo industry-standard testing to prove that its residues will not cause damage to the component or PCB if left on, uncleaned, after soldering. (It should be noted that although the term No-Clean is typically used for fluxes used in electronics applications, there are fluxes used in non-electronics applications that are designated as No-Clean, meaning their residues can be left on the part after soldering or brazing, with little or no concern that the residues will lead to problems stemming from corrosion. These so-called No-Cleans are subject to different standards than No-Clean fluxes formulated for electronics applications.). A water-soluble flux is a flux whose residues can be washed off with water after soldering. The water is sometimes agitated or heated (or both) to facilitate this washing, but the hallmark of a water-soluble flux is that its residues can be dissolved and cleaned off with water. Unlike a No-Clean flux, there is less concern about the residues harming the PCB or component, since they are going to be washed off after soldering anyways. This means that water-soluble fluxes tend to be more active than No-Clean fluxes, which makes them advantageous for applications that require a stronger flux. Of course, when using a more active, water-soluble flux, special attention must be paid to assuring that post-solder cleaning is done effectively, since uncleaned flux residues are likely to cause problems down the road. While the residues of a No-Clean flux are left on the board, there are No-Clean fluxes whose residues can be cleaned off with water after soldering. The residues of these water-soluble No-Clean fluxes are mild enough to be left on the board after soldering but water-soluble in case an application requires post-solder cleaning with water. As such, a water-soluble No-Clean flux will never be as a true water-soluble fluxes whose residues must be cleaned off after soldering.
