Hello everybody!

In this article I want to share my opinion on the approach to choosing liquid fluxes for soldering PCBs and what are the differences between liquid and gel fluxes. How does this affect the direct soldering of printed circuit boards?

To begin with, let me explain that the liquid form and the gel form of soldering fluxes differ only in different application processes. That is, in some place it is important that the soldering flux remains exactly where it was applied, for example, for soldering a BGA microcircuit. Of course, I also take into account the capillary effect. But in any case, the thixotropy of soldering fluxes is very important, as in solder paste, which, in addition to flux, also contains small balls of solder alloy. By applying bead solder paste or gel flux to a PCB, it will stay in place due to its thick form that becomes thinner at high temperatures. That is, until soldering, the applied composition will not spread anywhere, and this is very important in the electronics industry.

The liquid form of flux for soldering is no less important in the electronics industry, since there are a number of technical processes that require a liquid form of flux for soldering. For example, wave soldering, manual tinning of stranded wires, applying soldering flux using nozzles before dipping into a bath of molten solder. The liquid form of soldering flux penetrates more easily into holes and between small wires, thereby increasing the quality of tinning copper conductors in electronics.

And now the time has come to talk about choosing a liquid soldering flux. It also has the necessary characteristics that should not be forgotten. Especially if you solder at home and don’t delve too deeply into the details of technical processes. The old-fashioned approach needs to be replaced with a professional one, in which you understand exactly what you are doing and how you are doing it.

An important characteristic of soldering fluxes according to their classifiers.

The well-known No Clean soldering fluxes are classified as ROL0, REL0. If the flux for soldering electronics is produced in accordance with these classifiers, then you do not need to worry about your printed circuit board becoming covered with green after some time and corrosion processes will begin. Also, current leakage will be restrained by high current resistance. In the free market, many manufacturers do not even indicate these classifiers, because the average user knows nothing about it, but the No Clean inscription works magically and people don’t even think that most cheap Chinese manufacturers make absolute slag that does not meet any requirements. The cheapest materials will not produce a quality product. But many of you are happy with the low price and this very often leads to corrosion on your printed circuit boards and current leaks.

Highly active fluxes with mandatory cleaning, such as ROL1, ORH1. They are necessary in technical processes where you need to be absolutely sure that at high speeds and volumes of soldering everything was sealed properly. These technologies are used in mass production of electronics, such as smartphones and any consumer electronics. At the same time, you need to understand that the quality of cleaning printed circuit boards after soldering is at the highest level with control of the conductivity of cleaning liquids.

For convenience, look at the table of classifiers:

It is also necessary to understand that No Clean liquid soldering fluxes must be precisely matched to low activity. This is what guarantees that the printed circuit board will not become corroded and there will be no leaks. You should also be sure that at home you will not wash off all the flux from the printed circuit board, since it is very difficult to wash it out from under the components and microcircuits. Therefore, assume that some part of the soldering flux remains under the components and if you are confident in its quality, then you have nothing to worry about. But many cheap fluxes do not meet these criteria, and even the “No Clean” inscription should stop you from using such fluxes. By purchasing liquid soldering flux from the manufacturer, you can definitely guarantee that the quality of your printed circuit board will be at the highest level, even if you do not wash it.

By Robert Smith

John Smith: John, a former software engineer, shares his insights on software development, programming languages, and coding best practices.