Cleaning PCB with Isopropyl Alcohol. When IPA Really Works?

There are two opposite opinions about cleaning printed circuit boards with alcohol after soldering. Some people, including myself, say that alcohol IPA may leave a white, conductive residue on the PCB surface. Other people cleaning each PCB with alcohol and say - it works perfectly.

And the truth is, both groups are right — but it all depends on the quality of the soldering flux you used and flux classification. And because of this lack of understanding, millions of printed circuit boards around the world later corrode and fail.

The problem is not in the isopropyl alcohol itself, but in its reaction with flux residues and contaminants left on the PCB and under the electronic components after soldering. The thing is, the chemical composition of soldering fluxes varies — there are different classes of fluxes.

Many fluxes are made from cheap raw materials, while others are made from high-quality components. Most people don’t think about what they solder with and just buy what’s available. For some reason, people are convinced that they can clean everything with alcohol IPA and never have any problems.

Manual cleaning of printed circuit boards always guarantees the presence of flux residues under SMD components and under microchips — no matter how carefully you try to clean them.

You will never be able to clean a PCB completely by hand and if you still think your PCB is clean, I can assure you — it’s not.

Example 1.

You bought a cheap flux in a small jar. Maybe it soldering well. After soldering, you cleaned it with IPA alcohol. But remember the rule — flux always remains under the components.

What happens next? Ispropyl Alcohol seeps under the electronic components and starts reacting with the residues of cheap soldering flux. The conductivity of those residues begins to increase. When powered on, the PCB will behave strange, because of current leakage starts between the leads — but that’s only one part of the problem.

Second part is that the flux activity also increases. Chemical reactions start between the flux and the metal surfaces — green oxide coating appear on PCB, and white or gray deposits appear from reactions with tin, lead, and other metals on component leads.

These ionic residues begin to conduct electricity. These processes may not start immediately — sometimes after a week or even a month. It doesn’t matter what you use to clean low quality soldering flux — it will cause problems anyway. Alcohol just accelerates them. Don't be too happy, if your PCB works fine right after soldering — PCB might fail very soon.

Example 2.

You are using an active, water-soluble flux, but you don't realize it. You bought what was available. After soldering, you cleaned all flux residues with alcohol — or at least you think you cleaned. But after some time, the PCB becomes covered with gray or white spots. Especially between any components pins, you see something like a salt.

But why? The flux is expensive and supposed to be good. Where did the problem come from?

The thing is, water-soluble soldering fluxes can only be cleaned with distilled or deionized water. Moreover, the residues of water-soluble fluxes are always active, because they may be halogen-containing with 1 in the end, or high-activity with 0 in the end of its classes. ORL0, ORL1, ORM0, ORM1, ORH0, ORH1.

So if you use water-soluble flux, that’s meant to be cleaned with water, but you can try to clean it with alcohol IPA. White or gray oxides can form.

And remember the first rule — flux always remains under SMD components. That means conductivity and current leakage from the remaining flux residues are guaranteed.

Another problem is that flux manufacturers often don’t indicate the flux class, that leads you to problems. You think you bought a good flux, but because of missing information, you have doomed yourself to random results.

Example 3.

Sometimes you think you are using a high-quality flux — and maybe you really are. But for soldering you also use core solder wire, that often contains its own dry flux inside with its own classification.

Here’s what to look for:

Every proper spool of core solder wire always has the flux class indicated on the label.

For example, if you use external noclean ROL0 flux, but your solder wire contains a water-soluble flux, this almost always ends with gray residue on the PCB and conductive contamination.

Be careful and use rosin core solder wire with the same flux class that you apply separately. Also, you can use clean core solder wire without any flux inside! Always minimize the risk of unexpected defects!

Example 4.

You can clean PCB with alcohol IPA only when you sure that the remaining flux under the microchips and others electronic components does not conduct current — and that the residues are completely neutral to metals and won’t create oxides between the leads. This is no-clean, high-quality ROL0, REL0 classes of soldering fluxes.

The cleaning process of PCBs is closely tied to what kind of soldering flux you are trying to remove!

Different fluxes require different cleaning methods. Water-soluble fluxes are cleaned with water, rosin-based fluxes are cleaned with alcohol or with special PCB cleaners.

IPA Isopropyl Alcohol only removes organic contaminants!

PCBs can also contain chemical contaminants from soldering, heat, some oxides and dirt. Various gasoline formulas in PCB cleaners are used deliberately to remove chemical contaminants.

To remove both - organic and chemical residues, you need to use special PCB cleaners. Like a Flux OFF, although there are many different cleaners, but avoid contact cleaners, glass cleaners, surface cleaners and other cleaners — this is not what you need!

High-quality rosin-based ROL0 no-clean fluxes don’t need to be cleaned at all. Their residues don’t conduct electricity and completely neutral to metals. So, if you clean them with alcohol IPA or Flux-Off, nothing will happen — alcohol will evaporate, and the residues will remain inert and non-conductive. However, if you blindly use active fluxes without clearly indicating of flux class, you will always have a problems.

Yes, Alcohol is used only for local cleaning after manual soldering of components and wires — and only because engineers know exactly what flux they are needed to clean from the circuit boards.

But in reality, it’s not always that perfect. I have seen many PCB assembly manufactories during my consulting work, where people didn’t even know the basic principles of proper soldering, not to mention PCB cleaning. There are a lot of such manufactories out there, and I’m open for consultations. The link for ELECTRONICS MANUFACTURING CONSULTING

The argument between supporters and opponents of alcohol cleaning comes down to this:

Some people consciously use alcohol-soluble, high-quality ROL0 no-clean fluxes — and everything works fine for them.

Others buy unknown fluxes online with no class markings, and their results are usually disastrous — no matter what they use to clean them.

Thank you for reading!