Cleaning Printed Circuit Boards after Soldering.

Hi. In this article, I want to tell you about the methods used to clean printed circuit boards (PCBs) after soldering. What cleaning liquids and equipment are best to use, and how to clean PCBs to achieve high-quality results without contamination or white/gray residues.
Some cleaning methods are suitable after electronic PCB repairs, where only localized cleaning is required. Other methods are perfect for mass electronic PCBs production, where removing soldering flux residues is necessary. Of course, effective flux removal can only be achieved when you are using high-quality soldering materials, whose cleaning results can be predicted. I use soldering flux for repairing Diamond Flux FN231.

In cases where you are using unknown chemical soldering fluxes or cheap materials, guaranteed results are difficult to achieve. For every chemical and organic contaminant, a corresponding solvent and cleaner are necessary. This is especially important if you plan to apply a protective coating afterward. For protective coatings, the cleanliness of the PCB is crucial for good adhesion – this is the penetration ability between the coating material and the printed circuit board.

First on the list is FluxOFF. This product has been used by me for 20 years for electronics repair. It easily cleans small areas and can be wiped with a lint-free cloth. The lint-free cloth is excellent because it doesn’t leave any cloth residues on components, which could conduct electricity.
Other manufacturers on the market include:
• Techspray T1631-16S
• MG Chemicals PCB Cleaner
• Electrolube FLU400DB
There are other cleaning liquids as well, but sometimes they can be difficult to obtain.

Some time ago, for cleaning small batches of PCBs, I used a special cleaning liquid for manual cleaning – Vigon EFM, in 1-liter bottles. I would fill two small containers with cleaning liquid. In the first container, I would soak the PCB for 5 minutes and then use an ESD brush to clean both sides of the PCB. Afterward, I would transfer the PCB to the second container with clean liquid and rinse it with a brush for a minute. The result was excellent! Clean PCBs without any residue.
After cleaning 10 PCBs, I would drain the liquid from the first container to allow it to settle, and after some time, I would reuse it. After the second use, the liquid was disposed of, as it became saturated with contaminants. It’s not advisable to use it again to prevent the formation of residues.
If you can’t find VIGON EFM, you can use other liquids:
• Microcare Flux Remover
• Chemtronics Flux Remover FluxOFF ES132 1 gallon. Dilute 1 to 10 with distilled water.
• Or the same FluxOFF.
The problem with many cleaning liquids is that their effective cleaning temperature is around 50 degrees Celsius (122°F), which makes manual cleaning difficult at room temperature. For a small batch of soldered PCBs, you can use aerosol sprays, but you will need to rinse more thoroughly, and streaks may still remain. Streaks can be removed with a lint-free cloth.

For daily cleaning of 10 to 50 PCBs, bubbles baths work well. Two baths are used. The size of the baths can vary, and you can find the right volume depending on your needs. PCBs are vertically placed in baskets. The essence of bubbles cleaning is small bubbles in the liquid. Air tubing runs along the bottom of the bath with many holes, and a compressor pumps air through it, like in aquarium. The bubbles gradually dissolve the dirt. But most importantly, the bubbles create movement of liquid inside the bath, which helps to wash out the remains of soldering flux from under the microcircuits and other components. The liquid temperature should be around 50 degrees Celsius or 122°F. It is necessary to monitor the temperature carefully, as low temperatures reduce the cleaning efficiency, and high temperatures can cause the cleaning fluid to decompose.
In the first bubbles bath, you can use cleaning liquids like VIGON US, VIGON A250, VIGON FA+, Surclean SC 2500, Chemtronics ES132, Aquanox, or IONOX. In production, you need to carefully select the cleaning liquid based on your equipment and the types of soldering flux you are cleaning. Heat the liquid, turn on the compressor to supply air, and immerse the basket with vertically positioned PCBs into the liquid. The cleaning time is 10 minutes. After cleaning, remove the basket and leave it over the bath for 2 minutes to allow excess liquid to drain back into the bath. This is important to prevent transferring cleaning liquid to the second bath.
For the second bubbles bath, use distilled water. The temperature remains the same at 50 degrees Celsius (122°F), also with bubbles and a 10-minute time. The task of the second bath is rinsing. You need to rinse off all the residues, including the cleaning liquid from the first bath. After rinsing, let the basket stand above the bath for 2 minutes, allowing the water to drain back into the bath.
The third step is drying. Usually, drying is performed in drying ovens at a temperature of 60 degrees Celsius (140°F) for 1 hour. Forced drying is necessary because water may remain between components and the PCB.

When working with PCBs, use an ESD wrist strap and ESD gloves to prevent static electricity damage to the PCBs and to avoid leaving fingerprints. Link to the video about static electricity in description.

Remember that not all water in stores is distilled, even if it is written on the label. You need distillate without additives - pure H2O, real distilled water is not cheap! Search ChemWorld. If you are engaged in cleaning electronics on a regular basis, it is cheaper to buy an industrial distiller to obtain distilled water. Distilled water does not conduct electricity, since it does not contain salts, and its specific resistance is about 18 mOhm / cm - high resistance. Understanding the level of water pollution is based on this principle. When the conductivity of water falls below 4 mOhm / cm, it needs to be replaced, since the water is saturated with pollutant ions. You can measure the specific resistance with a TDS meter. Remember that you cannot use ordinary tap water, since it is saturated with many minerals, salts, etc. A TDS meter will help you understand what kind of water is in front of you.
Drinking distilled water on a regular basis is not advisable. Such water is empty and does not bring any benefit. Pure H2O molecules have free ionic bonds and useful salts and minerals that are necessary for the body easily attach to these bonds in our body and they are washed out. Drink ordinary filtered water, which contains useful minerals and salts.
This is the essence of rinsing in distilled water - ions of pollutants attach to free H2O bonds, improving the quality of washing by an order of magnitude. The more ions of salts, minerals, soldering flux residues and pollutants attached to a water molecule, the lower the resistance of the water and the higher the ability to conduct electricity. And that is why it is useless to use ordinary water for washing, the ionic bonds in it are already occupied by salts and minerals. You can make it worse for printed circuit boards and a sediment will appear - a white coating on the printed circuit board.

Using isopropyl alcohol to clean printed circuit boards can cause the appearance of a white and gray coating, since organic alcohol copes well only with organic contaminants - resins, fats and oils.
Alcohol copes very poorly with chemical contaminants. Such as cheap chemical fluxes without organics, water-based fluxes with the precipitation of salts. Other salts that arise during the reaction with fluxes and metals. Corrosion residues and copper oxides. After the alcohol dries on the printed circuit board, you will see a white or gray coating that is difficult to remove without mechanical cleaning. The coating causes conductivity and current leaks on the printed circuit board. Visible coating can somehow be removed, but the coating that has formed under the components and microcircuits is almost impossible to remove. You will need to re-solder.
I do not recommend isopropyl alcohol for professional repair and production of electronics. Write in the comments how often you encounter plaque after cleaning and how you solved this problem!

I don’t use ultrasonic cleaning for PCBs, but this is a vast topic, and I’ll be releasing a separate video on ultrasonic cleaning. I want to explain in more detail why I don’t recommend it. Make sure to subscribe to the Youtube channel Electronics Manufacturing Technologies so you don’t miss it!

In industry, the same methods are used – cleaning, rinsing, drying steps. For large volumes of PCBs, either conveyor cleaning systems or stationary spray cleaning systems are used. Spray cleaning is more common, with special water-based cleaning liquids and a closed-loop filtration cycle for liquids. (insert fragment). The principle of spray cleaning is very similar to a dishwasher, but the system is more complex.