PCB Cleaning Techniques and Tips

One of the things that distinguish a professional printed circuit board from an amateur made one is the final appearance. Gobs of sticky rosin flux detract greatly from an otherwise neat circuit. Cleaning the rosin off the board is one of the more misunderstood processes in making homemade boards.

Most amateur pc board instructions refer to cleaning off the rosin with "alcohol" which to the amateur means "rubbing" alcohol or the alcohol in the alcoholic beverages he drinks. The latter is too valuable to waste on pc boards and both of them are full of water, which decidedly rejects rosin. Rubbing alcohol or Isopropyl alcohol available in the drug store or supermarket is typically 40% water and in addition typically contains 1% of a "lubricant" (usually a glycol). The alcohol content could be either isopropyl alcohol or a denatured form of ethyl alcohol. Rosin itself is insoluble in water and the water in rubbing alcohol greatly reduces the solubility of rosin.

Pure isopropyl alcohol (99%) is only available as a lab or industrial solvent, so most amateurs would not be able to acquire it. Pure ethyl alcohol is a controlled substance and expensive. Pure methyl alcohol is quite poisonous and is not particularly good at dissolving rosin (it is too close to water in chemical characteristics). If you must use alcohol as a pc board cleaner, the best bet is "2B denatured" ethyl alcohol, commonly known as methylated spirits, or shellac thinner. It is 85% ethyl alcohol (for its good solvent action) and 15% methyl alcohol (so you go blind if you drink it). It should be available in the larger home centers like Home Depot and large paint stores as the proper thinner for shellac. Don't confuse it with "lacquer" thinner with is a totally different animal.

Now I am going to let you in on a secret. There is a product available in hardware and paint stores (at least here in Canada - I don't know about its general availability in the USA) that makes cleaning rosin off a circuit board a snap. What is it? It is called "Poly-Clens" and is marketed by the same people who bring you Poly-Filla and Poly-Strippa. It is labeled as a paint brush and roller cleaner and consists of a mixture (I think) of a paint thinner, an alcohol and a liberal dose of a surfactant (a fancy technical name for detergent) to emulsify the mixture in water.

To use Poly-Clens to clean circuit boards, pour enough of the liquid into a tray (non-plastic) to just cover the board. Place the board in the Poly-Clens and let it sit for 3-5 minutes (longer if you have a really heavy dose of dried on rosin flux). Then remove it, let it drain for a few moments and then wash the board thoroughly in running water. The Poly-Clens remaining on the board will emulsify (dispurse thru the water turning white like milk) and be washed away. As an added bonus, the water will remove any traces of the "activating agents" in the rosin flux which if left on the board could cause corrosion. Note: if your water is chlorinated, a final rinse in deionized or distilled water is often recommended. It is not essential.

Remove as much of the water from the board as you can by shaking it, then put it aside in a warm place to dry. An oven set to "warm" or less than 140^oF will greatly speed the process.

Warning: This process is not suited for components that have enclosed crevices such as inductors in cans, switches, and some connectors that might trap the cleaning solution. Leave them off the board and install them later after the board has dried. Also certain plastics are affected more or less by the Poly-Clens and they also should be left off before cleaning. The plastics affected are quite rare in modern electronic components (polystyrene is the most common) but if you are uncertain, test the surface with a little Poly-Clens on a rag. This precaution actually applies no matter what cleaning solvent is used.

I have been using this material for the past 15+ years in my commercial assembly operation without problems. The idea came from a customer who had been using it for some years before that. I have had complements on the cleanliness of my assemblied boards and asked how it was done. Well, now you all know the answer.

As mentioned above, Poly-Clens is very common in Canada. I have not checked its availability in the USA. There are other paint brush cleaner products available but I would not trust them in this application without extensive trials. The Poly-Clens can be used over and over until it gets quite loaded with rosin. I normally keep two containers of it for my use. The first removes most of the rosin and gets quite dirty. Then a rinse in cleaner Poly-Clens followed by a water rinse completes the process. When the first can gets really dirty, I put it aside and replace it with the second. The dirty material is quite good at removing grease from auto motors and machinery. Just spray it on with a hand pump sprayer and after a few moments use a pressure washer to remove the softened grease. It may leave a slight whitish residue of rosin which will come off with a final rinse with clean Poly-Clens, varsol or other solvent if you are really picky.

Disclaimer: Any application of the process described here is solely the responsibility of the user and it is their responsibility to determine the suitability of the process and their locally available materials for their application. In other words, don't blame me if it does not work for you. It works for me and that is all that is important.