Cleaning Flux From a PCB

In this how to I will show you my method of cleaning a PCB after assembly / soldering. It's not the only way to do this, but it is tried and tested.

DISCLAIMER - DANGER

You will use chemicals during this process, it's up to you to handle them correctly and take any safety precautions you see fit. I do not take any responsibility for how you work with them. Also keep in mind that not all the products mentioned are available everywhere in the world.

If you use the hair dryer, make sure it's well away from any water supply you use. It can be very dangerous to mix electricity and water!

The starting point

This picture above show the back of a recently soldered PCB, as you can see it has plenty of flux all over it. Generally thats not a problem for it's functionality - but it does not look good!

You will need:

Polycell brush cleaner, it sometimes goes by a different name (but similar) . Also it's not the only one, many other makes are just as good - look for something that's clear not misty coloured and is based on aliphatic/aromatic hydrocarbons (oil based). The only reason I mention this product by name is it seems to be world wide and easy to find and it's the one I use!

Optional: Isopropanol (95% or better), this will clean PCB's by itself - many tutorial s exist just using this. But here it's used as a cleaner mainly to get rid of the brush cleaner. You can use water to mix with the detergent as a substitute, but it does not clean as well and takes longer to dry.

Detergent (washing up liquid)

Tooth brushes

absorbent kitchen paper

rubber gloves are handy to avoid dry skin etc from the isopropanol

Optional: hair dryer.

water

Step 1

Mix about 60/40 Isopropanol (or plain water if you prefer) and washing up liquid, I normally keep a small jar full ready to use. If you use water keep in mind it's not as good at cleaning the brush cleaner away and takes longer to dry the PCB after. I prefer isopropanol because it also helps remove any flux the paint brush cleaner may have missed.

In the photo it's the pale green solution.

Step 2

Put a small amount of both the mixture from step 1 and brush cleaner into separate containers, I use the lids of small jars. You really only ned a very small amount.

Make sure you have a couple of sheets of kitchen paper ready to dry the water away. And tooth brushes in easy reach. Keep a towel handy to dry your hands with before you dry the board.

If you decide to use a hair dryer DO NOT get it near the water supply! It would be very dangerous to get it wet! I normally have it the other side of the room with the kitchen paper, that way you have to walk away from the water to get to it.

ready to go

Using the first tooth brush, dipped in brush cleaner gently (maybe not too gently) scrub the PCB surface all over in a circular motion. Pay attention to go up to the edges.

Keep the board at an angle, as shown in the second photo, work from underneath the board that way any liquid will tend to drain off the board and not onto the component side.

Repeat this for a few times round the board surface, probably about a minute in total.

You now need to repeat the the clean, this time using a second tooth brush and the isopropanol/washing up liquid mix. Again; scrub for about 1 minute.

You may notice this time a slight foaming as you go. it's ok, in the next step this will get deliberately more.

Now using the second tooth brush that you just used with the washing up liquid mix. Alternate between rinsing the brush under slowly running water and continuing to scrub the PCB.

You should see a slight foaming start as you add water.

keep going for about 1 minute.

It's now time to rinse the foam from the PCB, push the board, quickly, under a slowly running tap. Only just long enough to remove the foam. You may need to turn the board 180 degrees to get both ends clean.

Try at this point to minimise any water getting to the component side of the board.

Transfer away from the water supply and place wet-side down on the kitchen paper. You can then turn the tap off. I recommend doing this at leat 10 feet away from the water (other side of the room!) so as not to risk the hair dryer getting near the water.

MAKE SURE YOR HANDS ARE DRY BEFORE PROCEEDING.

Once you have the board away from the water pat it down with the kitchen paper to remove the majority of the water.

Make sure your hands are dry.

You can just put the board someplace warm and dry for a couple of hours at this point to dry.

Optional:

Use the hair dryer on a low setting to dry up any water remaining on the PCB - be careful not to get it to hot!

You can also use the dryer to blow over the component side, paying attention to the edges (where water may have made it's way to the wrong side of the board). Keep it as cool as possible so as not to damage components.

At this point, if you used it, you can remove the dryer from the wall socket and set it aside.

Clean up your left over container lids. To avoid polluting the wast water I normally poor the remaining small amount of liquid on to the used kitchen paper. This can them be disposed of in the household rubbish.

The results can be seen above