Cleaning Flux From a PCB
Introduction: 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!
Supplies
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: Get Setup Ready
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. 440
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
Step 2: First Clean
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.
Step 3: Second Clean
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.
Step 4: Final Clean
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.
Step 5: Rinse
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! 254