Flux removal HINT

After soldering components to a PCB there are many methods you can use to remove soldering flux.

I consider Isopropyl alcohol one of the least objectionable liquids to remove flux residue.
It can be frustrating to get all the flux and resulting stickiness off the board without using multiple rinses.

I soak the PCB in the alcohol.
Using a soft tooth brush go over the entire board, both sides.
After the brushing, I dump the alcohol back into a bottle labeled USED.
I then "immediately" soak the PCB in distilled water.
After a short time, I remove the board and with compressed air blow remaining liquids off.

The water removes ALL the alcohol and dissolved flux from the PCB.

NOTE:
Any components that may be damaged by water or alcohol should not be submerged.
ex: switches, some relays, speakers, jacks, SD sockets etc.
Add these after cleaning the PCB. Then clean their pads with alcohol and a Q tip.

This water method will save on alcohol and prevent flux residue from remaining on your boards.

rosin flux (the kind that soluble in isopropyl alcohol) doesn't really need to be cleaned off, except in the case of very sensitive circuits...

LarryD:
After the brushing, I dump the alcohol back into a bottle labelled USED.

And ... ?

Paul__B:
And ... ?

Use as moonshine ingredient?

Just kidding...

westfw:
rosin flux (the kind that soluble in isopropyl alcohol) doesn't really need to be cleaned off, except in the case of very sensitive circuits...

Its a good idea though - it can oxidize over time and darken. It will also absorb moisture and
become more conducive than bare board surface which matters for high voltage circuits. Exposed
to sunlight it will decompose slowly too.

After the brushing, I dump the alcohol back into a bottle labeled USED.

And ...?

I reuse the alcohol over and over again.

.

I use fresh 99.9 anhydrous alcohol and a hogs hair brush to clean rosin flux off. I don't soak, I don't want any residue to get into screw terminals or female headers for example and contaminate those contacts.

It's not that easy to find >70% isopropanol in local stores.
What about using denatured ethanol instead?

91% rubbing alcohol can be found in CVS most of the time (stocking is a little flaky)

If I rinse a board with water, I'll usually rinse it again with clean rubbing alcohol, as that will rinse off most of the water - and rubbing alcohol evaporates much more readily than water so your board spends less time wet.

You're right. The place down the street supposedly has 91% isopropyl alcohol in stock.

Is ethanol less effective? Or just more expensive?

If you use compressed air to blow off the water, it evaporates in seconds.

We get 99% Isopropyl Alcohol at COSTCO, 4 X 500mL bottles (2L) for $9.50CDN it works great.

I suppose a final rinse in fresh alcohol would remove 100% of any remaining flux.
But, I have not had any problems with using just one application with a water rinse afterwards.

Edit:
99.9% in electronic stores is ~$15.00CDN for 1L.

Ethanol is for drinking.
But, white lightning (gut rot) might work, so sad. :cry:

My "local" (30 minute drive) carries it in large bottles. I bought a gallon last time, is lasting me a while.

jboyton:
It's not that easy to find >70% isopropanol in local stores.

My wife found 91% rubbing alcohol (isopropyl) at Walmart. The only other ingredient is purified water. It even came in a convenient squirt-lid plastic container.

What about using denatured ethanol instead?

Bad choice. The "denatured" part can include any number of ingredients. Some will leave residue. Others may damage a PCB. All of them are in some way dangerous to humans.

Alcohol + purified water is the best choice.

LarryD:
Ethanol is for drinking.

Not if it’s denatured. People use denatured ethanol in stoves, as a fuel additive for automobiles and also as a solvent. I was just curious to learn if the use of rubbing alcohol for electronics is due to effectiveness, price or tradition.

LarryD:
We get 99% Isopropyl Alcohol at COSTCO, 4 X 500mL bottles (2L) for $9.50CDN it works great.
99.9% in electronic stores is ~$15.00CDN for 1L.

Anything over about 90% is a waste of money. At that concentration the water evaporates as the alcohol evaporates.

Plus...

If you use compressed air to blow off the water, it evaporates in seconds.

jboyton:
I was just curious to learn if the use of rubbing alcohol for electronics is due to effectiveness, price or tradition.

Yes. Yes. Yes.

And, availability. Ethanol, denatured or otherwise, can be difficult to obtain...

Isopropyl is available from any pharmacy (try to avoid denatured).

westfw:
rosin flux (the kind that soluble in isopropyl alcohol) doesn't really need to be cleaned off, except in the case of very sensitive circuits...

Like a flux capacitor?

Really? You can't buy denatured alcohol in a dry county? That's a little hard to swallow. :slight_smile:

Like a flux capacitor?

If you clean all the flux off you may end up in a year not of your choosing.
.