Using Ultrasonic Cleaners for PCBs

Thread Starter

dcbingaman

Joined Jun 30, 2021
566
After doing a lot of research about this subject, there appears to be a lot of opinions about the proper way to clean a PCB and when or if even necessary to use an Ultrasonic Cleaner. Which manufacturers make descent ones etc. After building up a board I normally clean it with an acid brush and copious amounts of Isopropyl Alcohol. The board was failing with a digital input to a CPLD having 3K of resistance to an adjacent pin that was an output pin. I had to literally spray at high pressure Isopropyl alcohol between the pins to get under the CPLD (A TQFP package) to get at flux residue under the part. This fixed the problem. Question is, can a Ultrasonic cleaner do the same? And if so what type of cleaning agent should be used and how to go about it?
 

ThePanMan

Joined Mar 13, 2020
368
HMMMmmmmm. I've used IPA too (IsoPropyl Alcohol). Trouble with that is the residue. Hard to get rid of.

For my experiences, many manufacturers have gone to "No Clean" fluxes - or "Water Soluble" fluxes. With the WS flux all you need is hot water, then a means to thoroughly dry the board before powering it up.

As for using IPA, I'd rather a better cleaner, one designed for cleaning flux from PCB's but off hand I don't have any advice what to buy. For as often as I might have to clean a board I find using No Clean flux works best. For those other times - rare as they may be - cleaning with IPA works well enough.
 

MrSalts

Joined Apr 2, 2020
1,762
Don't put IPA in the ultrasonic bath. Ultrasonic bath is not great for soft/tacky residue that is capable of damping the ultrasonic energy. It can take a long time to vibrate out the insoluble gel.
 

Thread Starter

dcbingaman

Joined Jun 30, 2021
566
HMMMmmmmm. I've used IPA too (IsoPropyl Alcohol). Trouble with that is the residue. Hard to get rid of.

For my experiences, many manufacturers have gone to "No Clean" fluxes - or "Water Soluble" fluxes. With the WS flux all you need is hot water, then a means to thoroughly dry the board before powering it up.

As for using IPA, I'd rather a better cleaner, one designed for cleaning flux from PCB's but off hand I don't have any advice what to buy. For as often as I might have to clean a board I find using No Clean flux works best. For those other times - rare as they may be - cleaning with IPA works well enough.
Thanks, I have been using standard paste flux I will try the No Clean flux. I would imagine you mean a product something like this?

https://www.digikey.com/en/products/detail/chip-quik-inc/CQ4300-2OZ/14636567
 

dl324

Joined Mar 30, 2015
14,484
Question is, can a Ultrasonic cleaner do the same?
My thinking is that it would. I plan on buying one someday.

When you cleaned with isopropyl alcohol and an acid brush, how long were the bristles? I usually cut them down to 1/16-3/16 of an inch so they're stiff enough to really scrub the board. I use 70% isopropyl alcohol and only resort to 99% or commercial flux remover for the stubborn cases.
 

Ya’akov

Joined Jan 27, 2019
5,676
Louis Rossman, who has become very well know in the right to repair community, repairs Apple products. He has quite a set of specific things concerning flux, solder, and rework methods and soldering techniques for SMDs. He uses ultrasonic cleaners and is a big advocate of them.

His YouTube channel has a lot of videos where he discusses all of this. His website has some things for sale, including flux (it's the one I use, and I am very happy with it) and ultrasonic cleaners, but unfortunately the smaller ones are out of stock the big one is nearly $1700.00.
 

Thread Starter

dcbingaman

Joined Jun 30, 2021
566
My thinking is that it would. I plan on buying one someday.

When you cleaned with isopropyl alcohol and an acid brush, how long were the bristles? I usually cut them down to 1/16-3/16 of an inch so they're stiff enough to really scrub the board. I use 70% isopropyl alcohol and only resort to 99% or commercial flux remover for the stubborn cases.
I do the same: cut bristles down to close to what you recommend. I tend to use 99.9% alcohol but that probably is not necessary. Just me being extreme. Though as I stated a ran into problems with this with high density SMD components having 'low resistance' bridges between pins' due to flux residue even after extensive cleaning, which is why I am looking for a better way.
 

dl324

Joined Mar 30, 2015
14,484
I tend to use 99.9% alcohol but that probably is not necessary.
Try 70% if you have it. If you're not immersing the board in the 99.9%, the faster rate of evaporation might be working against you. That's why I start with 70% and go to 90% if I need it.
 

Ya’akov

Joined Jan 27, 2019
5,676
What product do you recommend as an alternative?
What sort of components are you soldering? There are different options for different applications.

For SMD and SMD rework, I use Amtech MC-599-V2-TF which is a no clean “tacky flux”. You put on a glob and it will hold the part in place as you solder. All the pins are submerged and it gives excellent results. In this case “no clean” means you don’t have to clean it, but I certainly do clean it because it can be messy. Fortunately, it also means “easy to clean” and it comes right off with IPA.

For some SMD, wire to board, connectors, and the like I use Kester 959 no clean flux. It is really no clean though it will leave a light white residue on the board you might want to remove—but don’t have to. It comes is gallons (ha), and in needle bottles and pens. The pens are great for things like pin headers or SMD pad. You just paint them and the minimal amount is applied, all done.
 

MrSalts

Joined Apr 2, 2020
1,762
Try 70% if you have it. If you're not immersing the board in the 99.9%, the faster rate of evaporation might be working against you. That's why I start with 70% and go to 90% if I need it.
This is right, pure 99.9% isopropanol won't dissolve sole common components of flux. Look at SDS for flux cleaners and you'll see more ethanol in the mix ("denatured alcohol" is getting harder to find in the US - look for Shellac thinner or alcohol fuel. A 90% ethanol + 10% isopropanol mix seems most common. Or add a few 5% water (by weight) or 5% methanol to IPA to make a solution with higher. Polarity than pure ipa.
 

Thread Starter

dcbingaman

Joined Jun 30, 2021
566
What sort of components are you soldering? There are different options for different applications.

For SMD and SMD rework, I use Amtech MC-599-V2-TF which is a no clean “tacky flux”. You put on a glob and it will hold the part in place as you solder. All the pins are submerged and it gives excellent results. In this case “no clean” means you don’t have to clean it, but I certainly do clean it because it can be messy. Fortunately, it also means “easy to clean” and it comes right off with IPA.

For some SMD, wire to board, connectors, and the like I use Kester 959 no clean flux. It is really no clean though it will leave a light white residue on the board you might want to remove—but don’t have to. It comes is gallons (ha), and in needle bottles and pens. The pens are great for things like pin headers or SMD pad. You just paint them and the minimal amount is applied, all done.
I am soldering through hole and SMD including some very small SMD parts. Thanks for the advice. I have purchased both no-clean water soluble flux and no clean water soluble flux core solder.
 

Thread Starter

dcbingaman

Joined Jun 30, 2021
566
This is right, pure 99.9% isopropanol won't dissolve sole common components of flux. Look at SDS for flux cleaners and you'll see more ethanol in the mix ("denatured alcohol" is getting harder to find in the US - look for Shellac thinner or alcohol fuel. A 90% ethanol + 10% isopropanol mix seems most common. Or add a few 5% water (by weight) or 5% methanol to IPA to make a solution with higher. Polarity than pure ipa.
Thanks. The Lowes store in town has denatured alcohol as alcohol fuel (gallon metal can) which I think is basically ethanol? Is that correct? I am also moving the no-clean/water soluble flux.
 

Thread Starter

dcbingaman

Joined Jun 30, 2021
566
Try 70% if you have it. If you're not immersing the board in the 99.9%, the faster rate of evaporation might be working against you. That's why I start with 70% and go to 90% if I need it.
Sure, I see any department store (Walmart etc.) sells 70% and much cheaper than the 99.9%. I will give that a shot Thanks!
 

SamR

Joined Mar 19, 2019
4,212
Denatured alcohol is ethanol with a denaturant added (usually gasoline) to render it undrinkable (thus cheaper since no alcohol tax). Stove fuel is a petroleum product called white gas, naphtha, or naphthalene. Basically, light ends gasoline without any additives or dye (or road taxes). Alcohol is water soluble, gasoline is not.
 
Last edited:

Ya’akov

Joined Jan 27, 2019
5,676
Denatured alcohol is ethanol with a denaturant added (usually gasoline) to render it undrinkable (thus cheaper since no alcohol tax). Stove fuel is a petroleum product called white gas, naphtha, or naphthalene. Basically, light ends gasoline without any additives or dye (or road taxes). Alcohol is water soluble, gasoline is not.
Denatured alcohol is sold as “fuel” in many places. It’s just denatured alcohol but they are marketing it to campers, caterers, and people who want to use alcohol lamps for sciencey stuff.

Gasoline is used as a denaturant but several other things are used like IPA, methanol, acetone, benzene, pyridine, and acetone. Most of the denatured ethanol I find around here has methanol.
 

Delta Prime

Joined Nov 15, 2019
1,326
Hello there:)
I use a sonicator with an automatic sweep frequency function in combination with heater greatly
assist an EtOH bath as the cavitation affect occurs.
After a run of 100 boards or so.
The unused EtOH makes great punch to share with colleagues. ;)
 

tindel

Joined Sep 16, 2012
876
I run all my boards through an ultrasonic bath. I fill the bath with tap water, then insert a pyrex dish in the water, fill the pyrex dish with IPA, and place the board(s) in the IPA. I learned this technique while working as a technician at NASA where we cleaned everything using ultrasonic/IPA methods and used particle counters and ultrapure water to verify particulate cleanliness and size distribution.

My ultrasonic bath has a heater and can produce sine, square, and triangle wave pulses. I bought a cheap one off of Amazon. I have noticed that when I run the ultrasonic bath, my raspberry pi losses it mind, so it likely doesn't conform to conducted emission standards, but the boards come out clean.

I can't answer your CPLD question, but the BGA's I use seem to be pretty clean, but it's difficult to confirm for sure.
 

SamR

Joined Mar 19, 2019
4,212
In school we had labeled wash bottles of ethanol on the lab benches instead of distilled water. I was curious about it, so I asked the Professor about it. He laughed and told me they had a permit to distill their own. But to denature it so it wouldn't kill the idiots that tried to drink it they denatured it with phenolphthalein. Phenolphthalein is commonly used in labs as a pH indicator but in Pharmacology it's used as a laxative and is/was the active ingredient in Ex-Lax chocolate bars. It wouldn't kill them but it sure would make them think their insides were coming out their backsides.
 
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