Assembled PCB ultrasonic cleaning: it's always safe? (Crystals, mechanical etc.) - Page 1
Forum section: electronics / projects

author: mcinque
author_rank: Unknown
timestamp: October 18, 2017, 08:01:59 pm
content: I always wanted to have a proper ultrasonic cleaner instead scraping manually assembled PCBs with brush and IPA, but I'm wondering if it's safe to use them for all assembled PCBs: crystals, electrolytics, mechanical parts like onboard pushbuttons or some kind of memory can be easily damaged?If I can't use it on all circuits that fits in the utrasonic basket maybe doesn't worth the price.Of course I would purchase a proper, not a cheap chinese no-brand, ultrasonic cleaner (I've seen too much crap around in this kind of stuff: no grounding, no thermal safety etc.) but my doubts are about the health of the assembled PCBs I could clean with it.Does it worth the price? Do you have any suggestion about cleaning with ultrasounds an assembled PCB?

author: doktor pyta
author_rank: Frequent Contributor
timestamp: October 18, 2017, 08:24:43 pm
content: My experience is that chokes in SMD1812 package often failed open circuit after 1...3 minuts of ultrasonic cleaning. Crystals survived.

author: wraper
author_rank: Unknown
timestamp: October 18, 2017, 08:33:57 pm
content: Switches must not be washed in any case be it ultrasonic bath or just a brush with IPA. Crystals are not suggested to be exposed to ultrasonic. I would avoid washing electrolytic caps. Not all of them are solvent proof, especially larger sizes. And as they contain liquid, internal cavitation may damage them.

author: Ash
author_rank: Regular Contributor
timestamp: October 19, 2017, 01:44:02 am
content: I've seen specific warnings in Real time clock chips (with integrated 32KHz crystals) not to ultrasonically wash the units as the 32KHz "tuning fork" crystals are quite susceptible to damage when over driven. The cleaner is possibly running at a close frequency.Quote from: doktor pyta on October 18, 2017, 08:24:43 pmVery interesting.. Not something I would have expected but a good lesson! Can you point me to the parts in question? I'd be interested in looking at how they are made..I'd suggest that you check the datasheets for everything..Then maybe just resort to a wash in a cleaning solution with a brush... which is pretty much what I have to do. Electrolube safewash and saferinse work really well, but so does IPA with a bit more patience.Ash.

author: floobydust
author_rank: Super Contributor
timestamp: October 19, 2017, 02:02:14 am
content: No, it's not safe. Very hard on components and the PCB.You can see etched metal, fractured crystals, broken bonding wires etc.I suggest very short time like 30 seconds depending on the units intensity.

author: babysitter
author_rank: Frequent Contributor
timestamp: October 19, 2017, 10:31:04 am
content: Lets include dishwasher cleaning which i prefer...I am reluctant for transformers and speakers. Any recommendations regarding this method?

author: mcinque
author_rank: Unknown
timestamp: October 19, 2017, 04:38:43 pm
content: So any ultrasonic cleaning that normally a hardware repair lab do after a water spill damaged board is risky? I mean, only in that cases it worth the risk since the board it's already dead and it worth trying a clean?

author: Tomorokoshi
author_rank: Super Contributor
timestamp: October 19, 2017, 05:30:54 pm
content: For a certain circuit board I do service work on I clean it in water with a little Formula 409 and scrub it down with a soft bristle dish brush.After scrubbing down it gets rinsed, and then I swing it fast to move as much water out as possible. From there the water gets dabbed off with a towel. It spends at most 1 minute directly submerged in the water.Finally it goes in front of a dehumidifier for a few hours.I have not had any problems I can trace back to this cleaning method, and that's with perhaps 50 boards going through this process.The board construction is through-hole, containing the typical mix of a processor, logic, resistors, capacitors, triacs, electrolytics, a transformer, connectors, etc. Typical early 2000's types of components. No switches or trimpots go through this process.

author: janekm
author_rank: Unknown
timestamp: October 20, 2017, 07:39:56 am
content: Ultrasonic cleaning of PCBs should be done on a special ultrasonic cleaning machine that avoids using a fixed frequency (random frequency or fixed frequency) to avoid hitting any resonances.Certain MEMS devices like accelerometers and gyroscopes have notes in their assembly guidelines to avoid ultrasonic cleaning as it can break the bond-wires inside the package. Of course it's also no good for microphones, T&H sensors, barometers, gas sensors...

author: mcinque
author_rank: Unknown
timestamp: October 20, 2017, 07:50:34 am
content: So frequency sweep would be ok?

author: janekm
author_rank: Unknown
timestamp: October 24, 2017, 09:11:19 am
content: Quote from: mcinque on October 20, 2017, 07:50:34 amYes that's what I meant to write... swept frequency or randomised frequency. Assuming the components are otherwise OK with ultrasonic cleaning.

author: Jeroen3
author_rank: Super Contributor
timestamp: October 24, 2017, 03:49:02 pm
content: Anything that has small openings, moving parts or windings should not be ultrasonically cleaned.This excludes:- Unsealed relays.- Potentiometers and dip switches.- Transformers (not potted)- Inductors (not potted)- Switches/buttons.Most of the time boards can be rinsed, but not with aggressive degreasers. Check datasheet of parts.If you do rinse them, put them in an oven at 50/60C for 15 minutes to half an hour.Some electrolytics are not washable either. The plastics keeping the vent closed could dissolve.

author: MrW0lf
author_rank: Frequent Contributor
timestamp: October 24, 2017, 03:58:28 pm
content: Yet most are quite happy to expose their unborn children to ultrasound machines operated by personnel having no concept of physics

author: mcinque
author_rank: Unknown
timestamp: November 01, 2017, 05:46:28 pm
content: Ok so ultrasonics are never completely safe except you check datasheets for that kind of treatment and respect time and frequency limits.Of course crystals can be damaged for their nature.But at this point I'm confused, someone can explain me why some "professionals" on YouTube trow macbook logic board in ultrasonics without any worries?

author: helius
author_rank: Super Contributor
timestamp: November 01, 2017, 05:57:00 pm
content: Because those types of components are not present on the logic boards, by and large. They use clock generator chips instead of crystals, MLCCs or tantalums instead of electrolytics, potted inductors, and no DIP switches. The smartphone logic boards with MEMS gyroscopes would be a higher risk.

author: Jeroen3
author_rank: Super Contributor
timestamp: November 01, 2017, 06:04:53 pm
content: Because the boards are already broken?Sometimes just rinsing and scrubbing is enough, but that takes time. If you can put it in a bath with cleaning solution and go back to work while the bath does a mild scrub, it saves time.

author: mcinque
author_rank: Unknown
timestamp: November 01, 2017, 06:35:02 pm
content: understood, thanks for the details

author: m98
author_rank: Frequent Contributor
timestamp: November 02, 2017, 05:22:53 pm
content: Quote from: MrW0lf on October 24, 2017, 03:58:28 pmJust... No. Please, if you yourself have not even the slightest idea of what you're talking about, just keep it for yourself.

author: janekm
author_rank: Unknown
timestamp: November 04, 2017, 03:28:35 am
content: Quote from: helius on November 01, 2017, 05:57:00 pmThere will be some crystals (for the wifi chipset if nothing else). But the big difference it that if you're building 10 million boards, and ultrasonic cleaning damages 0.01% of boards with a latent defect that shows 5 months later, your have a big headache on your hands. If you're a repair shop, you'd never even know.

author: mcinque
author_rank: Unknown
timestamp: November 04, 2017, 11:37:50 am
content: Usually production lines that wash their PCBs use a dishwasher-like machine or what?