Ultrasonic pcb cleaner - Page 1
Forum section: electronics / projects

author: djsb
author_rank: Super Contributor
timestamp: April 21, 2010, 09:12:01 am
content: Hi,I've bought myself one of these ultrasonic cleaners.http://cgi.ebay.co.uk/NEW-6-5-LITER-INDUSTRIAL-ULTRASONIC-CLEANER-WITH-BONUS_W0QQitemZ390172147214QQcmdZViewItemQQptZUK_Jewellery_Watches_JewelleryBoxes_Supplies_CA?hash=item5ad8127e0eMainly bought to clean the carburretors in my motorcycles (and my dentures when my teeth fall out)I'm assuming that the output is a single frequency at 50W (misdescribed as 150W). I've been reading that single frequency units can cause damage to a PCB due to resonance. Articles suggest the use of a swept frequency instead.My question is it possible to modify the oscillator in these units to produce a frequency sweep of 40kHz +/- 3%? I was thinking some kind of varactor diode voltage controlled by a ramp waveform.Does anyone have any experience of using ultrasonics to clean boards?Thanks.David.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: April 21, 2010, 01:44:03 pm
content: I am not an specialist in those , but still I have the opinion, that the frequency sweep , has to do with more factors than the PCB it self , even the thickness of the metal , of the internal bath , could work as an negative factor.I have seen an similar device , working as cleaner for printer heads.The pulsing watter does all the work ..Any way .. I am not an specialist in those ..About the oscillator , I think that is not possible one oscillator to sweep as you have think of it.It more likely to have three locked oscillators , that powers up in sequence , and share the same output.( Just some thoughts )

author: DJPhil
author_rank: Frequent Contributor
timestamp: April 21, 2010, 02:41:51 pm
content: Quote from: djsb on April 21, 2010, 09:12:01 amI had the pleasure of seeing an ultrasonic cleaner rip forty years of crud off of some old Greyhound bus parts once, and it was near magical. They're absolutely awesome for automotive parts, but you do have to be a bit careful about overdoing it when working with parts that have a fine tolerance. I went a bit overboard once and pitted the heck out of a machined surface, lesson learned.Quote from: djsb on April 21, 2010, 09:12:01 amUltrasonic cleaners are fairly simple to manufacture and their use is usually quite forgiving of tolerance, so I wouldn't trust the specs to be very precise unless you can get info from the manufacturer (and trust it). A cleaner's power output can be subject to a similar level of ad-wizardry and jackassery as a hi-fi stereo. If you have the capability, I'd recommend taking your own measurements to get a baseline.The problem with frequency sweeping is the transducer. The electronics can be adjusted to output whatever power and frequency you like, but the transducer itself is only capable of a certain frequency response. It's similar to an audio speaker, but the physics is a bit weirder for having to deal with metal and fluid instead of just air. A typical transducer is made up of bonded layers of various materials in addition to the crystal and designed to have a resonant frequency at which it is most efficient, and departing from it's resonant frequency at significant power levels will cause attenuation and (worst case) possible damage to the transducer. Broadband ultrasonic transducers with wide flat frequency response do exist, and are likely available at high enough power to clean with, but my experience with them is low power non-destructive testing. It's very unlikely that the manufacturer used a high power (multiple watts plus) broadband capable transducer and left out the ability to sweep the frequency over a large range, as I imagine such a unit would be relatively expensive (and heavily marketed as such). The frequency response of a tuned transducer will have one good peak that it's designed for and usually at least one other peak (far) above and below that it can operate at with reduced efficiency, but will operate poorly in between. The cleaner I used for bus parts had the ability (highly touted) to sweep frequency a few KHz to keep standing waves from developing within the parts, and this is definitely a good thing.I imagine that the problem with cleaning a stuffed PCB ultrasonically is the parts themselves responding unpredictably. Sure enough, theIPC has a test method for it(love those guys, they've got something for everyone). You might have to upgrade to military spec parts, but if you can find parts that are IPC-TM(Test Method)-650 certified then you'll know what they're guaranteed to endure. My guess is that frequency sweeping is designed to cut down a good deal on the parts, leads, and joints resonating as opposed to the PCB itself. I think a bare PCB is much less likely to be damaged by a single frequency cleaner, but I suppose track adhesion and plated through holes would also be potential vulnerabilities. Then again, I suppose ultrasonically cleaning a naked PCB is a bit of overkill anyhow, and nowhere near as useful as cleaning a stuffed board.All things considered, were I in your shoes I'd definitely experiment with the cleaner as manufactured, you never know! Modifying it without replacing the transducers may work to some extent, and the reduced average power from broadband sweeping might work in your favor, but you'll still be delivering a huge spike of energy at the transducer's resonant frequency (plural, if you sweep that far), just less often. Using different transducers is an option, but they tend to be the bulk of the cost of a cleaner, so at that point you might want to consider building from scratch. It can be a real pain to get a transducer to behave efficiently, but it could be a neat project.I hope I got the details right, it's been a few years since I worked with ultrasonics. I trust peer review to straighten me out if I drifted to far.Hope that helps some.

author: XynxNet
author_rank: Regular Contributor
timestamp: May 14, 2010, 11:03:12 am
content: We cleaned laboratory equipment of chemical an biological residue with a more professional version of this device. It works really well. But be sure to use ear protection! Although you can't hear ultrasonic, it can damage your ears.

author: safarir
author_rank: Regular Contributor
timestamp: May 15, 2010, 05:04:24 pm
content: Quote from: XynxNet on May 14, 2010, 11:03:12 amHi,I don't think it necessary to wear ear protection. My mother is a dentist and used one for more than 40 years without any problem.Sorry for my bad english

author: rossmoffett
author_rank: Regular Contributor
timestamp: May 15, 2010, 06:56:05 pm
content: Quote from: safarir on May 15, 2010, 05:04:24 pmTwo issues with that, though. You have a sample size of "mother" and we don't know that her ultrasonic cleaner was of the same power as this one. Better to be on the safe side.

author: djsb
author_rank: Super Contributor
timestamp: May 16, 2010, 05:34:41 pm
content: Hi,I've used it a couple of times now and It's a noisy b****r. Ear plugs are indeed recommended.David.

author: safarir
author_rank: Regular Contributor
timestamp: May 16, 2010, 05:42:45 pm
content: Quote from: rossmoffett on May 15, 2010, 06:56:05 pmHi rossmoffett,The simple size it much bigger than just my "mother", it include all is employee. Also, I think it the same situation in all dentals "center" becauce my stepfather is also a dentist and is the same at is "center".I mush admit that I have no Idea of the power of these device.Sorry again for my bad english

author: shodan
author_rank: Contributor
timestamp: July 04, 2010, 09:20:56 pm
content: I've been itching to buy one of these since forever !!but the dimensions of the container are always disappointinga while ago I searched for just the transducer and just make my own welded metal tub of just the right sizebut I never got around to doing it ! :\I hope if you get this, that you won't plug it in, but take it apart !!!I'm curious to see how it's made and if we can make a better oneI think the only important part in there is the transducer, the rest is just a high power fixed "ultrasonic" frequency oscillator (could be anything 40khz and up, I heard of ultrasonic cleaners in the mhz range but need to confirm ...)for the ear protection I am a bit skeptical, the human hear has almost zero resonance at this frequency, I just don't believe it can absorb enough energy to cause damage to the ear drums... maybe if you stick your head in the liquidalso there's some specially made hydrocarbon-based solvent that supposed to be better than water than you can getalso I just remember that where I work we have a huge one of these, it's a almost 1 meter wide cubic tub with transducers welded to the tub and there's an external frequency generator/amplifier, looks like a very simple machine overall.. I'll try to find the product name and generic name of the ultrasonic cleaning fluidit's probably just stoddard dyed,rebadged and sold 5 times the price !!

author: Zero999
author_rank: Super Contributor
timestamp: July 05, 2010, 12:13:26 am
content: Quote from: shodan on July 04, 2010, 09:20:56 pmYou're right and not much energy will be coupled to the air anyway because of the large impedance mismatch between the liquid and the air.QuoteYes, divers can suffer damage to their ears from high intensity sonar.Only an idiot would put their head in an ultrasonic cleaning bath though.

author: djsb
author_rank: Super Contributor
timestamp: July 05, 2010, 10:01:47 am
content: In reality the bath is noisy. The noise comes from the stainless steel bath and cage (that holds the stuff to be cleaned) vibrating. Maybe this particular bath is noisy because it's one of the lower quality ones and if you spend more it would be quieter, I don't know.I don't intend stripping it down but if at some stage it stops working I may have to to fix it. It does a good job on cleaning the oxide off of the outside of carburettors. I've not tried it on anything else yet.David.