Are fixed frequency ultrasonic cleaners really that bad for PCB's? - Page 1
Forum section: electronics / general

author: _Wim_
author_rank: Super Contributor
timestamp: August 20, 2016, 11:24:05 am
content: I understand that fixed frequency ultrasonic baths have a higher (theoretical) likelihood of creating hot spots and cold spots , but it seems strange to me that swept frequency baths only have been available in the last decade or so… Could this new focus on swept frequency be a marketing gimmick? (because quality baths probably last for decades so sales was going down...) I can understand swept frequency is better, but when reading this forum and other forums it seems like using a fixed frequency bath will destroy any pcb in no-time. (little exaggeration from me side) So if that was so important, I would expect this to have been available much longer.I have no experience using the one or the other, but I am looking into buying such a batch for very occasional use, so buying a professional one with swept frequency is not really something realistically for my use. One the other hand I do also want to avoid destroying the pcb’s I put in there…Any thought from people who have been using a fixed frequency batch for cleaning pcb’s and other stuff?

author: voltsandjolts
author_rank: Unknown
timestamp: August 20, 2016, 11:32:00 am
content: As I understand it, the main concern is damage to quartz crystals/resonating components on the PCB rather than the PCB itself.

author: _Wim_
author_rank: Super Contributor
timestamp: August 20, 2016, 11:38:49 am
content: Because quarts resonators have such a narrow resonance frequency, I would think that even a "fixed" frequency batch "sweeps" enough in frequency to avoid being continuously exact on the frequency of the crystal. Also, we are talking here typically about0 at least a 100-th harmonic (for a 4Mhz crystal),I do not know if efficient coupling is still possible...

author: voltsandjolts
author_rank: Unknown
timestamp: August 20, 2016, 11:52:39 am
content: 4. Cleaning• AT-cut quartz crystals (not tuning fork crystals) Ultrasonic cleaning should be avoided due to the ri sk of damage to the crystal blank. If ultrasonic cleaning is used, there is a risk of generating mechanical resonances, which may cause an intermittent or permanent damage of the crystal component. Please be aware that ul- trasonic waves propagate over a board in a way which is not under control of the crystal manufacturer. Therefore it is impossible for us to confirm each customer's mounting and cleaning conditions, such as the mechanical resonance conditions of the board, the cleaner's type, the applied pow- er, the time, the placement in the cleaning tank and so on. Consequently, we are unable to define general conditions for cleaning or guidelines to protect our component against damage. If ultra-sonic waves are used during cleaning or ma nufacturing, please make sure to per- form an appropriate inspection to make sure that the quartz crystal still meets its specification. Moreover, if there is a change in cleaning conditions, board or placement of the component after a redesign of the board, please be sure to perform the same inspection for confirmation.• Tuning Fork Crystals It is strongly recommended not to apply ultrasonic waves during cleaning or manufacturing to tuning fork crystals, as their resonance frequen cies lie close to the ultrasonic frequencies being typically used during ultrasonic cleaning or manufacturing. Tuning fork crystal blanks might easily get partially or fully cracked by ultr asonic cleaning or welding.Reference:http://www.jauch.de/ablage/med_00000814_1410529797_Crystal_Handling_Cond_EN.pdf

author: _Wim_
author_rank: Super Contributor
timestamp: August 20, 2016, 12:01:12 pm
content: Thanks for that link.If I were a manufacturer of crystals, I would place that in my handling precautions also, just to avoid liability. However, they also do not say it is ok to use an ultrasonic cleaner with swept frequency, in my opinion they just state that it is theoretically possible to destroy a crystal with an ultra-sonic cleaner, so do so at your own risks.I am looking more for scientific info how realistic is it to make actual damage, and if this change of making damage is substantially decreased by using a swept frequency batch.Most info on the web comes from manufacturer of ultra-sonic baths, so that could be a little “coloured”…

author: voltsandjolts
author_rank: Unknown
timestamp: August 20, 2016, 12:15:48 pm
content: If I were in charge of a PCB production line, I would place that in my handling precautions also, just to avoid liabilityWe just use several stages of non-agitated baths (cleaners and rinse stages)For bigger throughput ops there are spray washers/cleaners:http://www.amth.de/en/products/neukum-elektronik/%C3%B6ko-1000

author: _Wim_
author_rank: Super Contributor
timestamp: August 20, 2016, 12:36:33 pm
content: Quote from: voltsandjolts on August 20, 2016, 12:15:48 pmThen I would for sure to the same. But my question was more related to a user who would use an ultrasonic bath maybe 6 times a year, with limited financial resources.I found this article which does contain scientific data (warning: big pdf of 13Mb):http://www.smtdetergent.com/UltrasonicCleaningOfPCBs-DamageFree.pdfGeneral conclusion is that the safety margin is quite high for a power density of 11W/liter and several minutes for cleaning. Use much higher power or extremely long cleaning times could result in damage.This should be a nice guideline what to buy as a DIYer to keep the cost down.

author: R005T3r
author_rank: Frequent Contributor
timestamp: August 28, 2016, 11:14:33 am
content: In my opinion, the most important factor for cleaning stuff is the filler liquid, not the machine type itself: fixed-non fixed influence only the radiation you have on the filler liquid, meaning that one type of cleaning will have effect on a wider variety of dirt than the fixed one, so it will take less time to clean the pcb for that specific kind of dirt, but if you want a really good clean and more importantly a non damaging one, use a specific filler liquid for pcb even if it does not come cheap: there's no point into having a $1000 cleaner and you use glass cleaner on it.To sum up what I've found so far, in addition to previously ones:->NEVER, ever use glass cleaner on silicon chips: you will screw up them.-> use distilled water, not tap water-> use an appropriate product for the job: don't destroy your board because you use dish cleaner on it.-> heat affects the reaction in a certain way: the downside is you may have an exaggerated etching on your board and you will kill it.-> use a proper basket for the cleaner and things don't have to stay on the bottom of it, the radiation there is very strong and you will etch your items. Also, the basket is engineered to work with your cleaner radiation. Different lengths means different radiation levels (that's why you don't have to keep the items on the bottom).-> cheap cleaner are the perfect tool to destroy your boards especially jewelery ones: they are meant for another use, not for electronics.Always think about it first before doing something stupid with your ultrasonic cleaner: when you screwed up something important you willfirst and thenbut it's too late.I tell you this story: once a friend of mine asked me if I could have given him an advice for a PSU because his boss asked him to find some gear. I advised him to NOT mess up with crappy electronic test stuff, especially PSU-related stuff if he wanted to power-up a $4.000 boards... Did his boss listened to him? Of course not and he ended up with: a cheap ultrasonic cleaner loaded up with supermarket cleaning stuff, 50 cheap not branded PSU, and a crappy brunch of oscilloscopes.... After 1 month my friend said his boss actually fired up 3 $1000 boards, and he broke other 2 $4000 ones and the ultrasonic cleaners didn't worked as supposed to: he broke up another board because he didn't even cared to use the basket, he just let them go on the cleaner's floor.To avoid going out of business, my friend was fired and now he's selling the PSUs online...

author: Fraser
author_rank: Super Contributor
timestamp: August 28, 2016, 02:49:23 pm
content: Great thread. My thanks to the OP for raising the question.I was asking myself the same questions a few months ago after watching the Louis Rossman Apple laptop repair video on Ultrasonic cleaning. Louis recommends an ultrasonic bath that is swept frequency and designed for electronics use. He also makes it very clear that the correct type of cleaning solution, mixed with Deionised / distilled water, is essential.Louis talks from the position of an end user and the cleaning performance that he has witnessed himself in the shop, combined with receiving PCB's for repair that have been abused in an Ultrasonic cleaner. His video on using such equipment is very interesting. He carefully limits the exposure of the PCB's to the ultrasonics to avoid potential damage.I started hunting eBay for an ultrasonic cleaner and found two major types available. Inexpensive and very expensive. The inexpensive types were designed for cleaning jewellery and tools. They tended to use simple ultrasonic driver circuits and appeared focussed on the amount of power they could produce. This inferred that more power was better....... Not always so, especially when working with electronics. Cheap ultrasonic baths are single frequency and use the minimum number of transducers possible, so you do get definite hot spots within the tank. Hot spots scour the item being cleaned in one particular area via cavitation, whilst other areas receive little cleaning effect at all.Louis has stated that some of the ultrasonic baths that he has tested have provided very patchy cleaning, and are not great for PCB work as a result. Even his expensive Branson bath was, in his opinion, not a great performer when used to clean PCB'sOnto the expensive ultrasonic cleaners .....Wow you can spend a lot of money on these things !To summarise what you are paying for :A brand nameA reputation for qualityQuality parts used in the productMultiple high quality transducersSophisticated transducer driverSwept frequency in some modelsCertification for some applications such as medical useLongevity due to quality design and buildDoes any of that above matter to a hobbyist like me ?Well I can repair component failures in the cheaper units but the more transducers and better driver for them is important to decent performance.What is the cost differential in the UK though ?Chinese cheap single transducer bath costs less than £150Professional bath for medical use with swept frequency is £1850 +20% VAT !Ouch !To sweep, or not to sweep, that is a question.......Single frequency ultrasonic baths still work well for cleaning items such a jewellery, tools and other 'open' items. By open I mean the cleaning fluid has easy access to all parts. The idea of a swept ultrasonic frequency came about after studies of ultrasonic energy distribution within the volume of the fluid tank. The single frequency tanks contained definite hot spots and cleaning could be patchy as a result.The sweeping of the ultrasonic drive frequency created wave interference patterns within the cleaning fluid and these were found to improve energy distribution throughout the tanks volume. The cleaning of difficult items with a less open structure was greatly improved and there were less issues with hot spots bombarding a particular area of the item being cleaned.. In short, swept frequency ultrasonic baths do perform better than fixed frequency baths...... But at an increased purchase cost ! They are not a sales gimmick.PCB cleaning takes many forms. Louis works on fluid damaged PCB's that have fluid contamination under BGA chips. These tight spaces under the chip can be hard to clean and a swept frequency ultrasonic bath is fully justified in his case. Cleaning a PCB populated with through-hole components or just for flux/dry contamination could likely be done with a cheaper ultrasonic bath.You do get what you pay for though. Take a look on the Internet at some of the Chinese ultrasonic bath driver schematics and compare them to the more expensive professional units schematics. The Chinese drivers .are very much built down to a price and can be very fragile wrt mains spikes killing the driver transistors.Me? I found a professional swept frequency ultrasonic bath on eBay for £100It was faulty but I was reasonably confident that I could repair it. The fault was a failed PT100 temperature sensor making the unit go into over temprrature alarm. My ultrasonic tank purchase is detailed on this forum. It is a Hygea unit designed for medical use and is certified for such. It contains a printer that provides a record of the completed cleaning cycle for medical records use. As a medical device it has to meet a standard for cleaning any item placed within its tank and there are weekly tests detailed in the manual to check performance. Certified cleaning performance is always better than a manufacturers, potentially inflated, claims. The tank takes 8L of cleaning fluid and uses four quality transducers plus a nice quality ultrasonic driver. This is the unit that costs £1800 +VAT new.I bought a used/faulty professional ultrasonic bath in preferable to a new cheap bath as I am not a heavy user and I wanted the best value for money without sacrificing performance. I was fortunate with my purchase. It cost only £10 to repair and it is an amazing bit of kit. Total overkill mind youHope this helps you make your purchase decision.Fraser

author: zapta
author_rank: Super Contributor
timestamp: August 28, 2016, 04:39:05 pm
content: Quote from: Fraser on August 28, 2016, 02:49:23 pmThat's a very entertaining video. He is talking to a group 'you know who you are' no-gooders and repeats every detail a few times to make sure they internalize it.Never heard of frequency sweeping ultrasonic cleaners before. I am using a fixed frequency ammo ultrasonic with tap water and dish soap to clean bike chains but now I know that this process is not electronics friendly.BTW, Rossmann is with two 'n's. He tends to repeat everything, including the letters in his name.