Cleaning PCBs - Page 1
Forum section: electronics / projects

author: Sky_hawk
author_rank: Contributor
timestamp: April 08, 2012, 12:18:15 am
content: I have some hand soldered PCBs I want to clean up, I tried to remove the rasin and other sticky stuff of the PCB using alcohol 96%, and Chemtronics Flux-Off VZ, but neither is working very well. After using the Chemtronics Flux-Off VZ, it seems now there is a sortof white filmly layer on the PCBWhat is the best way to clean them properly. I tried using Aceton on a old board, but aside from the risk of dissolving the silkscreen, it did not seem to the work well either.Greetings,Jan

author: Rerouter
author_rank: Super Contributor
timestamp: April 08, 2012, 12:38:33 am
content: to be fair you didnt say the age / vintage of the pcb, when you get past 20 years, it always gets harder to clean, as the masking and silkscreen start degrading to a level where most cleaning products strong enough to lift flux start lifting them aswell,i suppose if you dont end up finding anything, on some 30+ year boards, i have scrathed off the flux with a metal scribe and used some other lighter cleaner to tidy it up, but that gets into the region of how badly you want it to look nice,

author: Psi
author_rank: Super Contributor
timestamp: April 08, 2012, 12:46:36 am
content: Be careful getting any pre-made circuit board cleaner on your skin.I accidentally sprayed my hand while holding a pcb and my skin turned red in that area for 2 months.I dunno what it has in it, but it's not good for you.

author: IanB
author_rank: Super Contributor
timestamp: April 08, 2012, 12:49:47 am
content: You can use 96% ethanol, or methanol, or isopropyl alcohol. You need to apply the solvent liberally and use a stiff bristled brush to work the flux loose before rinsing it away. It won't just dissolve all by itself, it needs a bit of help.Oh, and as Psi said, wear rubber gloves to protect your skin.

author: TerminalJack505
author_rank: Super Contributor
timestamp: April 08, 2012, 01:25:53 am
content: Is the resin that remains due to a liquid flux you are using or is it the solder's core? You might have to switch to a different flux and/or a different solder.I use a so-called water soluble flux which is really easy to clean. Some of the solder I use has a rosin core which is a little tougher to clean. When I can, I use the water soluble flux and a solder that has no core. I can clean a board up using just water when I do this.Just for the record, once I'm finished soldering with a rosin core solder, I use isopropyl alcohol and an old toothbrush to clean the board. (Yes, I should be using an ESD safe, $50 brush. blah, blah, blah...) I dip the brush in the alcohol and scrub the board 'liberally', as Ian says. I then rinse the board under running water (just so long as there are no components that will have an issue with that.) A second cleaning is sometimes necessary.After wiping off the excess water with a paper towel I then I use an old hair dryer or my hot air station to dry the board.

author: T4P
author_rank: Super Contributor
timestamp: April 08, 2012, 01:50:12 am
content: Well i some weird arse alcohol i had around and clean a ROH1 soldered PCB , came out white-ish ...Now i use Kester 58 No Clean solder . And yes , RMA can be a bitch to clean .

author: bfritz
author_rank: Regular Contributor
timestamp: April 08, 2012, 04:03:26 am
content: The first thing to do, is to look up the solder and flux you are using. The documentation for the items you are using should tell you if the flux is water soluable or not. If it is not water soluable, you will need to use alcohol. Alcohol can be very drying to your skin, so I suggest rubber gloves if using alcohol.The residue you see after washing is the flux and possibly other contaminants in what you are using to clean with, moved around on the board. I highly suggest a post clean wash with DI water if you have it available, or distilled water.I like to use water soluable flux. (No clean fluxes do leave a bit of residue, it is just that the residue is not supposed to be conductive, and is not sticky and will not attract or hold dust.) My first wash is with tap water that passes through a charcoal filter, so some contaminants are removed. I use a shallow container with about a gallon of water, and use an "acid brush" that I have clipped the leads on so they are only about 1/4" long, so therefore a bit stiffer. I also use about 2 drops of dishwashing soap (I use Dawn) in the water, as a wetting agent. Be careful not to submerge boards with dip switches or other switches, that are not designed for water wash. The problem is that such devices can get flux carried into the switch by the water, which then causes problems. Many Dip switches have peelable tape strips, and as long as the tape strips are in place, these dip switches are water washable.After this first wash, I wash the board in DI or the distilled water. Just a short quick wash, with a fresh uncontaminated acid brush prepared as before.Finally the boards are given a quick blow with a handheld hair dryer, and finally put in a chamber kept for drying components or boards. If you don't have a chamber or board dryer, you just have to wait longer to be sure they are dry. I have seen some strange behavior from circuits that have fine pitch parts, and very high impedance nodes, when powered up not totally dry.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 08, 2012, 05:53:09 am
content: i use thinner. blow with air afterward. i'm satisfied, silkscreen not off.

author: Sky_hawk
author_rank: Contributor
timestamp: April 08, 2012, 09:45:12 am
content: Thanks everyone for the suggestions. I let you how it works out.

author: Unknown
author_rank: Unknown
timestamp: April 08, 2012, 11:43:01 am
content: Note that water soluble fluxes are very aggressive and should always be removed, unlike RMA or no-clean fluxes which can often be left on for many applications.Quote from: Psi on April 08, 2012, 12:46:36 amIt's always a good idea to read the MSDS before use.

author: Psi
author_rank: Super Contributor
timestamp: April 08, 2012, 12:53:13 pm
content: Quote from: alm on April 08, 2012, 11:43:01 amThis was just the jaycar stuff, not some super powerful industrial spray.I looked up its MSDS, its three ingredients are- Isopropanol- Hexane- AcetoneAll are skin irritants that can produce red skin and dermatitis.

author: ablacon64
author_rank: Frequent Contributor
timestamp: April 08, 2012, 01:17:20 pm
content: I use methyl acetate and am very satisfied with the results.

author: Unknown
author_rank: Unknown
timestamp: April 08, 2012, 02:06:39 pm
content: Isopropanol, hexane and acetone are quite safe as long as not ingested or inhaled in high concentrations, although I guess allergic reactions are possible.Prolonged exposure to high concentrations of each may cause defatting of the skin, but I wouldn't expect the short exposure from a single spraying to have this effect.

author: Wim_L
author_rank: Regular Contributor
timestamp: April 12, 2012, 03:48:55 pm
content: Hexane can become quite toxic in the case of chronic exposure. I wonder why they're not using heptane, which has similar solvent properties while being far less toxic. Sure, drying time will increase a bit, but not dramatically. Isopropanol and acetone are more benign (though of course a fire hazard, just like the hexane, and you don't want to inhale too much anyway). Drying and irritation of the skin are the main risks if you only use them occasionally.Take care with glove selection, many glove materials do not handle hexane or acetone well. Disposable latex or nitrile gloves will offer hardly any protection from acetone or hexane. Thick neoprene gloves may be a reasonable compromise between mechanical strength and chemical resistance for these kinds of solvents.

author: free_electron
author_rank: Super Contributor
timestamp: April 12, 2012, 04:40:39 pm
content: First off : depends on the flux you are using.Rosin dessilves readily in alcohol ( use isopropylalcohol , sometimes called isopropanol , or rubbing alcohol )No-cleans also dissolve in alcoholWater soluble flux.. eh well.. water of course .. water soluble flux saponifies in contact with water ( it acts as soap )Water soluble flux MUST be removed ! it absobs moisture from the air, forms a white film and is CONDUCTIVE !Rosin ( especially the activated one) is agressive and will eat away at your board. RMA is less agressive ( RMA = Rosin Mildly Activated )Some background :What is Flux and what is its function ?Flux is an agent that reduces the surface tension of liquid solder. by doin this it allows the solder to flow better and make better contact with the metals to be soldered. Think of it as 'soap and water' The soap decreases surface tension of water.But, it does more than that. Flux is also a very reactive chemical compound. It just loves oxygen. It loves it so much that it even manages to rip away oxygen atoms that have bonded with copper or tin / lead. So , if your board has been exposed to air and has oxidized ( oxidation = bonding with oxygen atoms ) the flux will strip the oxygen. When heating flux it becomes very reactive.In an ideal world you preheat to activate the chemical properties of the flux so it can eat away the oxide layer, then you go to the liquid phase. at this point the remnant of flux acts as a flowing agent to imporve the wettability of the surfaces to be soldered. eventually all flux has evaporated and the bond is made.At the end of the process there should be no flux remaining. the 'solids' remaining are inert and leftovers of the soldering process. these need to be removed.Here is how i do it for small boardsMake a mixture : 50% water , 25% IPA , 25% Chemtronics Flux-Off CZ and throw that in an ultrasonic cleaner. dip the board, ultrasound for 20 seconds : take the board out and douse it in pure IPA ( to displace the water ) . then blow dry with WARM aire ( do not use ambient temperature and esepcially don't try this with blowing air from your lungs... your breath contains too much moisture. the evaporating IPA cools down the surface temperature of the board and this will condensate the humidity in your breath... and you don't want that sublimating on your board... stomach acid and saliva ... NOT GOOD ! )If you lack an ultrasonic cleaner ( i use a small jewellry cleaner. holds boards up to 5 inch x 5 inch ) you alter the process25% water : 50% alcohol 25% Flux -off. and rinse with pure alcohol.Commercual flux off is toooo expensive. it works really well but cost a lot of money. IPA is cheap. go to any drug store (like Safeway, walmart) and buy 99% or 100% rubbing alcohol ( don;t get the green one with 'aloe vera' . just the simple pure rubbing alcohol ) you can get a large bottle for a few dollars.

author: Ajahn Lambda
author_rank: Regular Contributor
timestamp: April 12, 2012, 07:35:14 pm
content: If it's just one board or a small assembly, I use CRC QD Electronics Cleaner:Stuff's about $8 per can at Home Depot, O'Reilly's, etc. The best parts are that it doesn't melt plastic, leaves NO residue, and evaporates very quickly.DO NOT buy the similarly-labeled "Lectra-Motive" electric motor cleaner. That stuff WILL melt plastic.As others have mentioned, read your flux's label. If no joy, put some on you finger, and run it under water. If it doesn't wash away, you're going to have to use something that will cut 'traditional' flux, i.e. resin, grease, oil, etc., such as that QD Electronics Cleaner I first mentioned and pictured.There are faster, more-harsh chemicals out there -- I keep a gallon of trichloroethane on hand just in case -- but I would advise using the least aggressive first. Note that trichloroethane is very hard or impossible to obtain now, due to the Montreal Protocol, meaning it depletes the ozone layer. However, it is the cat's ass when it comes to cleaning electronics.

author: SeanB
author_rank: Super Contributor
timestamp: April 12, 2012, 08:04:59 pm
content: TCE is nice, I used to use it in an ultrasonic cleaner. Would clean a board in 2 seconds, strip the protective varnish in 5 ( except for those coated in Mesuopolet K) and delaminate the board in 10 seconds. If you did not want to use the ultrasonic side you could just use the vapour phase distillation it used to clean the solvent to degrease the boards. You needed 150l to fill the machine, and a 205l drum would last for around 6 months of normal use.

author: meffe
author_rank: Newbie
timestamp: April 12, 2012, 08:20:32 pm
content: Quote from: free_electron on April 12, 2012, 04:40:39 pmWhat is the point of adding Flux-Off?Cheers

author: T4P
author_rank: Super Contributor
timestamp: April 12, 2012, 08:26:15 pm
content: Chemtronics Flux Off No Clean Plus costs 8.80SGD at RSComponents ... go figure !But really , do ultrasonic cleaners work for removing flux ?

author: free_electron
author_rank: Super Contributor
timestamp: April 12, 2012, 09:01:28 pm
content: yes ultrasonics work fine , as long as you put something in it that can dissolve flux. like alcohol and flux-offthe advantage is threefold : you don't have to scrub , you don;t make a mess. and ... wait for it : the ultrasonic wave can push the alcohol in areas you can;t reach with your brush.Like between the balls of a BGA or studs of a flipchip. You can clean area's that ar enot cleanable by scrubbingthe point of adding flux-off is the following : it dissolves certain types of flux faster than IPA does.the mixture i make doesn;t care what type of flux you used during assembly or rework. Just dunk it in . it'll dissolve all fluxes , including waater soluble. Boards come out perfectly clean.

author: T4P
author_rank: Super Contributor
timestamp: April 12, 2012, 09:48:40 pm
content: Quote from: free_electron on April 12, 2012, 09:01:28 pmFlux off has hexaneI decided to get Ambersil's flux remover instead , but yeah , how do you even get anything underneath a bga packageDX has a 600ml 50W ultrasonic cleaner for 30.80 ..

author: TerminalJack505
author_rank: Super Contributor
timestamp: April 12, 2012, 09:54:20 pm
content: I've always wondered if an ultrasonic cleaner would work for PCB cleaning. That's something else to add to my list. Thankfully, they're not too expensive.Just being able to get at areas that a brush can't will be useful since I use the (conductive) water soluble flux. I've had it get under small packages such as resistor networks and screw with the circuit's operation.

author: bfritz
author_rank: Regular Contributor
timestamp: April 12, 2012, 11:28:24 pm
content: I agree that the ultrasonic cleaners work great. The heated ones work even better.Do remember to change the solution on occassion. At my workplace we pour it through a coffee filter daily, as we clean quite a few boards. We also clean the sediment out of the bottom of the cleaner at the same time. We change the solution weekly. As a hobbyist, you can probably get away with much longer timeframes.Do be careful to keep boards seperated. Two boards vibrating against one another while in the ultrasonic can damage components, or wear through the resist and copper areas on the PCB's.

author: IanB
author_rank: Super Contributor
timestamp: April 12, 2012, 11:48:58 pm
content: Quote from: Wim_L on April 12, 2012, 03:48:55 pmI think this is a very alarmist statement. In general terms, hexane is a rather innocuous substance, less toxic than many other solvents. To suffer ill effects from hexane you would have to breath air containing high concentrations of hexane vapor over a long period (e.g. continuous exposure every day for months at a time).For normal occasional use in the home, hexane is quite harmless. As with all solvents and volatile chemicals make sure you use it in a place with adequate ventilation and there is nothing to worry about.

author: Wim_L
author_rank: Regular Contributor
timestamp: April 13, 2012, 11:50:08 am
content: Quote from: IanB on April 12, 2012, 11:48:58 pmTrue, if you don't get exposed often, there's not much to worry about. Well, except flammability, but almost all good organic solvents have that problem (some halogenated ones are not so flammable, but environmental regulations tend to be stricter on those, and in some cases toxicity is a bigger problem).I just think it's a bit strange to include hexane into a standard flux remover, as in some industries those cleaners would indeed be used daily (though hopefully with adequate protection and ventilation).

author: Unknown
author_rank: Unknown
timestamp: April 13, 2012, 07:36:08 pm
content: Note that the permissible exposure limit for hexane is quite close to ethanol. Make sure to only drink beer in a fume hood with gloves and a respirator if you get exposed to it daily. As you state, it's not really much worse than many other common organic solvents. They're not harmless, but not worth worrying about for occasional hobbyist use.

author: IanB
author_rank: Super Contributor
timestamp: April 13, 2012, 08:18:45 pm
content: Quote from: Wim_L on April 13, 2012, 11:50:08 amHexane would come under the general category of petroleum distillates, and solvents like these are a common constituent of "Goo Gone" and similar products. In other words, they tend to be really good at dissolving stuff...

author: Wim_L
author_rank: Regular Contributor
timestamp: April 15, 2012, 07:26:59 pm
content: Oh, absolutely, but heptane would fit in the same solvent category, and doesn't get metabolised to things that (with chronic exposure) damage the peripheral nervous system.

author: poorchava
author_rank: Super Contributor
timestamp: April 16, 2012, 02:56:16 pm
content: I'm using either isopropyl or turpentine. The latter i use mainly when using flux-paste (which is designed for soldering extremely thick, heavy and oxidized stuff, works like a charm but leaves sticky, oily residue which won't come off with isopropyl). Turpentine you can but from paint shop. It has a downside of extremly strong odor of pine.

author: IanB
author_rank: Super Contributor
timestamp: April 16, 2012, 03:07:43 pm
content: Quote from: poorchava on April 16, 2012, 02:56:16 pmYou could try turpentine substitute instead, perhaps? It is sometimes called white spirit or mineral spirit. It is generally clear and odourless.

author: free_electron
author_rank: Super Contributor
timestamp: April 16, 2012, 04:51:11 pm
content: terpentine is not a good idea ...

author: T4P
author_rank: Super Contributor
timestamp: April 16, 2012, 09:57:15 pm
content: turpentine not the best idea , really .I had turpentine damage the plastic cases of DIP/SOIC and my skin .

author: Alex_arg
author_rank: Contributor
timestamp: April 17, 2012, 11:13:39 pm
content: Hi!, i use regular alcohol 96% to clean new and old resine an d flux from PCBs, the key to success here it's time, very volatile solvents like hexane or thinner evaporates before flux starts to dissolve, so you got to protect it from air, i do so by wetting a piece of cotton and applying it over the board and wait a while, old fluxes require more time.In case a white layer still on the pcb (it's only the dissolved flux) , you must repeat the process with a new piece of cotton and voilá! . You could use a nylon brush in hard cases previous wetted with alcohol.In other times i've used a contact cleaner from Philips, that do the same job in much less time, but i think they don't produce this spray anymore. The one i mention has a clear smell of turpentine.

author: Ajahn Lambda
author_rank: Regular Contributor
timestamp: April 18, 2012, 01:01:40 am
content: Acetone is fairly safe to us humans, aside from its flammability.But hoo boy, it will melt the shit out of any plastics in the area! Even the vapors can make some plastics gooey.

author: free_electron
author_rank: Super Contributor
timestamp: April 18, 2012, 04:28:06 am
content: Acetone is a non-no as it can attack the casings of components !Use rubbing alcohol / isopropylalcohol or real flux remover. Nothing else !