isopropanol question - Page 1
Forum section: electronics / beginners

author: Lucky-Luka
author_rank: Unknown
timestamp: June 29, 2019, 10:45:55 am
content: Hi allI've read that isopropanol is a good choice to clean up the board after the soldering is done.I've tried it with my second ever pcb.The result wasn't satisfying at all.After I brushed some 99.9% isopropanol on the back of the board a sticky white patina formed.I've tried to clean the mess using a polishing cloth.The result is in the picture.I'm not satisfyied at all.What's the problem?Cheers

author: frozenfrogz
author_rank: Frequent Contributor
timestamp: June 29, 2019, 10:53:19 am
content: ISO-propanol is not a magic formula. It simply acts as a solvent for the flux and needs to be thoroughly washed away.I usually take two plastic containers - one to pre wash and one to apply fresh ISO-propanol. Also I like using some tissue to cover the whole PCB and then add the solvent.The residue you are seeing is simply that: residue.Propanol is not going to dissolve flux. It is like washing your hands with soap. You still need to scrub and rinse.Edit:

author: Lucky-Luka
author_rank: Unknown
timestamp: June 29, 2019, 10:57:30 am
content: So, do I have to apply isopropanol multiple times to get rid of that mess?I mean first time I brush with isopropanol then I clean the board using a cloth then I rinse with isopropanol again and polish the board using a cloth?p.s. I've seen the video right now. Very useful. Thanks

author: ptricks
author_rank: Frequent Contributor
timestamp: June 29, 2019, 10:58:52 am
content: I use a tooth brush and alcohol to clean up flux.Flux is sticky stuff so if you use a cloth or anything with fibers to wipe any residue you can leave fibers that also give it a bad appearance.

author: Lucky-Luka
author_rank: Unknown
timestamp: June 29, 2019, 11:00:03 am
content: so what do you use? only a toothbrush?

author: ptricks
author_rank: Frequent Contributor
timestamp: June 29, 2019, 11:01:37 am
content: Quote from: Lucky-Luka on June 29, 2019, 11:00:03 amIf you scrub the board with alcohol and brush, then rinse it off with alcohol there should not be any residue, it will just dry clean, no wiping needed.

author: digsys
author_rank: Unknown
timestamp: June 29, 2019, 12:26:49 pm
content: I have slightly different experiences - I have found that just about every supplier uses a slightly (or even vastly) different formulation for their resist, and I have had to keep 3-4 different types of washes / cleaners. If one doesn't work, then I try the next, until I find one that is happy. Rarely come across a resist that didn't clean well.Edit: I have never found one cleaner that worked with every batch of pcbs

author: ebastler
author_rank: Super Contributor
timestamp: June 29, 2019, 12:40:29 pm
content: Quote from: Lucky-Luka on June 29, 2019, 10:45:55 amIt may be clear from the prior posts, but has not really been spelled out yet:The isopropanol (IPA) has nicely dissolved your resin -- there does not seem to be much of it left around your solder joints. But then you have let the resin/IPA mixture dry, instead of washing it off. The IPA has evaporated, and the resin has been left behind, now spread out all over the board, producing the white film.Hence: IPA is a good solvent for your resin, and you have done enough scrubbing (brushing) in your first attempt. Just make sure you quickly wipe off most of the resin/IPA mixture with a paper towel or such, then rinse with more clean IPA.

author: Lucky-Luka
author_rank: Unknown
timestamp: June 29, 2019, 12:46:18 pm
content: Quote from: digsys on June 29, 2019, 12:26:49 pmWhich kind of cleaners other than isopropanol?

author: digsys
author_rank: Unknown
timestamp: June 29, 2019, 01:42:22 pm
content: Quote from: Lucky-LukaThese are some I could find tonight .. eventhougha few may contain iso-p, their other additives do change how they react. I've had pcbs where the resist literally dissolves in a mush with one, then perfect with another. The Safewash 2000 is my goto, and usually works inmostcases, but no guarantee.

author: David Hess
author_rank: Super Contributor
timestamp: June 29, 2019, 04:21:27 pm
content: Isopropanol has the virtues of being inexpensive and readily available and safe but by itself is not a very good flux solvent.

author: ebastler
author_rank: Super Contributor
timestamp: June 29, 2019, 05:28:23 pm
content: But even the best solvent does not make the flux evaporate or otherwise dematerialize. The actual problem which the OP has encountered will remain the same: You have to get that solvent/flux mixture off the board, by wiping it off and/or rinsing.

author: bob91343
author_rank: Super Contributor
timestamp: June 29, 2019, 05:35:36 pm
content: I keep going back to 1,1,1 trichlorethylene. That stuff dissolves everything you want to dissolve and doesn't seem to harm anything nor leave residue.Unfortunately it's classified as hazardous and is thus hard to obtain. I am lucky enough to have stockpiled a lifetime supply for myself.Anyway it's better than anything else I have encountered. I use a toothbrush on boards. I drip it through pots and switches. It does the job.Like any other chemical, always test it on a tiny corner somewhere just in case the stuff could cause problems.

author: IanB
author_rank: Super Contributor
timestamp: June 29, 2019, 05:51:20 pm
content: Let's try an analogy. If you were to wet your hands then apply soap and rub to clean the dirt off, but then simply stopped and let your hands dry without rinsing, what would happen? You would end up with dirty, sticky hands. What do you actually do? You rinse your hands under clean running water before drying them.To successfully complete a cleaning process, you have to rinse thoroughly after cleaning to wash the dirt away.Same with cleaning a circuit board. You can apply solvent and rub with a soft brush to loosen the flux and dissolve it in the solvent, but the next step is you have to remove the flux that you have cleaned off. To do that, you have to rinse the board thoroughly in clean solvent to wash away the residue.If you get an ugly white film on the board it means you haven't washed away the flux, you have simply moved it around a bit and let it dry on the board.

author: ejeffrey
author_rank: Super Contributor
timestamp: June 29, 2019, 05:51:51 pm
content: I'm not sure the propanol is actually dissolving the flux at all. That looks like it softened the flux which then got spread around by the polishing cloth.Either way, a pretty standard procedure is to use an appropriate flux cleaner, using plenty of it and some scrubbing to get all the flux off the board. Then without letting it dry, rinse with DI water and blow off with filtered compressed air. That will avoid the solvent from drying and redepositing the flux residue back on the board.Organic solvents like isopropanol are often pretty dirty straight from the bottle. Pour some "clean" iso on a clean piece of glass and let it dry to see. That is why you want to rinse with DI water. Even the DI water will have some dissolved contaminants but it doesn't dry as fast as alcohol so it is easier to blow it off.

author: Shock
author_rank: Super Contributor
timestamp: June 29, 2019, 06:32:04 pm
content: Quote from: bob91343 on June 29, 2019, 05:35:36 pmDon't suggest people use Trichlorethylene (TCE) it has short and long term exposure risks.

author: ebastler
author_rank: Super Contributor
timestamp: June 29, 2019, 06:36:26 pm
content: Quote from: bob91343 on June 29, 2019, 05:35:36 pmHas it occurred to you that the classification may be due to the fact that the stuffishazardous?

author: IanB
author_rank: Super Contributor
timestamp: June 29, 2019, 07:12:17 pm
content: Quote from: Shock on June 29, 2019, 06:32:04 pmI remember using it as a child when it was sold as "Tippex thinners". I regret that it is not easily available now as it was very good for welding plastics. I wouldn't use it as a cleaner as it dissolves too many things.

author: bob91343
author_rank: Super Contributor
timestamp: June 29, 2019, 07:47:25 pm
content: I don't dispute the hazards of this solvent. However, I have been using it for decades and am a relatively healthy 86 years old. So maybe I will die from it but so far so good.

author: KL27x
author_rank: Super Contributor
timestamp: June 29, 2019, 07:53:52 pm
content: +1 to blotting up the alcohol before it dries.But the no clean paste that many pcb manufacturers use, defacto, is difficult to clean. The no clean flux residue may contain very little resin and a lot of ionic residue. Ionic residue (the white stuff) does not dissolve in IPA. You might experiment with other types of cleaners. But using a brush or an ultrasonic cleaner might be necessary.Rosin flux residues also contain these same ionic components. But they are bound up in a much larger volume of resin which dissolves in alcohol. When the resin is dissolved, it leaves most of the ionic residues floating around, freely/loosely, in tiny chunks (little white specs) that are fairly easily rinsed/flushed or brushed and blotted up off the board. If you view the board under a microscope while cleaning it, the alcohol looks like the contents of a snow globe. But when the resin component is very little (as it is in most pcb manufacturer no cleans, for esthetic reasons), the ionic residue is concentrated enough that it bakes itself to the solder mask in large, contiguous patches and is physically bonded there. It doesn't want to let go after the resin cap is dissolved.Think the difference of spilling crystallized/powdered sugar on the counter and cleaning it off vs applying sugar water to the counter and letting it dry and harden. Then trying to clean it off. (With a solvent that doesn't dissolve sugar.)If you were to you use this style of no clean for rework (not all of them are this annoying; this type of no clean is designed for stencil application in precise amounts), you will have a bad day when you apply alcohol. As soon as the resin is dissolved, the copious ionic residue will swell with the water in the alcohol and verily clog between the pins of ICs. With rosin flux, you can't use too much because of the bulky resin component. There's only so much residue that can remain between the pins before it flows out across the board, and it's mostly resin that easily dissolves in alcohol.

author: windsmurf
author_rank: Frequent Contributor
timestamp: June 29, 2019, 08:10:13 pm
content: I think the IPA is damaging the clear gloss coating on the board, and making it cloudy.Put some IPA on the board where its glossy, and let it sit. See if the glossyness has faded to a flat finish.If you think its IPA containing residue, test on a piece of glass to see if it leaves residue once it dries.

author: KL27x
author_rank: Super Contributor
timestamp: June 29, 2019, 08:13:38 pm
content: ^OP's pic looks like a professionally manufactured board. It most likely has an epoxy based soldermask, like 99% of professionally manufactured PCBs. This would be pretty much immune to alcohol.

author: ebastler
author_rank: Super Contributor
timestamp: June 29, 2019, 08:41:11 pm
content: Quote from: windsmurf on June 29, 2019, 08:10:13 pmVery unlikely. As others have stated above, there are stronger solvents than IPA. One benefit of IPA is that it does not dissolve things you don't want to be attacked -- plastics etc.. It also has been safe on any paint or lacquer coatings I have tried it on (once the paint is properly cured, of course). I am not aware of any solder masks which get attacked by IPA.QuoteI don't think anybody has suggested that the IPA contained residue to start with. It is flux that was dissolved and then allowed to dry again on the board when the IPA evaporated.

author: windsmurf
author_rank: Frequent Contributor
timestamp: June 29, 2019, 09:52:12 pm
content: Quote from: ebastler on June 29, 2019, 08:41:11 pmI agree its unlikely but putting it out there as my speculation in case there's a problem with the mask.Quote from: ebastler on June 29, 2019, 08:41:11 pmAlso just proposing an experiment to rule out a potential contamination of the bottle of IPA... are there any "rules" on what the remaining percentage of IPA can be?

author: GreyWoolfe
author_rank: Unknown
timestamp: June 29, 2019, 10:23:51 pm
content: I have both 91% and 99.5% IPA. I use both with Kim-wipes and an old toothbrush. IPA on Kim-wipe and scrub, repeat until flux is gone. No white residue.

author: digsys
author_rank: Unknown
timestamp: June 30, 2019, 12:22:55 am
content: Quote from: bob91343Yup, same :-) Still have heaps as well, and don't forget carbon tetrachloride - we'd wash our hands in it at high school !! Yup still alive :-) ahhhh memories

author: bob91343
author_rank: Super Contributor
timestamp: June 30, 2019, 12:53:25 am
content: Don't forget methyl ethyl ketone. That was the solvent of choice for a few years.

author: Shock
author_rank: Super Contributor
timestamp: June 30, 2019, 01:19:44 am
content: Quote from: bob91343 on June 30, 2019, 12:53:25 amGreat for dissolving plastics, pure Butanone not sure if I'd want to clean PCBs with that.

author: bob91343
author_rank: Super Contributor
timestamp: June 30, 2019, 02:57:35 am
content: Acetone is very powerful. But young women use it a lot to remove nail polish.

author: rcbuck
author_rank: Frequent Contributor
timestamp: June 30, 2019, 03:21:06 am
content: I use a toothbrush and denatured alcohol for the first cleaning stage. I follow up with IPA and a different toothbrush. I then rinse under running cold tap water for about 30 seconds. I have high water pressure here, about 95 PSI. Then immediately dry the board with a hair brush dryer set to high temperature and high blow speed. The boards always end up looking very clean. No signs of damage to the silk screen or solder mask.

author: jmelson
author_rank: Super Contributor
timestamp: June 30, 2019, 04:06:30 am
content: Quote from: Lucky-Luka on June 29, 2019, 10:45:55 amFirst, it depends on the flux used. There is no-clean, solvent-clean and water soluble. If you really need to clean the board, then use water soluble flux (WS) and just wash in water, maybe with a little gentle scrubbing with a toothbrush.If you use one of the other fluxes, then it can be difficult. There are flux remover preparations that have a variety of stuff to break down and hold the flux in suspension. One was roughly equal parts of isopropyl, ethanol and ethyl acetate.But, what I do for the non-WS flux is use plenty of alcohol, let it soak in for a minute, then brush with a toothbrush for about one minute, and immediately rinse with lots of water. You will see the alcohol turn white when the water hits it, that is the flux residue dropping out of solution. You need to wash it away as rapidly as you can, before it deposits back onto the board. Depending on the required level of cleanliness, one or two cycles of this process should get the board pretty clean.For ordinary digital boards, I use no-clean flux and don't clean the boards. For critical stuff like high-impedance or high voltage circuits, I use either solvent clean or water soluble.Jon

author: Shock
author_rank: Super Contributor
timestamp: June 30, 2019, 04:30:33 am
content: Quote from: rcbuck on June 30, 2019, 03:21:06 amPlain tap water is not good for electronics, especially finishing with it. Denatured alcohol contains additives as well.Instead I would dilute pure IPA with deionized water, or if you needed something more aggressive make either an IPA or deionized water solution along with some other electronics safe detergent or more aggressive solvent (this is what manufacturers do). Rinsing with deionized water or IPA (in a ventilated area) from a squirt bottle works well to wash it all off, you can always do a two step rinse.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 30, 2019, 05:25:09 am
content: You can get a bit too "precious" with cleaning PCBs, especially ones that have already been in service.These often accumulate a layer of dust & other "gunk" over the years, but continue to operate properly.As I now have to buy my own solvent, I have gone to plain old "methylated spirits".People say it leaves "a white residue", but in my experience, that is just dissoved flux that hasn't been wiped away properly.

author: Brumby
author_rank: Unknown
timestamp: July 01, 2019, 04:00:05 am
content: Quote from: ptricks on June 29, 2019, 11:01:37 amThis is how I do it. I have IPA in a spray bottle which makes for easy application.