How to Remove White Residue on PCBs

[jpanhalt]

I've used a few things over the years for cleaning (not PCBs) such as brake cleaner and either electronic cleaner or intake manifold cleaner, and sometimes it ruins the plastic.

You have to look at the chemicals involved, not what some marketing person calls it.  For example, I have 2 types of brake cleaner on the shelf.  One is virtually pure TCE (tetrachloroethylene/perchloroethylene/PERC) the other is labeled "non chlorinated" and has methanol, acetone, toluene, ethylbenzene (related to toluene) and various short-chain hydrocarbons.  Those are quite different.  PERC is relatively insoluble in water (0.015% or 0.15g/liter) ; acetone and methanol are miscible with water. There are both designed to remove oils.  Neither is designed for flux; although, I suspect the non chlorinated version would be better.

For the most part, I've never had IPA ruin anything and would assume letting the PCB sit in a IPA bath would clear away everything. I know that in the past I've poured IPA into a metal pan only to find it got discolored with mixing with whatever metal the pan was made from. So I was wondering what a safe metal pan would be to avoid this.

Alcohols show a striking difference in solvent properties when water is added.  Absolute ethanol is great for fats; 95% is not so good  As for your metal pan, IPA is not known to attack vigorously common cooking pans.  Of course, magnesium and lithium are not used for cooking.  Under some conditions, aluminum might react a tiny bit.  I suspect your observation is simply related to removing some cooked on residues.

Cellosolves are an ether and alcohol in the same molecule (e.g, alkoxy glycols).  Alkoxy describes an ether linkage (R-O-R'); glycol describes a molecule with two hydroxy (alcohol) groups (e.g., ethylene  glycol  [https://en.wikipedia.org/wiki/Ethylene_glycol ]).  Diethyl ether (a simple ether) is a good solvent for oils and some fats but not polymers.   

It's the combination of the two classes that gives cellosolves their unique solvent properties.  That is, water soluble and dissolves oils, baked on oil, polymers (e.g, acrylic wax) and so forth.  In their pure state, they attack paint and are used as paint solvents, but adding water diminishes that effect.  The recipe I gave is the same composition as Kester's newer, water-based flux removers.

I use it in an ultrasonic for 2 minutes, then rinse under running water, and another 2 minutes with DI/distilled water to get rid of any remaining salts. 

You are worried about the effect on plastic.  That is hard to predict.  Some solvents may not seem to attack the plastic right away, but months to years later cause crazing.

And alternative is a kitchen dishwasher with common dish detergent.  It is reported that name brand manufactures, e.g., Tektronix, used a dishwasher in its repair area.

Lastly, just live with the white residue.

[bostonman]

Personally I think leaving white residue behind looks ugly, and, in high frequency circuits, thought it could cause issues.

In any case, my feeling is simply that white residue gives the impression the job was done half fast. In almost all cases, anything I've fixed is something I care enough about to not experiment with and/or has components that may not be sealed along with mechanical plastic parts.

My plan several months ago was to get some sort of pan, pour four or five bottles of IPA in it, leave the section of PCB with the flux residue soaking, and then clean with an acid brush. These are the steps I took at my old job and seemed to still have residue remaining. As a previous post suggested, I use one pan as the "dirty" IPA and a second pan with "clean" IPA. While this may work, it certain will eat up quite a bit of IPA bottles.

The way I do it now, and maybe this is the issue: I keep a bottle of IPA (maybe 10-12oz bottle) nearby along with acid brushes and a tooth brush. Usually I turn the PCB sideways, scrub with the brush(s), dunk the brush in the IPA again, scrub more, and let air dry.

I've planned to buy an air compressor just so I could blow off the alcohol as using a can of air seemed to have better results.

One thing I don't understand is why the flux doesn't get burned off during soldering. It seems a dab of solder results in a puddle of flux many factors more than the dab of solder used.

[Ian.M]

That's seriously sub-optimal as IPA is hygroscopic, so if exposed to the air for an extended period, dilutes itself with the moisture in the air and as the water content increases, it passes a threshold and tends to drop the dissolved rosin out of solution leaving whitish gooey residue.

By all means, pre-soak in your tray of used IPA to soften the deposits, but to actually wash them off you need fresh dry IPA applied by spray or brush, sufficient to run off the edge of the board into your catch tray, + usually a fair bit of scrubbing.  After the final IPA rinse put the  board on edge on kitchen towel to let as much as possible run off and to blot the edge to prevent droplets forming and drying to leave sticky patches.

Also, to keep it as dry as possible, try to avoid opening your stock IPA bottle frequently by dispensing into a smaller well stoppered container for bench use, no more than can be used in a couple of weeks, and keep the bench container tightly stoppered when not in use.

Ionic residue (metal salts from flux action) can also leave white deposits, and the water in somewhat dilute IPA helps remove them but if the IPA is wet enough to precipitate rosin, it cant get to the metal salts embedded in the rosin.

[jpanhalt]

Have your not seen the Kester paper on white residue?
https://www.kester.com/Portals/0/Documents/FAQs/White_Residue.pdf

Also look up the SDS for Kester 5768 and its other water-based flux cleaner.

You say you don't want to experiment with the meaningful boards, yet that is exactly what you are doing.  You have tried IPA.  It didn't work.  So, now you seem to want to keep trying insignificant variations until it works.  Never say never.

Kester is a pretty well known name in the business.  It has already researched the subject.  Its discussion of the problem makes sense, and my personal experience is consistent with that. My usual method until I switched was absolute ethanol with or without a little acetone. I tried IPA and found absolute ethanol faster and better. 

On a recent PCB with a TQFP 44 chip, I could not get the residue completely off.  Board didn't look bad, but between the pins there was the precipitate.  So I tried the Kester formula, and it was like magic.  The attached picture was taken about a year later so there is some dust and lint on the board.  As for how to dry the board?  When taken out of the wash bath and rinsed with water, the board was effectively dry.  Solder resist is also water resist.  It is quite hydrophobic when clean.

IPA is miscible with water.  Why do you need an air compressor to blow it off?  If it is clean, it should just evaporate without leaving a residue.  If it is not clean, then get some that is.  Lack of an air compressor is not the problem.  Have you considered a water rinse to remove slightly contaminated IPA?

Anyway, you seem to ask questions for information, then argue against any suggestion that is contrary to your original plans.  I have given you the best advice I can and will be moving on.  BTW, soaking in IPA may not be the best thing long term for some plastics.  It may remove plasticizers without causing any immediate effect, but long term, the plastic may show crazing or be more brittle.

[Ian.M]

Chemtronics' notes on the subject are also worth a read:
https://www.chemtronics.com/the-dreaded-white-residues-why-they-form-what-to-do-about-them

[zapta]

I use isopropyl with a brush and cleanroom micro fiber wiperss to lift the dirt.  (Kimwipes are terrible for this application, making the entire board wipe).

https://www.aliexpress.us/item/3256805873860950.html

If I have larger cleanup jobs or multiple boards, I use an ultrasound cleaner, Branson EC Formulated Cleaning Concentrate and distilled water, and the result are great. You can find instructions on youtube, e.g. make sure to degass the solution.

https://www.amazon.com/gp/product/B071FBGMLC?th=1

Another option is to just use white PCBs.  ;-)

[zapta]

I've planned to buy an air compressor just so I could blow off the alcohol as using a can of air seemed to have better results.

I got this one for the same exact purpose. It's mains operated, very powerful, and does a great job. There are many others, including rechargeable battery operated.

https://www.amazon.com/gp/product/B0BN16MWVS

[bill_c]

Cold ultrasonic and / or isopropyl alcohol usually leaves white residue for me, hot ultrasonic and denatured alcohol solved it for me.  I do like the floor stripper idea though.

[bostonman]

Anyway, you seem to ask questions for information, then argue against any suggestion that is contrary to your original plans.

Didn't think I was "arguing". I was simply elaborating on the processes I've tried and asking any similar suggestions to further explain since part of the steps were similar steps I took.

From what I can tell, many cleaning variations exist and I need to re-read the suggestions in greater detail along with reading the links provided.

If I felt the need to argue with advice, I wouldn't ask for advice in the first place. I'm somewhat active on here, and have had some great help with my projects. White residue has annoyed me, and I wanted to emphasize that some of the boards I've worked on aren't simply components, but an assortment of hardware and components I question whether they are safe to drown in cleaning solvent.

[smh]

Out of interest, are you trying to remove the white residue because it aesthetically doesnt look very nice, or does it have an adverse affect on the pcb/components? (or both!?)

[bostonman]

A combination of both along with having not known what the white residue could do to components over time.

From this thread, it seems the white residue won't do much harm, however, I believe at high frequencies (which I haven't had any to repair recently) could cause impedance issues.

[HackedFridgeMagnet]

From what i discovered on youtube, cleaning a stain is a two part process.
I think you have only done one part.

1. Dissolve the white residue. 
2. Remove the dissolved stuff from the pcb.

I do step 1. by cleaning and dissolving the residue with IPA and a toothbrush.

Then for step 2.
Flood the still wet pcb with IPA via a pump atomiser.
Keep pumping for a while, keeping a steady flow of liquid running off the edge of the board.

Sometimes i may use IPA mixed with water, not sure why.

[bostonman]

I had some time and reread this thread along with the links.

A few questions.

Some suggestions were warm soapy water. I know water eventually evaporates, but I want to confirm that (literally) warm water from the faucet along with a mix of (assuming) Dawn dish soap. This is safe for things like surface mount ICs where the water may seep underneath the IC and take long to evaporate?

If this method works, it's a great suggestion and a cheap solution; but the drawback I'd assume is the wait time for drying before power can be applied to the board; unless I use a mini oven to dry the board (but then I run into issues with any plastic pieces on the board).

Ultrasonic (one person suggested warm ultrasonic) seems really cool, but can/will this loosen components and/or possibly crack any mechanical parts? I don't know anything about ultrasonic cleaning or "heated" ultrasonic, but I think being able to use such a unit to clean boards would be cool.

I do like those air blower guns and plan to purchase one on (Black) Friday. This certainly beats a compressor, but a bit of a concern for old boards where weak solder joints may result in components blowing off (I'm just thinking out loud as I've given thought to using air in the past).

Finally, Flux Off seems like a good solution. A bit expensive, but well worth the cost if it cleans the flux - I may also add this to my list of stuff to buy on Black Friday.

[CurtisSeizert]

In my experience, the solution to this is not so much in the cleaner as it is in the choice of solder paste. The residue from "no clean" type solder paste is difficult to get off. I have switched to using water washable solder paste, and it's not an issue anymore. For flux I use RMA. Both residues are easily removable with IPA, just a little brushing and rinsing required. To get the IPA out from under IC packages, etc., I use a battery powered duster for cleaning keyboards, etc. that I got on Amazon for $50 or so. For fA circuits, I would probably spring for HPLC IPA, but "ACS grade" from Amazon is fine at the single digit pA level. Perhaps there will be a Black Friday deal. I need to restock. Post cleaning, I usually bake between 75 and 125 C for an hour, but sometimes I don't bother if I am reworking a prototype. The ADA4530-1 datasheet has some information about solder pastes and cleaning.

I am an organic chemist by training, and I have no problem using more aggressive solvents, but they all present a waste disposal concern. This may be no problem if you are a company and you have a contract with another company who will take the stuff away, but in my house, my preference is to avoid generating hazardous waste streams where possible. I do use the various canned flux removers if I am in a hurry and don't feel like cleaning the whole board. The hygroscopicity of IPA is not a real concern if you're turning it over and closing it when not in use. It forms a good azeotrope with water, so the liquid phase left behind as it dries will decrease in moisture content. This is a property I have exploited many times as a chemist to reduce the moisture content of non-volatile products. If you are going to use an aqueous cleaning solution, I would wash with DI water and rinse with IPA.

If for some reason you are in a situation where you have every available solvent and need to clean a stubborn organic residue off, THF is unbeatable. It is the source of that distinctive smell in the purple PVC primer, and it will go through 6 mil nitrile gloves in about 3 seconds.

[bostonman]

I agree that solder paste and flux is probably the start and a good one makes cleaner easier.

That's seriously sub-optimal as IPA is hygroscopic, so if exposed to the air for an extended period, dilutes itself with the moisture in the air and as the water content increases, it passes a threshold and tends to drop the dissolved rosin out of solution leaving whitish gooey residue.

I think this summarized what I've seen best and explains quite a bit. Often times I've soaked the area with IPA, brushed and brushed, and thought, this is it, the board should be clean. Later I look, and the board looks horrible.

I plan to buy a can of flux off, but will also work on some methods listed.

Most likely much of this is my fault because I had a similar issue with paint brushes recently. I used oil based paint, and, to clean the brushes, I was told to use paint thinner. Well, I poured paint thinner in a pan, put the brush in it, pressed the bristles, turned, etc... The next day the bristles were still moist, the day after the bristles were hard.

I thought it was just them being dried, so I manually bent them until they soften and used the brush again. Used the same cleaning method, and the same issue occurred. Eventually I returned to the store to discuss the issue and was told to use one "dirty" pan and one "clean pan", so I bought a new brush. I told the guy I'll buy a fresh can of paint thinner and he said the one I have will be perfectly fine.

Afterwards, I did the method he described, and I still have the same issue happening with the bristles. So it's obvious I'm not following the methods correctly and probably why my PCBs get white stuff when they dry.

Is an ultrasonic cleaner safe for boards or can it cause the components to vibrate lose from the solder connection? I think having an ultrasonic cleaner would be pretty cool, but not sure if it's worth it.

[CurtisSeizert]

I agree that solder paste and flux is probably the start and a good one makes cleaner easier.

That's seriously sub-optimal as IPA is hygroscopic, so if exposed to the air for an extended period, dilutes itself with the moisture in the air and as the water content increases, it passes a threshold and tends to drop the dissolved rosin out of solution leaving whitish gooey residue.

I think this summarized what I've seen best and explains quite a bit. Often times I've soaked the area with IPA, brushed and brushed, and thought, this is it, the board should be clean. Later I look, and the board looks horrible.

Water absorption from bulk IPA is an unlikely root cause because the effect is likely to be minimal. Even in a PE bottle, I would be surprised to see moisture content rise 1% over 12 months. It is routine (if not best-practice) to put a feed line in a ventilated IPA bottle on an HPLC system and leave it there for months at a time (especially in academic labs). This is a system where moisture ingress into the IPA would cause drift in the results over the lifetime of the bottle, but I haven't seen this causing issues. I use the same IPA over and over for a pre-clean of boards right after they cool from being reflowed, and I haven't seen a case where this seems to be happening. It is possible that it happens to some extent while drying the boards, but you can fix this by rinsing the board with fresh IPA before blowing it off. This sort of moisture ingress is a problem mostly either when you are dealing with things that are much more sensitive to moisture (i.e., smaller effects matter) or when you are using solvents with a high vapor pressure because the surface of the solvent is cooling from evaporation and creating areas of high local relative humidity near the surface of the liquid.

I have seen the same effect you describe with no-clean paste/flux and IPA, and I think it is more likely that under IPA the residue becomes transparent the way that salt crystals become transparent when you drop them in water. I had originally thought that this was from the residue dissolving and those places being rinsed insufficiently, so I cleaned some specific areas between the leads on an SO8 package with a dental pick and cleaned the board again in IPA. The places I had cleaned stayed clean, and the others stayed dirty. Sonication in IPA at up to 40 C, even with long exposure times (1 h) did not solve the problem for me. Most packages are OK with sonication, but best practices are to avoid sonicating quartz crystals. There were two solutions that did an OK job with no-clean flux that I found. One was using a flux remover from Chemtronics that seems to have been discontinued (probably due to VOC regulations, I think it used something halogenated from them smell), but they have other products that are targeted at no-clean flux. For me, this took multiple cycles and a lot of brushing. The other was to boil boards in IPA for about 10 minutes. I would not recommend the latter as it presents a fire hazard, but it was pretty clear that the flux residue is minimally soluble in IPA because even at boiling it tended to flake off and sink to the bottom without going into solution.

I believe you will find if you switch to water washable paste and flux that this is not an issue anymore and all the more extreme solutions are unnecessary. I banged my head against the wall with this for some time and have spent too many hours trying to clean flux residue just to find out that "no-clean" means "don't clean". With no-clean paste, you may be able to avoid white residue by curing in the oven at 150 C for some time after reflow, but I haven't tried this. Also, last I checked, Amazon only has no-clean paste in stock, and you'll have to go to a proper distributor to get water washable stuff. If you're on Amazon, though, you may invest $30 in a Peltier fridge to put your solder paste in. It'll get you down to about 6 C and extend the life of your solder paste.

The leaded paste I use is SMD4300AX250T5 and the lead-free is SMD4300SNL250T5. I have had good results with both cleaning with a brush in room temperature IPA.

[tooki]

I'm resurrecting an old thread that I originally started.

Recently I repaired a vintage Commodore mouse with plastic mechanical parts. Due to the plastic and age, I was reluctant to use anything but Isopropyl alcohol. As usual, I grabbed a brush (tooth brush this time), dipped it in the Isopropyl alcohol, and scrubbed all the flux. After drying, not only was the section I brushed white with flux residue, but spread to other areas.

I repeated the wash and got it cleaner, however, some was still sticky. The only thing that seemed to work was using a can of air to wash off the alcohol and dry it quicker.

If I remember correctly, back at my old job I'd leave a PCB submerged in alcohol, scrub it clean, and would still see white residue after it dried.

My assumption would be the Isopropyl alcohol is strong enough that it deludes the flux, scrubbing it clears it away, more fresh alcohol, eats the remaining, and then another dose of alcohol, and it dries clean.

This doesn't seem to be the case. My confusion is what am I doing wrong, and, also, I'd like to put a few bottles of Isopropyl alcohol in a metal pan to wash boards in the future but sometimes the alcohol mixes with the metal and causes the alcohol to become mixed with metal tarnish residue.

Does anyone have recommendations for a pan and ways to stop my boards from remaining white/sticky?

First of all, it's important to distinguish between sticky residue and white residue, because they're very different things. (They can occur alongside each other but are not the same thing.)

Sticky residue is, plain and simply, leftover flux. Thin layers of it dry glossy.

White residue is the result of chemical reactions in the flux during soldering, producing ionic contaminants that are not solvent-soluble. (This is oversimplified, the Chemtronics document linked above goes into more detail.)

Sticky or glossy residue is removed by simply cleaning longer. If you're submerging the boards, let them dwell longer. I sometimes just wet the board in solvent, and place it into a ziploc bag together with a paper towel soaked in the same solvent. This prevents the solvent from just drying off right away.

White residues won't go away anywhere near as easily, because the entire problem is that they aren't soluble in the solvent being used.


Regardless, what seems missing from all of your cleaning regimens is actually removing the residue-laden solvent. It sounds like you think solvents destroy the residues, but all they do is mobilize them. If you use solvent to dissolve the residues, but just brush them around the board, they're not actually gone, they'll just be spread out once dry. Similarly (and reiterated in your paintbrush story) soaking in solvent simply dilutes the residues, but whatever solvent is left on the board (or brush) still contains residues. You have to remove the residue-laden solvent if you want to remove the residues. Otherwise you're just moving them around and redepositing them elsewhere.

(This reminds me of people who mop their floors in a single pass, without going back with clean water and a well-squeezed mop afterwards. Sure, the mop has picked up some of the dirt into the bucket, but you're also leaving behind a film of dirty water everywhere. Unless you actually lift that dirty water away, you're depositing dirt and soap everywhere.)


I have mostly moved away from cleaning PCBs by drenching with copious amounts of solvent. Instead, I use a brush dipped in solvent to scrub an area of the board, then use this brush (the "dirty" brush) to mop up the residue with a kimwipe (or other lint-free wipe). Stubborn areas may require this step to be repeated. Do this for the entire board until there is very little residue. If you have an air compressor, blow out underneath chips, too.

Then take a fresh wipe, lay it onto the board, and take a second brush (your "clean" one) dipped in clean solvent to mop it clean. In essence, think of how you use Windex and paper towels to polish a window. The "clean" brush's purpose is really just to let you manipulate the wipe, since our fingers are much too fat to be of use.


If, after all this, your board exhibits sticky or glossy residue, then your cleaning was simply incomplete and needs to be redone. But if it exhibits white residue (and no sticky/glossy residue) after drying for a few hours, then you need to find a different solvent.

[tooki]

From this thread, it seems the white residue won't do much harm, however, I believe at high frequencies (which I haven't had any to repair recently) could cause impedance issues.

Read the Chemtronics link again; depending on which type of white residue it is, it can lead to galvanic corrosion and dendrite growth.

Some suggestions were warm soapy water. I know water eventually evaporates, but I want to confirm that (literally) warm water from the faucet along with a mix of (assuming) Dawn dish soap. This is safe for things like surface mount ICs where the water may seep underneath the IC and take long to evaporate?

Yes and no. Hot tap water is fine as tour wash water, but not as the final rinse. You should rinse with distilled/deionized (DI) water, and ideally follow with an IPA rinse to help the DI water dry quickly. Use your compressed air to help blow it out from under chips and connectors and stuff.

Water-soluble fluxes should be fine with no detergent at all, or dish liquid if you want. But non-water-soluble fluxes are untouched by dish liquid. You need a proper saponifying PCB cleaner (like Safewash) or equivalent "hack" (like Zep floor stripper, which apparently is chemically practically identical). I wouldn't be surprised if some household cleaners worked, too, but I don't have any suggestions.

Unfortunately, Electrolube just discontinued Safewash in the aerosol can. Now you have to buy canisters of it.

Ultrasonic (one person suggested warm ultrasonic) seems really cool, but can/will this loosen components and/or possibly crack any mechanical parts? I don't know anything about ultrasonic cleaning or "heated" ultrasonic, but I think being able to use such a unit to clean boards would be cool.

Loosen components?!? Maybe if you left a board in for hours and hours instead of the 3-5 minutes it should take. Ultrasonic PCB cleaning isn't a hack, it's a well-established process for which there exist dedicated chemicals and machines. The well-known restrictions are quartz crystals, as well as any components that cannot be submerged, like many types of sensors and switches. If you go ultrasonic, check the component datasheets to make absolutely sure they don't prohibit ultrasonic cleaning! (Some parts, like many environmental sensors, do not allow cleaning of any type because any liquid ingress will kill it. Some are OK with careful manual cleaning with the sensor hole taped over, others not even that. You have to check datasheets and application notes.)

Pro tip for ultrasonic: to avoid having to fill the entire machine with your solvent (which is dangerous to do with flammable solvents like IPA), fill it with water, and then put your PCB into a small container (for example, a beaker) filled with your solvent, and place that into the ultrasonic bath. You can also use ziploc bags to the same effect. (Some recommend double-bagging.)

Finally, Flux Off seems like a good solution. A bit expensive, but well worth the cost if it cleans the flux - I may also add this to my list of stuff to buy on Black Friday.

I am decidedly on "team commercial flux remover", rather than IPA. While IPA is cheaper, it's simply not as good as the blends of solvents used in commercial flux removers. That means you can get away with using far less of it, and it takes less time. To me that's well worth the $10-15 per can. Especially if done using the "mopping" method above, rather than flooding/submerging, since you need far less solvent.


Another electronics technician in another department at work (whom I used to work with) swears by Safewash, so now that the aerosol cans aren't sold anymore, he's ordered a canister and is going to share some with me. Hopefully I can get an ultrasonic cleaner to use it in. I also have wondered if it's feasible to use it in one of the labware dishwashers in the chemistry labs. (That is another established, accepted PCB cleaning method.) I just don't know whether those labware dishwashers allow disabling the automatic detergent dispensing to let you manually use a different cleaner. I have also been considering switching to water-washable flux, but I need to do some testing to ensure it's safe in the long run. And of course I wouldn't use it for stranded wire at all, since there's no way to clean it.

[bostonman]

Loosen components?!? Maybe if you left a board in for hours and hours instead of the 3-5 minutes it should take.

I was thinking of a somewhat recent board I repaired (over the course of several months) for my Agilent oscilloscope. I found the solder for the components to be weak.

In fact, I had to replace a ZIF connector on this board and the pins nearly pulled off the solder. The connector was in a tight location and I was shocked to find how easy it was to remove. I don't remember the degree of how easy the pins removed from the solder, but I began questioning the entire board at that point.

Also, on a side note, this board had RF covers over the four channels. The covers easily came off, however, there were tiny metal clips that the RF cover (shield) went into. The acid brush kept getting stuck in these clips, and that caused lots of issues with trying to clean the board properly; especially since two chips required hot air and it had lots of flux in the area.

If you go ultrasonic, check the component datasheets to make absolutely sure they don't prohibit ultrasonic cleaning!

Good to know. Unfortunately most of any work is repairing, so I end up with a mix of components and/or components that don't have a part number on them, however, obviously this is worth keeping in mind. I knew crystals would certainly be dangerous to put in ultrasonic.

[uer166]

I've been washing PCBs in my dishwasher with Alconox with much greater success than using solvent here or there. They require a baking process afterwards, but come out absolutely clean.