Soldering sponges: the "thermal shock" myth

[MaximRecoil]

I've seen a lot of people on the internet claim that cleaning your iron on a damp sponge will cause the plating on the tip to crack/degrade/fail due to thermal shock. If that's true, it's funny that most soldering iron manufacturers, including the most reputable names in the industry, include a place on the workstand for a sponge, and some of them even market their own line of sponges.

When I worked at a PCB factory in the late 1990s, we all used damp sponges to clean the tips, Metcal brand sponges. There was no brass wool in the entire factory that I know of.

In any case, if your tip can't handle the thermal shock from a damp sponge, then it definitely can't handle the thermal shock of soldering. Solder is way more thermally conductive than water is:

Water - 0.58 W/mK
Solder (63/37) - 50 W/mK
Solder (SAC) - ~60 W/mK

Here's an example of what happens when you solder:



The temperature of the tip drops almost instantly by about 75° C, and that's with some of the highest-performing irons on the market. The temperature drop with lesser irons is even more. Not only is that a lot more thermal shock than wiping the tip on a damp sponge, but it happens a lot more often, unless you wipe your tip after every joint (and who does that?).

[AlfBaz]

I've seen a lot of people on the internet claim that cleaning your iron on a damp sponge will cause the plating on the tip to crack/degrade/fail due to thermal shock.

First I've heard of it, and my tips last for ages doing just that. It is quite possible that a lot of people on the internet have an opinion about everything but that's just my opinion

[Fgrir]

In any case, if your tip can't handle the thermal shock from a damp sponge, then it definitely can't handle the thermal shock of soldering. Solder is way more thermally conductive than water is:

Water - 0.58 W/mK
Solder (63/37) - 50 W/mK
Solder (SAC) - ~60 W/mK

I don't think the thermal conductivity difference is very important here.  The difference is in the two different material phase changes you are having to dump energy into.  Solder melting at ~180C vs. water vaporizing at ~100C.
I've used wet sponge forever as well so I'm not saying you are wrong about tip reliability, but while you have provided interesting data to show the thermal shock of soldering you have nothing to support your assertions that a wet sponge case would be less stressful.

[Neilm]

I believe that the tips cracking is more prevalent on lead free systems due to the composition of the tip.

[MaximRecoil]

In any case, if your tip can't handle the thermal shock from a damp sponge, then it definitely can't handle the thermal shock of soldering. Solder is way more thermally conductive than water is:

Water - 0.58 W/mK
Solder (63/37) - 50 W/mK
Solder (SAC) - ~60 W/mK

I don't think the thermal conductivity difference is very important here.  The difference is in the two different material phase changes you are having to dump energy into.  Solder melting at ~180C vs. water vaporizing at ~100C.
I've used wet sponge forever as well so I'm not saying you are wrong about tip reliability, but while you have provided interesting data to show the thermal shock of soldering you have nothing to support your assertions that a wet sponge case would be less stressful.

Regardless of phase changes, it boils down to the amount of temperature change in a given amount of time. A tip wiped across a damp sponge isn't even being submerged in water (and a sponge only has to be ever-so-slightly damp in order to work for this), while solder, which is about 100 times more thermally conductive than water, typically flows all around a tip when soldering a joint.

I don't have the equipment to measure temperature changes in real time while soldering or wiping on a damp sponge like the folks a JBC who made that chart do, but I'd be willing to bet that soldering cools the tip more. Neither one cools the tip enough to prevent you from immediately soldering another joint if you have an iron with a fast recovery time. During the time that I had a cheap $7 Radio Shack wall iron, soldering slowed me down more than cleaning the tip on a damp sponge did.

[saturation]

Its not just 'internet' banter but mentioned in professional circles as well as Hakko's  older comments on brass wire.

http://www.eptac.com/ask/wet-sponge-cleaning-vs-dry-brass-sponge-cleaning/

http://www.circuitnet.com/experts/80463.html

I don't know if the issue of thermal shock via wet sponge is worse versus brass wool nor has it been tested to prove its enough to be a concern.

Hakko no longer mentions that and just says this:

http://www.hakko.com/english/products/hakko_599b_feature.html#productNav

[thm_w]

They give some good arguments:

• No water required for cleaning, minimizes the drop in tip temperature at each cleaning to ensure better workability.
• Dome-shaped design reduces solder splash
• Flux contained in cleaning wires prevents oxidation of soldering tips

Brass lasts longer than sponge and is simpler/faster to use.
I hope manufacturers all switch to brass only (I see some models like this but not many).

[stj]

I believe that the tips cracking is more prevalent on lead free systems due to the composition of the tip.

lol - BS
the tips are the same, they never changed.
some people will blame anything on lead-free!!

[saturation]

Also see their maintenance link:

http://www.hakko.com/english/products/hakko_599b_maintenance.html#productNav

I've used the sponge for several decades but I too like the wool more because the tip is always kept fluxed and shiny.  Now the only use for the sponge is to truly clean out the tip to apply fresh flux and solder, which I do far less often.  Excess solder balls up and if you shake the Hakko brass container solder falls to the bottom of the container, makes it easier to clean too and last longer.

They give some good arguments:

• No water required for cleaning, minimizes the drop in tip temperature at each cleaning to ensure better workability.
• Dome-shaped design reduces solder splash
• Flux contained in cleaning wires prevents oxidation of soldering tips

Brass lasts longer than sponge and is simpler/faster to use.
I hope manufacturers all switch to brass only (I see some models like this but not many).

[jonatanrullman]

I believe, although I'm not sure I recall that correctly, that I switched to brass for the simple reason that it seemed to make more sense to me. And my sponge was on its last elbow so I had to buy something anyway.
Brass just had that shine of obvious improvement that sounds logical but perhaps isn't. I also like the added benefit that it lasts longer and doesn't need have water added to work. That alone was worth the small investment.

Cheers

[tautech]

I went away from sponges the very moment alternatives were available to:
Not brass but stainless wool. 

With the hobbyist irons I've always had, thermal shock was never the issue per se but the recovery time of the iron was and right when you're in the middle of solder and the tip needs cleaning. 
When you don't solder for a few days the sponge was always dry......how dry ? Well when it was covered in scorch marks you know it was too dry. 

[MaximRecoil]

Phase changing takes a LOT of energy. Think of this, water or ethanol based heatpipes have much higher thermal conductivity than copper, in the range of 10x to 10kx.

They can have a higher effective thermal conductivity than copper, but it greatly depends on the design/length of the heat pipes. It is a tuned system, optimized for cooling. There is also circulation involved, which, in and of itself, makes a huge difference. Randomly, rapidly evaporating water isn't drastically more effective at cooling than water that is barely evaporating. You can stick the tip of an e.g., Metcal in a small container of water and it will boil it all away, without ever cooling too much to continue boiling it.

Consider how easy it is to boil water on the stove top. Have you ever seen water stop boiling after it started because the rapid vaporization cooled things down too much? Now dump in a box of macaroni (e.g., from a standard size box of Kraft Macaroni & Cheese). It will stop boiling (assuming you're using a typical burner, 2-quart pot, and 6 cups of water as directed), because the macaroni, despite its very low thermal conductivity, has enough mass for the heat to dump into that it pulls the water down significantly below its boiling point.

With a damp sponge, we are only talking about a minuscule amount of water that evaporates when you wipe the tip on it. You would probably need a very precise scale to even measure it. If you want to try, wet a sponge, wring it out as much as you can, weigh it, immediately wipe a hot soldering iron tip on it, then immediately weigh it again.

On the other hand, the amount of solder you are melting onto an iron tip for a typical through-hole joint has enough mass that it can easily be weighed on an inexpensive consumer-grade scale. For example, I weighed 1 inch of 0.025" 63/37 solder wire, 1.1% flux, and it was 0.09 grams.

Keep in mind that flux also vaporizes when soldering, more or less depending on the type of flux.

[jpanhalt]

I see a lot of stuff here about the heat of vaporization of water.  Have you forgotten about the Leidenfrost effect (https://en.wikipedia.org/wiki/Leidenfrost_effect )?  Vaporized water acts as a thermal insulator and inhibits cooling.  That is why oil is much more effective at cooling than water, if that is what you want to do.

[sleemanj]

I can't spill my copper wool like I can a bottle of water which I would inevitably leave on the bench and forgot to cap :-)

[SeanB]

I have both types, and also a block of resinous pine wood to rub the tip on to clean hard deposits off using the rosin in the wood. The sponge is nice, the brass scouring pad ( a lot cheaper at the grocers than at the electronics shop) in a small tin can is also good, plus the brass holds the solder balls nicely.

[Bud]

Speaking from experience, 15 years of soldering using the same Weller chiesel tip and wet sponge, still good as new and is preferred over a recently bought JBC.

[MaximRecoil]

Speaking from experience, 15 years of soldering using the same Weller chiesel tip and wet sponge, still good as new and is preferred over a recently bought JBC.

I think issues with the plating is a cheap tip problem, not a damp sponge problem. I've never seen the plating on a Metcal tip go bad, for example. Metcal is all I've ever used since I learned to solder at the PCB factory in 1997; not counting the $7 Radio Shack wall iron I had before getting my own Metcal in 2007. The tip on that Radio Shack iron was junk from day one.

I've been using the same STTC-126 tip cartridge since I bought it new in 2007, and it is still like new. I've never even seen a Metcal tip oxidize by any perceptible amount. At the PCB factory, I never even bothered to tin the tips I used there, and I never had any problems with them. I knew of the practice, because I saw other people doing it, or other people's tips in the stand with big blobs of solder on them, but I didn't know why people did it, and I never noticed any benefit to doing it so I didn't bother. When I was done work each morning, I simply wiped my tip on the damp sponge and put it in my locker, and it was always still shiny silver and working perfectly the next night. I tin my tip at home when I'm done with it, just because I've since learned the reasoning behind it and it seems like a good precaution, but I'm not religious about it. Sometimes I've forgotten to do so, and like the identical tips I used at work, I've never had a problem because of it.

[KL27x]

Here's another data point. Flux. Flux has low boiling point solvents. Touching the tip to a load of flux will reduce the temp quite a bit. This busts another myth, IMO, that flux, in and of itself, increases thermal transfer to the joint. Err, no. It can increase thermal transfer via increasing the speed/formation of solder bridge between tip and joint. But flux, itself, can only reduce the temp, at least until the solvent is all boiled away. The main thing is does, IMO, is increase the liquidity and wetting of the solder, once it has reached its melting point.

In practice, I can easily melt a joint with zero flux, as long as there is good solder bead to touch to... BUT the melted solder will look solid because it's chunky and not totally liquid. It won't look like it is melted, and it wouldn't bridge itself to, say, a jumper wire. But pop the button on the solder sucker, and it all gets sucked up... and doesn't clog the device with sticky flux residue.

Anyhoo, I use the brass wool to remove parts from the tip. To clean my tips, I SCRAPE THEM! With a bit of brass tubing. This removes the crusted flux. And to date, this has no ill effect on the iron or chrome plating. There is no wet sponge in my soldering.

[MaximRecoil]

Here's another data point. Flux. Flux has low boiling point solvents. Touching the tip to a load of flux will reduce the temp quite a bit. This busts another myth, IMO, that flux, in and of itself, increases thermal transfer to the joint. Err, no. It can increase thermal transfer via increasing the speed/formation of solder bridge between tip and joint. But flux, itself, can only reduce the temp, at least until the solvent is all boiled away. The main thing is does, IMO, is increase the liquidity and wetting of the solder, once it has reached its melting point.

In practice, I can easily melt a joint with zero flux, as long as there is good solder bead to touch to... BUT the melted solder will look solid because it's chunky and not totally liquid. It won't look like it is melted, and it wouldn't bridge itself to, say, a jumper wire. But pop the button on the solder sucker, and it all gets sucked up... and doesn't clog the device with sticky flux residue.

Anyhoo, I use the brass wool to remove parts from the tip. To clean my tips, I SCRAPE THEM! With a bit of brass tubing. This removes the crusted flux. And to date, this has no ill effect on the iron or chrome plating. There is no wet sponge in my soldering.

I don't use separate flux for anything other than plumbing with 1/8" diameter solid-core lead-free solder wire and a propane torch. At work, drag soldering wasn't allowed; every solder joint had to be done one at a time with fresh solder fed into it, so I never used separate flux for anything there. They probably had some there, but I never saw it. Plus, I can drag solder if I want to with just flux-core wire, though I still don't usually drag solder anything. The only type of electronics soldering I know of that requires separate flux is when you use a large tip and store solder on it for use on multiple joints (the flux already in the solder would soon burn away, so you'd have to put separate flux on each joint). I don't do that either.

I've never put separate flux on a joint before desoldering with a Soldapullt, nor do I know what the point of doing it would be. When people are having trouble desoldering a joint with a solder sucker, it is because of improper technique. When I trained new employees at work to solder/desolder, a common mistake they made was trying to desolder without the iron, i.e., they would put the iron to the joint and then remove the iron and quickly try to get the solder sucker tip onto the joint and pull the trigger. I think they were afraid that the iron would melt the "plastic" tip if they didn't move the iron out of the way, or that the tip of the solder sucker wouldn't be able to fit over the joint if the iron was in the way. Of course, that's an exercise in futility. At best you'll only get partial removal of the solder in the joint. It should be like this when you pull the trigger:

 

The flux in the solder wire I've always used (i.e., the same stuff I used at work: Alpha Metals Cleanline SMT Core Plus) doesn't leave any residue/crust on the tip, at least not any that remains after a quick wipe on a damp sponge.

[nctnico]

I'm not a fan of brass wool because it seems to abbrasive to me. I only use it if a tip is so crusty it cannot be cleanedwith a sponge. IMHO the biggest disadvantage of a sponge is that it needs to be wet (I have a squeeze bottle with water for that purpose) and many people use it upside down so it falls apart quickly.

[Carl_Smith]

I can't spill my copper wool like I can a bottle of water which I would inevitably leave on the bench and forgot to cap :-)

I use an old contact lens solution bottle for wetting the soldering iron sponge.  It won't spill more than a drip or two if tipped over.  It's a bit of a fight to pry off the cap to refill it since they are pressed on, but I don't have to do that very often since a full 12 oz bottle will wet the sponge many times.

[MaximRecoil]

I go to the sink so that I have a place to thoroughly wring it out. At work the closest water source was a water fountain, so I used that. Some other people there used water bottles, but I don't like the sponge to be any wetter than it needs to be.

[tggzzz]

I'm not a fan of brass wool because it seems to abbrasive to me.

Brass: 3 mohs
Steel: 4-4.5 mohs
Harddened steel: 7-8 mohs

http://www.jewelrynotes.com/the-mohs-scale-of-hardness-for-metals-why-it-is-important/

[madires]

I've used the wet sponge for a long time and never had any issues with tips becoming bad early because of this. A few years ago I've moved to brass wool, and I like the convenience of not having to wet the sponge each time. The solder which is removed from the tip while cleaning simply falls down into the wool's container. And no corroded sponge holders anymore.

[KL27x]

I've never put separate flux on a joint before desoldering with a Soldapullt, nor do I know what the point of doing it would be.

We agree on this. I've seen a lot of people recommend adding flux when desoldering, to "increase thermal transfer." In fact adding a little flux can help you to melt the joint a little faster in some cases where you can't get a good contact to the joint. But mostly, it just LOOKS "more melted" and you get to clearly see exactly the point when it melts vs a dried up joint, because it will go shiny and surface tension will make it ball/flow!

As for never using additional flux... Well that's fine if you were born with 3 hands, lol. Holding solderwire with one hand is not always an option. Some people use little octopus helping hands. I use flux.
 
I believe you mentioned, before, that you did thru hole soldering at your work. Extra flux is not needed for thru hole manual soldering. You need to feed so much solder wire into the joint, the flux will be there, anyway.  Fluxing the joint and then adding solder is commonplace in industry. Google "wave soldering." For SMD, drag soldering is used in military/aero, I believe. Seen videos by NASA trainers/workers doing drag soldering, anyhow.

And sometimes you simply need flux. Try installing a BGA without flux.

A common saying you might have heard before: you can't use too much flux. A lot of professionals and hobbyists use flux. It is helpful in a lot of situations.

*Also, as I mentioned before, the Metcal is top notch for not burning up the flux. That's what it is great at. Break out your Rat Shack for a solder session. You will have crusted flux.