Desoldering SMD capacitors - Page 1
Forum section: electronics / beginners

author: janoc
author_rank: Super Contributor
timestamp: May 09, 2017, 04:14:04 pm
content: Hello,The last weekend I have learned the hard way that attempting to desolder a SMD electrolytic capacitor using hot air is not the brightest idea. The *POOF!* noise wasn't only the sound of my brainfart ...What technique are you using to remove these?I have seen some videos of a guy trying to butcher it using the hot tweezers but it wasn't working too well - his caps have either exploded as well or didn't want to budge (not enough heat getting to the leads under the can). I would prefer to get the cap off in one piece, cleaning the electrolyte from the board is not exactly fun, not to mention the risk of popping capacitors near one's face.Any tips?Jan

author: Zero999
author_rank: Super Contributor
timestamp: May 09, 2017, 04:40:01 pm
content: I've had that happen to me before.If you reduce the temperature of the heat gun so it just gets hot enough to melt the solder, then this shouldn't happen.I just use my soldering iron. Add a little extra solder, then if it still won't come off, then preheating the board will help.

author: Cliff Matthews
author_rank: Unknown
timestamp: May 09, 2017, 04:40:50 pm
content: Small flat head screwdriver between pcb and the plastic base and it's up in a sec with a small soldering iron.

author: james_s
author_rank: Super Contributor
timestamp: May 09, 2017, 06:38:23 pm
content: Grip it firmly with pliers, push *down* and twist as though you are removing a bayonet lightbulb in a stiff socket. Sounds crazy but it works great, comes off clean with less risk of damage to the PCB than any other method I've tried. Follow up with a soldering iron to remove any bits of leg that remain.

author: janoc
author_rank: Super Contributor
timestamp: May 09, 2017, 06:42:21 pm
content: Quote from: Hero999 on May 09, 2017, 04:40:01 pmIt is one of those darn lead-free boards, so the cap tends to cook off and blow up before the solder even melts (had the gun at 400C).Quote from: Hero999 on May 09, 2017, 04:40:01 pmOK, I will give that a shot with a blob of leaded solder on each side.Quote from: Cliff Matthews on May 09, 2017, 04:40:50 pmWith that you are risking pulling up the trace as well, especially if you pry it up before the solder has completely melted. I have seen people try to twist them off and what not too - but all that risks damaging the board even more than having the cap puke the electrolyte there.

author: james_s
author_rank: Super Contributor
timestamp: May 09, 2017, 06:44:32 pm
content: Usually the electrolyte has already leaked. It's not a problem to spill a bit as long as you wipe it off. The damage occurs when these capacitors leak for weeks/months/years, especially when the equipment is energized with electrolyte on the board.

author: RGB255_0_0
author_rank: Frequent Contributor
timestamp: May 09, 2017, 07:00:15 pm
content: If you really struggle then you can use Chip Quik.I tend to run the hot air at about 150°C and a fine tip of the iron. One side will top up and you can repeat, or if really adventurous, wiggle it up and down and the lead will snap off.

author: Ian.M
author_rank: Super Contributor
timestamp: May 09, 2017, 07:12:13 pm
content: If possible use a board preheater - it makes a hell of a lot of difference to only have a 120 deg C temperature differential sucking the heat away from the pads rather than a 200 deg C differential.

author: james_s
author_rank: Super Contributor
timestamp: May 09, 2017, 07:16:41 pm
content: Don't wiggle, seriously just push down and twist, they will pop right off. Try it on a scrap board if you don't believe me. I've been re-capping equipment for years, I've replaced literally thousands of these SMD electrolytic caps, I've tried every method I know and the push-and-twist trick is the best I've ever found.

author: drussell
author_rank: Super Contributor
timestamp: May 09, 2017, 07:48:40 pm
content: Yup... +1 for the "press down and twist them off with pliers" method.There is actuallywayless chance of damaging the board doing it that way than trying to actually de-solder them.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 09, 2017, 08:05:59 pm
content: Best way to unsolder most 2-terminal SMDs is to use two soldering irons. Much easier than soldering tweezers as you have more control of the angle of each tip.

author: janoc
author_rank: Super Contributor
timestamp: May 09, 2017, 10:39:34 pm
content: Quote from: mikeselectricstuff on May 09, 2017, 08:05:59 pmThat's what I am normally using. I have an old Solomon iron on my bench in case I need to dual wield. I was considering getting the hot tweezers, but the cheap ones are crap and I don't need it that often to be able to justify the cost of a Hakko or another Ersa station.However, these caps have only little of the leads poking out. There is not much space to transfer heat to, so it wasn't really working well.EDIT:Managed to get the caps off without blowing them up or destroying the board - after turning the iron temperature up to 400 C. I am used to leaded solder where I am using 320C max - that was obviously not enough to melt that lead-free. D'oh!

author: daveyk
author_rank: Frequent Contributor
timestamp: May 09, 2017, 11:29:31 pm
content: Quote from: james_s on May 09, 2017, 07:16:41 pmI wish o would have known that about a month ago or so.Sent from my iPhone using Tapatalk

author: JoeN
author_rank: Frequent Contributor
timestamp: May 10, 2017, 03:21:22 pm
content: Quote from: james_s on May 09, 2017, 07:16:41 pmI've never heard of this before and it is counter-intuitive because any normal person would think "I'm gonna wreck my board" but I am certainly going to try this the next time.

author: Electro Detective
author_rank: Super Contributor
timestamp: May 12, 2017, 01:23:21 am
content: This looks like a better deal than trial by fire, I haven't tried it yetMr Carlsons Lab on youtube btw

author: yada
author_rank: Frequent Contributor
timestamp: May 12, 2017, 01:32:18 am
content: Quote from: james_s on May 09, 2017, 06:38:23 pmI think hes trying to save the caps. Other wise he would just use snips then cleaned the board.

author: Shock
author_rank: Super Contributor
timestamp: May 12, 2017, 02:50:13 am
content: Smd tweezer hack.(image removed)

author: james_s
author_rank: Super Contributor
timestamp: May 12, 2017, 02:54:39 am
content: Why try to save the caps? SMD electrolytics are not worth saving.I used to use the snip method for a long time, but push and twist works better. It avoids having bits of capacitor ricocheting off the ceiling and electrolyte all over the hands.

author: mariush
author_rank: Super Contributor
timestamp: May 12, 2017, 03:03:04 am
content: I almost never save them, not worth it. Just replace with leaded capacitors where possible.I use norcal's method, jump to 10:30 :

author: james_s
author_rank: Super Contributor
timestamp: May 12, 2017, 04:00:40 am
content: I normally replace them with tantalum or ceramic chip capacitors, or dry polymer types depending on the application.

author: BMack
author_rank: Regular Contributor
timestamp: May 12, 2017, 05:02:52 am
content: Cut them above the plastic, then the plastic comes slides right off. I've also used the push and twist method but it always makes me nervous.BTW, this is another great use for the Engineer screw removal pliers, they're great as screw extracting but I use them anytime I need to grab something round.Regular size:https://www.amazon.com/Engineer-PZ-58-Screw-Pliers-GT/dp/B002L6HJAA/Small size:https://www.amazon.com/Engineer-PZ-57-Screw-Pliers-M2/dp/B001D7KU7W/

author: janoc
author_rank: Super Contributor
timestamp: May 12, 2017, 03:28:56 pm
content: Quote from: blueskull on May 12, 2017, 05:17:31 amThe electrolyte will start to boil at roughly 100 C, so any air temperature that actually melts solder will make the cap blow up if you keep heating it sufficiently long. Even normal iron could make then pop like that.What temperature are you using? I have set mine to around 400C and a lot of air since it is leadfree - and it was barely softening the solder. But the cap managed to blow up already.

author: janoc
author_rank: Super Contributor
timestamp: May 12, 2017, 07:48:11 pm
content: Quote from: blueskull on May 12, 2017, 04:49:58 pmAh ok, but that's a low temp solder. The board I had to remove the caps from used regular lead free. Wasn't melting at all before 380C or so on the iron.For normal eutectic leaded solder I am using 320C too.Quote from: blueskull on May 12, 2017, 04:49:58 pmWell, normal leaded solder doesn't really melt before 270 C and normal lead free at around 360-380 C, so sooner or later the cap will pop the seal, even if the electrolyte boiling point was at 200C. On the other hand, it is possible that the caps I had were not the best quality - the board is old, so who knows what happened inside them before already and what cheap junk they were (there is no manufacturer on them).

author: janoc
author_rank: Super Contributor
timestamp: May 12, 2017, 07:57:49 pm
content: Quote from: blueskull on May 12, 2017, 07:54:27 pmYes, but try to solder that SnPb with iron at 183C. I should have said that I meant the temperature of the iron needed, not truly the melting point of the solder, my bad.

author: mariush
author_rank: Super Contributor
timestamp: May 12, 2017, 10:33:47 pm
content: You never use the soldering iron set at a temperature close to the melting point of solder. The copper pads on the circuit board and the component itself would suck up the temperature from the tip and the tip itself may have a very small "reservoir" depending on the shape of the tip... so you pretty much always have to use slightly higher temperature that the solder melting temperature.As for electrolyte boiling at 100c and all that talk, the metal can of the capacitor, the leads, the pads and traces on the circuit board will basically act as a shield/heatsink, preventing the contents from reaching so high temperatures so fast. You have a few seconds to put solder on a capacitor pads and leads without the electrolyte inside being damaged.63/37 solder isn't "low temperature" at least the way i see it. Low temperature solders imho would be those Chipquick solders, those that have bismuth in them and they melt at around 138 degrees Celsius and stay semi-liquid/liquid for a longer period of time.Anyway, another suggestion for desoldering such capacitors would be to get a hot air gun (could be something cheap as a paint stripping gun) and heat up the pcb under the capacitor to around 60-80 degrees then add a drop of flux on the ends of each capacitor and use proper tip (for example one of those cup style which can hold some solder in a depression, used for drag soldering) to put some solder on the pads. Just by heating up the solder by moving the tip from one side to another, you should be able to quickly push the capacitor off its location.This technique is often used to repair broken LED backlights on monitors, where they use aluminum circuit boards - they heat up the boards from the bottom to a reasonable temperature in order to minimizer the iron tip temperature effect on the plastic case of the leds.

author: Rerouter
author_rank: Super Contributor
timestamp: May 12, 2017, 10:45:58 pm
content: In cases like this where you have a heat sensitive work piece , high wattage and high thermal mass work the best, the goal is to have the joint melted and done before the heat has any chance of flowing up the pin and heating the electrolyte, compared to the pins the capacitor has a high thermal mass, so if the time is short, only a tiny amount of heat reaches the electrolyte.The fact that your cranking your iron so high would imply your not even adding lead solder to the joints first, which creates a lower melting point and weaker joint that is easier to seperate. After part removal you would then clean the mixture off the pads and use your solder of choice.

author: janoc
author_rank: Super Contributor
timestamp: May 12, 2017, 11:25:52 pm
content: Quote from: Rerouter on May 12, 2017, 10:45:58 pmAs I have mentioned above, yes, I did in fact add leaded solder for this exact reason. I hope you realize that those caps are reflow soldered and when you add leaded solder, you are adding it to (and heating with the tip of the iron) only maybe 10% of the lead that is accessible, the rest is soldered under the case of the cap. So the effect is limited in this case, as is the heat transfer effect.Preheating the board from the other side would likely help but I don't have anything suitable to preheat it with. Will have to figure something out for the future because similar jobs are starting to be more frequent here.

author: KL27x
author_rank: Super Contributor
timestamp: May 13, 2017, 01:04:46 am
content: I remember removing these caps before. Quite a few of them. But somehow I don't remember how, lol. I have some bismuth solder, and maybe I used some of that. I may have just done the lift one end at a time, method, back and forth until the bead disconnects. Either way, I don't recall having much of a struggle, using only one iron.I might have even used hot air, before, but I think that's going to end. I've never exploded one, and I'd rather keep it that way.