Desoldering SMD capacitors

[janoc]

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

[Zero999]

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.

[Cliff Matthews]

Small flat head screwdriver between pcb and the plastic base and it's up in a sec with a small soldering iron.

[james_s]

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.

[janoc]

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.

It 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).

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.

OK, I will give that a shot with a blob of leaded solder on each side.

Small flat head screwdriver between pcb and the plastic base and it's up in a sec with a small soldering iron.

With 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.

[james_s]

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.

[RGB255_0_0]

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.

[Ian.M]

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.

[james_s]

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.

[drussell]

Yup...  +1 for the "press down and twist them off with pliers" method.

There is actually way less chance of damaging the board doing it that way than trying to actually de-solder them.

[mikeselectricstuff]

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.

[janoc]

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.

That'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! 

[daveyk]

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.

I wish o would have known that about a month ago or so.


Sent from my iPhone using Tapatalk

[JoeN]

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.

I'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.

[Electro Detective]

This looks like a better deal than trial by fire, I haven't tried it yet 

Mr Carlsons Lab on youtube btw 

[yada]

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.

I think hes trying to save the caps. Other wise he would just use snips then cleaned the board.

[Shock]

Smd tweezer hack.

(image removed)

[james_s]

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.

[mariush]

I almost never save them, not worth it.  Just replace with leaded capacitors where possible.

I use norcal's method, jump to 10:30 :

[james_s]

I normally replace them with tantalum or ceramic chip capacitors, or dry polymer types depending on the application.

[BMack]

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/

[janoc]

Desolder one pin, bend the other pin to lift up the desoldered pin, then desolder the other pin. No need to use a hot air gun.
BTW, I use hot air gun or reflow oven on these caps, and they don't blow up. Control your temperature. If your hot air gun can soften plastic molding of chips or pop capacitors, then it is definitely too hot.

The 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.

[janoc]

I use SAC305 solder and 280C hot air temperature setting. I never go beyond 320C even for the toughest parts. If I feel I need higher temperature, it's oven or hotplate time.
Reflowable SMT caps are designed to survive 260C peak temperature and shouldn't pop at that temperature.

Ah 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.

Yes, water boils at 100C, but not all caps use water based electrolyte, and even for those use water based one, ion concentration can significantly increase boiling point, somewhere to above 150C.
The pressure inside aluminum can will further raise boiling temperature, and this is a dynamic equilibrium. At the point where saturation vapor pressure of electrolyte exceeds maximum structural strength of aluminum can or its vent, it pops.

Well, 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).

[janoc]

Whaaaaat? SnPb 63/37 solder melts at 183C, while SAC305 melts at 217C. Both are eutectic (SAC305 is not truly eutectic, but nearly eutectic).

Yes, 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.

[mariush]

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.