Author Topic: Desolder Aluminum Capacitors from ungodly huge mass of copper?  (Read 1755 times)

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Offline iamdarkyoshi

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I need to replace some bodge caps on my old graphics card, but I could not remove the old caps with any success, and the leads just pulled out of the body, and I bodged some sanyo electrolytics from a server motherboard to the original leads for testing (it works!) but I cant seem to get the holes cleaned out. I can get the original legs out, but it takes a long time to heat up and lots of pulling. I dont want to damage the board with heat, but I also dont want to damage it with excess force either. My soldering irons are a conical 45w cheap digital and a cheap weller 40w with a homemade brass chisel tip. I have multicore 60/40 .7mm solder, electrolube flux and multicore desoldering braid. I just cant seem to get the original holes empty of solder because the massive power plane is sinking all of the heat.
 

Offline Ian.M

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Re: Desolder Aluminum Capacitors from ungodly huge mass of copper?
« Reply #1 on: June 09, 2015, 04:00:08 pm »
100W soldering gun or similar, preheat board to 90 deg C, remove old leg and clean up what's possible with flux and braid, apply a little fresh solder, then push a very lightly oiled steel needle a bit thinner than the hole diameter, mounted in a wooden handle through from the non-power-plane side while heating the power-plane side to keep the solder liquid.  Keep twiddling the needle as it cools so its loose in the hole.  Once you've got a hole right through, you can clean up with flux and braid round the hole and surface tension should be enough to keep the hole open as you reheat it as long as you don't bridge over the hole with iron or braid.

If that seems too dodgy to you, get some chipquik, which will reduce the melting point enough that you should be able to desolder and clean up a preheated board with your existing tools.
 

Offline iamdarkyoshi

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Re: Desolder Aluminum Capacitors from ungodly huge mass of copper?
« Reply #2 on: June 09, 2015, 04:05:43 pm »
100W soldering gun or similar, preheat board to 90 deg C, remove old leg and clean up what's possible with flux and braid, apply a little fresh solder, then push a very lightly oiled steel needle a bit thinner than the hole diameter, mounted in a wooden handle through from the non-power-plane side while heating the power-plane side to keep the solder liquid.  Keep twiddling the needle as it cools so its loose in the hole.  Once you've got a hole right through, you can clean up with flux and braid round the hole and surface tension should be enough to keep the hole open as you reheat it as long as you don't bridge over the hole with iron or braid.

If that seems too dodgy to you, get some chipquik, which will reduce the melting point enough that you should be able to desolder and clean up a preheated board with your existing tools.

I think my friend has a spare 100w soldering gun (though I have never used a soldering gun, they are so bulky), and would a heat gun work to warm up the card if someone else held the heat gun?
 

Offline Ian.M

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Re: Desolder Aluminum Capacitors from ungodly huge mass of copper?
« Reply #3 on: June 09, 2015, 04:25:53 pm »
Heat gun will work, but if its not thermostatically controlled you need to be really careful.  Use a shoebox or similar to confine the airflow and block drafts so the whole board heats up.  Its not worth keeping blowing air once you start working on the joint as you can no longer control the drafts and the air flow will probably take more heat from your bit and the needle than it contributes.

You can also use a halogen heater at a distance suitable to get a surface temperature near to but not over 100 deg C.  Heat from the back and do a test run with a temperature probe on scrap board with a similar colour soldermask.   A dry cloth over the component side of the board will reduce air circulation and allow it to get up to temperature more easily.  If you wear clean white cotton gloves to reflect the heat you may well be able to keep the heater on at a lower setting or greater distance as you work.
 

Offline SArepairman

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Re: Desolder Aluminum Capacitors from ungodly huge mass of copper?
« Reply #4 on: June 09, 2015, 04:26:24 pm »
Another way of getting solder out of PITA heavily coppered holes is to use compressed air..

I attached the hot air gun to some clamp to gently raise the temp of my board and then did desoldering aswell.
 

Offline iamdarkyoshi

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Re: Desolder Aluminum Capacitors from ungodly huge mass of copper?
« Reply #5 on: June 09, 2015, 04:44:41 pm »
my heat gun has two settings: hot, and really friggin hot. I reflowed a laptop GPU with it before and it worked. I was able to get light to go through the holes when I tried preheating to around 50 degrees, but they were pretty small beams of light so there was still solder in them. something I might also try is just placing my flat tipped weller over both holes full of solder and pushing a pre-trimmed cap into the holes. Thanks for the advice everyone.
 


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