Thruhole cap desoldering advice (multilayer PCB) - Page 1
Forum section: electronics / beginners

author: lpc32
author_rank: Frequent Contributor
timestamp: March 23, 2014, 02:13:29 pm
content: I'm trying to desolder some caps on a graphics card, and getting nowhere. I'm using a 30W iron with a blunt conical tip, and solder wick (ancient, but I doubt it matters?).The wick's just getting slightly splotchy, no real suction. When heating over the wick the solder below barely melts. I also tried adding some solder to the existing joint, or heating the joint directly and gently pulling the lead from the other side, to no avail.I suspect the temperature may not be enough, or the tip shape/size doesn't allow good contact.What do you reckon?

author: Monkeh
author_rank: Super Contributor
timestamp: March 23, 2014, 02:23:18 pm
content: A 30W iron and some manky wick are not going to get you anywhere with the ground plane(s) of that card. You will need more appropriate tools.

author: icon
author_rank: Regular Contributor
timestamp: March 23, 2014, 02:32:53 pm
content: How about; melt one connection, rock the cap over as far as it will go, repeat on the other side, keep repeating until the cap comes out. Then clean the pad up with the solder wick soaked in flux. Then clean the burnt flux off with some IPA.If the iron won't even melt the solder in step 1, above, then you're on a hiding to nothing anyway, and you need more oomph!John

author: Monkeh
author_rank: Super Contributor
timestamp: March 23, 2014, 02:36:36 pm
content: Quote from: icon on March 23, 2014, 02:32:53 pmAnd when the through-plating comes out with the lead...

author: BravoV
author_rank: Super Contributor
timestamp: March 23, 2014, 02:45:27 pm
content: Quote from: Monkeh on March 23, 2014, 02:36:36 pm+1 , if that happened, it is even worst than a lifted trace, been there before.

author: mariush
author_rank: Super Contributor
timestamp: March 23, 2014, 02:57:43 pm
content: How I do it when there's a weak iron.. gently twist the capacitor from side to side (just a few degrees) until the leads weaken and break under the capacitor - you'll be left with less than a cm of wire in the holes.let your iron heat up , get some leaded solder and add it to that hole... then as you keep the iron on the blob of solder grab what's left of the leads on the other side and push it slowly through the hole. The blob of solder will stay on the lead and the lead will go through the pcb.

author: peter.mitchell
author_rank: Super Contributor
timestamp: March 23, 2014, 03:59:23 pm
content: I assume you don't want to keep the capacitor? Aka, it is faulty and you are trying to replace it? get your ugliest cheapest pair of cutters and cut it up, leaving just the two leads going through the holes.Heat the leads and take them out one by one.

author: schwarz-brot
author_rank: Regular Contributor
timestamp: March 23, 2014, 04:50:46 pm
content: On multilayer boards I simply rip them out with a strong pair of plyers and a fast pull. Leaves the two pins in the holes which can be used to solder a new cap to without going through the hazzle of making sure to get a good connection to any plane.Try a few times on an old pc mainboard or something like that. Works a treat.

author: dfmischler
author_rank: Frequent Contributor
timestamp: March 23, 2014, 05:09:23 pm
content: If you can't properly tin the tip then you will not be able to move much heat. It might not be enough iron even if you can get it tinned.

author: Yago
author_rank: Frequent Contributor
timestamp: March 23, 2014, 05:18:18 pm
content: My advice would be to get some scrap boards, practice the skills and iron out tool selection, before attempting a repair.

author: G7PSK
author_rank: Super Contributor
timestamp: March 23, 2014, 05:44:14 pm
content: I just cut the capacitors through slightly above the rubber seal (side cutters)and then pull the rubber seal off the wire stubs, this does two things reduces the total thermal mass by removing the aluminium foil and also allows you to heat each wire and pull it out as soon as the solder melts, no need to waggle the cap just a straight pull once the solder is melted. Not damaged a board since I started doing it this way.

author: Technicial
author_rank: Newbie
timestamp: March 24, 2014, 12:58:08 am
content: i find coating the wick with some flux from a flux pen helps wicking action. Got any flux pens?

author: pickle9000
author_rank: Super Contributor
timestamp: March 24, 2014, 01:09:39 am
content: Quote from: G7PSK on March 23, 2014, 05:44:14 pmThis is a very good method, pulling the lead from the side that has the most copper (mass) helps as well.

author: Psi
author_rank: Super Contributor
timestamp: March 24, 2014, 01:22:28 am
content: hold the iron against BOTH component legs<IRONIRONIRON>L1 L2FLOOD the thing with solder so now it looks likeXXXXXXXXXX<IRONIRONIRON>XL1XXXXXXXXL2XXXXXXXXXXXXXXXXWait 20 seconds and then try remove the component.

author: sleemanj
author_rank: Super Contributor
timestamp: March 24, 2014, 01:25:55 am
content: If you don't care how it looks, break the cap off as others have described, leave the old leads where they are and then solder the new cap right on to the old leads :-)

author: lpc32
author_rank: Frequent Contributor
timestamp: March 24, 2014, 10:10:32 am
content: Thanks for the suggestions!I tried wiggling the caps to break them off, but they're quite durable. I'm afraid it might damage the vias. Yanking them straight out looks even more potentially destructive. Cutting the leads is an option, but what cutter do you use? There's barely 1mm of height clearance, plus components around that further limit access.I'm not going to solder to the existing leads. That's too ugly, and I havefar greater plans.Psi, won't 20 seconds of heat damage the board/traces?The tip is tinned. Just not enough heat, I suppose. Would those 10-15$ adjustable 60W pen irons do any better? (And why do all those 220V versions come with US plugs?)Any specific suggestions for cheap flux, and an ESD safe solder sucker with a durable tip, off eBay or a Hong Kong/China store?Monkeh,Yago, what tools specifically do you have in mind?

author: Yago
author_rank: Frequent Contributor
timestamp: March 24, 2014, 03:22:10 pm
content: Well there are lots of threads on tools etc.I use a weller magnastat, it's an older iron and I would say it can just about cope with these type of heavy planed boards.What I am trying to say is that it is better to work all this out on scrap boards.Then when you have the technique and and the tools you can approach repairs.Call at a local PC shop, they will have plenty of knackered mother and video boards they will give away.

author: London Lad
author_rank: Regular Contributor
timestamp: March 24, 2014, 04:40:42 pm
content: A much hotter iron used for less time.Rock the cap outClean up with new solder braid or re flux the old stuff

author: Yago
author_rank: Frequent Contributor
timestamp: March 24, 2014, 04:52:10 pm
content: Would that really be a hotter iron, or one with a (real)higher power rating?The problem being that the plane sinks the heat from the iron leaving the solder too cold.

author: London Lad
author_rank: Regular Contributor
timestamp: March 24, 2014, 05:02:25 pm
content: Quote from: Yago on March 24, 2014, 04:52:10 pmYes sorry I should have said an iron / tip with more capacity, probably hotter too :-)I find that a higher capacity / hotter iron used for less time is nearly always less destructive than the reverse.

author: rstoer
author_rank: Regular Contributor
timestamp: March 24, 2014, 05:55:26 pm
content: Any of the methods suggested might work, but does no one (other than me) still use a solder sucker?Of course the iron has to melt the solder or nothing will work, but I've never had any luck with solder wick on through-hole stuff - especially with double sided boards. My Edsyn and I do fine without it. Yes, you can pull the trace off the board if the trace is thin and your technique is poor, but every method requires some skill.

author: mariush
author_rank: Super Contributor
timestamp: March 24, 2014, 06:08:49 pm
content: On video cards and other parts, the pad around the hole is very small and due to lots of layers in the pcb, it's very hard to suck out the solder. Also, the hole is barely big enough to fit the leads of the capacitor so the capacitor leads will suck the heat quite fast.It's much easier to use the method I've described above, Breaking the capacitor off the board by gently twisting it for 20-30 seconds until the leads metal weakens and breaks. This way you don't have lots of aluminum in the capacitor to suck the heat even more. Place a blog of leaded solder on the other side, which basically lowers the melting temperature from 230c or whatever the lead free solder temperature is, to about 180c, now your job is easier.Now heat the blob and push the lead of the capacitor through the board and the blob of solder will stay on the lead and the hole will remain open. If you pull the lead leaving the blob of solder on the other side, solder will get inside the hole and it will be a pain to remove it.Oh.. another method I've used on motherboards... Stainless steel dental picks or desoldering needles you find on eBay for 1$, like this one :http://www.ebay.com/itm/Hollow-needles-desoldering-tool-for-electronic-components-/121303420620?pt=LH_DefaultDomain_0&hash=item1c3e3f4eccThey work, for motherboards and stuff using larger holes.. on video cards the holes may be a bit too small. As they're stainless steel the solder won't stick to it so you can heat the blob of solder and carefully push the pick or needle from other side to clear the hole. If you're too rough, you can however break the pad or the metal inside the hole, connecting the layers of the pcb.

author: London Lad
author_rank: Regular Contributor
timestamp: March 24, 2014, 06:24:22 pm
content: Quote from: rstoer on March 24, 2014, 05:55:26 pmI use suckers, spring loaded and vacuum ones, braid and sometimes two soldering irons!I think you just get used to what works for you.

author: dfmischler
author_rank: Frequent Contributor
timestamp: March 24, 2014, 07:46:11 pm
content: Quote from: rstoer on March 24, 2014, 05:55:26 pmI have anEdsyn DS017 SoldaPullt. For some things I find it easier than wick.

author: Yago
author_rank: Frequent Contributor
timestamp: March 24, 2014, 09:39:46 pm
content: Quote from: mariush on March 24, 2014, 06:08:49 pmI'll give this a try, cheers sir

author: mcinque
author_rank: Unknown
timestamp: March 24, 2014, 09:41:12 pm
content: In some cases, even with a good desoldering gun, you won't be able to pull out easily the pins soldered to groundplanes.Try to preheat the spot with a hot air gun, like in smd.

author: Phaedrus
author_rank: Frequent Contributor
timestamp: March 24, 2014, 10:02:09 pm
content: I grip the cap from the bottom with a pair of pliers. Then I apply a solder ball to my iron and wick it back and forth between the solder points in question. I get both molten at the same time, wicking back and forth with the iron, while pulling down with the pliers, rocking the cap back and forth a bit. It usually pops right out. Then I pick up the solder with solder wick and clean with isopropyl. Don't do this if you want the cap to still be usable; the pliers usually dent them. Practice on a board you don't care about first, because if your heat is too high you can scorch the PCB or lift a trace.I've recapped several PSUs that way, including some 4 layer DC-DC boards with solid ground layers. Never done it on a GPU or motherboard though.

author: lpc32
author_rank: Frequent Contributor
timestamp: March 25, 2014, 02:38:52 pm
content: Hot air gun! It's gone the whole spectrum from flux all the way to that.Anyway, I broke off the cap (hopefully no damage to the via) with repeated tilting in opposite directions. Pushing with a needle, and with some extra added solder, I was ultimately able to get the remains of the leads out. Then wicking, and more needle pushing, to try to get the hole clean. While I was sometimes able to see the beginning of a hole, it's doesn't clean well and mostly remains clogged.I'll get a solder sucker and see how that goes. Maybe also some flux (any eBay suggestions?). How likely is it to find alternative tips for a generic iron with a two-sided screw holding the tip (not threading near the handle)? A chisel shaped one might be more practical.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: March 25, 2014, 05:09:19 pm
content: +1 on cutting the cap off and leaving the leads and soldering the new cap onto the leads. If I liked the graphics card I would not want to disturb, mechanically or thermally, what's there. Repeated heating seems like a bad idea to me. So I guess it depends on how much you like the board.

author: lpc32
author_rank: Frequent Contributor
timestamp: March 25, 2014, 05:20:00 pm
content: For future's sake, and in expectation of fishy capacitors or just side effects due to changing the type, instead of soldering directly I'm going to try using this:

author: Monkeh
author_rank: Super Contributor
timestamp: March 25, 2014, 06:15:45 pm
content: Those have a tendency to eject round leads..

author: mariush
author_rank: Super Contributor
timestamp: March 25, 2014, 08:00:51 pm
content: Also, switching power supplies (including DC-DC converters like the ones in video cards) are often designed to put capacitors with as little wire as possible. More than a few mm of extra lead is not recommended, because those leads act like an inductor in series with the capacitor. That's why capacitors are often very close to heatsinks and switching ICs, to minimize current loops, reduce EMI etc etc.Those headers also introduce other problems.. additional resistance, poor contact, longer leads, issues with two different metals... etc

author: chibiace
author_rank: Regular Contributor
timestamp: March 25, 2014, 09:36:10 pm
content: id use a cheap solder sucker to get all/most of the solder out of the holes then if needed heat both leads and wiggle from the other side.to clean up the holes probably reapply solder and suck out.

author: lpc32
author_rank: Frequent Contributor
timestamp: March 27, 2014, 12:57:12 pm
content: Monkeh, they seem to grip quite well, at least the ones I have.mariush, I suppose it's slightly less ideal than direct soldering, but any idea if it matters in practice? Assuming it *seems* okay, what latent side effects should I be looking for?chibiace, yeah, will try a sucker. It's occured to me, and maybe was alluded to earlier, that it's probably also more difficult to desolder with 30W because it's lead-free.

author: Monkeh
author_rank: Super Contributor
timestamp: March 27, 2014, 01:20:59 pm
content: This is what happens with most of the methods described here, sooner or later:Especially when you have a little 30W iron. I strongly suggest getting a more suitable iron and preferably a high power desoldering iron if you plan to do this sort of thing.

author: lpc32
author_rank: Frequent Contributor
timestamp: March 27, 2014, 03:42:09 pm
content: The plan is to get a better iron once US logistics allow.