When you say “recapping” it conjures up an image of a dusty old chassis with point-to-point wiring with a bunch of dried-out old capacitors or dodgy-looking electrolytics that need replacement. But time marches on, and we’re now at the point where recapping just might mean removing SMD electrolytics from a densely packed PCB. What do you do then?
[This Does Not Compute]’s answer to that question is to try a bunch of different techniques and see what works best, and the results may surprise you. Removal of SMD electrolytic caps can be challenging; the big aluminum can sucks a lot of heat away, the leads are usually pretty far apart and partially obscured by the plastic base, and they’re usually stuffed in with a lot of other components, most of which you don’t want to bother. [TDNC] previously used a hot-air rework station and liberally applied Kapton tape and aluminum foil to direct the heat, but that’s tedious and time-consuming. Plus, electrolytics sometimes swell up when heated, expelling their corrosive contents on the PCB in the process. 100uf Ceramic Capacitor
As brutish as it sounds, the solution might just be as simple as ripping caps off with pliers. This seems extreme, and with agree that the risk of tearing off the pads is pretty high. But then again, both methods seemed to work pretty well, and on multiple boards too. There’s a catch, though — the pliers method works best on caps that have already leaked enough of their electrolyte to weaken the solder joints. Twisting healthier caps off a PCB is likely to end in misery. That’s where brutal method number two comes in: hacking the can off the base with a pair of flush cutters. Once the bulk of the cap is gone, getting the leads off the pad is a simple desoldering job; just don’t forget to clean any released schmoo off the board — and your cutters!
To be fair, [This Does Not Compute] never seems to have really warmed up to destructive removal, so he invested in a pair of hot tweezers for the job, which works really well. But perhaps you’re not sure that you should just reflexively replace old electrolytics on sight. If so, you’re in pretty good company.
hmm. seems that i cannot post comments from my phone since the new “update”, but. I stongly oppose his method. you should NEVER pull on the cap. just grab it with a pair of pliers and rotoate while PUSHING it against the board. that way the two pins stay on the board and most of the times are pulled from the cap or are sheared of by it. after twisting it, just let go of the cap. NEVER PULL. it will just fall of. you are left with the pads exposed and ready to be desoldered with your solder iron. so again: NEVER PULL. keep pushing until you’ve made a full rotation or until it is separated from the board.
Heyy!!! It’s exactly what I wanna say. Twist it and PUSH it. We are at least 40 people doing it at my work. And it’s the best method!
test. thirdt try. now with cookies enabled.
Oh My. he does it it almost good, but the crucial part is NOT PULLING. he should PUSH the capacitor against the pcb while rotating the cap. only then are the pads preserved. that works even with perfectly unleaky caps.
so, just PUSH and twist.
you are left with the pads intact and ready for the remaining wires to be desoldered and the pads to be cleaned
Oh My. he does it it almost good, but the crucial part is NOT PULLING. he should PUSH the capacitor against the pcb while rotating the cap. only then are the pads preserved. that works even with perfectly unleaky caps.
so, just PUSH and twist.
you are left with the pads intact and ready for the remaining wires to be desoldered and the pads to be cleaned
I concur for the most part. I’ve had success with pushing the cap into the board and twisting back and forth just a little bit and repeatedly, rather than pushing and giving one turn. I find that this fatigues the leads, making them more likely to tear or crack before they even deform the solder fillet. It takes a bit longer, but makes me worry less about ripping off the pad.
Ah. finally a comment posted. it seems that my other email is blocked. good to know… irritating that there is no message telling you this, just a broken comment system as a hint…
You mean the one about the pushing instead of pulling? It might just have been under moderator queue.
previously it showed that: “waiting for moderation”. they might have that developed away to give it a more clean information less apple like interfarce. (not a typo..)
20+ years ago, my $ony 8mm video camera developed bad caps. Solder tweezers were out of reach for us mere mortals. Maybe I could have rescued it with [macsimski]’s suggestion.
For some reason, many of us rebel against the idea of destructive removal. But as one fellow said to me years ago, when you are doing repair, the goal is to preserve the board above all else. When I remove a through hole IC, the best way is to chop the leads off, remove the body then desoldered each lead one by one. So flush cutting the cap, then desoldering the remnant sounds smart to me for these electrolytics.
Even with leaded resistors I’ll cut one lead close to the body, using the resistor itself to help remove the lead still attached to it. And with the lead I cut being free to float, removing it is also easier. Then braid or a solder sucker to clean out the holes, and on to the next.
I’ve also used your method with SOIC packages, but it’s tricky and you have to be really careful. A REALLY sharp blade close to the body – NOT trying to cut the leads in one stroke – allows you to cut the body right out of the leads. Then the leads can be drag-soldered off the board. But the cutting can damage the board or even tear pads off if you’re not careful, so it’s best to practice on scrap boards first. And the blade really needs to be sharp, and thin. Small break-blade box cutters work well.
Pro tip for thru-hole repair: You always end up with that one hole that won’t clean out easily, and going at it over and over with heat will often damage the board. An easy method that greatly reduces the stresses on the board is to simply drill the solder plug out.
Get one of those little hand-held pin vises they sell for hobby work. They’re the size of a pen with a little pin chuck on the end, and often come with a small selection of tiny drill bits stored it in the body. They’re like ten bucks for a decent one with half a dozen bits.
Solder (especially solder in a partly-open hole) is really soft, much softer than the copper via plating. Even on a plugged hole, if you did a decent job of solder removal the drill tends to find itself in the little divot in the center. And the holes were probably a few mil oversize to begin with.
If you just go in gently and slowly, you can easily clean out enough space to get a new lead through as the solder comes out in a long thin thread, which you can easily wrangle, while doing virtually no damage to the board.
I’ve broken a few dental drill bits trying to drill through Pb Free solder. Then I had a problem similar to a broken stud extractor. B^P
Best method I’ve found is to position the board so you’ve got access to both sides. Flow the solder with an iron from one side, and use a solder-sucker to suck it out from the other. Counter-intuitively, you sometimes need to add a bit of solder prior to doing this to ensure that the entirety of the via is flowing.
I have found that a partially plugged or oft re-heated hole is difficult to clean. I add a little fresh rosin core solder and the old solder sucks right out.
More than 30 years ago, Fujifilm began producing a series of digital printers/processors for photography professionals. One of the early “printers” (actually a photo paper exposure machine) had an image processor board with 120+ SMD electrolytic capacitors that started leaking when the printer was about 3 years old. All at the same time, almost the same day! Fujifilm never accepted responsibility for this – well, if it happened outside the warranty period, you had to buy a new PCB for about 7,000 DM (I don’t know what the US price was).
So I took the PCB repair job for about 10% of the cost of the board, which was a lot of money during the war and hyperinflation in Serbia (Google says that prices rose by 116.5 thousand billion percent in 1993!). After a while, I found that the best way to remove old electrolytic capacitors was to cut them with a cutter flush, right across the narrowed part near the bottom. After that, the rest of the capacitor was easily removed and the pins were desoldered one by one.
It seens the early surface mount electrolytic capacitors were poor quality and used to leak the modern capacitirs are bettet the problem is solder tabs are too short anf you neef to heat the track the capacitir is solderrd too before soldering the small wire end electrolytics or tantalum smd capacitors are better i have used smd electrokytics in projects but find them a bit of a pain i am using more smd parts in my ptojects now i hate drilling holds and ogten surface mount wire end parts
Use of hot air gun for replacement of this components will be damaging it , suggestions on any other information ?.
https://youtu.be/t_9n04WXrhE
I’m finding more and more late 90’s and earlt 00’s Tektronix gear has leaking SMD caps. TM5000 gear, TDS scopes, etc.
I just pinch the cap with my fingers and rock it back and forth while pushing down and they snap off clean. Never pull, you run the risk of lifting a pad.
Once all the caps are off, I run the PCB through the dishwasher while wife isn’t looking (yep, it’s fine. I’ve washed 1GHz scope acquisition boards, rf generator boards, power supplies, the lot. Never killed a board from the wash. Just let it dry properly for a few days in a warm place and use some compressed air or hair dryer to gently blow any moisture from under chips etc). Then I use lots of flux and new solder to remove the electrolyte corroded solder (stinky…) from the PCB, then once that muck is all cleaned off with isopropyl alcohol and any other damage to traces and other components is repaired, the new caps go in.
I have found a little tiny drop of flux on each pad first, followed by the cap, then soldering each leg from each side while holding the cap down works great.
Which reminds me, I have to go order a bunch of caps to replace the leaking ones in an SG5030 leveled sinewave generator.
If you can’t get enough heat into those solder joints to GENTLY remove the cap, how do you think you’re going to get sufficient heating to have proper solder joints on the new cap? Personally, I’d go with a board heater (or preheat with a heat gun) and thermal tweezers or double iron. If you preheat the board, you can use it’s heatsink behavior (think groundplane) in your favor. These guys then pluck right off with tweezers.
Clean off the old lead free solder and use leaded solder which needs a lower temperature.
Even 60/40 makes cold solder joints on a Heavy PCBA’s ground plane. I’m used to reworking to IPC-7711/7721 class 2 and class 3 so what do I know? Work like a pro and you’ll get pro results. 😎
I would usually sit the board on a hot plate,150c. silver tape off any other components near by especially plastic. Apply flux gel and while heating with the hot air pencil in the left hand and a big 3mm flat tip in the right. I may use some solder regular 218c paste or if need be use normal reel of lead solder. Paste gets to start the joint off a lot quicker. Hopefully it will start to lift one side at a time. Clean up with braid. Safe removal. You should always be able to rework again and again without damaging the board.
I work as a rework technician
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