Important not to spread aluminum capacitor legs at the body? - Page 1
Forum section: electronics / beginners

author: SamIAm
author_rank: Newbie
timestamp: September 29, 2016, 08:24:19 am
content: Hello everyone. This is my first post here.I have recently gotten an old MSX computer and Sony BVM (professional CRT monitor) to work again by replacing their aluminum electrolytic capacitors. These were my first real soldering projects. I was very happy when they turned on and functioned properly, but my heart sank when I googled something I was concerned about and foundthis poston another forum.In short, the author of the post says that spreading the capacitor legs at the body can seriously compromise the capacitor itself, and I'm afraid that that is exactly what I did in many instances during my repairs. While I don't think I ever exerted really strong force on them, I did bend them where they meet the body and probably spread them so that they made something like a 45 degree angle.Here is a picture from the post that I am taking the liberty of using that shows the correct way (left) and the incorrect way (right) to bend the legs.I see now that what I should have done was use needlenose pliers to clamp down on the legs near the capacitor base, then bend them out so that the stress would occur only on the leg itself. This is essentially what all of the manufacturers' instruction sheets say to do, although Nichicon curiously says only to bend the legs without putting "too much" stress on the body.Anyway, in your experience, has bending the legs of capacitors like this caused problems? Do you think the risk of a problem in my case is high enough that I should re-do some of these with fresh caps? The ones I used spanned a large range of diameters, from ~5mm to ~15mm, and came from multiple manufacturers. Like I said, the legs of some of them were spread to ~45 degree angles. For the BVM especially, I am very concerned about high-voltage capacitors failing prematurely and causing catastrophic damage, so if you think the risk is high, I will probably swap them.Your input would be very helpful and appreciated. Thank you!

author: mariush
author_rank: Super Contributor
timestamp: September 29, 2016, 10:05:59 am
content: I think it has to do with the rubber/plastic/whatever seal, if you bend the leads too much you may put pressure on the seal and cause it to eventually let air or humidity inside the capacitor.Also, the bottom caps are usually shaped in such a way as to make room for solder which may wick up on the capacitor leads. If the leads are bent and touching the bottom when you solder the capacitor the solder may wick up and damage the rubber?The bending in your picture is not that serious, at least i wouldn't consider it that bad.

author: SamIAm
author_rank: Newbie
timestamp: September 29, 2016, 10:30:11 am
content: Thanks for your reply.The general lack of discussion I'm seeing about this when I google the topic makes me think I'm probably just fretting over nothing. It could be that the cap manufacturers putting those warnings in their documentation are just trying to cover their asses.I just tried taking two old capacitors, one large and one small, and bending their legs all over the place for a couple of minutes until they actually broke off at the base. I see no sign of rupture. If they were really so sensitive that one small parting like what I did in my repair could cause problems, I would think that being repeatedly bent around to extremes would cause a noticeable effect.Still, I suppose I could imagine that with prolonged tension and heat, something could go wrong. I'd be very curious to know if keeping the legs straight at the base is ever taught as a common-sense/good-practice thing.Later, I'll try yanking the legs out.

author: amyk
author_rank: Super Contributor
timestamp: September 29, 2016, 10:54:52 am
content: It's called a bung, and although it is soft and rubbery, excessive stress will break the seal. The manufacturers just don't want you to be mounting caps so their legs are almost being torn out sideways. As long as the leg is straight where it enters the bung, it should be OK.

author: helius
author_rank: Super Contributor
timestamp: September 29, 2016, 10:56:59 am
content: The leads connect to the capacitors' plates on the other side of the rubber bung. Bending the leads like that has two undesirable effects: Firstly, it exerts a pulling force on the rubber seal, which is then more likely to leak electrolyte or make the cap dry out prematurely. Second, it presses inward on the plates, which can affect their properties. Both a reduction of capacitance and a lower working voltage rating are possible.When adapting capacitors (or other components) with a small lead spacing to holes spaced farther apart, lead-forming pliers are a useful tool.

author: Zero999
author_rank: Super Contributor
timestamp: September 29, 2016, 11:33:47 am
content: I agree with all of the above.Also, it's possible the legs could form a short circuit on the capacitor's can.

author: Gyro
author_rank: Super Contributor
timestamp: September 29, 2016, 12:05:11 pm
content: Ok, we've all done it at some time or another, you've probably got away with it as long as the capacitor leads were fairly soft. The leverages and strains involved are fairly huge though. This is something that should be considered with most components, especially as plated steel leads become more common. Bending a lead changes its cross section, this is a problem if it happens right against the package of things like epoxy packaged transistors and especially LEDs. The problem is even worse once the component has been soldered with its leads under stress.

author: SamIAm
author_rank: Newbie
timestamp: September 29, 2016, 02:04:24 pm
content: Thanks, guys.I got a few more old caps and managed to yank out the negative pins. It was very interesting to see the metal plates, and what the materials were like.I was surprised that the rubber bung is actually quite soft. When I put my needle-nose pliers in one of the holes and squeezed, it chewed through it almost like bubble gum.That said, I could also see how the leg is much thinner than the sealing piece it connects to inside of the bung that goes between it and the plate. It seems like a little gentle spreadingmightnot compromise it at all.So, if you were in my position, would you replace any of the caps?

author: stj
author_rank: Super Contributor
timestamp: September 29, 2016, 02:10:29 pm
content: if you bent the leads before you put the caps on the board, i would leave them.the real problem is people who just spread the legs like a V shape and ram the cap down onto the board.that puts a permanent diagonal stress on the bung.

author: dfmischler
author_rank: Frequent Contributor
timestamp: September 29, 2016, 02:11:03 pm
content: Quote from: SamIAm on September 29, 2016, 02:04:24 pmIf this was a spacecraft that would cost millions to fix if it failed, or a critical safety system whose failure would risk human life, then yes. Otherwise, probably not.

author: Ian.M
author_rank: Super Contributor
timestamp: September 29, 2016, 02:13:47 pm
content: That depends. Unless the board has really delicate tracks that electrolyte leakage could easily destroy, I'd say leave it till it goes wrong again if you are keeping the kit, or replace them if you are selling and care about your reputation. Exception: critical caps in the PSU or EHT generation circuits which should be replaced immediately if compromised.A quick bending jig for the legs can be a slot in a 1mm or 2mm piece of plastic that's filed to be a snug fit with the can down flush to the plastic and the legs touching either side of the slot. It supports the legs when you bend them outwards, preventing significant movement at the seal.Once you have bent the legs out, NEVER twist them sideways while holding the can or the other leg as that's a sure-fire way of stressing the seal.

author: SamIAm
author_rank: Newbie
timestamp: September 29, 2016, 02:15:53 pm
content: Quote from: stj on September 29, 2016, 02:10:29 pmThat's kind of what I did, though, minus the ramming down part.I can actually remember one specific cap where I pushed on it, though. I'll probably replace that one soon.QuoteI'm definitely keeping them for personal use.Hmm. I do know of a few caps in the BVM power supply that I replaced where I had to spread the legs just a little. Since I have extra caps, I will probably replace those for peace of mind.

author: SamIAm
author_rank: Newbie
timestamp: September 29, 2016, 03:01:09 pm
content: I poked around at a few of the other dead caps, as well as some spare new ones, and the bungs are not always as soft as the first one I tried. My fingernail couldn't rip or scratch them, and they seemed to retain their shapes better. Also, when trying to pull out the plates out of some of these, the leads actually broke off before anything visibly came out at all, and this was with alotof force.The dead caps are all over 20 years old; I wonder if they use stronger materials for bungs now?I'll experiment more tomorrow, but I'm inclined to say the extent of my bending was usually not so much that these caps are going to die a whole lot faster.Then again, I don't want to be the guy who comes asking for advice and then only takes his own, so feel free to tell me if you believe my thinking is incorrect.

author: Ian.M
author_rank: Super Contributor
timestamp: September 29, 2016, 03:46:08 pm
content: Quote from: SamIAm on September 29, 2016, 02:15:53 pmIf you only spread them a little and they weren't left under spreading strain from the board, I mostly wouldn't bother. Maybe if any were in the feedback path to the chopper control chip (assuming a switching PSU). Sony stuff is generally well enough designed that most faults cause it to die quietly and repairably rather than emitting smoke and flames.

author: djQUAN
author_rank: Frequent Contributor
timestamp: September 29, 2016, 03:51:37 pm
content: When I worked for a Japanese company, they never allowed bending cap leads too, only preformed leads are used.The explanation was the same as the link. Bending the leads would eventually result to the electrolyte leaking and causing trouble in long term.

author: SamIAm
author_rank: Newbie
timestamp: September 30, 2016, 12:17:19 am
content: Not bending the leads at the base certainly makes a whole lot of sense. It's what I'm going to do from now on, absolutely.This morning, I took three new caps with three different diameters from three different makers and tried abusing them for science.The 5mm Nichicon cap had the toughest bung, and its leads put up a really good fight against being pulled out. I had to pull as hard as I could for several seconds on each of them, using one pair of pliers in each hand. One lead broke off before the plate came out.The 10mm Nippon Chemicon and the 15mm Rubycon leads each came out with only a second or so of hard pulling. Of course, I can't say whether their size or their brand/bung materal was responsible.The interesting thing was taking these extracted metal leads, holding the fat part which forms the seal at the bung with needle-nose pliers, and bending the thin legs back and forth by hand like I did when I put in the other caps. You get a good sense of how much torque is exerted on the fat part by doing this.Not that anything is really conclusive. I suppose all it really convinced me of is that a small bend to the side might compromise the seal, and it might not. The rubber/plastic seems pliable enough that it could hold the seal even as the metal bit moved under heavy torque, but that same pliability might allow for the metal bit to move far enough for the seal to break.Just going by what I can see, and I know that ain't worth much, it does not appear that the fat bit actually moves at all when bending leads at the base of a cap.I know of two caps that I'm definitely going to replace because I think I put them under a relatively high amount of stress. Unless people here say I should do otherwise, however, I will probably leave most of the other caps whose legs I bent.Does that sound reasonable?---------------------EDIT: This is a picture I found that is akin to what I did during my repair.This next one, I assume, is a bad idea:

author: Ian.M
author_rank: Super Contributor
timestamp: September 30, 2016, 03:49:48 am
content: You are on the right track. I've done both of those pictures before, but I've always supported the leg at the bend by holding something like a PC slot cover plate against it so it bends about 2mm from the cap bung rather than on the lip of the lead hole in the bung. Its really just common sense and a bit of experience. If you tried handling old-fashioned components that roughly the leads would often break right off so you soon learnt to support leads at the body when forming them.

author: SamIAm
author_rank: Newbie
timestamp: September 30, 2016, 11:38:16 pm
content: First, let me say thanks again to everyone who replied. I really appreciate your help.Now, just in case anyone finds this interesting, and before this topic fades into the ether, I thought I would share a few pictures. Last night, I took some clippers to those three capacitors whose leads I had yanked out, and I didn't stop until I had gotten the bungs out completely. Below, you'll see the result, including an extracted lead and another cap in the same series for comparison. Here are a few observations.- The bung on the biggest cap is thicker. However, the bung on the smallest cap is the same thickness as the medium-size one.- The bung on the smallest cap appears to have been squished the most horizontally by the casing. Given how hard it was to get the leads out, this makes sense.- The aluminum casings all held the bungs very tightly. I don't think there is much potential for them to move up and down, much less side-to-side, no matter how you pull on the leads.- The layers of material inside the casing are very tight and hard. At a glance, it can look (and feel) like solid metal. I was expecting a higher ratio of fluid. I don't think the metal plates on the leads have any room to move unless you are pulling them out.- Notice how the edge of the bungs are not indented. The casing actually compresses the rubber. If I stick the leads back in, they move quite a bit more easily now.- Finally, a small observation: if I put the leads back in the bungs and wiggle them around while pinching the rubber, the fat part of the lead inside the bung moves a lot more when I pull the lead laterally in the direction of its mate. Things may be different when the bung is properly compressed, but bending the pin outward seems to put the lead's fat part up against rubber near the edge that is being compressed the hardest, so it doesn't move as much. Therefore, while you shouldn't bend the leads outward at the body, you especially shouldn't bend them inward.(this last one is zoomed in a bit more)

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: September 30, 2016, 11:58:38 pm
content: I actually splay them out carefully all the way when replacing axial caps with radials. With a solid bung like a Nichicon I see no problem at all with this. It is not damaging anything. It's not pulling on anything. If the cap is heavy I put some silicone on it in case of shock.

author: Sj77
author_rank: Newbie
timestamp: November 28, 2020, 04:51:48 am
content: Hello everyone.This is my first post here and apologies for reviving an old thread. My knowledge of electronics is extremly limited and I am just looking for help/reassurance, so please excuse the ignorance in my post.The attached photos show the soldering joint/leg of one of the capacitors on my Z490 Aorus Master PC motherboard. I've been using it since July and the PC is fine, however, I've just noticed that one of the capacitor leads is bent/soldered at an angle compared to other, nearby capacitors. I assume this particular solder joint was touched up manually during QC at the manufacturing plant and this is why the solder looks less then ideal - based on youtube videos, this is a part of the manufacturer's process. But I think it does not appear to be a potential 'cold joint' etc.What about the capacitor leg bend - do you think this is an issue based on the discussion above (Bung damage, leakage etc.)? Or could be in the future? I do not know what kind of component this is - I've highlighted it in one of the photos. The text at the top reads: 'FP 9ZCG 561 6.3'.Considering the board appears to be ok, do you think I should be concerned?Thanks a lot for your help!

author: helius
author_rank: Super Contributor
timestamp: November 28, 2020, 05:15:42 am
content: If it came that way from the factory, there is very little to be worried about in terms of bent leads. The stock of capacitors will be matched to the hole pitch on the boards so no bending is possible. The bending is mainly an issue in repairs, where the correct formed lead components are not available. Is it theoretically possible that some "Monday morning shift" put in wrong components? Yes, but worse problems than lead pitch could have occurred in that case.What your pictures show is mainly that the leads protruding from thesolder sideare not parallel, which is normal. When thru-hole components are stuffed into circuit boards, they are handled from both sides. The components are pushed into the holes from thecomponent side, and then soldered from thesolder side. This can be a manual soldering operation, in which case the whole board is flipped so the solder side is up; or it can be automatic or semi-automatic using wave-soldering or selective-soldering machines, which work from the bottom side so the board stays upright. To prevent the components which were just stuffed from falling out, their leads are bent, and then trimmed so they stay in place. This is almost universal for thru-hole components and quite familiar to anyone who has soldered a circuit board.The issue being discussed in the thread above is between the component body and the board on thecomponent sidewhich is not visible in your photos. If the way the component leads extend downwards interferes with inserting them into the holes in the board, one way to force them to fit is by bending them. This bending or lead-forming operation must be done correctly to maintain the integrity of the component, it should not be done willy-nilly. However, whether this was done is never visible from thesolder sidefor the reasons mentioned above.

author: Sj77
author_rank: Newbie
timestamp: November 28, 2020, 05:58:36 am
content: @helius. Thank you for your prompt reply. I really appreciate it.Yes, the board came like this from the factory and the component itself is fine. There is another capacitor right above this one, in the same section, and it is the same type and has the same code. So as you pointed out, this must be due to how the lead was trimmed and then the solder joint could have been touched up after wave soldering.I feel much better now. And I appreciate the detailed explanation.Thanks again and have a good day/night!

author: Sj77
author_rank: Newbie
timestamp: November 28, 2020, 06:29:35 am
content: Sorry - one more question. I believe these capacitors were soldered using wave soldering because the solder joints of all capacitors around the VRM bank are very uniform. But the leads are different lenght and they must have been trimmed before soldering because they have small droplets of solder on the tips. Is the trimming done manually or can it be automatic too? I am just wondering how it is possible that dozens of leads are almost perfect and pararell (though differet length) and just this single one was trimmed like that. Could it have been too long after the automatic process and so the person duing the qc trimmed it?

author: helius
author_rank: Super Contributor
timestamp: November 28, 2020, 04:07:32 pm
content: Depending on assembly methods, the thru-hole components can be placed by machine, or by hand. In machine insertion, the P&P machine usually forms and trims the leads in one operation as they are inserted (leaded components are supplied on reels for this type of machine). For hand insertion, the leads can be bent outwards by hand or with pliers and then trimmed, or some special pneumatic tools exist that bend and trim with the press of a button. Leads aren't always bent outwards if the component can be held firmly during soldering, as is sometimes done using padded board clamps. But they do need to be fixed somehow, even for wave soldering, as the leads are buoyant in the solder bath and would try to lift the whole component out if not held in.It used to be "standard", at least for high-vibration assemblies, to bend the component lead flat against the solder pad. I think this fell out of style as more automated processes were adopted; it wasn't because of damaging the components. The thickness of the PCB keeps strain away from the component body, so there is no real problem. It makes rework more exciting, though.Also: it is preferred to trim before soldering instead of after, as the solder fillet will protect the core of the lead from corrosion. Many leads are made of steel and would otherwise be exposed to the environment.

author: Sj77
author_rank: Newbie
timestamp: November 28, 2020, 06:38:46 pm
content: Hi again helius,This is educational for me - thank you very much. I have even watched a few videos of 'selective soldering machines' in action based on your replies.Also, this now puts my mind at ease about my board as I am a bit OCD.I really appreciate you taking the time to explain all this to me.Warm regards,

author: mariush
author_rank: Super Contributor
timestamp: November 29, 2020, 04:33:45 am
content: Quote from: Sj77 on November 28, 2020, 04:51:48 amThose are polymer (solid) capacitors, they don't have electrolyte in them. So it's less important how the leads are bent.Doesn't matter that the capacitor is slightly at an angle... i suspect it isn't, and it's just the lead that's slightly bent or cut in a way it makes look like capacitor is not sitting perfectly flat.

author: Sj77
author_rank: Newbie
timestamp: November 29, 2020, 07:22:31 am
content: Hi mariush,Yes, you are right. The capacitor is sitting perfectly flat in the board and looks the same as the one right next to it. No angle on the component side.Thank you for the additional reassurance that all is in order. Appreciated!