Removing large through-hole PSU capacitors with Chipquik bismuth solders - Page 1
Forum section: electronics / repair

author: tggzzz
author_rank: Super Contributor
timestamp: April 23, 2020, 09:45:00 pm
content: I've got an HP spectrum analyser that shows spurs originating in its SMPS, so Ioughtto replace some of the large aluminum electrolytics. There are also some "delayed action smoke generators" (Rifa capacitors), and theydefinitelyhave to be replaced.All of those are through-hole components on a densely populated 4-layer PCB, so there is an increased chance I'll damage the PCB when I extract them. This question is about reducing that risk.Chipquik makes DMD, a low-temperature solder based on bismuth which melts at about 58C.https://www.chipquik.com/store/product_info.php?products_id=210002Chipquik regard the principal maket being removal of SMD ICs, but I have PTH components.So, has anybody used Chipquik SMD to remove large PTH components? If so, what hints and tips can you pass on?ThanksBackground: I've decapped and replaced many capacitors in Tek scopes over the years. So I know some come out easily, some, um, "less easily".

author: bob91343
author_rank: Super Contributor
timestamp: April 23, 2020, 11:59:35 pm
content: Your casual tossing about of acronyms without definition prevents me from giving any suggestions. rifa? PTH?

author: wraper
author_rank: Unknown
timestamp: April 24, 2020, 12:13:08 am
content: Why would you need this crap to remove capacitors? Also you are forgetting the fact that you need to flush pads on PCB and soldering iron with regular solder twice before soldering new parts. Otherwise solder will be contaminated and solder joints won't be reliable. That certainly does not reduce stress on PCB.

author: wraper
author_rank: Unknown
timestamp: April 24, 2020, 12:14:50 am
content: Quote from: bob91343 on April 23, 2020, 11:59:35 pmIf you don't know what those are, he probably does not need your suggestions. RIFA - paper capacitors which explode. PTH - plated through hole.

author: TheMG
author_rank: Frequent Contributor
timestamp: April 24, 2020, 12:21:21 am
content: For stubborn capacitors I usually heat one lead, then gently rock the capacitor to one side a bit so the heated lead starts to move out of the hole ever so slightly, heat the other lead and rock the capacitor the other way, repeat until capacitor leads are out of the holes.

author: Photoman
author_rank: Regular Contributor
timestamp: April 24, 2020, 01:12:12 am
content: I was just in the similar situation. A MosFet with chunky legs, bent at an odd angle and a small thru hole.No matter how much new solder, flux and sucking from my hakko desoldering gun, they wouldn’t come out.I used FAST CHIP from SRA (same kind of bismuth alloy)https://smile.amazon.com/gp/product/B07NPZTR8J/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1.Probably an inch of the stick was needed for all 3 legs. Ran over it with the iron and I was able to wiggle it out.It wont hurt to try the chip quick or the sra one. After I got the part out, I reflowed the open holes with normal solder a few times.Sucked it clean between then cleaned with a flux cleaner. Just to make sure I don't have the alloy left to mix with new solder.Just a note of caution, the alloy stays molten for a long time. Its easy to flick off a drop on to the board or your hand.So be careful. Solder burns suck!

author: wraper
author_rank: Unknown
timestamp: April 24, 2020, 01:17:31 am
content: Quote from: Photoman on April 24, 2020, 01:12:12 amCut the legs, desolder each leg separately, then use desoldering gun or solder wick to clean the holes. At least 10 times faster and less stress. Or use large tip and a lot of solder to cover all 3 solder joints simultaneously and easily pull transistor out.

author: Rasz
author_rank: Super Contributor
timestamp: April 24, 2020, 03:12:09 am
content: but why?$32 + shipping for consumable is almost as much as cheapest hotair station

author: WattsThat
author_rank: Frequent Contributor
timestamp: April 24, 2020, 03:37:41 am
content: Quote from: Rasz on April 24, 2020, 03:12:09 amHot air station? The OP is talking about through hole parts.Cutting the out part out first is always the best way to start when possible.When you cannot cut leads, I re-solder the part first to preheat the area then desolder. When the vacuum drops out, keep the pin moving with the desoldering tool until it cools. Parts will fall out. Every time.

author: tggzzz
author_rank: Super Contributor
timestamp: April 24, 2020, 06:04:22 am
content: Quote from: TheMG on April 24, 2020, 12:21:21 amThat's a technique I've used in the past when recapping.In this case the geometry makes it look difficult in some, if not all, the cases. As you can see in the pictures, the 6 Rifas (count them!) and 4 of the electrolytics are closely packed and the latter are rather squatIn addition, I've read reports that the board is a "fragile 4 layer board", so I'm prepared to take a belt and braces approach.EDIT: see reply #28 for better pictures

author: tggzzz
author_rank: Super Contributor
timestamp: April 24, 2020, 06:20:16 am
content: Quote from: Photoman on April 24, 2020, 01:12:12 amThanks for the pointer to the alternative supplier, and the tip about the length of time it stays molten. Given the lower melting point that seems obvious -afterthinking about itI still have a small and unimportant solder blob scar from 40 years ago

author: tggzzz
author_rank: Super Contributor
timestamp: April 24, 2020, 06:24:03 am
content: Quote from: wraper on April 24, 2020, 01:17:31 amThat's one of my normal techniques.Unfortunately in this case it is impossible to cut the legs of radial capactors, plus the caps are large and attached to a ground plane.Hence there is a lot of thermal mass to be heated via the vias

author: tggzzz
author_rank: Super Contributor
timestamp: April 24, 2020, 06:27:00 am
content: Quote from: Rasz on April 24, 2020, 03:12:09 amHot air guns are problematic for large components attached to groundplanes. Surrounding components/joints would get up to temperature long before the relevant joints have melted.

author: tggzzz
author_rank: Super Contributor
timestamp: April 24, 2020, 06:43:27 am
content: Quote from: WattsThat on April 24, 2020, 03:37:41 amI've only got an unheated solder sucker pump without a continuous vacuum.However I've just blundered across a suprisingly cheap heated solder pumphttps://www.amazon.co.uk/dp/B01N2H1CLS/ref=pe_3187911_185740111_TE_itemand ordered it.Looks like I'm going to have some experiments to do before attacking the objective

author: Haenk
author_rank: Super Contributor
timestamp: April 24, 2020, 08:00:43 am
content: Quote from: tggzzz on April 24, 2020, 06:04:22 amThey made really, really sure, it will explode one day

author: tggzzz
author_rank: Super Contributor
timestamp: April 24, 2020, 08:32:38 am
content: Quote from: Haenk on April 24, 2020, 08:00:43 amYou can't see it in the low resolution photos, but cracks are visibleI've had them remove the prepreg from a PCBHaving just paid for almost the right schematics, the line input module also has intrnal capacitors. Oh joy.Bonus: you can still get exactly the same Rifas, so that should remove the need for paying very close attention to the dimensions

author: brabus
author_rank: Frequent Contributor
timestamp: April 24, 2020, 09:02:07 am
content: Am I the only one thinking that those electrolytics may be perfectly OK and don't need changing at all?If noise is coming from the SMPS, I would be looking at the secondary side of the converter first.If you absolutely need to remove those caps, I would use my favourite method: cut the soldering joints flush and drill them through with progressively larger bits, from 0,5mm to 1mm, to 1.25, 1.50 and even 2mm, until the hole is clean. Make sure to be dead center, though.

author: tggzzz
author_rank: Super Contributor
timestamp: April 24, 2020, 09:55:51 am
content: Quote from: brabus on April 24, 2020, 09:02:07 amHarumph. Yes, having been able to look at the circuit diagram since my first post, I am tending to think that for the electrolytics. However, they are 1989 vintage, so 30 years old...<expletive deleted> Rifas have to come out, though.QuoteMost definitely; I'm just going through the parts list.In fact there are two separate switching PSUS, one for the main body and one for the CRT.Having waved a scope probe around in the air, it looks like the CRT is at the right frequency, and that matches something I've seen on the groups.io mailing list.I'm also checking a few tant beads, too.QuoteI haven't heard of that interesting technique, thanks. I'm unconvinced I could satisfy that caveat

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 24, 2020, 02:48:53 pm
content: Quote from: Rasz on April 24, 2020, 03:12:09 ami bought Zephyrtronics's low melt in 2010 and i only used a bit from it to desolder few many legged ICs (including recent soic8) and keep reusing the used blobs over and over until when i consider them "not low melt" anymore, so far the blobs can still be used for the purpose where the rest of 99.9% of the stock are still untouched. for any repairers, i will say low melt is a must have item on their bench. imho whoever says we have to re tin the pads with normal solder 2 to 10 times are too academics, i will usually clean the IC pins and pads with solder wick once until there is no more significant leftover and resolder the old or new IC into place once and i dont see any problem so far. we cant argue that there will be 1 or 2 low melt molecules got blended, but like i care when there are 99% of normal solder mixture in there. for stubborn board that even low melt and wiggling kungfu cant solve it, i think we need to go back to how to they were made... ie complete reflow (cheap oven).

author: wraper
author_rank: Unknown
timestamp: April 24, 2020, 02:52:22 pm
content: Quote from: brabus on April 24, 2020, 09:02:07 amNice way how to destroy hole metallization.

author: WattsThat
author_rank: Frequent Contributor
timestamp: April 24, 2020, 06:28:55 pm
content: Rifa: tick tick tick BOOM

author: edpalmer42
author_rank: Super Contributor
timestamp: April 24, 2020, 07:12:11 pm
content: Quote from: tggzzz on April 24, 2020, 06:43:27 amI doNOTrecommend that tool. I have one that looks identical. The temperature isNOTcontrolled and I found it was very easy to overheat the board.There is a reasonably priced, heated, variable temperature, vacuum desoldering gun that has had good reviews. I picked one up and it has been okay in light usage. I did have a heating element go open so you might want to pick up a spare. I also recommend that you get the three different size tips. Search for S-993A. There are multiple sellers and youtube reviews on it.Ed

author: Rasz
author_rank: Super Contributor
timestamp: April 24, 2020, 07:17:38 pm
content: Quote from: tggzzz on April 24, 2020, 06:27:00 amThis thread should have a subtitle 'I have bad equipment therefore I am considering bad solutions'like this:Quote from: tggzzz on April 24, 2020, 06:27:00 amand doubling down on more crappy tools:Quote from: tggzzz on April 24, 2020, 06:27:00 amyou should transfer this one straight to the binHotair in this case is for preheating pcb before desoldering components. Controlled preheating is very important when dealing with large ground planes, helps with bubbling, deforming and delamination.Quote from: brabus on April 24, 2020, 09:02:07 amYou are not. Input caps rarely die, they live an easy life. Their size makes people jump into wrong conclusions.Quote from: Mechatrommer on April 24, 2020, 02:48:53 pmYou are applying something akin to industrial waste. Highly corrosive to dissimilar metals, high resistance, lower thermal conductivity. All because you are probably using 40 year old 60W soldering iron.Its not entirely the same, but good analogy:Same deal as people playing with liquid metal in cooling applications.

author: rcbuck
author_rank: Frequent Contributor
timestamp: April 24, 2020, 07:26:33 pm
content: QuoteThat is a really, really bad idea for a 4 layer board. The power and ground traces may be connected to the inside layers. Even if they are not, you risk shorting the internal layers together or to the outer layers when you install the new caps.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 24, 2020, 11:11:45 pm
content: In my experience, a soldering gun and desoldering pump has always worked for removing large capacitors with the capacitor getting slightly warm at most.

author: Photoman
author_rank: Regular Contributor
timestamp: April 25, 2020, 01:28:12 am
content: Quote from: wraper on April 24, 2020, 01:17:31 amThat would work on a smaller package but not on this particular fet. I also didn’t want to cut the legs in case they were good and I could reuse them.They were a obsolete part only available with a 2 week lead time from china. Though I did order them 2 weeks ago just to be safe...one was dead the other not.I will only cut the legs if I really need too. Legs up the Hakko 808 isn't a good idea. They sometimes get a little stuck.Also adding that much solder and heat could delaminate the board, remove pads or damage other components nearby.Again in this case, the legs were close to other components that would have been damaged.The SRA solder worked really fast and without any issue.

author: wraper
author_rank: Unknown
timestamp: April 25, 2020, 02:02:31 am
content: Quote from: Photoman on April 25, 2020, 01:28:12 amAnd then you need to clean everything from this crap at least twice. If package is something Like TO-3P. I would wiggle it out while heating each solder joint a few times in succession.

author: Photoman
author_rank: Regular Contributor
timestamp: April 25, 2020, 02:31:16 am
content: Quote from: wraper on April 25, 2020, 02:02:31 amI wouldn’t suggest using it for every joint on the board, just for the impossible ones. Especially if you need to save a component or not damage the board.Yes cleaning takes a little time, an extra minute or 2. To avoid destroying the component and the board, it was worth it for me.Also sometimes leveraging the component can destroy the thru hole. I had a board a while ago that if you looked at it wrong, the pads would come off.I used this stuff for one cap that needed to be replaced. No lifted pads and it only took a few minutes.Sure its expensive but that tube will last years.

author: tggzzz
author_rank: Super Contributor
timestamp: April 25, 2020, 08:51:40 am
content: In general I take the attitude that you should strive to do "more with less" and become a master of the tools available to you. There's truth in the old saying that "a bad workman blames their tools". However a good engineer/technician always knows the limits of their skills and tools, and chooses the right tool for the job.I've now removed the board and been able to compare it with the schematic. This is more tricky than other boards I have recapped, so I was right to believe I need to improve my techniques.The red ellipses indicate the capacitors I want to remove, and some of their pads on the underside. Key points:capacitors are close together, so wiggling them will not be easyit is a four layer board, with buried groundplane and with some very small pads; getting the right amount of heat to the solder is non-trivialgiven the appearance of the capacitors on the top, I do not understand the groups of three pads under the axial capacitorsSo thank you all for your experiences and suggestions; please keep them coming!

author: Messtechniker
author_rank: Frequent Contributor
timestamp: April 25, 2020, 09:52:52 am
content: Yes these 3-legged electrolytics exist. See link here:https://www.nmr.mgh.harvard.edu/~reese/electrolytics/cap_gallery.jpeg

author: tggzzz
author_rank: Super Contributor
timestamp: April 25, 2020, 09:59:26 am
content: Quote from: Messtechniker on April 25, 2020, 09:52:52 amI've seen those before, and removed them from Tek scopes amongst other places.But the ones on this board are tall, thin, andaxial- there is the wire coming out the top. So what exactly is at the other end?Oh well, I'll find out in a few days time

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 25, 2020, 11:01:34 am
content: those big caps look easier to wiggle. those axial type also look more easier to wiggle, just in different way. ie visible solder joint on the top side should make the job much more easier. i will hold soldering iron steady there (with boost button keep pressed), from bottom if no access from the top. and pry up the top leg connection with tweezer. i think every hobbiests will try to do more with less at first, its blended in their DNA. only when they know its unfeasible then they start to search for other the right tools. btw i dont own a AIO desoldering gun (yet) so far i can deal with what i already have (hakko sucker hand pump) but calson did a review in case you are interested...

author: ogden
author_rank: Super Contributor
timestamp: April 25, 2020, 11:54:43 am
content: Quote from: tggzzz on April 25, 2020, 08:51:40 amI would want to remove lefmost in black sleeve as well. - To gain room for "wiggle desoldering". When marked area is clean (from caps), only then proceed putting new back.

author: tggzzz
author_rank: Super Contributor
timestamp: April 25, 2020, 12:54:03 pm
content: Quote from: ogden on April 25, 2020, 11:54:43 amRemoving "extra" capacitors is a dilemma, since it is another chance to damage the board. However, in this case that black capacitor is scheduled for clearance since it is part of the HT supply, and I suspect the HT inverter is the source of the spurs.I'll also carefully note the type of each capacitor removed from each socket, in case there is something equivalent to the Tek24x5 "swapped capacitors" problem. Now I'm sureHPwouldn't make such a mistake, but therearemultiple PSU variants for the 8562.

author: tggzzz
author_rank: Super Contributor
timestamp: April 25, 2020, 01:31:21 pm
content: Quote from: Mechatrommer on April 25, 2020, 11:01:34 amI'm not convinced those techniques would be sufficient forthesecapacitors, hence my questions and looking for new (to me) tools.QuoteThat video shows some of the usual yootoobe video problems. The first 20 minutes shouldn't be a video, since moving pictures aren't needed - and if in the form of text+pictures, I could absorb the information in 30s flat. However, the second halfdoesmake good use of moving pictures, even if a little editing could have reduced it from 20 minutes to 5 minutes. Thanks.

author: ogden
author_rank: Super Contributor
timestamp: April 25, 2020, 01:43:00 pm
content: Quote from: tggzzz on April 25, 2020, 12:54:03 pmRight. I would just label them using sharpie, take a picture.I second to advice using plain sn+pb solder and powerful enough soldering iron, without overdoing temperature. Initially I just make rounds between cap pins adding solder so much that they can't take anymore. On lead-free board it is good idea to wick/suck first mix of solder away to add sn+pb again and get lower temps in result. After that wiggle-solder step by step it out of the board. Preheating PCB area with (85..105oC) air usually increase chances of success. Even hair dryer can make difference, thou make sure you hold to board ground while doing that or just use ESD strap.

author: tggzzz
author_rank: Super Contributor
timestamp: April 25, 2020, 01:57:12 pm
content: Quote from: ogden on April 25, 2020, 01:43:00 pmYes indeed. I'm a belt-and-braces person, and I assume that no one way will be sufficient!QuoteThis (1989) should be pre-ROHS, so it should be Pb solder - but your point is well taken.I have various hot air guns, ranging from a temperature/volume controlled solder station with multiple nozzles, through hair dryers, to paint strippers.I've only used the solder station to remove/replace single SMDs on a Tex24x5 controller board, using polyimide tape to shield other components. I think this may be a case where I will use it to preheat the area.

author: edpalmer42
author_rank: Super Contributor
timestamp: April 25, 2020, 04:07:50 pm
content: If you're worried about damaging the board, the 'wiggle' method of capacitor removal should not be high on your list. This method requires you to heat the pads over and over. This will put a lot of heat stress on the pads. Using the 'wiggle' method with ChipQuik might be an interesting combination. It should reduce the heat stress due to multiple meltings.The three holes under the capacitor could be for a three-legged capacitor where the third terminal is only for mechanical support. That's not unusual with large capacitors. It could also be to accomodate multiple physical capacitor sizes - maybe from different manufacturers. That way, you don't have to respin the board if you change capacitors. This could also be to accomodate second sourcing.I've found that, particularly with pins that are connected to ground, it takes a lot more heat to unsolder that pin. It's always important to use an iron that has lots of power behind it. A small iron has to be held in place for a long time to heat up the traces and pin. This alone can damage the board. A larger iron will do the job fast so you can get in and out quickly and minimize damage to the board. The same comment applies to the size of the tip. Don't try to unsolder a large pin on a ground plane with a tiny tip.Ed

author: ogden
author_rank: Super Contributor
timestamp: April 25, 2020, 04:41:49 pm
content: Quote from: edpalmer42 on April 25, 2020, 04:07:50 pmNot actually. Thermal inertia helps. Also if you need more than 3..4 "wiggles" - you are doing it wrong. Try PCB preheating?QuoteWhat's that?

author: Rasz
author_rank: Super Contributor
timestamp: April 26, 2020, 03:14:10 am
content: There is using what you have, and there is using wrong tool for the jobI dont see anything particularly fragile, or especially difficult about this board. Its not like its 8 layer pcb LGA socket replacement job.Damage usually happens when cheap tools dont have sufficient power/thermal mass and user tries to compensate by bumping temperature.

author: tggzzz
author_rank: Super Contributor
timestamp: May 02, 2020, 11:56:40 am
content: Thank you all for your suggestions. In the end I used several techniques and the board has now been recapped.I played around with a couple of PCBs:a 1972 PCB containing core memory,, fine tracks, double sided PTHs and old(!) solderan ATX PSU, ground planes, single sidedAs predicted, the cheap heated 40W solder pump was a little fierce for my comfort. However, running it from a variac and reducing the voltage by 15% also reduced the temperature by ~15% (not 22.5%?!).The Chip-quik bismuth solder might have formed alloys that reduced the required temperature, but definitely had the benefit of providing a good thermal contact at a relatively low temperature.The heated desoldering pump was good at quickly removing the solder used for large snap-in capacitors. That was mainly because there was a lot of solder in a large hole, and once it started sucking into the pump, it all ended up there. The vacuum on its own is only partly helpful at removing the solder; equally important is that a strong draught into the pump picks up solder and removes it. Hence melting the solder and then holding the pump tip at an angle (to allow a draught) often worked best.None of the techniques were excellent with small holes and closely fitting leads. I tended to use the pump to remove as much as possible, then desoldering wick with flux.Sometimes that left a difficult-to-shift solder bridge deep in the hole. Tthe best technique was to melt the bismuth solder and allow it to flow into the hole. Then it could transmit the heat to the lead solder, and both could be removed with a wick.The three legged capacitors are unlike anything I have seen. The third "axial" leg is just the can, and that is insulated from both the other terminals. I wondered if that is to allow some extra shielding connected to the ground, but that doesn't seem to be the case.

author: tggzzz
author_rank: Super Contributor
timestamp: May 06, 2020, 09:17:17 am
content: Some follow-up questions...The local hackspace is considering whether it is worth buying a "proper" desolderer, either one of the "S-993A" mentioned above, or perhaps ahttps://cpc.farnell.com/duratool/d00672/desoldering-station-uk-eu-plug/dp/SD01384and we feel we would like to hear experiences of using any such tool.Starting questions are:how easy/difficult is it to remove the solder from inside the tool? Previous experience from decades ago leads me to believe it can be a pain, plus the tool will be in a "hostile environment"how large is it in the hand, and does that cause any issues?where the vacuum is supplied via a hose, does that mean it takes a long time for the suction at the nozzle to increase/decrease?where the vacuum is supplied via a hose, is the hose a "tail that wags the dog"?Your opinions and experiences would be welcomed...

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: May 06, 2020, 03:43:53 pm
content: To add something to the original question:After having bought some "bismuth" solder that turned out to be fake, i now learned this:As of today, you cannot get a bismuth solder wire with flux in it, as the alloy is to brittle for the process that is needed to put in the flux cores. Flux core wire is basically made by first making an aloy pipe, filling it with flux and then continuously rolling it down to the desired diameter. You apparently cannot do that with Bi58Sn42 as it will just break. That's why the BiSn wires as of now are all solid without flux - or a paste.However!The German comnpany Felder has announced they will be launching a flux-cored bismuth solder later this year. They apparently found a way to pull it off and have patented it.As soon as i can get my hands on it, ill be sending some to Daves mailbag and hope he will give it a run for its money.To answer the obvious question: No pricing available yet. I am guessing it won't be cheap and they will be cashing in on their research.You can find their press release here: (in German and English)https://www.felder.de/aktuelles/produktneuheiten/produktneuheiten-details/snbi-l%C3%B6tdraht.html?file=files/felder/content/Aktuelles/Produktneuheiten/Neu2020.pdfI for one would be very happy with that stuff. I restore a lot of old test gear (GAS, guilty as charged) , and this stuff could really help to not lift the pads off from elderly crumbling PCBs