Really Hard Desoldering Old PSU - Page 1
Forum section: electronics / beginners

author: DW1961
author_rank: Frequent Contributor
timestamp: June 13, 2023, 03:45:14 am
content: I'm having a REALLY hard time getting these solder point to release. I'm using flux and extra solder to help, but man these solder points jsut do not want to release easy, at all. Any suggestions?I'm using a 900 series station to desolder at up to 360CI'm using a Hakko T18-C3 (3mm) tip60/40 solder on top of factory joints

author: agehall
author_rank: Frequent Contributor
timestamp: June 13, 2023, 04:54:26 am
content: Pre-heat the board.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: June 13, 2023, 06:49:26 am
content: Bigger tip and hotter iron. Turn it up all of the way.

author: Vovk_Z
author_rank: Super Contributor
timestamp: June 13, 2023, 07:09:17 am
content: Yes, you need the largest tip. And it will be more easy with a better soldering station, like T12.900-series is just not good enough at actual time.

author: m k
author_rank: Super Contributor
timestamp: June 13, 2023, 08:13:27 am
content: One possibility is to try the opposite, sort of.Melt all legs at once and deal the solder later.First you wrap some wire around and then fill everything with plenty of solder.You can then use even a mini torch for melting.With big heat source you also still have the other hand for pulling the component.Downside is that plastic connector chassis is also affected.So for moving parts this is not very gentle way.Though for string of square pins in round hole this can be the only way.

author: DW1961
author_rank: Frequent Contributor
timestamp: June 13, 2023, 05:08:19 pm
content: Any suggestions on tip size? The one I have above is 3mm.I also have a T12 station. If you think that will really matter vs 900 station, then I'll buy the tip for the T12.

author: DW1961
author_rank: Frequent Contributor
timestamp: June 13, 2023, 05:09:05 pm
content: Quote from: JustMeHere on June 13, 2023, 06:49:26 amAll the way? Won't that destroy the tip quickly?

author: Vovk_Z
author_rank: Super Contributor
timestamp: June 13, 2023, 05:26:06 pm
content: Quote from: DW1961 on June 13, 2023, 05:08:19 pmAnything T12 larger 3mm is large enough, from my experience.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: June 13, 2023, 06:20:10 pm
content: Quote from: DW1961 on June 13, 2023, 05:09:05 pmHasn't hurt mine. Don't leave it on. They can be replaced.It's all about transferring heat faster than the component you want to desolder can transfer heat away. It seems backward, but you can do more harm with a lower temp setting. If I'm trying to take large components off of a board, I'm at 450c.You want as much energy at the end of your iron as possible. So that means the biggest, fattest tip you can fit into the work space. Get it hot.You should.be able to do Dave's copper sheet soldiering iron test with ease if you are set up correctly.

author: Jwillis
author_rank: Super Contributor
timestamp: June 13, 2023, 08:14:23 pm
content: Not sure what your defining as a 900 series solder station. How many watts is the iron?Watts sustains the heat in the iron when applied to a cooler surface. Using a higher temperature isn't always the answer or the best practice as it can damage the components. Fewer Watts and the heat travels into the leads to far before the solder melts. This can damage the component. With higher watts the heat remains more localized without travelling into the component before the solder melts.Higher heat also accelerates oxidation making it even more difficult to remove components.Lead free solder can be troublesome to de-solder with low Watt irons. Try adding some 60/40 to the solder joint. That will lower the melting point. Use solder wick to remove excess solder. Use extra flux.If you have no solder wick a piece of stranded wire and extra flux can work as well. Some times heating the joint to melting and giving the board a smack on the table helps to remove excess solder.Remove adhesives and heat sinks before attempting to de-solder.If your not concerned about the PCB you can cut away the PCB around the really difficult components. A Dremel comes in handy for that. Even just cutting back wide traces can help.Good luck.

author: DW1961
author_rank: Frequent Contributor
timestamp: June 13, 2023, 09:11:53 pm
content: Quote from: JustMeHere on June 13, 2023, 06:20:10 pmOK I had no idea I need that much. I'll give it a go.

author: DW1961
author_rank: Frequent Contributor
timestamp: June 13, 2023, 09:20:52 pm
content: Quote from: Jwillis on June 13, 2023, 08:14:23 pmThanks. I am using flux and 60/40. The 900 series is a 60 watt station. (900 meaning it takes 900 series Hakko tips, not the newer cartridge tips.) The T12 station is 75 watts.

author: MathWizard
author_rank: Super Contributor
timestamp: June 14, 2023, 06:01:14 am
content: 60W should be enough, I used to struggle with a 40W iron, but did get them done. But yeah even with my Hako FX888, I think 65W, I set like 750F/400C, and melt on a lot of 60/40 solder, and remove it, then melt on more, and remove it, with desolder pump when possible,...to dilute the factory solder.I find the flux burns so much, I don't like going over 400C. So go slower, put more heat into the joints. Try not to scratch-off/cook-off the solder mask.

author: JohanH
author_rank: Frequent Contributor
timestamp: June 14, 2023, 06:40:38 am
content: Iron at minimum 420 °C, wrap a copper wire around the legs, add generous amount of 60/40 solder, keep the iron on the copper wire and the component drops right off. It's messy but works.If your soldering iron isn't able to heat up both the copper wire and solder around the component legs, then it's probably too low powered. My old 70W CSI station (T12 style) works fine also with large ground planes.

author: BrokenYugo
author_rank: Super Contributor
timestamp: June 14, 2023, 03:15:26 pm
content: I usually use a K tip for that sort of thing, you need mass, the S3 might be even better but I haven't tried one. Note that the genuine tips are supposed to fit the heater better and perform better, but I've had no issue desoldering stuff like that, with a clone station and cheap tips, usually don't even go over 400C unless it's a really hard part like a huge heatsink/RF shield tab.

author: Smokey
author_rank: Super Contributor
timestamp: June 15, 2023, 03:02:23 am
content: I've noticed the same thing. Why do PC power supplies have such terrible thermal relief on their circuit boards?

author: DW1961
author_rank: Frequent Contributor
timestamp: June 15, 2023, 04:50:47 pm
content: Quote from: Smokey on June 15, 2023, 03:02:23 amBy terrible you mean really good thermal protection from heating? If so, that seems obvious. But is that ability to transfer heat about the board itself?

author: Smokey
author_rank: Super Contributor
timestamp: June 15, 2023, 06:46:16 pm
content: Quote from: DW1961 on June 15, 2023, 04:50:47 pmYou can thermally couple the pads to the planes in a way that allows them to both sink heat from the part AND not be a nightmare to solder/desolder. That is possible.

author: coppercone2
author_rank: Super Contributor
timestamp: June 15, 2023, 06:49:57 pm
content: I hate that, shit like that always breaks especially near big components.stop accommodating the usb micro irons.I would try a 5mm tip.Every time you want to turn up temperature you should just put a bigger tip if its not a problem.just don't work too fast with the largest possible tip on a shitty iron, what happens is that there is often not enough heat sinking on the base and it will melt into the thread holder for the base if you keep pumping flux through it (they all have design weaknesses). For high volume work you want a physically larger iron for this kind of thing. Like keep an eye on the temperature of the bottom of the iron, if it starts getting really hot let it cool off.

author: tooki
author_rank: Super Contributor
timestamp: June 15, 2023, 10:03:58 pm
content: Quote from: Smokey on June 15, 2023, 06:46:16 pmSo… you think it can selectively be a thermal insulator or conductor depending on the heat source? This I need to hear…

author: Smokey
author_rank: Super Contributor
timestamp: June 16, 2023, 12:16:35 am
content: You only need the copper area to cover the current rating of the connection. Anything over that is just making soldering harder. So you make the spokes of the thermal relief big enough so the pad can still solder AND it won't fail from continuous current. If you have enough copper to handle the continuous current, then you by definition have enough copper to heatsink whatever is soldered to it.If you need to have a 100% direct connection from the plane to a solderable pad, you probably need to rethink your connection choices.

author: BrokenYugo
author_rank: Super Contributor
timestamp: June 16, 2023, 12:18:20 am
content: Quote from: Smokey on June 15, 2023, 03:02:23 amWhy would a cheap production board need to be easy to hand solder?

author: Smokey
author_rank: Super Contributor
timestamp: June 16, 2023, 12:29:51 am
content: Quote from: BrokenYugo on June 16, 2023, 12:18:20 amSome of these power supplies aren't cheap. And they have nice boards and manufacturing quality.Even if they wave solder all the through hole parts, you have to get all the internal planes up to temperature for the solder to flow well. I agree that in production that's less of an issue, but it doesn't take much more effort to add some thermal relief and make the boards reworkable.Unless you plan on scrapping all the production boards that don't pass test...

author: james_s
author_rank: Super Contributor
timestamp: June 16, 2023, 12:50:47 am
content: I had this challenge recently re-capping an industrial PC motherboard that had dozens of bulging and/or leaking capacitors. It was a thick board with huge power and ground planes that would just suck the heat out as fast as I could put it in. I had to turn my iron up all the way and then I used my hot air rework station to heat the board in the general area I was working to around 100C and that was just enough that I could get the caps out and then use my desoldering gun to clean out the holes. It was a proper pain in the rear but it worked.

author: DW1961
author_rank: Frequent Contributor
timestamp: June 16, 2023, 01:51:46 am
content: Quote from: Smokey on June 16, 2023, 12:29:51 amNobody from the manufacturer on down is interested in reworking these boards. Even really good computer PSU in the 800watt region can be had for less than $100.00. So it's not really worth it, and by the time they may need a new cap or two, it's end of life anyway. So I guess that's why they are so damn hard to desolder.I was just doing it for fun, as I found that Antec 800 watt literally tossed on the side of a road. However, it's NOT FUNI will test some of the components to see if they measure in spec, because that is funBut I think I'm about ready to toss this POS in the recycle.On the other hand, my brother has a Paradigm 10 UltraCube subwoofer we bought back in 2008. It was 1200.00 US so it Is something you would want to rework. The guy in this Youtube video said he had a really hard time getting caps and other stuff off. I'm pretty sure now he was experiencing the same thing. He got it done though.My brother's UltrraCube suffered his idiocy in that he had it in a hot enclosure. It lasted for years, but finally stopped and I'm pretty sure it needs to be reworked like the guy did in that video. maybe someday I'll give it a try.

author: tooki
author_rank: Super Contributor
timestamp: June 16, 2023, 09:19:35 am
content: What are themechanicalconsequences of thermal reliefs? I can imagine that it could affect, for example, resilience to vibration or drops, especially for heavy parts. Even if the advantage of direct connections is only small, it would still outweigh any disadvantages in reworkability.

author: Smokey
author_rank: Super Contributor
timestamp: June 16, 2023, 10:11:25 am
content: NoRapidly approaching zero mechanical consequences. It's not a full cutout on the fr4, it's just a spoke pattern on the copper layer around pads that connect to planes.

author: tooki
author_rank: Super Contributor
timestamp: June 16, 2023, 01:12:00 pm
content: Quote from: Smokey on June 16, 2023, 10:11:25 amI know what they are. That wasn’t my question.I don’t think the argument can be made that it has NO mechanical consequences. The spokes are much less copper than a full connection, so there’s no way this doesn’t weaken ir mechanically. The question is by how much, and what kinds of forces it is more susceptible to.

author: Nusa
author_rank: Super Contributor
timestamp: June 16, 2023, 04:44:55 pm
content: If you're talking about the power supply through-holes that have 4 18 gauge wires stuffed into them, you have to keep in mind how much current that copper has to support. 20 amps? More? Thermal reliefs in this instance could actually be an unwelcome fuse/failure point!

author: DW1961
author_rank: Frequent Contributor
timestamp: June 16, 2023, 05:13:20 pm
content: Quote from: Nusa on June 16, 2023, 04:44:55 pmI just gave up trying to get the wires stuffed into them. I cut them off at the board level, and left the solder in the hole. The insulation was melting off before the wires would let go. The heat was transferring alright, right into the wires, but the solder joint was not. that's some heat dissipation, for sure.

author: james_s
author_rank: Super Contributor
timestamp: June 16, 2023, 06:18:22 pm
content: A couple times I have used a small butane torch to get enough heat into something like that to desolder wires.

author: Smokey
author_rank: Super Contributor
timestamp: June 16, 2023, 08:25:54 pm
content: Quote from: tooki on June 16, 2023, 01:12:00 pmFor a through hole part like pictured, with a proper solder flow and fillet on both sides of the board (which is significantly harder to achieve if you have unnecessary 100% plane connections!), the mechanical consequences of spoked thermal relief on the planes are probably approaching zero.For a surface mount part, if you are relying on just the plane connections to the copper layer for your mechanical connections of parts that you are worried might get broken loose, then again, you need to reconsider your design decisions.

author: Smokey
author_rank: Super Contributor
timestamp: June 16, 2023, 09:35:45 pm
content: Quote from: Nusa on June 16, 2023, 04:44:55 pmThat's why we are engineers, and know how to design stuff so it won't unexpectedly fail.Lets go with 20A.You would want about 12AWG wire. So that's 80mil copper diameter for the wires. If you are soldering that direct to the PCB thru-hole that means you would probably want a 100mil hole minimum, with a 175mil annular ring. That's a circumference of about 550mil for the ring.https://www.4pcb.com/trace-width-calculator.htmlIf you are concerned with current through the PCB, you should be using 2oz copper at least.** 20A, outer layer, 2oz copper, 25C rise = 211mil total / 4 = 52mil spokes. **(Note: That is technically for a single trace by itself, not a super short stub connected to a plane acting as a heatsink for the trace. You probably need even less copper if you were to take that into account, but lets roll with it for now).Using a 25mil plane backoff that results in a super clean looking pad with both thermal relief and enough copper to handle the required current. It's about a 38% copper connection between plane and ring of the pad.Lets say you have a plane on an inner layer that needs to take that 20A:If you are using an inner layer for the plane, you would be a crazy person to just use the inner layer connection to the plated hole for all the current (thru-hole plating is not nearly as thick or consistent as outer layer plating). Instead you would use the exact same outer layer pad with spokes as described above and ring it with vias to conduct the current down into the inner layer plane (with the addition of the weaker thermally relieved inner layer plane connection too).Also keep in mind that thermal time constants are really long. So under normal operation the super short thermal relief spokes have plenty of time to suck out the heat into the plane, while also allowing plenty of isolation for the high impulse heat of the soldering iron to do its job. A short duration of higher current also won't melt the spokes because it takes time for them to heat up enough to melt and they are really short. If that is a concern, then you need to resize everything to account for the new worst case.

author: coppercone2
author_rank: Super Contributor
timestamp: June 29, 2023, 12:42:08 am
content: no consequences? that is the type of pad that will detatch during rework.Infact when I see that pad near big parts on lead free boards I instantly get the rivet kit and copper shims on standby

author: Smokey
author_rank: Super Contributor
timestamp: June 29, 2023, 03:33:19 am
content: Quote from: coppercone2 on June 29, 2023, 12:42:08 amIf one designs the board with proper thermal relief (and clearances) then the solder will actually melt when one tries to rework the part and the part will essentially fall out. One only rips off pads when one is being impatient (or using the wrong tools) or the PCB was designed so poorly that the solder never melts because of unnecessary direct connection to all the planes.

author: coppercone2
author_rank: Super Contributor
timestamp: June 29, 2023, 06:18:57 am
content: or it just fails because glue area, because thats a ideal PCB parameter, they are always made with infallible glue. And the plating does not crack on the via so it never pulls right out.the pcb manufacturer that did not existyou can fix this by cutting a disk out of copper shim, then drilling a hole in that, then riveting it to the PCB after its been scraped.