Best Way To Solder Copper Terminals Onto PSU Output Tabs? - Page 1
Forum section: electronics / beginners

author: Trurl
author_rank: Regular Contributor
timestamp: September 20, 2024, 05:03:27 pm
content: I made the following terminals from scrap copper sheet and would like to solder them onto a server PSU's output tabs, and eventually bolt on cable lugs.I'd like to minimize heat transferred into nearby caps and perhaps other sensitive parts.I'm thinking that it would be best to heat a copper terminal first above solder melting temperature & away from output tab, then slide it onto an output land(pre-fluxed), afterward continue to apply heat to one side/edge(flat edge) of the terminal & output land while feeding solder from the other side(upright edge) of the same land so the solder would wet out towards the heat source, and repeat on the underside.My biggest question is, would it be better to pre-tin the output lands before sliding on the hot terminal, or should I just slide on the hot terminal without any solder on the output land?I'm not sure if pre-tinning would hamper capillary action of the solder, or worse yet cause the terminal to get stuck in an undesirable position which would then require A LOT of heat input to get the terminal free again.Note: I do have experience brazing and welding so the concept of "wetting" metal is familiar to me.

author: Ian.M
author_rank: Super Contributor
timestamp: September 20, 2024, 05:20:13 pm
content: Solder will wick into a clean pre-tinned joint more readily as it doesn't have to wet the surfaces.Handling >>220 °C copper parts to position them will *NOT* be fun and risks scraping the pads off the PCB. I'd go with sweating them i.e. heavily tin the pads and the terminal both sides, flux them and assemble cold. Then heat the terminal quickly (>100W soldering gun or blowtorch) on the terminal, not the pad, till the solder reflows, adding more if needed. Don't hang about - minimise time at temperature. Then blow cool air to get the heat out as quickly as possible without thermally shocking it.

author: BrokenYugo
author_rank: Super Contributor
timestamp: September 20, 2024, 05:46:02 pm
content: I'd go about it about as Ian.M describes. Only heat the terminal, use a big high power iron with a big tip (ideally tip mass is many times mass of the joint), assemble cold pre tinned and heavily fluxed, do one terminal at a time to minimize heat into the PCB.You can get big 100-300W irons cheap on eBay.

author: Trurl
author_rank: Regular Contributor
timestamp: September 20, 2024, 05:59:05 pm
content: Quote from: BrokenYugo on September 20, 2024, 05:46:02 pmI assume you meant 'only heat theterminal'(i.e. copper terminal) as it takes the longest to heat up(so direct heat would be more efficient) and would minimize immediate/direct heat transfer to surrounding parts while the terminal is heating up. Having both copper terminal and PCB tab/pad approach solder melting temperature as close to each other as possible would be ideal so applying heat to the copper terminal and letting the tab/pad (with much less mass and heat required) heat up via the copper terminal/solder contact makes sense to me.

author: BrokenYugo
author_rank: Super Contributor
timestamp: September 20, 2024, 07:42:52 pm
content: My bad, edited for clarity, correct, you dump all the heat into the heavy heat tolerant part, then it transfers enough heat to the more delicate PCB pads that they just barely reach soldering temperature. Then add some more solder for a full connection and nice fillet and it's done.You may have to do it one side at a time depending on how powerful the iron is.

author: thm_w
author_rank: Super Contributor
timestamp: September 20, 2024, 11:08:00 pm
content: A high quality iron (jbc, metcal) will have no problems soldering this as shown. What is your iron?If you don't have one, put on a large short tip, crank the temperature, tin the PCB first (with flux) then same with that copper piece on the top. Then maybe assemble and try to join the two soldered areas together. If iron is not powerful enough will have to look into preheating/using a torch/heatgun/etc.I would not worry about heat transfer to the capacitor if your iron is on the bent copper piece for a while.

author: Trurl
author_rank: Regular Contributor
timestamp: September 21, 2024, 08:41:01 am
content: I have the following heat sources:1. HAKKO FX-601 with T19 (3.2mm) chisel tip, 42W(220V), 240~540 degrees C.2. Oxy-Butane Torch (butane + oxygen concentrator)3. Heatgun (Stanley 2000W), industrial type not for electronics.I can surely tin the pads with my modest iron, but I'll have to just try it with the copper terminals and see if tinning is possible.If not, surely my torch will work, as I can melt brass for fillet brazing with the torch. Hopefully I won't have to use this with the terminals on the PCB tabs as it would require careful aiming and aluminum foil heat shielding in front of PCB components.The heatgun might be a more convenient alternative to the torch as it wouldn't require running the noisy oxygen concentrator, wouldn't oxidize the copper so much, and be safer. But due to its nozzle size (without any nozzle diameter reducing attachments), it would only be an option for tinning away from the PCB pads.I'm thinking, after tinning the copper terminals, and the solder has solidified but the terminal is still quite hot I could slide it onto the PCB pad and reheat the terminal(with the soldering iron). That way, the time to solder melting temperature would be minimized.Hopefully, my modest iron will surprise me and knock the socks off the copper terminals.

author: jpanhalt
author_rank: Super Contributor
timestamp: September 21, 2024, 12:12:52 pm
content: I did some 0.025" buss bars with a 80W Weller. A lower temp solder may help (i.e., one of the bismuth alloys). I agree on heating the tab, not the pad. You probably know that when sweat soldering, the solder wicks toward the heat Thus, I would start on the tab to get it preheated, then concentrate on the bend until it starts to flow. Once it starts to flow, you won't need to add much more heat as it will be almost instantaneous.Because FR4 doesn't conduct heat very well, a damp/wet towel around it probably won't help, but I can't see that it would hurt either. One may also help quench the heat after soldering so it doesn't soak into the boardI have a different opinion on pre-tinning. If it is thick the pieces may wobble or even get voids once it melts. When soldering copper pipe, one does not usually pre-tin. The clearances are quite small and wicking fills them completely or to overflow. Rather than pre-tim, you might consider solder paste. However, I would probably depend on sweating a good fit with the low-temp solder. Be sure every surface to be soldered is fluxed. This is one instance when an activated solder flux might be desired.As the supply is more expensive than the tabs, I would also test my technique on a scrap piece of double-sided PCB and an extra tab first.As for heat, a pinpoint flame done carefully would probably be quicker. Since you have that apparatus, you probably know how to control heat well. Specially made materials are available to block unwanted flame spread. As an alternative, I have found crinkled aluminum foil (heavy duty) is easily conformable and is what I almost alway use. The only time I have used commercial heat shield was when flame soldering out of position very close to the floor joists and underlayment of my home. If uncomfortable with flame, I would go to a large (e.g., >60W) soldering iron. Hot air would from that blower would be my third choice as it will be slow and hard to confine.

author: tooki
author_rank: Super Contributor
timestamp: September 21, 2024, 12:54:29 pm
content: Just an observation: there’s already been confusion within this thread because of the word “tab”, which has been used to describe both the PCB pad (by OP) as well as the copper terminal. Just be aware of this when reading the thread!

author: Trurl
author_rank: Regular Contributor
timestamp: September 21, 2024, 03:36:04 pm
content: Quote from: tooki on September 21, 2024, 12:54:29 pmThanks for pointing that out. It should be clear that the heating should be applied on the copper terminals(which have more mass and require more heat), and not the thin output pads on the PCB.Quote from: jpanhalt on September 21, 2024, 12:12:52 pmI may try placing a thin strip of wet paper towel along the PCB between the output pads and the parts (the green solder masked area with multiple through holes), as the strip would soak up a considerable amount of heat from being transferred to the caps etc.Quote from: jpanhalt on September 21, 2024, 12:12:52 pmVoids in the solder joint was one of my initial concerns, and still kind of is. But I think I can manage to get the thickness of the tinning to be minimal. Also I'd make sure that the gaps between the pads and the terminal are tight enough that the terminal would not shift even when the solder melts. The pads would be horizontal so this would also minimize any shifting of the terminals when the solder melts(I had initially considered laying the PSU on its side so the pads would be vertical to encourage downward flow of solder along the joints, if I were to solder the terminals without pre-tinning, in which case shifting of the terminal would definitely be more of a concern).I don't have solder paste(solder in paste form) and would prefer to not get the fancy stuff for this purpose.I do have Burnley soldering paste (flux) which I hope will suffice. The surfaces to be tinned would be cleaned first with a blue(relatively light duty) 3M scouring pad, then wiped clean with alcohol before tinning. So I'm hoping I don't need any fancy flux either.Quote from: jpanhalt on September 21, 2024, 12:12:52 pmI do have more scrap copper sheet, so I'll cut up a similar amount as the terminals and test heating/tinning on the test scraps. Good idea...Quote from: jpanhalt on September 21, 2024, 12:12:52 pmThe tip shown on my torch is a Meco OX T2 Multi-Port Tip(purchased from TMTechnologies - Kent White R.I.P. apparently passed away this past May 2024!) which can provide a very hot focused source of heat if necessary such as if only the upright section(of the copper terminal) were to be heated because it has been placed on the PCB for example. Or the heat could be spread evenly over the entire terminal by placing the torch tip like 15cm(or like 6 inches) away. But this would be my last resort, as I'd like to prevent potential oxidation or soot formation on the copper terminal which would require tricky clean up afterwards.I do have heavy duty(thick) aluminum foil which could be formed to maintain its form against the pressurized flame from the torch, but I'd like to avoid using the torch at all, especially with the terminal on the PCB, if possible.I'll browse online for some cheap soldering irons with muscle, as BrokenYugo has mentioned it seems there are some cheap ones available.The heatgun does take quite some time to heat up metal pieces, but it doesn't cause soot buildup and can heat the whole terminal at once (away from the PCB of course), so I may give it a try as the first alternative to my modest soldering iron. Cheers~

author: hexreader
author_rank: Frequent Contributor
timestamp: September 21, 2024, 05:18:37 pm
content: Why not just drill (say) 3.2 mm hole through each PSU land (two holes if you are paranoid).Use serrated washers for good contact.Screw (say) M3 screw, washers and nut for each connection, along with (say) M3 tag terminal or M3 crimp connector.Just my thoughts - feel free to ignore

author: tooki
author_rank: Super Contributor
timestamp: September 21, 2024, 06:13:30 pm
content: Quote from: Trurl on September 21, 2024, 03:36:04 pmVoids are unlikely to be a problem if you are able to heat the whole copper mass up sufficiently, which shouldn’t be a problem, and are using solder wire.Quote from: Trurl on September 21, 2024, 03:36:04 pmSolder paste isn’t “fancy”, it’s a completely normal, basic product for electronics nowadays.With that said I don’t think it’s ideal for this purpose, precisely because you could end up with lots of voids.Quote from: Trurl on September 21, 2024, 03:36:04 pmDO NOTuse that for electronics! It’s corrosive due to the zinc chloride, and the chlorides are nearly impossible to clean off thoroughly enough.Quote from: Trurl on September 21, 2024, 03:36:04 pmI would buy some gel or paste fluxfor electronics, specifically an RMA (ROL0, ROL1, REL0, or REL1) type. (Can be no-clean, but with one of those four codes.) Do not get a water-soluble flux unless it’s “water-soluble no-clean”.Those also aren’t “fancy”, they’re basic supplies for electronics.Quote from: Trurl on September 21, 2024, 03:36:04 pmUmmm… you know that copper is anextremelygood conductor of heat, right?? The heat from the point flame will spread readily to the rest. Remember, this is soft solder, so even if you’re using lead-free solder, the melting point is just 227°C. It won’t take long to heat it up enough for solder to flow. You certainly do not need to use a big flame from 6 inches away, where you’d be heating up all the components you want to protect.Quote from: Trurl on September 21, 2024, 03:36:04 pmThe only thing that may (but ideally doesn’t) get burnt when carrying out electronics soldering is the rosin in the flux. If anything else is getting burnt, like the PCB or components, then things have gone horribly, horribly wrong.Your bare copper terminalwilloxidize when you heat it, no matter what you do. Just accept that you’ll need to give the mating surfaces a nice cleaning afterwards. I’d do this with a rubber eraser for ink, since that’s a mild abrasive that works beautifully for things like this.

author: edpalmer42
author_rank: Super Contributor
timestamp: September 21, 2024, 06:27:41 pm
content: Quote from: hexreader on September 21, 2024, 05:18:37 pm+1 for this idea!Your heat sources are either too big or too small. Using your soldering iron for anything runs the risk of cooking the board and lifting the copper layer. The torch and heat gun put out too much heat with the same danger. If you really think a soldered joint is required, what's wrong with just drilling a hole through the board, stuffing a wire through, and using something like a precision propane or butane torch to do the soldering on both sides? One time I used a precision propane torch to attach a #10 AWG stranded wire to a metal clip without any trace of heat stress on the insulation.Here's another possibility for you:https://www.oemhardwareparts.com/photo/pl7365021-6_32_x_1_4_inch_snap_in_pcb_mount_screw_terminal_with_nickel_plated_brass_screws.jpgOne thing you haven't mentioned is how many volts & amps are we looking at here? The current level in particular might help guide you to one solution or another.

author: jpanhalt
author_rank: Super Contributor
timestamp: September 21, 2024, 10:06:33 pm
content: Quote from: tooki on September 21, 2024, 06:13:30 pmI disagree. How much experience do you have doing rework of copper plumbing? I would far rather have a fresh, new, not tinned joint than a joint with previous solder (aka tinned) on it.Quote from: tookiKester 44 has bromides in it. It doesn't always need to be cleaned and is used widely for electronics.Quote from: jpanhalt on September 21, 2024, 12:12:52 pmQuote from: tookiThe speed of heating is important. That's why welding with TIG or MIG gives a much smaller heat affected zone than welding with oxy-acetylene The same holds for soldering with propane vs. real MAPP or oxy-acetylene. Of course, the same joint temperature is needed in those cases, but MAPP or oxy-acetylene gets there much quicker and adjacent stuff (e.g., T-joints and valve seals) are not as affected.

author: IanB
author_rank: Super Contributor
timestamp: September 21, 2024, 10:20:46 pm
content: Quote from: Trurl on September 20, 2024, 05:03:27 pmA different answer from the rest of the thread, but I wouldn't do this.The output tabs of the power supply are an extension of the circuit board. The circuit board material is not constructed for mechanical strength, and is not designed to resist bending. If you solder those big copper lugs onto the board, and then bolt wires to the lugs, then significant mechanical loads will be transferred to the circuit board. It may not cause immediate failure, but it would leave me feeling uncomfortable about the long term durability of the arrangement.It rather seems that the power supply is designed to be plugged into some kind of receptacle. It would be better, perhaps, to find the matching receptacle or socket? Or construct some kind of clip that can slip over the tabs on the power supply?

author: golden_labels
author_rank: Super Contributor
timestamp: September 21, 2024, 10:55:57 pm
content: How much current is this PSU supplying? I see some small output capacitor there and edge connectors have their limits too. Those massive copper pieces seem greatly oversized.In either case, wouldn’t it be easier to solder two one-row headers into those holes behind the connector?If you choose to use those copper tabs, be careful with moist or salty environments. Search term “galvanic corrosion” to understand why.

author: artag
author_rank: Super Contributor
timestamp: September 21, 2024, 11:59:56 pm
content: Quote from: golden_labels on September 21, 2024, 10:55:57 pmServer power supplies like that can often provide 60-100A at 12V.

author: golden_labels
author_rank: Super Contributor
timestamp: September 22, 2024, 07:28:33 am
content: Is that 100 A delivered over a 50 mm wide(1)edge contact? Not denying, just asking. Not those huge copper slabs would save OP some trouble.(1)It’s two-sided, I counted both.

author: Trurl
author_rank: Regular Contributor
timestamp: September 22, 2024, 11:17:41 am
content: Quote from: hexreader on September 21, 2024, 05:18:37 pmHow did you know I'm paranoid? I was hoping no one noticed...Anyhoot, I've not yet seen info that guarantees that drilling holes into the output pads of an HP HSTNS-PD43 server PSU is safe (i.e. I don't want to risk shorting the pads with internal layer traces which may not be the same function as the pads - when the output section is held towards a light source, silhouettes of traces between the output pads, in the multi-layered PCB can be seen).Quote from: tooki on September 21, 2024, 06:13:30 pmDon't get me wrong, I LOVE "fancy" stuff.Just that this purpose is quite an unusual case for me and I'd need so little of it that getting an entire tube or jar of the stuff would likely not be used for a long time and just sit in my refrigerator, which is another thing I'd like to avoid.Quote from: tooki on September 21, 2024, 06:13:30 pmThanks for "de-ignorantizing" me about Burnley soldering paste & zinc chloride. It is indeed a pain to remove even with alcohol. I've been curious about such gel/paste flux you mentioned anyway so I'll look into this "RMA (ROL0, ROL1, REL0, or REL1) type" flux.Anything that isn't obviously displayed in a shop(i.e. so I have to ask the owner), to me is "fancy". Again, this is not a negative... I LOVE "fancy" stuff.Quote from: tooki on September 21, 2024, 06:13:30 pmI worked at a company that specialized in CPU coolers, that's where I encountered solder paste for copper heatsink fins and heatpipes. Yes, I know copper is a good conductor. Solder paste is cool stuff.I'd use the torch say 6 inches away from the terminal for example for tinning away from the PSU's pads. If I were to use the torch with the terminal on the PSU's pads, I would now likely choose to point the torch tip away from the PSU's internal components, and have the torch tip close to the terminals portion that is extending outward(like a pool's diving board) from the pads. I'd be focusing heat on the area that diver's would hop on and have the flame bounce off away from the "diving board"(and away from the PSU). In this case I wouldn't even need to use aluminum foil heat shields. If the soldering iron turns out to be too wimpy, I'll use the torch as this would allow getting (heat) in & out fast.Quote from: tooki on September 21, 2024, 06:13:30 pmInteresting... Thanks...Quote from: jpanhalt on September 21, 2024, 10:06:33 pmNow we've come full circle to my initial question... "to tin or not to tin"I'm almost tempted to just flux the pads and terminal joints, slide the terminals onto the pads cold without any tinning, and just use the torch - focusing heat on the edge of the "diving board"(flame pointing away from the PSU) and feeding solder from the opposite side/pad ("anchored end of the diving board"). This would allow getting (heat) in & out fast.Quote from: jpanhalt on September 21, 2024, 10:06:33 pmThanks...Quote from: IanB on September 21, 2024, 10:20:46 pmYour concern is valid, and certainly this should not be done if the lugged cable were to transfer stress directly to the PCB. BUT, in my case, the PSU will be installed in a plastic briefcase and the lugged cables will connect to panel mount XT90 connectors installed on the briefcase's sides. Therefore, this internal cabling will be entirely stress free, and the PSU's PCB outputs will not get stressed by any cable stress external to the briefcase. Also, I may add silicone rubber supports under the terminals to fill the gap between them and the plastic briefcase.Quote from: golden_labels on September 21, 2024, 10:55:57 pmThe HSTNS-PD43 is rated 1400W 117A Max @12VDC 200~240VAC.I'd be using it at around 12.8 ~ 14.6VDC 96~117A Max, but realistically probably never need to use it above 50~60A @ 14.6VDC.It's intended for use during automotive diagnostics/ECU programming for keeping the battery charged up.Appreciate all ya'll's input. Cheers~

author: Gyro
author_rank: Super Contributor
timestamp: September 22, 2024, 12:01:47 pm
content: Quote from: Trurl on September 22, 2024, 11:17:41 amThat sentence set a small bell ringing. Beware of using a server PSU in an automotive environment that it wasn't designed for, where it may be subject to accidental reverse polarity, load dump etc. At the very least you're going to need a [Edit: large parallel reverse protection diode, maybe a TVS, and a] big fuse.

author: artag
author_rank: Super Contributor
timestamp: September 22, 2024, 12:43:29 pm
content: Quote from: golden_labels on September 22, 2024, 07:28:33 amI checked a 100A one I had to hand and it used 12 pin positions on each side for a 32mm tab, or 64mm combined width, 24 pins.So about 4A per pin, which sounds reasonable.The layers appear to be plated through to connect both sides but I don't know how the copper is layered inside the board. Could be multiple planes.

author: Trurl
author_rank: Regular Contributor
timestamp: September 22, 2024, 01:59:23 pm
content: Quote from: Gyro on September 22, 2024, 12:01:47 pmCurrently, I've prepared a 100A "kill switch" for the negative side, so I can have the PSU ON and the external cables connected to the car's +/- terminals, but the PSU NOT connected to the car when the "kill switch" is OFF, during which I can set the PSU's voltage to be higher than that measured on the car's +/- terminals, to prevent reverse current into the PSU.But as this is a topic that strays from the original topic of this thread, I'll start another one, and hopefully you'll chime in with more details. Cheers.

author: golden_labels
author_rank: Super Contributor
timestamp: September 22, 2024, 08:10:46 pm
content: Ok, so maybe just solder a thick wire along the connector? Avoids strains, should be easier to solder, avoids the problem of putting solder under a large, flat, copper element.You can then either put a an eye connectors on the wires, if you have the right crimping tool,(1)or solder the wires to your copper tabs.(1)At 100 amps poor crimping will be a problem.

author: Trurl
author_rank: Regular Contributor
timestamp: September 23, 2024, 04:04:25 pm
content: The intent of my copper terminal design is to minimize any bottle necks that would increase resistance which would in turn cause more voltage drop and heat. For the intended purpose of the PSU, the output voltage needs to be steadily maintained between 13~14VDC up to say 60A continuous output.Therefore, I made an effort to maximize the surface area of joint contact between the copper terminals and the PSU's output pads, even if it is perhaps a bit overkill or redundant, I figure it would be better to have cooler low resistance connections.Also, by having the connections on both sides(top & bottom) of the outputs with the terminals kind of "biting" onto the pads, any vertical force on the terminal's connection point that would also cause pulling on one of the pads would be countered by the opposite side's connection, reducing the pulling force applied on the pads.

author: tooki
author_rank: Super Contributor
timestamp: September 23, 2024, 08:05:12 pm
content: Quote from: jpanhalt on September 21, 2024, 10:06:33 pmI don’t have experience doing plumbing soldering. But that’s neither here nor there: I was replying to OP’s concern about non-pretinned terminals not flowing properly.Quote from: jpanhalt on September 21, 2024, 10:06:33 pmAnd? Another “correction” that is not pertinent: bromides aren’t chlorides. The fact remains — and thisisfact, not opinion — that Kester 44 is designed for electronics (so, um, “duh” that it’s widely used for electronics), and that Burnley is not. Even zinc chloride bearing fluxes designed for electrical work are not safe for electronics, because PCB traces are so thin.Quote from: jpanhalt on September 21, 2024, 10:06:33 pmUm… ok? What does this have to do with my advice to OP to follow YOUR previous advice to use a small flame, and not OP’s idea of using a large flame from farther away?