How to solder a heatsink to a PCB? - Page 1
Forum section: electronics / beginners

author: MarkS
author_rank: Unknown
timestamp: March 02, 2023, 03:58:14 pm
content: I used a massively overkill heatsink for a project that has solder posts at the base. I knew that soldering would be difficult, but even while using my hot air rework station set to 500°C and full air, I couldn't get solder to melt/fuse. This isn't critical to the application, so I can leave it as is, but I would like to know how to accomplish this in the future. I'm guessing that this would be done in an industrial setting via wave soldering? Other than using a blow torch, what's the best method to do this at home? Or should I invest in a tiny die set and cut threads in the posts?

author: BillyO
author_rank: Super Contributor
timestamp: March 02, 2023, 04:14:08 pm
content: Wave soldering might not be effective either, but a re-flow oven would get the job done. You could try a toaster oven.

author: MarkS
author_rank: Unknown
timestamp: March 02, 2023, 04:22:32 pm
content: Quote from: BillyO on March 02, 2023, 04:14:08 pmThat's on my list of things to build.

author: Haenk
author_rank: Super Contributor
timestamp: March 02, 2023, 07:52:41 pm
content: Maybe try some high wattage iron, like 200W or 500W, available for soldering roof drainage pipes etc. I used a 200W, but found it too weak for the pipes I had...

author: edpalmer42
author_rank: Super Contributor
timestamp: March 02, 2023, 09:06:43 pm
content: Pictures of the heatsink would be helpful.Often, larger heatsinks aren't soldered to the board, they're screwed. Many of the heatsinks are aluminum extrusions so it's trivial for them to design in channels that fit an appropriate bolt or screw. Larger ones have large feet with threaded holes for mounting bolts. I've also seen heatsinks that had small solderable tabs riveted to the unsolderable aluminum heatsinks.Ed

author: MarkS
author_rank: Unknown
timestamp: March 02, 2023, 09:51:39 pm
content: Quote from: edpalmer42 on March 02, 2023, 09:06:43 pmHere you go:https://info.boydcorp.com/hubfs/Thermal/Air-Cooling/Boyd-Board-Level-Cooling-Extruded-5000.pdfI have the 513102B02500G.

author: shapirus
author_rank: Super Contributor
timestamp: March 02, 2023, 11:07:49 pm
content: Quote from: MarkS on March 02, 2023, 09:51:39 pmI soldered almost exactly the same heatsink, the only difference being that mine is 33 mm tall and yours is (per the datasheet) 38 mm, literally 1 hour ago, to a breadboard. Used a Ksger T12 station with a cheap chinese D52 tip, 60/40 solder, temperature boosted to 380 deg.C.No difficulties whatsoever. Yes the solder solidifies very quickly when the tip is removed, but once it is back in contact, solder melts right away.With a real PCB I would probably need to use a more massive tip and/or the help of a (de)soldering hot air gun, but it still wouldn't be too much of a problem.

author: edpalmer42
author_rank: Super Contributor
timestamp: March 02, 2023, 11:09:13 pm
content: Those pins look like they'd pull out really easy. I'd pull them and use screws. Threading them is possible, but they're not designed for that so they might not be strong enough (they could even be hollow) or they might spin while you're trying to thread them because they're not well anchored.Another thought would be to pull the pins, then solder them into the board and press the heatsink back onto them. Without the heatsink to, well, act like a heatsink, they'll solder easily. I've never tried something like that, but if it's for a personal project it's worth considering.Other than that, I'd use a large soldering iron or gun. Big irons are hard to find and expensive, but big soldering guns can be found at local hardware or home reno stores. A big soldering gun can come in handy occasionally. There've been a few times that I was glad I had one.Ed

author: donlisms
author_rank: Frequent Contributor
timestamp: March 03, 2023, 09:19:59 am
content: I like the "healthy soldering iron with a big tip" approach. A little flux couldn't hurt, and it might help the flow.I was just thinking... if you're using hot air, maybe you're used to SMD most of the time? If so... this is not that! Big old hot tip in direct contact, little flux, flow a little solder between the tip and the pin to conduct the heat, count to 10 or 20, flow the real solder in, and Bob's your uncle.Air is a pretty poor heat conductor; I don't how we ever got started down that road. :-)

author: Siwastaja
author_rank: Super Contributor
timestamp: March 03, 2023, 09:31:08 am
content: Nearly impossible with hot air, even with reflow oven. With long enough time in oven, the whole heatsink would heat up and eventually solder, but that could damage other parts in the meantime.Good old large iron tip does the job easily. Just handsolder. Remember to wet the tip with solder. Molten solder acts as a heat transfer medium.

author: wraper
author_rank: Unknown
timestamp: March 03, 2023, 09:36:44 am
content: Preheat heatsink with hot air and then solder with soldering iron.

author: M0HZH
author_rank: Regular Contributor
timestamp: March 03, 2023, 10:02:12 am
content: Heat up the heatsink, either with a hot plate or an induction hob.

author: Berni
author_rank: Super Contributor
timestamp: March 03, 2023, 10:57:46 am
content: Should not be too hard, these pins on heatsinks are made hollow to reduce heat transfer.Just heat up the heatsink with hot air to reduce the amount of heat it can pull. Then use the shortest thicket tip on your soldering iron set to 450°C to solder it.Same trick works for any difficult to solder PCB (Like aluminium core boards), preheat with hot air then solder while still hot.

author: rdl
author_rank: Super Contributor
timestamp: March 03, 2023, 11:35:47 am
content: That's the same heat sink I used on my dummy load. I used a similar type of perf board also. I just sort of reamed out the holes until when I pushed in the pins it was a very tight fit. With a lot of knocking around over time they might get loose, but it's plenty solid now. If it does eventually get loose I'll probably resort to some kind of glue.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 03, 2023, 11:42:59 am
content: Metcal or JBC iron with a big tip will do this easily

author: shapirus
author_rank: Super Contributor
timestamp: March 03, 2023, 11:50:39 am
content: Quote from: mikeselectricstuff on March 03, 2023, 11:42:59 amJust like any other sufficiently powerful system, with direct heating tips much preferred (otherwise the tips that can do the job tend to get uncomfortably big). It's not limited to specific brands.

author: Psi
author_rank: Super Contributor
timestamp: March 03, 2023, 12:22:26 pm
content: Put the heatsink into the oven at 100C for 10min.Then take it out with piles and quickly solder it onto your board.Since it's already at 100C you're iron doesn't need to work anywhere near as hard to solder itBut yeah, i agree with what others have said. A proper iron should be able to do this.I'm going to guess your iron uses tips that fit over the heating element like 900M style.They are old tech and really don't work well compared to modern irons that uses tips permanently bonded to the element.You don't have to spend hundreds to get something decent. The china clones that take Hakko T12 tips work pretty well, but I would check the mains wiring inside them. Sometimes the earth to case is bad due to paint under earth nut, and the power switch is sometimes in neutral.

author: rdl
author_rank: Super Contributor
timestamp: March 03, 2023, 01:00:40 pm
content: It's a pad per hole board. Are the pins actually small enough to go through the holes? I'm pretty sure I went with press fit because on my heat sink the pins were so big that if I'd enlarged the holes until the pins would go through easily, there wouldn't be enough, if any, of the metal rings left on the board to solder to. Even so, with that type of board and that size heat sink, is anything really gained by soldering?edit:looking closer I see you've tried to bridge multiple holes with the solder. This maybe does add something in the way of strength.Nevermind. Ignore my whole post because those weren't your pictures I was looking at.

author: shapirus
author_rank: Super Contributor
timestamp: March 03, 2023, 02:22:23 pm
content: Quote from: Psi on March 03, 2023, 12:22:26 pmSometimes there is no earth to case connection at all, like it was in mine. Easy to fix as long as you have a drill and understand that anodizing acts as a dielectric and has to be removed at those spots where electric contact has to be made.

author: Psi
author_rank: Super Contributor
timestamp: March 04, 2023, 01:55:17 am
content: Quote from: shapirus on March 03, 2023, 02:22:23 pmYep, definitely needs to be checked.

author: Teledog
author_rank: Regular Contributor
timestamp: March 04, 2023, 04:16:52 am
content: Small induction coil for heating?I've found them fascinating!

author: BillyO
author_rank: Super Contributor
timestamp: March 04, 2023, 05:30:50 am
content: Quote from: Teledog on March 04, 2023, 04:16:52 amInduction coil near an electronic circuit board?Sounds like a task for Electroboom!

author: MathWizard
author_rank: Super Contributor
timestamp: March 04, 2023, 09:06:58 am
content: Sometimes I just anchor them / tie them down. I tin the end of some wire , wrap it around the HS post's, and try and solder it. And if I can at least solder the wire together, and with a blob on top sometimes......then just feed the other end of the wire into the PCB, and if it's a proto board, or if' you're lucky, there's a big space to solder down the wire to the board. Then the HS is on an angle tho. So if I really want to , just wedge a little scrap of wood under the HS to level it, or insulate it, and make it tight.I never tried using screws tho, I'll try that too. On a proto-board tho, using a wooden riser, and wires to anchor the HS, it can be very solid, so long as the copper on the heatsink is soldered enough. You could also just tie enough wire around a HS to to it this way in a jam.

author: geggi1
author_rank: Frequent Contributor
timestamp: March 04, 2023, 09:20:46 am
content: Pull the pins and use self tapping screws.

author: Psi
author_rank: Super Contributor
timestamp: March 04, 2023, 10:18:31 am
content: Quote from: geggi1 on March 04, 2023, 09:20:46 amhehe, that's the equivalent of the NASA/Russia "using a pencil" thingLove it

author: edpalmer42
author_rank: Super Contributor
timestamp: March 04, 2023, 02:34:10 pm
content: Quote from: Psi on March 04, 2023, 10:18:31 amNo it isn't. Larger heatsinks are often screwed down because the screws have better holding power than the pins. Sometimes, I've even seen professionally manufactured boards that use screws and then solder the screws in place. I'm not a fan of that!Ed

author: Teledog
author_rank: Regular Contributor
timestamp: March 04, 2023, 07:25:14 pm
content: Quote from: BillyO on March 04, 2023, 05:30:50 amUm,, who mounts major heavy components AFTER installing semiconductors???Like putting on your boots and then your socks after!??Hope your not a MFG engineer!