How to desolder large SMD inductor? - Page 1
Forum section: electronics / repair

author: thomasx
author_rank: Contributor
timestamp: September 07, 2020, 11:09:12 pm
content: HiI need to desolder this inductor, marked 472 in the photo.Any good suggestions on how I go about doing that? I have a normal soldering station and a hot air station at my disposal, and a normal ovenThanks!

author: ataradov
author_rank: Super Contributor
timestamp: September 07, 2020, 11:35:18 pm
content: Do you need inductor to survive? If yes, then pre-heating and then hot air is the only real option.If you don't care about the inductor, then just hot air from the inductor side, trying to avoid the PCB itself initially. But that will definitely overheat the inductor, possibly ruining the internals.

author: thomasx
author_rank: Contributor
timestamp: September 08, 2020, 01:08:21 am
content: HiYes, I need it to survive.I managed to get another one off, but that one had the pads just visible on the sides, so I could get it with one soldering iron on each side.On this one the pads are not reachable.I tried heating up a feeler gauge with a torch and inserting under to see if that would melt the solder, but unfortunately not. Perhaps if I attach the feeler gauge to an powerful soldering iron and tin it firstThe data sheet says the component will survice 260C reflow for 40 seconds three times.

author: ataradov
author_rank: Super Contributor
timestamp: September 08, 2020, 01:18:12 am
content: The only somewhat reliable way is to preheat the board from the bottom, then blast with hot air from the top. Preheating using the same hot air station may work, but much less reliable, since it would be hard to hold the temperature.I doubt feeler gauges will not do anything. You won't get good heat transfer even if you attach it directly to the soldering iron.

author: Mp3
author_rank: Frequent Contributor
timestamp: September 08, 2020, 02:01:04 am
content: If you need the component to survive one of my most reliable ways is preheating the board then adding a bit of solder to the pads then wicking it away while wiggling the component. I don't have SMD plier type irons, so this is my best option for only having a plain soldering iron handy.

author: thomasx
author_rank: Contributor
timestamp: September 08, 2020, 02:33:59 am
content: I have a good quality temperature controlled hot air gun I could use for preheating from beneath, and then use the hot air station from above.What temperatures to set on hot air gun and hot air station you think?

author: bdunham7
author_rank: Super Contributor
timestamp: September 08, 2020, 03:27:58 am
content: Silly question: do you also need the board to survive?

author: ataradov
author_rank: Super Contributor
timestamp: September 08, 2020, 03:31:27 am
content: The preheat temperature must be lower than solder melting temperature. But you also need to take into account surrounding components. If there are no plastic parts that can melt, the you can go quite high.Temperature regulation on the air gun does not mean much, it has to be calibrated to the temperature on the surface of the board. So having a way to measure that would be a plus.The temperature of the hot air station should be basically maxed out, or way higher than solder melting temperature. The goal is to quickly cross the melting point from the preheated state, the faster you could do that the better.

author: ataradov
author_rank: Super Contributor
timestamp: September 08, 2020, 03:31:58 am
content: Quote from: bdunham7 on September 08, 2020, 03:27:58 amProvided that inductor needs to survive, I assume the board needs to survive too.

author: Haenk
author_rank: Super Contributor
timestamp: September 08, 2020, 05:08:14 am
content: Don't those pads at the marking "L1" lead to it? Maybe put some solder & flux there and have it flow below...

author: WillTurner
author_rank: Regular Contributor
timestamp: September 08, 2020, 07:16:27 am
content: You could try a low temperature solder like Chip Quik. The idea is to change the composition of the solder at the joint by adding the low temperature alloy so that the joint stays liquid long enough to remove the component. Search your favorite video provider.

author: thomasx
author_rank: Contributor
timestamp: September 08, 2020, 01:09:20 pm
content: Not at all a silly question, and the answer is, not really, the board must not survive, but preferablyThe visible L1 "pads" unfortunately do not connect with the inductor pads.I did another with chip-quick, but this one I can't get to the pads, so no way of getting the solder in there, as I can see.I'll see if I can give it a go with preheat and hot air.

author: bdunham7
author_rank: Super Contributor
timestamp: September 08, 2020, 01:34:02 pm
content: Quote from: thomasx on September 08, 2020, 01:09:20 pmThe reason I asked is because your preheat method--the hot air gun--is not ideal or precise. If the board was important, you would have to be careful with it. Since it is less important, you can be more aggressive with the preheat. The more you roast it from the bottom the better your chances are of getting the part off safely. I've salvaged miscellaneous parts off a few boards this way by just flipping them over and hitting the board with a heavy duty heat gun (flooring removal) until the parts just fell off.

author: Haenk
author_rank: Super Contributor
timestamp: September 08, 2020, 04:24:35 pm
content: 2nd idea - how about just buying one?https://au.element14.com/coilcraft/xfl4020-472mec/inductor-pwr-4-7uh-5a-20-26mhz/dp/2289218RLThere are certainly more offers, somewhere on thsi planet(I assume that's the same one?)

author: thomasx
author_rank: Contributor
timestamp: September 08, 2020, 11:55:32 pm
content: Buying one was of course an option. Though it is considered cheatingshipping is like 20 times the cost of the component, and takes several days to get itOn the other hand, I managed to desolder it.I took some copper tape, cut it to dimension and pushed under the inductor on both sides along the pads, fluxed, tinned and used chip-quick and after a while with one soldering iron on each side it came off.