Technique to de-soldering a SOT23 - Page 1
Forum section: electronics / beginners

author: gogoman
author_rank: Regular Contributor
timestamp: August 13, 2021, 05:05:41 am
content: Hello, the PCB has several SOT23 which require removal and are near a connector. I tried hot air and the bugger remain stuck in place.Is it possible to remove the SOT23 with a single solder iron, how? I have a china special iron/hot air gun and varies tips at my disposal.thanks

author: Kleinstein
author_rank: Super Contributor
timestamp: August 13, 2021, 07:17:28 am
content: One can use a normal soldering iron and lift the part one side at a time. So use a needle or tweezers to lift one side while heating one side. Just be careful to not use much force to rip of pads. With a knife edge soldering tip one can use the same techique also for SO8, heating up a whole side at a time.

author: bobbydazzler
author_rank: Regular Contributor
timestamp: August 13, 2021, 07:30:39 am
content: Does it matter if you destroy the sot23 devices? You could wick away some solder then cut the leads.

author: Berni
author_rank: Super Contributor
timestamp: August 13, 2021, 07:43:07 am
content: SOT23 is easy with a soldering iron,Just put a huge blob of solder on it then quickly alternate the soldering iron between the two sides (set to a pretty high temperature of say 400°C). The big blob of solder is important to give it more thermal mass, that way it stays molten for long enough to get the soldering iron to the other side and melt that too. At that point you push against the chip with the soldering iron to slide it off the pads and it will fall off or stick to the soldering iron tip where you can just flick it off into a trash can.This works well for any small component like 3 to 5 pin ICs and SMD resistors and capacitors. It can even work for 8 pin SOIC chips, but that's about as large of a chip you can do (Unless perhaps you use a giant soldering iron tip)

author: wraper
author_rank: Unknown
timestamp: August 13, 2021, 07:52:25 am
content: I remove them with 2 soldering irons. One heating the pin on one side, another both pins on the other side.

author: Whales
author_rank: Super Contributor
timestamp: August 13, 2021, 07:55:58 am
content: Quote from: wraper on August 13, 2021, 07:52:25 amI can definitively say that at no point in my life have I ever dual-wielded soldering irons. I now suddenly feel like I'm missing out.

author: Berni
author_rank: Super Contributor
timestamp: August 13, 2021, 08:07:23 am
content: Quote from: Whales on August 13, 2021, 07:55:58 amYou sure are.I only tend to bother with it when i have a lot of things to desolder, but boy is it fast when i do. Its like picking components off a desk with big fat chop sticks. They just come off like they are not even soldered.

author: magic
author_rank: Super Contributor
timestamp: August 13, 2021, 08:27:42 am
content: Will have to try it one day.Quote from: Kleinstein on August 13, 2021, 07:17:28 amThis works and you have to be careful.Quote from: Berni on August 13, 2021, 07:43:07 amThis also works and you have to be careful. If you push too strong on the IC and the other side solidifies, you risk ripping off a pad. And if you don't push enough and the part was glued to the board before reflow (which they usually are) the part may not come off.

author: CJay
author_rank: Super Contributor
timestamp: August 13, 2021, 11:03:55 am
content: Pair of tweezers or pointy stick, apply a blob of solder to both sides, melt the solder on one side while applying a little 'lifting' force, you'll feel the part move slightly, swap to the other side, repeat until part is off the board.Once you get the hang of it, it's faster than cleaning the tips on my Pace hot tweezers.

author: harerod
author_rank: Frequent Contributor
timestamp: August 13, 2021, 01:24:19 pm
content: Well, an SOT23-3/5/6 shouldn't pose a problem to either a soldering iron or hot-air. Preheating the PCB will further reduce resistance. As written before - don't put too much stress on the pads. It is also good to know whether the assembler used glue for that component.Anyways, since it is Friday, I thought I might share an old report of a prototype assembly session, where I screwed up royally. In many cases the PCB and the surrounding components are more valuable than the offending component. If a mill router is at hand, there is a way that looks dramatic, but actually puts little stress on the board.Just mill the component off the board and remove the remaining pins one by one with a soldering iron. It doesn't matter if the SMD/THT-pin is connected to one or more heat sinking planes. I have successfully used this method to remove THT-pins that where connected to three large power planes. Might require pre-heating, though.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 13, 2021, 09:57:36 pm
content: Quote from: Whales on August 13, 2021, 07:55:58 amObligatory Simpsons reference,Personally, I find the alternate-side-blobs method sufficient for the most part. Clean up the pads with a bit of flux, solder wick, then alcohol. I might prefer that over hot air because of the connector (and yeah, you need to soak the board pretty good before hot air does the trick, if you're not getting enough heat it'll simply never melt).Tim

author: gogoman
author_rank: Regular Contributor
timestamp: August 16, 2021, 02:27:29 am
content: thanks

author: joeqsmith
author_rank: Super Contributor
timestamp: August 24, 2021, 01:33:20 am
content: I would normally use a hot air gun but I finally bought a set of PACE MT-100 MiniTweez along with a wide set of tips. I can turn the iron on a pull a SOT23 in a few seconds now.Using the heat gun....https://youtu.be/Dchy-0u-W7A?t=447

author: BlackICE
author_rank: Regular Contributor
timestamp: August 24, 2021, 07:09:01 am
content: I use 2 soldering irons, a pointed tip in one and a knife tip the the other.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: August 25, 2021, 01:53:26 am
content: Put your hot air on "hot hot" and work a wide circle into a smaller one. Pratice on a scrap board. It should be very easy. A little pratice and you'll figure put what you're getting wrong.Remember one leg will likely be attached to the ground pane (NPN) so you will need to give that time to heat. Maybe even give that pin a tap with a hot iron.You can try putting little paste on the ground pin to see if it's getting hot enough.Also, flux is your friend.Don't pull. Nudge it until it moves then pick it up.

author: gogoman
author_rank: Regular Contributor
timestamp: August 25, 2021, 05:43:27 am
content: This worked for me, using two soldering irons. The first with a bent tip which I shape with a file, a second iron with a normal tipgogoman

author: IDEngineer
author_rank: Super Contributor
timestamp: August 25, 2021, 04:02:05 pm
content: SOT-23's are about the easiest of all SMT components to remove:* Apply a slight lifting force under the body using tweezers or a similar tool* While maintaining that lifting force, heat the single lead on one side until the body rotates up and the lead just clears the pad* Heat the two leads on the opposite side (simultaneously) until the body lifts off the boardTakes just a few seconds. The reason the SOT-23 is easier than two terminal SMT's is because it has actual leads. When you heat the first (single) lead, the other two can flex slightly to allow the body to rotate away from the PCB. This simplifies everything. With SMT resistors, caps, LCC's, QFN's, etc. there is no such "bending" possible and you're required to get all of the connections hot at the same time (unless you don't care about destroying the part).Removing a SOT-23 this way easily keeps both the part and the PCB reusable. The SOT-23 pins may require a slight rebending back into their normal shape but otherwise everything is clean and undamaged.

author: gnavigator1007
author_rank: Unknown
timestamp: August 25, 2021, 04:26:46 pm
content: You could always get some low melt solder and make things even easier. I don't care for some of the lifting methods others have mentioned, but it certainly is doable. Really, you should be fine with hot air. As someone else mentioned, the part may be glued down as well. Snip the legs. You can then cut the package from the board with a fine blade. I've also cut strips from soda cans to get underneath bga parts with underfill. Not ideal, but works in a pinch