Hot air desoldering and cleaning through holes - Page 1
Forum section: electronics / general

author: wblock
author_rank: Regular Contributor
timestamp: January 08, 2016, 08:38:22 pm
content: An interesting technique: after desoldering a through-hole part with hot air, use the air pressure to clear the holes:.It never occurred to me to try that. Possibly not that effective on multilayer boards. It doesn't work on a couple of ground pins in the video.

author: orion242
author_rank: Unknown
timestamp: January 08, 2016, 08:43:41 pm
content: Slick.Beats the hell out of the desolder pump on each pin. I'll have to give that a go.

author: bitseeker
author_rank: Super Contributor
timestamp: January 08, 2016, 08:55:06 pm
content: That was pretty neat. Thanks wblock.

author: Shock
author_rank: Super Contributor
timestamp: January 09, 2016, 01:13:31 am
content: Looks cool never thought of using the nozzle for that. I wonder how much a mess on the other side it leaves though. He mentioned it was only on vintage double sided PCBs and not multilayer boards or ones with a large ground plane.There is another video of a guy using an air compressor, makes quite a mess but gets the component out easy as well.

author: nanofrog
author_rank: Super Contributor
timestamp: January 09, 2016, 05:43:19 pm
content: Very slick indeed!Thanks for posting this.Regarding multilayer boards, a preheater of some sort might allow this technique to work. I've an el cheapo Tenma unit, so I might be able to test this out.

author: janoc
author_rank: Super Contributor
timestamp: January 09, 2016, 05:51:48 pm
content: I am using this technique for a while already, it is certainly easier than desoldering DIPs using a solder sucker/gun. I thought that hot air component desoldering was a common trick? On the other hand, the downside is that it is very very easy to scorch/delaminate the board if you aren't careful.I haven't tried to blow-clean the holes like that though. Interesting idea, but wearing protection glasses would probably be a good idea in case of hot solder splatter.

author: clay_cowgill
author_rank: Contributor
timestamp: January 13, 2016, 07:28:31 pm
content: Ah, so *this* is why the YouTube views spiked-- linked back from Hackaday. ;-)If you didn't read the YouTube comments or description I'll comment on a few things you all were wondering about.* Pre-heating (either with the hot air on the back, or a hot plate) can help and is pretty much mandatory for multi-layer boards and RoHS solders (I generally never run in to through-hole DIP RoHS stuff though, YMMV).* In the video, the board is actually sitting on a hot plate that is *off* (because my plastic camera tripod was sitting on it too). As the solder was blown out it was instantly re-freezing when it hit the thick steel plate-- that's why the grounds and some other pins didn't blow clean the first try (little solder stalactites heat sinking down to the plate). Also, the ground pads were close to the outer edge of the board where there's more convective cooling going on. Once I got the board elevated a bit more everything cleaned up with the air alone-- I didn't need to use any braid or anything before sticking in sockets and new DRAMs.* I've been doing this since the mid 90's (originally to salvage parts on the cheap from surplus PCBs), so I'm sure I make it look easier than the first time you try-- use a scrap board! You *will* brown some (white) silkscreen and bubble soldermask and maybe delaminate some FR4 before you get good at it. With some practice though you just get to see the change in surface tension on the solder and know when it's good to pull.* On my Hakko 850 I use the 0.25"/6mm tip for pressure to blow the holes clean. With the system set to '5' and '5' (basically half power on the blower and heater) that gives ~525°F/~274°C at the tip which is enough to flow old leaded solders nicely, but not so hot that you're burning everything else.* You can adapt depending on what you're trying to do-- in the video I was most interested in not damaging the board (the DRAMs were junk), so I had things set low and slow. If I wanted the chips only and didn't care about the board I'd set the temperature higher and airflow *lower* to make the process go faster. If I burn the mask or silkscreen when all I want is the chip, it's no big deal.* Doing bigger parts (40-64 pin DIP), you do need to be a little careful while removing them. The heat will soften the encapsulating epoxy and they can 'flex' a bit. I just slowly slide that wedge shaped tweezer I use in the video under the end of the IC once the solder is melted and gently push it farther and farther underneath as I heat the pins nearest to the fulcrum. It will gently lift the chip out without bending the package or the pins. For ceramics (they will crack before they bend) I repeat the process from end to end. (Don't try to pull a ceramic MC68000 from one end only if you want to be able to re-use it.) ;-)* There can be a fair amount of splatter (kinda depends on how generous the OEM was with hole diameters and wave profile), so "maintain situational awareness"-- don't do it while wearing shorts. ;-) I usually just elevate the board a few inches above my bench and the solder loses some of its heat during the 'fall'. It'll still 'splatter', but only to the thickness of a few folds of aluminum foil and it's easy to just scrape off for cleanup. (Doing it over the cold surface of the steel hot plate also makes for easy clean-up.)* You can also just pull all the parts in one quick pass (you basically draw the heat along and work a row at a time) and then go back and blow out the holes later. It's a little slower, but not by too much. Here's a much older video where I was doing that:https://youtu.be/e_LlGOIDQwQ(Sorry, not sure how to embed video here.)-Clay

author: george graves
author_rank: Super Contributor
timestamp: January 14, 2016, 11:06:35 am
content: Quote from: clay_cowgill on January 13, 2016, 07:28:31 pmHope you don't mind Clay. It seemed worthy of sharing. Nice video/technique BTW!

author: Shock
author_rank: Super Contributor
timestamp: January 14, 2016, 12:46:02 pm
content: Whats your hourly rate Clay I have a stack of PCBs here.

author: bitseeker
author_rank: Super Contributor
timestamp: January 14, 2016, 07:00:31 pm
content: Quote from: clay_cowgill on January 13, 2016, 07:28:31 pmThanks for the rundown, Clay, and welcome to the forum.

author: artag
author_rank: Super Contributor
timestamp: January 21, 2016, 09:45:36 pm
content: I was interested to see that you apply the air form the top - I've tried from the bottom (assuming the chips will fall out when the solder melts) and pretty much always failed and cooked the FR4.

author: azer
author_rank: Regular Contributor
timestamp: January 22, 2016, 11:15:41 am
content: If there is a large ground plane or if the board is multilayer it is possible to use something like thishttp://www.ebay.com/itm/8PCS-Hollow-Needles-Desoldering-Tool-IC-Extraction-Set-For-DIP-PCB-Soldering-EW-/231472868503Not the most efficient for getting the component out, but very handy for removing the last solder stuck in the hole.There is a video of it in action here (in French, but it was the only one I found)https://youtu.be/qeC1oUM2tvg?t=163and an old threadhttps://www.eevblog.com/forum/projects/how-are-these-used-'hollow-needles-desoldering-tool'/