Heat Gun: Desoldering Resistors, Transistors, etc. - Page 1
Forum section: electronics / beginners

author: DW1961
author_rank: Frequent Contributor
timestamp: June 04, 2021, 05:44:46 pm
content: I'm confused about de-soldering heat sensitive components using a de-soldering heat gun. Since the heat is all over the component, doesn't the heat required to de-solder heat up the chip or resistor enough to harm it?

author: andy3055
author_rank: Super Contributor
timestamp: June 04, 2021, 05:55:39 pm
content: Not necessarily. The idea of the gun is to have a high temperature to quickly melt the solder. Then you suck it up immediately and remove the gun fro the board.I have one of these (https://www.ebay.com/p/6031090946?iid=232864958017) that works fine. It was much cheaper two years back-around $80.00

author: DW1961
author_rank: Frequent Contributor
timestamp: June 04, 2021, 06:40:19 pm
content: I can get this unit here for a free program I belong to (reviews):https://www.amazon.com/dp/B093QF3ZK2We still have to pay taxes on it, so I'd be out around $30.00 bucks. It just seems pricey, but I guess for 30 bucks it isn't, lol.Still, that is a lot more heat than most of those components are rated for, right?

author: mindcrime
author_rank: Unknown
timestamp: June 04, 2021, 07:35:29 pm
content: Totally not an expert, but I think the basic idea is that there's a (big?) difference between "the heat a component can tolerate continually, when powered up" and "the heat a component can tolerate for 1-3 seconds while being soldered or unsoldered." So components can be heated up like this, you just can't apply the heat and keep it there indefinitely. And even in the latter scenario, there must still besomeupper bound. But it's probably higher than you would intuitively expect.Consider that most modern electronics are assembled using reflow soldering, where the entire assembly, components and all, are put into a big oven and baked at upwards of 200° C. But it doesn't harm the components, because the process is brief, and even more so the time at the actual peak temperature.Quote from: DW1961 on June 04, 2021, 06:40:19 pm"Range of the Hot Air Gun of 212°F ~ 932°F / 100°C ~ 500°C"TBH, 500°C does sound insanely hot and almost certainly WAY more than you would ever need for de-soldering. But as long as the thing is adjustable and lets you select a lower value, there's no reason you can't just ignore the fact that it's capable of going that high.

author: penfold
author_rank: Frequent Contributor
timestamp: June 04, 2021, 07:57:23 pm
content: Look up some SMT reflow profiles, the dwell time at peak temperature can be 10s of seconds. It's likely that most devices are only verified to stay good with only a single temperature cycle that high, but likely will remain close to spec after a few. For most components I doubt it would be particularly noticeable and most circuits should be designed to be quite tolerant of parameter variations.

author: wizard69
author_rank: Super Contributor
timestamp: June 04, 2021, 11:07:01 pm
content: Quote from: DW1961 on June 04, 2021, 05:44:46 pmit really depends upon the component. Some will be damaged there is no doubt at all here. However as has been pointed out there is some heat tolerances in components designed for wave or reflow soldering. Simply put the components need to be designed to resit baking to reflow temperatures for at least a few seconds.By the way one approach I've used to salvaging components, from boards I don't intend to reuse, is to heat the back side of the board with a propane torch held a reasonable distance away from the board. With the board held upside down the chips drop off the minute the solder melts which should minimize heat pick up of the chip itself. In this case you are heating the back side of the board not the component itself. The difference here is that you are often putting more heat on the chip package than the leads when heating from the front. At least hta tis my theory.

author: DW1961
author_rank: Frequent Contributor
timestamp: June 05, 2021, 12:57:36 am
content: Quote from: wizard69 on June 04, 2021, 11:07:01 pmHA! That's a great idea, really. I was mainly talking about removing SMDs of different types, including IC chips, that are soldered down on the top of the board. In that instance, like you said, you're baking the chip package. Now that I think about it, for example, the 'package' will be mostly off the chips themselves, offering some insulation to heat.

author: james_s
author_rank: Super Contributor
timestamp: June 05, 2021, 01:08:42 am
content: Slightly less brutal, I use a heat gun (like the kind for stripping paint) to heat the back of the board for salvage. I've used the torch trick too for really heavy boards but you really need to do that outside with a bit of a breeze because the fumes are nasty.

author: wizard69
author_rank: Super Contributor
timestamp: June 05, 2021, 09:28:34 pm
content: Quote from: james_s on June 05, 2021, 01:08:42 amYes! Just so people understand using a torch is a salvage solution not a repair solution. It does work very well though and doesn't seem to cause as much heat damage to good chips as you might think. I actually think that you end with a higher good chip yield.I forgot to mention in the above post some items will be damaged from excess heat. Sometimes these might be items added after reflow via hand or other soldering methods. In some cases they are socketed. If you want to salvage such parts you need to be real careful with the soldered in ones. That might mean one pin at a time desoldering or other techniques that don't involve soaking the part with heat.

author: DW1961
author_rank: Frequent Contributor
timestamp: June 06, 2021, 02:10:10 am
content: Quote from: wizard69 on June 05, 2021, 09:28:34 pmMakes perfect sense.

author: WattsThat
author_rank: Frequent Contributor
timestamp: June 06, 2021, 02:19:30 am
content: Boards that I intend to strip parts off, primarily IC’s, I preheat in a toaster oven at 250F for 5 minutes before the heat gun treatment. Heat and lightly tap the board every five seconds or so. The chips fall off the moment the solder melts. The preheat cycle really reduces the time under the gun. I’ve recovered lots of 128x8 static ram with that method, zero failures over five plus years.

author: lapi
author_rank: Contributor
timestamp: June 06, 2021, 08:44:11 am
content: For a historical reference: The first issue of the Byte magazine,https://archive.org/details/byte-magazine-1975-09see article "Recycling Used ICs" on page 20.I'm not saying you should use that method these days, though...