Hot air gun removing DIPs?

[duskglow]

So I'm playing with my new hot air gun, and I discovered that they rather effectively remove DIPs from double sided boards.  These have been impossible to remove using a soldering iron.  The chips do get hot, but I figure if they're designed to take reflow temperatures for a few minutes, they'll take that heat for as long as it takes for me to cut the chips loose.

I figure I'm probably shortening the life of the chips, which is fine with me because they would just get thrown away if I didn't, but are there any other gotchas I should know about?

[brabus]

I've done it a gazillion times, never had any problem.

Obviously you are not going to use those scavenged ICs in a final product, right? So, lifetime is quite not an issue...
I used them just to save some bucks in homemade prototypes, and always worked like a charm.

In any case, I think the most critical moment is the cooling down: if it's too fast, some cracks may easily appear on the case. We are just talking about hypothesis; as I said, for me zero problems.

To be honest, I used a car workshop hot air gun, to be used to heat up the car bodywork in order to fix dents. 
At least, heating was pretty fast! 

[Paul Price]

You should try the highly adventuresome but very effective Chinese parts recovery methods.

You pour a good pint of peanut oil into a large frying pan and slowly heat it to a solder melting temperature and immerse the board within.  Then with a final stroke of bravado, once you can see the solder melting and flowing on the board, you grab the board with a pliers and slam it down on an awaiting Chinese newspaper and all the ICs and all the parts, IC's resistors, etc,  just fall off the board thanks to the G forces. 

I am not kidding. I have seen this done. The parts come out shiny and clean.  Much of the "Pulls" IC's that were available on the web were recovered like this at one time.

Watch out for fires, even peanut oil can catch fire, make sure an exit is handy, and sooner or latter you have to deal with a few small burns, be sure to borrow an asbestos suit and above all, wear gloves and glasses, but you got to do whatcha gotta do to make a buck in this world.

The persons I saw doing this didn't ware anything but an apron.

[Psi]

Just watch the air temp. It's easy to damage/scorch the PCB when using hot air to remove chips.

I find it best to remove all the solder you can first. Then use the hot air to free up the remaining small solder joins so the component can be pulled out.

[eKretz]

Also watch out for those boards that are/were wave soldered. I have been recovering a lot of spares with hot air and the boards that were wave soldered are often a PITA because they glue the parts down before they solder them. Some of the glues stick like a bear even at solder-melting temps. I have had some boards where I thought my temp was off on the hot air because the SMD ceramic resistors and caps wouldn't budge. Turned out I had to use my heavier tweezers and give a sliding/twisting motion to get 'em loose. I discovered that it was the glue after I poked the tweezers into the solder and found it was already liquid, but the parts wouldn't lift off.

[digsys]

IF you have a lot to remove - make yourself a DIL Flute. You can pick up hot-air gun attachments quite cheap and modify them,
or make your own. You're only directing hot air. The idea is to ONLY direct air along ALL the pins ! and at one time.
Turn the PCB upside down, apply a thin smear of flux along the pins (heat transfer is quicker and more even, plus it conditions
any solder that has "gone off" / oxidised). Use a chip-puller on the bottom. ICs will come out faster than you can imagine,
PLUS they'll suffer very little heat stress.

[mariush]

The Hakko 808 is a pleasure to use on through hole stuff, you can see how it works at around 3:30 here:



If you only want to reuse parts for prototyping and not for actual reuse you can use this method :

[duskglow]

I've been using a temperature of 700 degrees with moderate airflow, seems to do the trick nicely.  I haven't baked a board yet.

I think my leasing office wouldn't be happy with me heating peanut oil, so I'll have to stick to this method.

The biggest challenge is that, for some reason, the through hole stuff on double sided boards is nearly impossible to get all of the solder out of, so what I do is heat up the pins so that the solder is melted, and then take a chip puller after it and carefully yank it out.  It takes maybe fifteen to thirty seconds per chip, but the chips come out looking nice.  I haven't tested one yet, though, hah.

[Smokey]

I've been using a temperature of 700 degrees with moderate airflow, seems to do the trick nicely.

I hope you mean 700F. (371C)

That's still a little hot.  At that temp you can damage the PCB and crack chips if you heat them too fast or leave the air in one place too long.  It will melt the hell out of anything plastic real quick too. 

The deal with Hot Air is that doing it right takes WAY longer than you want it to.  You ideally should be following the heat curves for reflow and that just seems like an eternity when you are waving that hot air handle in the air above your board.  I guess this is one of those "no free lunch" things.

[duskglow]

Yes, 700F.

I did crack a couple of chips, so I guess I have a little more experimenting to do.  None of the boards I've been playing on I really care about, so I can afford to make mistakes.

What temperature do you recommend?

[c4757p]

What temperature do you recommend?

I stick to 300C when I'm being careful, 320C when I'm impatient, and 350C when I'm right pissed at the board! 371? 

[duskglow]

What can I say.  That board offended me and it's going to PAY.

[duskglow]

Yeah, that temperature worked better, thanks.  Though I still haven't gotten the hang of removing BGAs yet.

[Psi]

I damaged/scorched a PCB the other day using 360C hot air, but it was quite old PCB and probably more susceptible than modern boards.

Also the IC was soldered to a HUGE ground plane and took a good 60 seconds of point blank air to get the solder to melt.

The area between the IC pins started to discolor and a small bit went dark and chipped off.
Luckily it had no internal layers and no tracks were damaged.

[eKretz]

I usually stick to 300°-310°C (~560°-580°F), although the first time I ran into a wave soldered board with the tenacious glue I was all the way up to 370°C (700°F). There was a lot of damage at that heat level.