Hot air tip- Desoldering SMT parts - diyAudio
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Old 18th January 2003, 02:35 AM   #1
Dave is offline Dave  New Zealand
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Default Hot air tip- Desoldering SMT parts

Has anyone tried desoldering SMD chips (ie 28 pin SSOP) with one of those hot air tips you can buy with some portable gas soldering irons?
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Old 24th January 2003, 09:25 PM   #2
Dave is offline Dave  New Zealand
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Any other ideas?
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Old 24th January 2003, 10:04 PM   #3
haldor is offline haldor  United States
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Are you going to try to reuse the chip? Also are there any other surface mount components near the chip? I've had pretty bad luck using an SMT hot air soldering pencil to remove anything bigger than a cap or resistor. Other parts tend to get blown off the board along with the part I wanted to remove.

At work I have a hot air SMT rework station that you put different tips on depending on the kind of chip you are removing (SO-8, quad flat pack, PLCC, etc). The tip includes shields on the sides to deflect hot air away other parts and includes a suction cup to pull the part off after the solder is melted. Works great, but very pricy ($3000 US).

Depending on your soldering iron you can get SMT tips that heat all the pins at the same time and make it possible to remove a chip that way. I have an SO-8 tip for my Hakko 936 soldering station. It's ok for removing parts, but I wouldn't trust it for installing them.

Depending on the kind of lead on the part, the safest way to remove an IC is to just cut the leads off the chip and then remove each lead individually. Much less chance of damaging the PCB that way.

For gull wing leaded parts, I have had good results using a dental pick and a fine tip soldering iron. Just start at one end, slip the point of the dental pick behind a lead, melt the solder under that lead with the iron and pry it up from the board with the dental pick. Repeat until all the leads are free. Afterwards go over the SM pads with solder wick to clean it up. It's even possible to reuse the chip afterwards, just bend the leads back into their original position.

Phil
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Old 24th January 2003, 11:17 PM   #4
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Default Been Using One For Years.

Weller have a hot air attachment for the Pyropen Junior that has an exhaust nozzle about 2mm diameter, and these are fine for removing smd chips.
It takes a little practice to get the temperature right and not blister the pcb.

Eric.
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Old 26th January 2003, 08:07 PM   #5
Dave is offline Dave  New Zealand
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At the moment I don't need to reuse the part. Just get it off without damaging the board. I fugure a gas iron would be the easiest to get hold of.

Has anyone else had any experience with these hot air nozzles?
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Old 26th January 2003, 08:40 PM   #6
Elkaid is offline Elkaid  Canada
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I've worked with hot air stations but I would suggest using standard "forks" that fits on any standard soldering iron.

They're pretty cheap and does a correct job.
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Old 26th January 2003, 09:05 PM   #7
hifiZen is offline hifiZen  Canada
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Or you can try a heat gun instead. One like this will do the trick very nicely for larger ICs, even 208-pin PQFPs and such. The airflow velocity is not so high, so parts don't get blown off the board. But, the most important thing is that they're temperature controlled, so boards won't blister easily (set the temp to around 650-700F for desoldering). In fact, I've never had a problem with blistering when using one of these heat guns. Don't forget to apply some liquid flux to the pins of the device you want to desolder before you heat it. This will improve heat transfer and the final result when removing the chip. Use a dental pick or fine tweezers to gently lift at the edge or corner of the chip while you heat it up. As soon as the solder's molten, it will immediately become completely loose, at which point you can pick it up with a vacuum tool or tweezers. I use a gun made by Ideal Industries, and it does a splendid job. There are also ESD protected versions available, and the tool is relatively affordable.
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Old 26th January 2003, 09:14 PM   #8
hifiZen is offline hifiZen  Canada
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Also, if you want to shield adjacent parts from the heat, you can use aluminum foil, and build a custom-fit shield, though I've never found it necessary to do this. A good heat gun will work just as well as one of these expensive rework stations, if you are attentive to your work. The only difference is that you have to lift the chip manually, rather than having the built-in vacuum pick-up.

Another valuable piece of advice I have is to start heating the board gently from several inches away, and not to let the hot air source get too close to the board. The closest I ever get the nozzle to the board is around 1 inch, and that's after it's had some time to warm up at a greater distance. It doesn't take long to get the hang of it, but you may want to practice on some scrap PCBs first.
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Old 26th January 2003, 09:33 PM   #9
Nisbeth is offline Nisbeth  Denmark
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Remember if you use something like a Pyropen Jr. that some hot air exits to one side. If you pull the pen along the pins of a chip you risk turning the pen without knowing it and so damaging other components near by. Heatshielding is greatly recommended. (No, I have never actually destryed any components myself, but I removed all the hair from my left forearm once )

/U.
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Old 26th January 2003, 10:52 PM   #10
mirlo is offline mirlo  United States
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Default not quite what you want, but still interesting

http://www.usbmicro.com/apps.html

This is a SMT soldering pencil made from a cheap radio shack desoldering iron and an aquarium pump.
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