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I usually use hot air gun to solder components on the PCB. However I am afraid of using hot air on SMD LED - they have that clear plastic on top and i am afraid of melting it with hot air, so I usually used two solder irons to place SMD LEDs on the board, which is quite cumbersome.

I have regular solder paste and low-temperature paste (about 125 °C). Would it be safe to use hot air on these LEDs with regular or low-temp paste?

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    \$\begingroup\$ Reflow soldering and wave soldering are things. Just don't violate the recommendations in the datasheet. \$\endgroup\$ – Ignacio Vazquez-Abrams Oct 5 '16 at 4:48
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    \$\begingroup\$ You shouldn't need two irons or even paste for initial placement, just one iron, tweezers and any form of solder and of course flux - do one side and then the other. Rework is a different story, if cloudiness is an issue plan to use new LEDs rather than re-use the removed ones. \$\endgroup\$ – Chris Stratton Oct 5 '16 at 4:52
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    \$\begingroup\$ Hot air is not harmful for SMD LEDs -they can be soldered via reflow soldering method (as we do in the factory). But care must be taken. Please refer to the datasheet. You can find some suggestions (temperature, duration etc) about reflow soldering for the LED. Of course you won't use reflow soldering method but you can have some information about the temperature limits. \$\endgroup\$ – Rohat Kılıç Oct 5 '16 at 5:04
  • \$\begingroup\$ 125C sounds pretty low for solder melt temperature. Since I have never used it before it makes me a bit nervous. \$\endgroup\$ – mkeith Oct 5 '16 at 14:42
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There's no way to be sure about potential damage without knowing the part number of your LED, which is needed to obtain its datasheet. The datasheet will outline the temperature specs of the LED (including max storage temp and max operating temp) as likely also its performance characteristics at various temperatures. I picked three random SMD LEDs from Digikey as a small sample (1 2 - the third is 160-1446-2-ND, but I lack the repu to post the link), and they have operating temps up to 80-85 degrees C. Max storage temp for one is 120C, but the other two max at 85C. Because of this variation, you need to know exactly what the specs of your LED are, but you'll might be cutting it a bit close. Some datasheets outline reflow info for their part, so your best method will be to follow that guide. Personally, I wouldn't be very worried about doing what you're doing as long as you have back up LEDs just in case, but if you don't have extras and/or can't risk damage to the PCB, then you'll do best to check the datasheet for all the info mentioned above.

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I've had mixed results and its reasons like these that I finally built a reflow oven. My experience has been that if I use the hot air at 250 deg celsius more than about 30 seconds the clear lens starts melting. Usually you should be able to solder 0805 sized LEDs with a soldering iron and no need for a hot air gun.

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  • \$\begingroup\$ Guys, Thank you very much for your comments and answers! Great community! \$\endgroup\$ – Alex Zarenin Oct 7 '16 at 0:04

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