I'm training how to use the hot air gun at my hobby electronics station. It's a brand new machine. I can solder easy enough but the hot air gun is well so far only useful for wire shrink tube.

Here's what I do: I turn it on both to 395° Celsius. I use the iron to put solder on the pads, then I add flux before using the hot air and heat the solder ball up, put the part down, and all looks great. Then the part and solder ball comes off the PCB pad. What am I doing wrong?

The PCB is one of those cheap kits on eBay. It has a bunch of SMD resistors and an LED that lights to show it works afterwards. Any tips or demos related to what I'm doing wrong actually any information would be greatly appreciated.

  • \$\begingroup\$ Generally you put solder paste down, put the part into the (cold) paste and then apply heat. The paste will melt and bond to the part once it's hot enough. Alternatively, if you already have solder on the pads, you can put the part in contact with the solder, add flux and then melt with an iron. \$\endgroup\$ Commented Dec 30, 2019 at 21:36
  • \$\begingroup\$ I hope you realize you can solder SMD components with an iron as long as the pins are at the edge of the component. You don't even need to do it one by one or be very accurate. You can just drag the bead of solder on the iron after applying flux along the pins. You only really need hot air if the pad is under the component. \$\endgroup\$
    – DKNguyen
    Commented Dec 30, 2019 at 21:38
  • 3
    \$\begingroup\$ Sounds like you're not heating up the board enough. If the pad on the PCB is cool, the solder won't stick to it. Just heating up the solder by itself will not suffice. \$\endgroup\$
    – SteveSh
    Commented Dec 30, 2019 at 21:38
  • 1
    \$\begingroup\$ If you could add some pictures, it might help us to visualize what's wrong. \$\endgroup\$
    – rdtsc
    Commented Dec 30, 2019 at 22:22
  • 1
    \$\begingroup\$ Sounds like you have the air temperature a bit high and are getting surface oxidation unmitigated by flux. Things will not "look good" and then fail - looking good means that the solder spreads out and flows, if there is still a "ball" sitting on the pad it has not really bonded at all. \$\endgroup\$ Commented Dec 31, 2019 at 2:50

1 Answer 1


I was mimicking what I seen in youtube videos when it comes to replacing SMD components. I add solder to pad since this uses the flux I then add-flux grab the part heat the solder lay part down then it looks ok and then after it cools the part and solder slide of the pad it loses it's weld and i don't know why

I don't know what videos you saw, but it seems you are doing everything backwards.

You don't need flux if you are using solder paste, but if you want to use it you apply it either before solder paste (to prepare pads) or after soldering (to repair bridges).

You don't heat solder before placing the part. First you apply solder paste to pads, then place the part into cold paste (you can warm-up component before placing, but it is not necessary). Then you heat the board and component evenly and gradually. When paste changes its appearance (releases flux) you bring heat gun closer and wait till solder melts and part pins "sink" into it. Then remove heat gradually but without delay.


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