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I set my hot air device to 320 °C and at 20% flow. Using low melt solder paste it takes quite some time to desolder BGA chips which I think get singed! Increasing to 400 °C is faster but the tiny components nearby get singed.

Can someone experienced with hot air stations suggest settings for me?

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  • \$\begingroup\$ Welcome! Do you use enough flux? \$\endgroup\$
    – Hans mitm Flammenwerfer
    Commented Dec 18, 2023 at 9:30
  • \$\begingroup\$ @HansmitmFlammenwerfer. First flux, then the solder paste ... \$\endgroup\$
    – Omowright
    Commented Dec 18, 2023 at 9:34
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    \$\begingroup\$ It's not uncommon to use shrouds to protect nearby smaller components. \$\endgroup\$
    – Arsenal
    Commented Dec 18, 2023 at 9:51
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    \$\begingroup\$ You could try preheating the board to a little under 200C, then get in as close as you can with a slightly higher temperature \$\endgroup\$
    – Frog
    Commented Dec 18, 2023 at 9:55
  • \$\begingroup\$ I am grateful for the suggestions about preheating and the shroud. I will start preheating to 120C (because of the low melt solder). I used to shroud with aluminium foil but other components got hot. I now intend to use heat resistant tape. \$\endgroup\$
    – Omowright
    Commented Dec 18, 2023 at 12:33

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I'm not saying it can't be done without, but I would really recommend a board pre-heater.

These devices apply lower, non-soldering heat to the whole board to make it easier to reflow the solder. If you consider that the room temperature might be 20 deg C, and you need to get the solder in excess of 210 deg C that's a big jump. All that heat having to come from one hot air source makes it very difficult to get the solder you want - particularly solder that's underneath a chip that will insulate it - hot enough without damaging it.

Whereas if you preheat the whole board, even just to 100 deg C, it's much easier to apply the hot air gun, because you need to use a lot less heat. You can go higher on the preheat if you like, just be mindful of what else is on the board and whether this will be a problem.

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  • \$\begingroup\$ I will henceforth preheat the whole board which I hadn't thought of before. I cannot afford the larger size preheaters and will thus use the hot air handle, checking the temperature with a laser thermometer. \$\endgroup\$
    – Omowright
    Commented Dec 18, 2023 at 11:20
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    \$\begingroup\$ Sure it's nice to have a separate preheater, but even doing a preheat with the gun can help a lot. I've been using a relatively cheap £100 unit for my preheat for a few years now, so you don't have to spend too much if the budget becomes available later. \$\endgroup\$
    – LordTeddy
    Commented Dec 18, 2023 at 11:23
  • \$\begingroup\$ +1 for this. Preheating the board really works wonders. \$\endgroup\$
    – feynman
    Commented Dec 18, 2023 at 19:26
  • \$\begingroup\$ Usually really nice hot air BGA stations will come with a preheater (it's not really a preheater though, it's more of a bottom heater you turn it on while you're doing the hot air work) \$\endgroup\$
    – Voltage Spike ♦
    Commented Dec 19, 2023 at 6:54

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