Electronics > Repair
Solder IGBT on thick aluminium PCB. Hot air station suggestion?
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_Emil:
Hello,

I'm repairing a tig welder, i have found some bad IGBTs which i will be replacing. But im having trouble desoldering them, and the new ones will probably not survive soldering them ;D The PCB have a thick aluminium backside. I only have a 858D hot air station, so i guess now is a good time to upgrade to something like Atten ST-862D?

I got two IGBTs off but it took way to long time. Used flux and max heat on the 858D. When installing new IGBT, can i use low melt solder or something else to make it easier?

mikeselectricstuff:
For ali. PCBs you really need a hotplate
_Emil:

--- Quote from: mikeselectricstuff on September 28, 2024, 08:34:25 am ---For ali. PCBs you really need a hotplate

--- End quote ---

Thanks! Would a "946C" one work? How would i use it when installing new IGBTs? Preheat with hotplate and use hot air to bring the solder up to melting point? :)
mikeselectricstuff:

--- Quote from: _Emil on September 28, 2024, 08:44:23 am ---
--- Quote from: mikeselectricstuff on September 28, 2024, 08:34:25 am ---For ali. PCBs you really need a hotplate

--- End quote ---

Thanks! Would a "946C" one work? How would i use it when installing new IGBTs? Preheat with hotplate and use hot air to bring the solder up to melting point? :)

--- End quote ---
yes - I have a 946C and it works fine.
No need for hot air
Just put plenty of flux on, prepare the new parts with leads formed and flux on them, maybe a bit of solder paste on the tabs -  hotplate it til the solder melts, pick off the dead ones and plop the new ones on.
(When heating, it helps to push the PCB down onto the plate in the  area to be reworked with a small screwdriver, though probably less of an issue with  ali. than FR4.)
 
Then slide if off the plate to an adjacent metal plate &  let it cool.

As regards temperature, probably better too hot than too cold, so you can get it done quickly - guessing around 300C

The thing about a hotplate compared to hot air is that with hot air, it always needs to be hotter than needed due to losses, so some parts are likely to get overheated. A hotplate just needs to be hot enough to melt the solder , and nothing will get hotter than the plate temp.

If the board has conformal coating then it would be good to remove it with a solvent first if possible- not impossible without doing it but could get smoky and smelly as the coating burns off.
_Emil:

--- Quote from: mikeselectricstuff on September 28, 2024, 08:54:52 am ---
--- Quote from: _Emil on September 28, 2024, 08:44:23 am ---
--- Quote from: mikeselectricstuff on September 28, 2024, 08:34:25 am ---For ali. PCBs you really need a hotplate

--- End quote ---

Thanks! Would a "946C" one work? How would i use it when installing new IGBTs? Preheat with hotplate and use hot air to bring the solder up to melting point? :)

--- End quote ---
yes - I have a 946C and it works fine.
No need for hot air
Just put plenty of flux on, prepare the new parts with leads formed and flux on them, maybe a bit of solder paste on the tabs -  hotplate it til the solder melts, pick off the dead ones and plop the new ones on.
(When heating, it helps to push the PCB down onto the plate in the  area to be reworked with a small screwdriver, though probably less of an issue with  ali. than FR4.)
 
Then slide if off the plate to an adjacent metal plate &  let it cool.

As regards temperature, probably better too hot than too cold, so you can get it done quickly - guessing around 300C

The thing about a hotplate compared to hot air is that with hot air, it always needs to be hotter than needed due to losses, so some parts are likely to get overheated. A hotplate just needs to be hot enough to melt the solder , and nothing will get hotter than the plate temp.

If the board has conformal coating then it would be good to remove it with a solvent first if possible- not impossible without doing it but could get smoky and smelly as the coating burns off.

--- End quote ---

Thanks a lot! I ordered a 946C. Now im just missing solder paste, never used it before. What kind would you suggest? :)
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