Solder IGBT on thick aluminium PCB. Hot air station suggestion?

[_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 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]

For ali. PCBs you really need a hotplate

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]

For ali. PCBs you really need a hotplate

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?

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]

For ali. PCBs you really need a hotplate

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?

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.

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

[mikeselectricstuff]

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

Doesn't really matter - just get stuff that comes in a syringe as opposed to a pot for screen printing, as the  former flows more easily.
 

[CharlotteSwiss]

Couldn't you cut all the pins and then unsolder one pin at a time with the pump? To solder the new ones, it's not the temperature that's harmful, but using a non-antistatic soldering station.

[mikeselectricstuff]

Couldn't you cut all the pins and then unsolder one pin at a time with the pump? To solder the new ones, it's not the temperature that's harmful, but using a non-antistatic soldering station.

No because the tabs are soldered down

[Gyro]

If it's just a single PCB, you could try the frying pan with layer of sand approach. The Auminium PCB would help equalize temperature across the surface too.

[_Emil]

If it's just a single PCB, you could try the frying pan with layer of sand approach. The Auminium PCB would help equalize temperature across the surface too.

Haha i guess that would work. But i already ordered a hotplate

[_Emil]

For ali. PCBs you really need a hotplate

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?

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.

Thanks again, it worked really good using hotplate. I did remove most coating using acetone. Now my welder seems to be working again, it did power on

[T3sl4co1l]

For heating big boards and metal parts, I make an ersatz oven with high-temperature blankets.  (I have some fiberglass batting here, which, isn't exactly the most convenient and pleasant choice, but welding blankets, woven fiberglass, nomex, etc. would be recommendable.)  Even just putting parts on insulation on the table, helps a lot, and further with insulation draped over extended areas of the board (around where you're soldering).

If a hotplate is available, it's an excellent choice for something like metal-core.

Tim