Mosfet removal

[JorgeHernan]

Does anyone know how to remove motherboard mosfets i tried soldering iron but it is impossible and almost caused damage to the board.Thanks in advance

[PCBONEZ]

Re: Mosfet removal

I lift and bend up the little legs first and then work on the heat sink part.
- For the heatsink side.
I use something for a grabber to latch on to the MOSFET.
Can't do much pressure in grabbing or you might crack the casing. Make a mess.
Solder iron in one hand applied to the heatsink.
Grabber in the other hand.
When it comes free lift.

Grabber could be tweezers, mini-needlenose, hemostat.

Other folks may have a better way.

.

[JorgeHernan]

Re: Mosfet removal

I lift and bend up the little legs first and then work on the heat sink part.
- For the heatsink side.
I use something for a grabber to latch on to the MOSFET.
Can't do much pressure in grabbing or you might crack the casing. Make a mess.
Solder iron in one hand applied to the heatsink.
Grabber in the other hand.
When it comes free lift.

Grabber could be tweezers, mini-needlenose, hemostat.

Other folks may have a better way.

.

Yes.I was searching for mosfet removal on google and found some info .Someone said he used hot air gun. that would be interesting.The problem is what kind of what temperaure etc?

[PCBONEZ]

Re: Mosfet removal

I don't do it that way so I don't know.
Seems that might melt loose nearby SMD parts though.
Be careful.

[Harvey]

Re: Mosfet removal

Use plenty of solder too - lots on the tip of the iron and lots on the heatsink tab. Then apply lots of heat, wait, wait a bit more and it'll come off.

Remember the board will get hot though, so give it a few minutes to cool down before moving onto the next mosfet.


Hot air works if you have a small nozzle and lots of control over heat/air flow, but I always find it easier with a soldering iron.

[davmax]

Re: Mosfet removal

A broad hot air gun will cause problems with surround components.

It is important to use a high powered soldering iron 50 watts or more. The heat energy is removed fast by the MOSFET heatsinking. Use plenty of fluxed solder.

[Brian C]

Re: Mosfet removal

My method is...
(1) lift up and bend the 2 little legs as mentioned by PCBONEZ. or cut it off.
(2) heat up the the MOSFET area using hair dryer for 10~20 seconds.
(3) use high power soldering iron to remove the transistor.

Hot air gun is a better choice. But do not set too high air-flow as it may damage the surrounding components.

It depends on the MOSFET package. DPAK is easier to work with as compared to D2PAK.

[PCBONEZ]

Re: Mosfet removal

Hmmm,
Hot air for a pre-heat...
That's a really good idea Mr Brian.

.

[davmax]

Re: Mosfet removal

Remember heat kills electrolytics and if a hot air gun was raising temp to 260C it would be bad news for cap.

[starfury1]

Re: Mosfet removal

I did a reply to this more detail but lost it cause FF went west on a page I was trying to open
I agree with the above posts on the pro and cons

the biggest problem is getting a lot of heat into the tab to melt the solder but without exposing everything else to a lot of heat.

pre heating isn't a bad idea its just controlling it
Still I don't recommend blasting away with something like a paint stripper....maybe a hair dryer as above
(the idea being to warm up the component and immediate area)

I suggest you use a flat broad type soldering iron tip (chisel not a conical tip)
Make sure its clean and put some solder on it then put it on the tab adding a bit more solder
the extra solder will help with heat transfer
(and thats what your after good thermal contact to conduct the heat and melt the solder)
Then use tweezers or small pliers to grip the body, as soon as you feel it float free lift it off

If you are sure the MOSFET is dead I'd just cut the legs near the case with nippy cutters
(being careful not to cut into the PCB)

If you are wanting to remove one for testing..."as above" free the legs first before going for the tab.

Its easy to remove the legs once they are free of the body with a LOT LESS risk to the solder pads
(same thing thought clean tip smidgen of solder to the tip for better heat transfer, you wont need to add extra thought...well if you get the smidgen right)

clean up excess with solder wick when component is gone

adding extra flux will cause the solder to ball on its self which helps.
(I think its a case of too much solder does a bad joint make)

There are tools you can get for this type of work, like these here

I have used these to remove mosfets,
they do make it a little less painful.
BUt $$$$

So try the above ideas on junk MB's if you got some
you should practice on some really...
as you say the last thing you want to do is damage the PCB

It shouldn't take long to get a feel for it
how will heat is conducted to and away will probably determine how long it takes
which is why you need a nice hot iron with good thermal inertia
(heat sink effect cooling the tip off)

HTH

Cheers

[davmax]

Re: Mosfet removal

Small point Starfury. The MOSFET does not need to be removed for testing, just lift the two leads. This will minimise temperature stress if the device is still good.

[starfury1]

Re: Mosfet removal

yeah True ...thinking cap wasn't on
thinking more of discrete size transistors when it was easier to remove them for more through testing.

Mosfets tend to fail in a more catastrophic way. like short and burn the place down ok maybe not that bad but I've known them to claim quite a few PCB's in my time (not sure on MB side of things thought)

Thanks davmax for the correction there

Cheers