Soldering MOSFET tab


 
What I do is to put some solder on the pad and some on the back of the mosfet. Make sure you have the legs bent correctly. Once you have the mosfet on the board take something to lift the HM off the work table. I use my cutters and also have something to push down the mosfet. Heat up the solder with the iron along the edge and push down at the same time. You will know when it's melted as solder will get squished out and hold it for atleast 30 seconds to make sure it's has cooled.
 
Steve, the instructions say it is not required if you are using the standard blower... which I am not. John, thanks for the answer! Couple follow ups before I give it a go? when you say "put some solder on the pad and the mosfet", do you mean take the solder in its solid state and use some flux paste to get it to stick, or do you mean to melt some solder onto the tab and onto the board, then heat it up to the point it melts?

Also, how many watts is your soldering iron to do this? I'm working with 40 watts. thanks.!
 
I just take the solder and soldering iron to each nothing else. As for wattage, as long as it's able to melt the solder in a fairly quick time then you won't have any issues. My solder iron is set to 400° or so, not sure of wattage. It shouldn't take much solder on either. I just put enough to cover the pad(just a little goes a long ways) and a drop on the part. It's takes a few. seconds to melt them. There shouldn't be any damage to the part as it's designed to take alot of heat.
 
RalphTrimble said:
I wouldn't do it, no need, you're just opening the door for complications IMHO.
Click to expand...

The tab is there for a reason. I've never had any issues soldering the tab, and do similar to John's procedure. If you ever decide to use a larger fan, you may need the heat dissipation.
 
Thought I should chime in here since the MicroDamper doesn't use the standard blower. I haven't bothered soldering the mosfet tab and have zero problems, just in case you MD people would like to know.
 
There is no harm in doing it, that's what it's there for. It helps to even out the heat on the board. There is absolutely no reason not to do it.
 
No reason to do it, the Mosfet isn't gonna over heat driving this blower or even one quite a bit larger. The tab is there to contact a heat sync, I don't see the logic behind transferring heat to the circuit board, that's not where you want the heat to go.... and typically they are held to the heat sync using some sort of clip rather than actually soldering. If you ever have to troubleshoot the blower circuit good luck getting the MOSFET off without damaging the board. So I still say don't bother, could cause more harm than good.
 
Last edited:
RalphTrimble said:
No reason to do it, the Mosfet isn't gonna over heat driving this blower or even one quite a bit larger. The tab is there to contact a heat sync, I don't see the logic behind transferring heat to the circuit board, that's not where you want the heat to go.... and typically they are held to the heat sync using some sort of clip rather than actually soldering. If you ever have to troubleshoot the blower circuit good luck getting the MOSFET off without damaging the board. So I still say don't bother, could cause more harm than good.
Click to expand...

Good point. Never really thought of it that way.
 
But the heat sink is the ground plane. The Eagle cad part is is designed for the grounding tab. Virtually all mosfet of this type are grounded to the ground plane.
 
The tab on the mosfet is connectedto the drain leg, which is +12v, not ground. The small copper pad on the PCB can hardly be considered a heat sink.
 
John Bostwick said:
But the heat sink is the ground plane. The Eagle cad part is is designed for the grounding tab. Virtually all mosfet of this type are grounded to the ground plane.
Click to expand...

Right, and why would you want to transfer heat to your boards ground plane? Generally a heat sync is something with fins, sometimes just a curly piece of metal that clips on the transistor and floats in air... The key point being it transfers heat AWAY from the board.
At any rate, I feel a heat sync is not needed at all, if you're worried about heat you'd probably be better off standing the mosfet up straight rather than pressing it against the board.
 
You must log in or register to reply here.

 

Back
Top