Hi guys ,i want to know why does mosfet (150n03)shorted after desoldering it from the board with soldering iron (350°) !!
I test the mosfet before removing it from the board the test is OK, but after removing and discharging the electrostatic from the mosfet it become damaged !!

 

Are you leaving the gate open when testing? It could look shorted in that case. Discharging is not enough. Put a resistor between the source and gate and check for the short again.

 

Are you leaving the gate open when testing? It could look shorted in that case. Discharging is not enough. Put a resistor between the source and gate and check for the short again.

How can i leave gate open ?

 

How can i leave gate open ?

That means it's not connected to anything.

 

Lets try wording it this way: With the MOSFET removed from the board, put a resistor between the source and gate and check for the short again between drain and source. You may have been charging the gate with your ohmmeter depending on sequence of tests. Also the 150N03 is a N-Channel MOSFET and the body diode between source and drain will conduct depending on meter probe polarity. So when testing source to drain, test it as if its a diode. What you think is short may actually be body diode.

 

Certainly "body diodes" can be misleading!! The check for a shorted device needs to use a low enough voltage to not forward bias the diode. REversing polarities should give two different resistance readings if the device is not shorted. Usually!!

 

Mosfet has large input capacitance (few nano Farads). If that "capacitor" is charged, mosfet will be on. In that case drain- source will appear as dead short (milli Ohms). Typical DMM on continuity check has some 3V across probes - more than enough to turn on many mosfets.

When i use multimeter, i prefer to take readings directly, without reaching for parts bin. In this case i simply connect all three leads together to discharge this capacitance, then check drain-source, then charge gate and check drain-source again

 

One additional thought!! If you used a solder-sucker it can EASILY generate a high voltage pulse that will destroy most transistors!! Been there, done that, learned the lesson the hard way. AND it was a bipolar trensistor, not a mosfet!

 

I think you can even short the gate to the source when checking for a shorted source / drain

 

Is there a way to search these forums for some thread about testing this sort of semiconductors SAFELY??? THAT might provide a valuable resource for us!!