Recently I ordered some tiny SMD MOSFETs (AO3400) I never paid any attention to ESD. After soldering several MOSFETs on SMD to DIP conversion boards for prototyping I noticed they didn't function correctly after some searching I found out that it is because of ESD.

I understand the gate pin is the most sensitive but what about drain and source, how does the sensitivity different pins compare? if I finally solder them on PCB and the drain is to be an output (to be connected to LED strips) do I have to provide ESD protection for this pin? What about touching the board? Is putting some glue or epoxy on the MOSFET any good?

  • \$\begingroup\$ After it's soldered it's less of an issue. I prefer to buy protected MOSFETs for hand-soldering, i.e. with built-in ESD diode. Plenty exist. \$\endgroup\$
    – Fizz
    Nov 11 '15 at 21:28
  • 2
    \$\begingroup\$ Always touch the antistatic bag first then take out the mosfet and place it on top of the bag. Handle the bag first and last and things shouldn't really go wrong. When holding the mosfet touch the target board with your other hand and place the FET on the board. Don't solder in the close presence of van der graaf generators or active tesla coils. \$\endgroup\$
    – Andy aka
    Nov 11 '15 at 22:09

If you exceed the Vgs voltage given in the datasheet, you can blow through the gate insulation layer. You will never feel 200V of static charge, but it will ruin a MOSFET. As Respawn pointed out, they are not as sensitive after being soldered in because there are other places for charges to go besides right through the FET.

If you're going to be working with stuff like this a lot, you'll probably want to set up an anti-static mat, get a wrist strap, and reduce influence from carpet and clothing while you're building the PCBs.

And always transport your boards in metallized mylar bags!

  • \$\begingroup\$ Thanks for your reply. So if I manage to solder the MOSFET on the PCB without damaging it do I have to worry about the drain (output) pin? A stripped wire may be hanging from it and may be touched frequently. \$\endgroup\$
    – ahmadx87
    Nov 12 '15 at 13:14
  • \$\begingroup\$ If you expose wires to the outside world like this, it's best practice to include varistors or clamping diodes or transorbs or something like that (as appropriate) to help shunt ESD away. \$\endgroup\$
    – Daniel
    Nov 12 '15 at 23:29

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