Ruining mosfets with a transistor tester and tweezers

[Phil1977]

Have you ever checked the FETs function with something beside the little but mighty 328 tester?

I often experienced that high power semiconductors are not well recognized while nearly all small signal devices are.

[David Aurora]

What did I do wrong?

so I bought myself two kinds of mosfets (or "MOSFETS" if you like) on AliExpress.

know, I know - those are not the real thing and they are not up to specs (if working at all)

I rearranged it a bit so it's easier to follow

I know this post pissed the OP off, but it couldn't be more on the money.

While it is definitely a great idea to delve into good handling practices or try to understand potential causes of failure like you're doing, at the end of the day the only smart move is to buy some legitimate, known good devices from a reliable source so you can at least confirm if it's a testing problem or a dud parts problem.

To use an analogy, right now it's like you're saying "I found some discount sushi at a petrol station and ate it for lunch. I got sick. Was this because it was rotten or because I have gastro?". Either is possible, one is more probable, the smart move is to eat something fresh for dinner and see how you feel in the morning.

[magic]

Bullshit.

Any MOSFET without gate protection will fail under such testing.
For instance, any "honest and true to the original" 2N7000.

[DimitriP]

Any MOSFET without gate protection will fail under such testing.
For instance, any "honest and true to the original" 2N7000.

Not to split hairs, but he had no issue with the 2n7000s he tested.

[Phil1977]

Bullshit.

Any MOSFET without gate protection will fail under such testing.
For instance, any "honest and true to the original" 2N7000.

Be carefull saying BS, it could easily fall back on your art of typing letters...

Unprotected MOSFETS may be easily damaged by this handling. But even then they don't fail when tested in the transistor tester. They may never fail, or the chance of failing e.g. at high temperatures during a voltage spike from the AC Net raises.
Companies spend billions on ESD safety not because the components *directly* fail as soon as some employee looks at their box without ESD-certified glasses.

They may fail long times later. And believe it or not, for most companies that´s worse than failing before EOL.

For tinkering reasons I sometimes ordered cheap Low-RDS-on FETs from little sellers on AliExpress. They arrived in a *normal* plastic zipbag, without tape or any ESD-protection. Their solderpads and housings clearly indicated they have been -probably manually- recycled from some scrap electronics.
Most of these FETs were operational in the tester. Some of them failed during my tinkering - because of ESD? No one knows. But it would be criminal to use parts of this type for any high quality product that requires a certain reliability.

[shapirus]

But even then they don't fail when tested in the transistor tester.

...unless a damaging potential is created across the gate isolation layer.

[Phil1977]

But even then they don't fail when tested in the transistor tester.

...unless a damaging potential is created across the gate isolation layer.

No. If the gate isolation is damaged but still functional the tester won't notice anything. The damage may result in a failure a long time later.

If you find a way to detect ESD damage before failure you can easily get billionaire.

[shapirus]

No. If the gate isolation is damaged but still functional the tester won't notice anything. The damage may result in a failure a long time later.

I misunderstood what you meant, then. If you meant that a partially damaged transistor may still be recognized as good by a transistor tester, then yes, I agree.

I thought you were saying that transistor testers don't damage transistors.

[Phil1977]

Yes, okay, now I got you right, sorry for the misunderstanding.

Anyhow it´s always good to be clearly aware of the difference between "potentially damaged" and "failed". Even in industry I sometimes experienced people who said this part was ESD-mishandled but it´s working fine, so we had good luck and nothing has happened. That´s just dangerous.

[magic]

It's not ESD damage, it's 100μA or more of AC current pushed through the gate continuously for a meaningful fraction of a second.

It's absolute nothing for any device with built-in ESD protection, but unprotected discrete MOSFETs are destroyed immediately and for good. I personally blew a few 2N7000 and some other type I forgot this exact way (except it wasn't the transistor tester but other circuit powered by a wall wart). The outcome was the same - fairly low resistance between source and drain, permanently.

[Phil1977]

It's not ESD damage, it's 100μA or more of AC current pushed through the gate continuously for a meaningful fraction of a second.

It's absolute nothing for any device with built-in ESD protection, but unprotected discrete MOSFETs are destroyed immediately and for good. I personally blew a few 2N7000 and some other type I forgot this exact way (except it wasn't the transistor tester but other circuit powered by a wall wart). The outcome was the same - fairly low resistance between source and drain, permanently.

No need to argue about that, but the thread initiator asked if just handling with bare hands and tweezers makes a FET instantaneously going to heaven. That´s hardly plausible.

Of course, a 110V-AC-0.5mA source (like typical wall warts relative to ground) can be FET-lethal - especially for the small devices with low Ugs-rating.

EDIT: I´ve just read that the OP has used the transistor tester while powered from the wall wart. In that case, I suppose he has destroyed the TO220-power-transistors by an AC current from the wall wart over the cooling tab through his body to earth. The 2N7000 may have survived due to their plastic case that easily withstood this comparatively low voltage... Just as a possible explanation.

EDIT2: If possible, always use these transistor testers battery powered. This parasitic power supply current may also be quite dangerous for the 328-tristate-inputs and last but least it´s just a source of noise that just can be avoided.

[VSV_electron]

Thank you all for your helpful replies and detailed discussion on the subject. So much to learn!
By the way - It's good that those were budget Ali MOSFETs, not the real expensive ones