Transistor ESD detector

[zappedagain]

I remember reading a while back about a transistor that has a very consistent breakdown voltage. I believe it a was around 150V so it was handy to build into a circuit to monitor if an ESD event had occurred (if it is blown your trace experienced ESD). I vaguely remember it being a Fairchild part but don't remember the part number. Does anybody know of this part or have any other recomendations for an ESD detector? Thanks.

 

[IRstuff]

The BVceo of a transistor is usually not a permanent damage threshold. Permanently damaging your "monitor" is a poor solution. Additionally, killing the transistor tells you nothing about whether what you're monitoring damaged anything else or not. Additionally, you'd need to remove the part to test whether it was damaged and by how much.

If you know the situation well enough to put a monitor there, you can put a ESD discharger there as well to ensure that no damage occurs whatsoever.

If you want an ESD monitor, you do a websearch for one:

http://www.gotopac.biz/index.asp?Pa...=esd monitor&OVKEY=esd monitor&OVMTC=standard

There are literally dozens of choices. 3M sells a cheap alarm monitor for about $80:

http://www.gotopac.biz/index.asp?PageAction=VIEWPROD&ProdID=8447

TTFN

 

[jraef]

I've never done this myself, but I've heard of putting a fuse link in series with a transorb, so the link only melts when the transorb has conducted. So theoretically if you have a trace that can handle 10V, and you put in a 10V transorb with a fuse link, if the circuit gets hit with a 30V ESD pulse the transorb conducts it to ground through the fuse link, and if it's enough current, the link melts. Of course once it does, that transorb is out of the circuit so you would need to have more than one. Maybe at different voltage limits, i.e. 8V with the fuse link, 10V without so there is still protection after you have been hit? Like I said, I have never done it, just had it explained to me once.

I've never heard of a single device like you describe though.

 

[IRstuff]

At that point, you might as well use a zener or an SCR, like they do on the chips themselves. Which brings up another issue altogether, which is that most ESD sensitive chips already come with ESD protection.

TTFN

 

[zappedagain]

it - Thanks for the link. The beauty of this transistor that I'm searching for is that you can place one on the board and then run it through your entire process (ovens, assembly, packaging, etc.). Even though everyone states their station is ESD safe, if a device is blown at the end you know something is out of compliance.

 

[IRstuff]

That's sort of closing the barn door after the horses have escaped. If you've blown a device, you've also wiped out a sizable amount of WIP, which is way more expensive that a transistor and probably way more than the instruments needed to properly monitor the ESD conditions.

While the approach is interesting, the point at which you determine that you've had a problem is too far downstream to make immediate corrections and salvage the production.

TTFN

 

[waross]

I don't think that a transistor just sitting on the board is going to be usefull unless it is connected to the circuit.
If you are having a problem with failed boards at the end of the manufacturing process, then that is your indication of ESD. Don't jump to the conclusion that a work station is causing the problem. Do you check your components before installing them? Remember that it is probably more likely that ESD damage is done handling and/or transporting the boards from station to station than during the process at the stations.
However, don't be discouraged in your approach. While experience suggests that this may not be the best aproach, many of us gained our experience by trying something that turned out to be not the best approach. Even though we may not have always solved our immediate problem, we almost always learned something that was valuable sooner or later.
yours