I'm having some probs repairing some gear with Si9410BDY SO-8 pkg mosfets in them.
The FET will appear to be faulty - replaced it - still no go......replace it again - it works - WTF!
It's happened too many times to be finger trouble or gremlins. I thought maybe it was ESD - even though I'm working on a grounded mat with a grounded iron. Are they particularly sensitive??
Data sheet:
cheers. D.
in
it
ded
The faster and smaller the MOSFET the more static sensitive it will be but I don't think that that is your problem.
Try putting your DVM on both AC and DC between various "ground" connections on your bench. Any reading over 0.1V is cause for concern.
Your circuit design is probably faulty and you are exceeding the SOAR curves.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
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A simulation, struggling to converge, is telling you something
Maybe your idea of a ring of current mirrors is flawed ?:-)
The very word MOSFET alone should say to anyone in the industry "very ESD susceptible". Remember folks, it boils down to the potential required to breach a single pn junction. These features are pretty damned small.
ESD is now, has been for decades, and should be, a major part of the electronics industry, and I find it ludicrous that some engineers downplay susceptibilities. I have seen the micrographs.. parts that didn't even fail... right away. It looked like an Iraqi roadway.
Proper ESD workstations and handling procedures should always be followed... as a rule... not merely when handling known to be susceptible devices. Even fields can cause failures on parts that haven't been placed yet. Even non volatile parts can build up and keep a charge, and discharge into a susceptible part, so proper procedures should be used at all times to ensure that every step possible was taken to keep all parts at as close as can be to a net zero stored electrostatic charge.
Such tiny stored charges can be all the energy it takes to kill a pin on a sensitive device.
Hey Arch, your living in the dark ages, BGW. You are correct about some MOSFET devices will blow if you just get near them, especially if they have unprotected inputs. The gate on a MOSFET is the most sensitive pin and on these larger devices they look like 10nF to the other nodes. They are rated at +/-20V but can withstand >40V. So your 100pF body must be charged to >3KV to blow the junction. The OP sounds very careful so I am betting, like most others that ESD is not the problem. Cheers,
Harry
However, those are pretty fat devices. Ok, tennis shoes and non-treated tile could still do ESD damage.
SD5400 and similar low capacitance devices are another matter. I had a tech almost throw his coffee mug at me when he swapped a SD5400 four times and I told him it's still damaged. He was sure it was my design until I sat down, soldered one in and everything worked.
What really helps is to make sure that the air in the room doesn't become bone dry. I always make sure I wear natural fiber clothing, cotton and stuff, nothing with mixed in acrylic fibers etc.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
"your"? "BGW"? Bwuahahahahah!
As little as 20V electrostatic charge on a person can blow just about any modern chip made these days. 3kV WILL blow anything. The chip makers that tout resistance to such voltages refer to parts IN CIRCUIT, wired in a specific manner. This discussion is about raw parts, as assemblies are being populated, etc.
Even a "High Voltage Diode" is actually a STACK of pn junctions. A single one of those pn pairs would be susceptible. Being in a stack is what makes it an HV Diode.
In a chip, however, the features are very, very tiny and very, very frail. Far more so than they were back at the advent of CMOS and ESD concerns.
Also, before an FET goes in, especially with a high sensitivity device, merely touching the pins with fingers, grounded or not, and solder iron tips can blow them.
If his iron is not a modern, ESD compliant type, there is no way to know if it is grounded at the tip or carrying a floating AC potential. If he grounds the tip, is he also incorporating the 1 MegOhm series limiter?
We had some transducers that were FET included that had the leads wired together for handling prior to installation, and installation required a specific procedure. Yes, many blew before we decided that indeed, it IS a concern.
OK big parts? Then they are a bit more hardy, but I would still not stress any segment of one.
Even though it is the best choice, cotton and especially the artificial fibers can hold a charge. Cotton simply is not a great generator, whereas the synthetics are huge generators.
When a body is electrostatically charged, the electrons sit on the surface of the insulator. A conducting body, like a person's hand,can build up charge by peeling electrons off of charged bodies. This is all with respect to the "ground" one's ESD workbench and hopefully, the bulk remainder of one's assembly and parts sits at.
One does not have to actually see (read witness) a direct failure off the line to have ESD damage cause a failure later on when the product is in service.
Yes, cotton, and at least 50% RH. Our lab hovers around 60% actually. Smocks abate one's field however, and should also be considered when sensitive devices are utilized. Our smocks have ground leads to the bench, and our smock sleeves connect to our body and that drains us. So we do not need wrist straps, and even our smocks are grounded.
Going barefoot really helps to reduce the ESD issue. In the previous company I worked for, we had a charge meter. It was interesting looking at different things like people and plastic bags. Found a batch of pink poly bags that had static cling.
-- Mark
in
it
grounded
Thus speaks one who only wears shoes when he drives a car ;-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
My simulation, struggling to converge, is telling me something
Maybe my idea of a ring of current mirrors is flawed ?:-)
And only when you drag race? ;-)
--
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There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.
they'd be high heels of course. :)
Thanks for the many replies guys. I have no control over the design (which seems reliable in service), the faults I've got at the moment are the down side of production yeild.
My ESD procedures are reasonable but I'll take a bit more care with the handling and see if that makes any difference. I might make a few measurments as well and see if there are any stray potentials "floating" around.
thanks. D.
in
it
grounded
And watch the shoes. I found that some brands of sneakers can cause a lot of ESD grief so we had straps that go over the heel and bleed charge off into the (treated) VCT floor. Didn't work too well but at least it helped.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
And those track pants made from parachute type material that young guys like to wear..... Spraying chair squabs / backs with a squirt bottle mix of water & fabric softener every now and again seems to help as well.
in
it
grounded
Pink poly only works in properly humidified environments. In dry air, it will not generate a charge, but it doesn't dissipate one either.
They are pretty useless (especially for circuitry) other than that the alternative is the bad poly, so I guess they have their place. I prefer black, dissipative media, or the metallized bags with the bubble linings.
With the new carbon nano-tube technologies being what they are, I am surprised we do not have perfect packaging films and table top mats, etc. for this industry. The old, powder form carbonized media is past its prime.
Breach a single PN junction? Fets die from blown gate oxide.
This is a big part here, with lots of gate capacitance. It's rated for
20 volts on the gate, so its actual zap level is probably many times higher. Most modern power mosfets are hard to zap.It's much more likely that the OP has a bad circuit design than that he has zapped fet gates. But all he has to do is pull one of the "bad" parts and test it.
John
I prefer parachutes above my head, plus one spare just in case :-)
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
What an image: a huge chalk line, a row of contestants crouched in their starting blocks, the gun sounds,... a roar of CLACKing sounds, like a geiger counter gone mad.
The next Olympic sport!
John
here are videos online, if you have the guts to watch them. ;-)
It was a bad 'Saturday Night Live' skit, with one of the Monty Python characters, years ago.
shows of 115,000 hits for drag racing in heels. The BIG question is, could Jim win one of these races? After all, he's always bragging about being the best, and that he likes drag racing. :)
-- http://improve-usenet.org/index.html If you have broadband, your ISP may have a NNTP news server included in your account: http://www.usenettools.net/ISP.htm There are two kinds of people on this earth: The crazy, and the insane. The first sign of insanity is denying that you\'re crazy.
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