TAPR TICC boxed
On Sat, 8 Apr 2017 16:30:38 -0400, you wrote:
David wrote:
I mentioned this in connection with some manufacturers using gold
doping in transistors which would not normally be expected to have
gold doping. So you end up with a bunch of lessor named 2N3904s which
meet the 2N3904 specifications but are useless if you were looking for
low leakage diodes.
I believe all 2N3904s and 2N3906s are gold doped. National's certainly
were (Processes 23 and 66), and TI's and Fairchild's are. Not heavily
doped, like 2N2369s (with storage times of ~20nS), but just enough to
bring the storage time down to ~100nS. 2N2219s, 2N2222s, and 2N4401s
are also lightly gold doped.
I ended up qualifying 2N3904s based on manufacturer and lot and I
think we ended up using ones from Motorola. I wish detailed process
information like National had was available from every manufacturer.
What was funny was when we did this, the lower frequency transistors
that I tested like the 2N5088/9 were much worse.
If [4117 leakage is] not being tested, then where is the maximum specified
leakage number coming from? For a small signal bipolar transistor it
will typically be 25nA, 50nA, or 100nA, but the InterFET datasheet (1)
shows 10pA maximum and 1pA maximum for the A versions.
* * *
When this discussion of low leakage input protection started, I did a
quick search for inexpensive alternatives to the 4117/4118/4119 JFETs
and came up with nothing; all of the inexpensive JFETs are much worse
Same as any "guaranteed by design" spec -- by the device design. The
4117 series is unlike any other JFET -- the geometry is TINY, and the
4117 Idss is only 30-90uA (hundreds of times lower than other low-Idss
JFETs). [BTW, lowest Idss is why I recommend the 4117 over the 4118 and
4119 for use as a low-leakage diode. The 4118 and 4119 have higher Idss
-- up to 240uA for the 4118 and 600uA for the 4119 -- and tend to have
higher gate leakage, as well.]
Best regards,
Charles
If the 10pA specification is guaranteed by design, then wouldn't they
have to be testing the 1pA "A" parts?
Hi
If anybody gets into this sort of thing in the future — There are black / optical
blocking die coat materials out there. They are silicone based and quite stable.
We used a lot of the stuff on watch modules after it was discovered that the
watch died when exposed to a heavy dose of sunlight (right through the LCD
and into the chip … poof!!)
Bob
On Apr 9, 2017, at 1:10 PM, David davidwhess@gmail.com wrote:
I have run across the conductive carbon filled plastic problem before.
We did not actually use just paint. We took black mastic electrically
insulating tape, dissolved it in thinner, and painted the parts with
it. It dried to form a pliable black coating.
On Sat, 8 Apr 2017 17:49:01 +0000 (UTC), you wrote:
You need to be careful how you paint the package black. My first electronics job was in a place that made, among other things, mass spectrometers. We made very high input impedance electrometers for the mass specs using TO-5 can mosfet transistors. One batch was found to be very photo sensitive through the glass/ceramic lead interface. Someone had the idea to spray paint the bottom of the package with black paint. Not a good idea. The black paint, likely loaded with carbon, decreased the electrometer input impedance by many orders of magnitude. Considering that our electrometers had an input impedance of 1E-12 to 10E-15, even a fingerprint made a huge difference. The carbon filled black paint was practically a short.
Maybe an overcoat with silicone or some other type of low leakage sealant, then the black paint?
Tom
From: David davidwhess@gmail.com
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Saturday, April 8, 2017 10:00 AM
Subject: Re: [time-nuts] TAPR TICC boxed (input protection)
On Fri, 7 Apr 2017 01:06:17 -0400, you wrote:
....controlling the offset voltage.
We ended up painting the diodes black after soldering.
I have also heard of it happening with metal TO-18 packages through
the lead interface under the package.
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There are other ways that light can cause unexpected behavior.
In 1983 I worked on a process control system whose maiden installation
was in a corn processing plant, with lots of big valves and motors being
controlled. The cards that did A/D and D/A conversion of control signals
had UV erasable EPROMs for their microprocessors. There were a lot of
those cards.
One day the plant operators began complaining about the equipment
misbehaving on a large scale. The problem went away when the guy taking
flash pictures of our equipment stopped taking pictures.
We put black tape over the UV lenses.
Ob timenuts: This system later had a pulse frequency input card that I
connected to the power line. Used the operator's trending display for
process variables to watch line frequency change over time. It also had
pulse outputs, and a little work got it to play "Daisy, Daisy" like HAL
9000 in "2001: A Space Odyssey."
Bill Hawkins
-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces@febo.com] On Behalf Of Bob
kb8tq
Sent: Sunday, April 09, 2017 1:34 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] TAPR TICC boxed (input protection)
Hi
If anybody gets into this sort of thing in the future - There are black
/ optical blocking die coat materials out there. They are silicone based
and quite stable.
We used a lot of the stuff on watch modules after it was discovered
that the watch died when exposed to a heavy dose of sunlight (right
through the LCD and into the chip . poof!!)
Bob
David wrote:
I ended up qualifying 2N3904s based on manufacturer and lot and I
think we ended up using ones from Motorola. I wish detailed process
information like National had was available from every manufacturer.
It is, if you ask the process engineers for it. (From the Big Boys,
that is. These days it seems discrete devices are being fabbed by
dozens of "garage" operations. I can't speak for them, and wouldn't
think of buying product from them.)
Best regards,
Charles
David wrote:
I ended up qualifying 2N3904s based on manufacturer and lot and I
think we ended up using ones from Motorola. I wish detailed process
information like National had was available from every manufacturer.
It is, if you ask the process engineers for it. (From the Big Boys,
that is. These days it seems discrete devices are being fabbed by
dozens of "garage" operations. I can't speak for them, and wouldn't
think of buying product from them.)
Best regards,
Charles
David wrote:
If the 10pA specification is guaranteed by design, then wouldn't they
have to be testing the 1pA "A" parts?
That assumes the parts are produced by exactly the same process, which
is very often not a safe assumption. One of them may undergo extra
process steps, for example, or one or more process steps may be
modified. That's not at all uncommon, BTW -- "A" versions are often the
product of process tweaks, not selected "non-A" devices.
Best regards,
Charles
Hi
On Apr 11, 2017, at 7:05 AM, Charles Steinmetz csteinmetz@yandex.com wrote:
David wrote:
I ended up qualifying 2N3904s based on manufacturer and lot and I
think we ended up using ones from Motorola. I wish detailed process
information like National had was available from every manufacturer.
It is, if you ask the process engineers for it. (From the Big Boys, that is. These days it seems discrete devices are being fabbed by dozens of "garage" operations. I can't speak for them, and wouldn't think of buying product from them.)
If you dig into where your simple discrete part was made, you might be surprised. That’s even true of outfits you would
consider to be a “Big Guy” from days gone by. The real answer to selection today is to buy the automotive part.
That’s about the only thing anymore that locks down the sourcing, testing, and the process. If you buy a “normal” part,
it might have been made anywhere by just about any process. Yes, that’s scary and it raises a lot of questions. It is
a change that has happened over the last decade or two without a lot of publicity.
Bob
Best regards,
Charles
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Hi
Testing can mean a lot of different things. Did they test every single part they shipped for every parameter?
Did they just do a sample of parts and decide the lot was good? Did they test a sample of parts for a sub-set
of the specs and decide they were good? Did they test them after packaging or at the wafer level? Did they test
a completely different (but much easier to test) part at the wafer level and decide the whole wafer was good? Did
they test one wafer out of the batch and decide the rest of the day’s production was good?
The further down that list you go, the cheaper the part gets. I rarely go looking for the most expensive part when
I’m doing a sort on the distributor site. I do toss out a few outfits I don’t trust, but that’s about it. I doubt I’m the only
one who shops this way. That drives the whole process to ever lower cost approaches.
If you really need a specific parameter, test it yourself. Depending on a supplier to 100% test this or that is not
a good idea. Unless you have an agreement with them to do the testing and get the data from the tests, there is
no certainty that your idea of “tested” and their idea are the same thing.
Semiconductors are by no means unique in this regard. Your wrist watch, wall clock, or Cesium standard has
the same dynamics driving it’s production. They all are impacted. That’s not always a bad thing. We get stuff
for less money. Other approaches to QA now drive the quality of the product where 100% testing once ruled.
Bob
On Apr 11, 2017, at 7:44 AM, Charles Steinmetz csteinmetz@yandex.com wrote:
David wrote:
If the 10pA specification is guaranteed by design, then wouldn't they
have to be testing the 1pA "A" parts?
That assumes the parts are produced by exactly the same process, which is very often not a safe assumption. One of them may undergo extra process steps, for example, or one or more process steps may be modified. That's not at all uncommon, BTW -- "A" versions are often the product of process tweaks, not selected "non-A" devices.
Best regards,
Charles
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I have a really naive question: how can picoamp leakage parts be relevant in low impedance input pulse conditioning to an interval counter?
Tim N3QE
On Apr 11, 2017, at 7:46 AM, Bob kb8tq kb8tq@n1k.org wrote:
Hi
On Apr 11, 2017, at 7:05 AM, Charles Steinmetz csteinmetz@yandex.com wrote:
David wrote:
I ended up qualifying 2N3904s based on manufacturer and lot and I
think we ended up using ones from Motorola. I wish detailed process
information like National had was available from every manufacturer.
It is, if you ask the process engineers for it. (From the Big Boys, that is. These days it seems discrete devices are being fabbed by dozens of "garage" operations. I can't speak for them, and wouldn't think of buying product from them.)
If you dig into where your simple discrete part was made, you might be surprised. That’s even true of outfits you would
consider to be a “Big Guy” from days gone by. The real answer to selection today is to buy the automotive part.
That’s about the only thing anymore that locks down the sourcing, testing, and the process. If you buy a “normal” part,
it might have been made anywhere by just about any process. Yes, that’s scary and it raises a lot of questions. It is
a change that has happened over the last decade or two without a lot of publicity.
Bob
Best regards,
Charles
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Hi
If you go back in the thread, it started out as a “general purpose front end” design. One of the
suggested parameters on that design was a high impedance input capability in the 1mega ohm range.
Noise on a hi-z input is always an issue and input protection just makes it worse.
About the only thing we have not dug into is the question of just how robust this or that protection
approach is. A setup that will withstand being plugged into an European 250V wall outlet for 24 hours
would likely be a bit more parts intensive than something that withstands the occasional exposure
to +12V …. This all may seem a bit “nutty”. It’s worth noting that the HP 5335 is not at all happy
if you drive it with a 5V square wave and set the input attenuator to zero db (= you probably blow out
the input).
Input protection does matter and getting it right is not a trivial thing. There will always be compromise.
Bob
On Apr 11, 2017, at 8:22 AM, Tim Shoppa tshoppa@gmail.com wrote:
I have a really naive question: how can picoamp leakage parts be relevant in low impedance input pulse conditioning to an interval counter?
Tim N3QE
On Apr 11, 2017, at 7:46 AM, Bob kb8tq kb8tq@n1k.org wrote:
Hi
On Apr 11, 2017, at 7:05 AM, Charles Steinmetz csteinmetz@yandex.com wrote:
David wrote:
I ended up qualifying 2N3904s based on manufacturer and lot and I
think we ended up using ones from Motorola. I wish detailed process
information like National had was available from every manufacturer.
It is, if you ask the process engineers for it. (From the Big Boys, that is. These days it seems discrete devices are being fabbed by dozens of "garage" operations. I can't speak for them, and wouldn't think of buying product from them.)
If you dig into where your simple discrete part was made, you might be surprised. That’s even true of outfits you would
consider to be a “Big Guy” from days gone by. The real answer to selection today is to buy the automotive part.
That’s about the only thing anymore that locks down the sourcing, testing, and the process. If you buy a “normal” part,
it might have been made anywhere by just about any process. Yes, that’s scary and it raises a lot of questions. It is
a change that has happened over the last decade or two without a lot of publicity.
Bob
Best regards,
Charles
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