The inline testers take too long to settle?
Manufacturers think the board leakage will negate a 0.1% specification?
John Devereux
high value 0.1% resistors
Mar 26, 2014
100 Replies
Ohmite has 1%ers in 0603 up to 10 meg:
http://www.ohmite.com/cat/res_minimacro.pdf
So more than likely you could get them to sort for what you need if
you can stand the tempco and the shift in R from soldering.
You're grasping at straws and trying to shoot the messenger.
It works. I just want to improve the statistics for production. You clearly don't have issues around production.
I am looking for the right parts. That's why I started this thread, to see if any real engineers here might suggest a vendor.
We avoid charging for NRE, so there is never any doubt about IP ownership.
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
They are available in 1206 and 0805. I wonder why 0603 is different. Maybe high ohms/square material isn't stable enough?
ROHS process temperatures sure don't help.
People do make high voltage 0603 resistors, so leakage may not be their concern. It's not their problem, anyhow.
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Tempco is no big deal; the operating range is moderate.
Vishay has some 0.5% parts, stock at Mouser.
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Doubt it. They'll just charge for the time.
Then why would larger resistors be available?
Since we're guessing, mine is that the package isn't large enough for the resistance. I can't find anyone who makes 1-10K .1% 0408 quads, either. I use a bunch of discrete .1% 0402s (up to 64 per board, so far). It would be nice to consolidate them.
Good point.
99% of 2 megohms is 1.98 megohms, so to drop a perfect 2 megohm
resistor down by 1% only requires shunting it with 198 megohms.
To drop it by 0.1%, the shunt is 1998 megohms.
Kinda tough to get and keep under a 0603, I think.
John Fields
I know ohmcraft makes high value >>meg precision resistors, but my memory is that the 0805 are only .5% - but larger sizes are .1% - admittedly vague memory.
jb
People sell 0603s up to at least 100G ohm.
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I have some 0805s at 1T ohm. Apparently it's OK if the board process is clean.
John Larkin Highland Technology, Inc
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
That's what I thought, maybe. But as krw and JL pointed out you can get them in larger packages. So I think it is the sheet resistance thing.
It does need rather a lot of optimism about board cleanliness though.
John Devereux
Perhaps prohibitively expensive, but these guys claim to be able to do it:
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Funny, the resistive material is said to be Ruthenium oxide, not very exotic. Maybe they just do it really well.
Best regards, Spehro Pefhany
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
Does that involve electronic design?
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
date
the
resistor
The rev B
build
to find.
A combination maintenance and warehouse building with advanced day lighting controls including dimmable LED lighting, Class 1 Division 1 hazardous materials storage and spray booth, Class 2 Division 2 blast booth, power distribution and communications for automation friendly warehouse, and many other fun features. We are looking for LEED silver certification for the building as well. Fun stuff.
?-)
Change order means send me money or talk to my lawyer. That is how the game is played.
So in this case, the customer should be happy to pay for new engineering.
Sure, but the eventual apparent resistance in the circuit doesn't
just depend on just the resistance of the resistor unless all of the
leakage paths are accounted for and dealt with.
Then, of course, there's the TCR and the VCR to deal with, as well
as the stresses left over from soldering and the differences in the
TCE of the resistor itself and the PCB substrate.
Nor did I when I was doing that sort of thing, since the issues were
resolved before the PCBs were laid out and the parts were bought.
https://www.youtube.com/watch?v=yqHXy8frOgY
John Fields
Interesting. It looks like the VCR might be the "problem" for the 0603 sizes.
George H.
You could franchise a chain of Word Salad Restaurants.
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
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