Not likely. SMD met films are all mass laser trimmed after a few samples are taken. The film from lot to lot varies, so they 'calibrate' the trimmed length by a few samples, and the entire remaining lot are all within a couple tenths of a percent of the 1% window.
Why spend the money trying to actually find them. Vishay all the way.
Sounds like a weak picker placer machine. That factory floor needs to run right out and buy a couple more machines.
We have some 5% parts in stock, but all new buys are 1%. Even the 5% parts seem better than 1% in real life.
We also use the Susumu 0.05%, 10 PPM resistors.
John
What do you pay for 'em? I'm considering switching some of our stuff to resistor arrays because our op-amp gains are often unity and we could use some accuracy in the Howland Current Pumps. A small number of arrays would help more than hurt, I think.
Around 35 cents. We also use some SO8 4-resistor thinfilm networks that match very well; not cheap.
A couple of people make SOT-23 dual resistors, thinfilm on silicon; also not cheap.
It's usually more cost-effective to just buy an in-amp, INA157 or some such.
John
Must be nice not to have to deal with controlled goods at all.
Oh, yes. When you're buying 20 or 50 reels it makes a bit of difference.
Are ALL the 1% parts made with 1% type specs (tempco and all that stuff) or are some of them 5% parts trimmed to 1% tolerance?
Some of the 0603 resistors I've been using lately cost $20 apiece. ;-)
Yikes! What are the specs on them? We have an intern this summer, and one of his jobs will be to characterize the actual tc of the Susumu "10 ppm" resistors.
John
0.01% +/-0.05 ppm (typical), but I misspoke, they're the big 0805 ones. They're not overkill. :-(
Wow, those machines must be pretty ancient. Even the Siemens and Matsushita (?) machines we used in the 80's could carry a whole lot more reels. Maybe shop for new ones? This economy would be the time to net some sweet deals on used machines.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
DigiKey will gladly sell you 5% 0603 resistors -- multiple vendors to choose from.
Although we never did a formal test/documentation, we've found that Panasonic
0603 resistors tend to have better (flatter) RF performance than some of the other random brands we happened to have used over time.---Joel
I bet that's a little spender than .15 cents each. :-)
Because I'm thinking of advocating that we switch to just 1% values (when it otherwise doesn't matter) here, so this is a little informal survey of what other places are up to.
Back at the place I used to work where it was "all 1%," while they did have all the E96 values around, you were supposed to try to limit yourself to E24 or even E12 values when possible, for just that reason -- trying to reduce the number of different items on the board.
---Joel
But be careful when you guys do pulse circuitry. 5% resistors are often carbon types that can take a huge surge while metal film types can't. That has at times forced me to spec in 5% and mention in the module spec not to switch to "better" resistors without obtaining pulse load data in writing.
Surge failures can be nasty, in the form of field failures after a certain amount of service time.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
But I've yet to see carbon composition SMD resistors :-)
-- Thanks, Fred.
previously
Did I say "Yikes!"? Whatever you're doing, I bet it won't be built by the million in China.
On some of our stuff, we laminate a thin pcb to an anodized aluminum slab, slap a Minco heater on the other side, and do a temperature loop on the whole thing. That helps a lot.
We also sometimes add temp sensors, LM71s and such, or RTDs and 24-bit ADCs, and apply software corrections. You can do some things, like trimming FPGA prop delays, once and nail the factors. The bummer there is that if you have to cycle every unit, that's a real pain.
John
My guys talked me into that. It makes sense when there's hardly any difference in price.
We have a Perl script that scans our stock and finds ratios.
We do try to limit the number of different values, r's and c's.
John
Don't be so quick on that. The damage doesn't need to be melt-the-wire-all-at-once, any abuse can eventually kill the connection. Just as a little axe can't take down an oak with one blow, yet a half-hour of chipping away ends with the tree on the ground.
Current spikes can (if big enough) explode the wire. If smaller, they can strain and work-harden it. In neither case does the wire have to melt to fail...
I had a single CMOS gate that took out several power supply pass transistors that way. I didn't solve it until I filed off the top of the (2N2222) transistor and examined the damage under a microscope.
I actually think I saw one somewhere, but I can't recall where.
John
Thanks, I'll keep that in mind.
---Joel
What, not PowerBasic?!
:-)
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