Silly resistor values

[Fred Abse]

If you're completely confident your assembly guys won't inadvertently
subsitute 5% resistors on you when you mean 1%

They wouldn't be *my* assembly guys very long, if they did.

 

[krw]

They wouldn't be *my* assembly guys very long, if they did.

Does anyone's "assembly guy" stuff 1K 1% resistors, rather than
P/N 1234567? Why does the "assembly guy" even care if it's a
resistor?

 

[Joerg]

No, idiot. The one you posted a link to was a 5 watt power resistor.

Quote from my link "0.25 Watt (1/4 Watt)"

What in that quote is it that you don't understand?

And, as I stated, it is a High Voltage Resistor.

I have given you another example because it seems you haven't looked
around. From Stackpole, 10% resistors that I have designed in.

You did not read what I wrote. These are not standard, everyday parts,
they are purpose specific.

The Stackpole parts aren't everyday parts? And yeah, those 10% resistors
are purpose-specific like most everything else in life. Their purpose is
to shave off cost.

I know what it smells like when it burns (the PCB media), so that alone
should tell you enough. That memory originally dates back to the late
sixties. Of course subsequent events indicates further experience.

Then you have probably never designed very cost-critical stuff. I have,
a lot.

 

[Joerg]

Answer: I have some experience in electronics manufacturing, including
the use of bulk media (not count, material of construction) and high
voltage types of resistors. I have seen a large array of what can be
expected in resistors. I am sure there are those I have not seen.
I have seen resistors that stop trains.

I am designing electronics for a living, for over 20 years. Oh, and
during a summer job between my time at the military and start of
university I actually built resistors that stop trains. Brazilian
freight trains, to be exact.

They are not as cheap as you might think. Those are "pulse
withstanding" thick film devices, and I'll bet that they ALL cost more
then the std Vishay stuff in the local catalogues.

Carbon resistors are cheap, in China. That plus Malaysia and a few other
countries is where all low-cost electroncis get produced. The trick is
this: You produced resistors with the least amount of process control
and preferably no trimming.

You cannot obtain much info about that from US sources. Datasheets like
the one I showed you, yes, but not Chinese pricing.

So, maybe you should look closer... and again.

I have, starting around 1994 or so. That was the first time a client
came back to me with this request after I finished a design: "Our
Chinese contract manufacturer is asking which of those 5% resistors we
can ease off to 10% or more. Can you please identify those? Datasheet
comes via fax." (This was the day where not all companies had scanners).
My billed time for this effort was 1/4 hour. The cost savings were IIRC
around 5c per unit, times 50000/year, times 15 years, and counting (it's
still in production). That kind of ROI is stunning. Yet none of this
seems to be taught at universities or anywhere else and most people
don't bother to educate themselves about it, probably because it's
perceived as boring.

Someone who has ever designed with a team in Asia (I have) knows the
drill. They had reams of computer paper hung on hallway walls, updated
about weekly, with fresh commodity pricing of electronic parts. And yes,
all the way down to the lowly resistors and diodes. This wall is what
drove the design process, not elegance or whatever.

Piss on RoHS, I am exempt. I don' need no stinkin' compliance badges...

Same for most of my design. But not for all of them.

 

[Joerg]

That's the way I've always done it.

It's the only way that works. One client's contract mfg violated this,
once, and promptly hit a brick wall. An expensive one, had to trash
thousands of units. A "more economical" electrolytic had x times the
leakage and they didn't notice that it was in a timing circuit ...

 

[Joerg]

]

E12 values in 1% are as common as mud, everyone uses them, mostly due to old
habits as everyone has the E12 range drilled into their head.

Dave.

Alas, i design to E24 by default. But back when i was starting i
found the premium for E24 parts to be worthwhile. The habit remains.

Go to places like Shenzen and design consumer stuff, then you'll be back
to E12. But the 10% variety ;-)

 

[Joerg]

I left that world behind when I left STC. I never got involved with
fibre though STC were working on it.

The high rel requirement led to conservative design approaches. PCBs
were only just being introduced in 1976, everything before then was
made on custom tag boards with tags mounted on perspex. The fear was
that chemicals could leach out of the pcbs over 25 years in a sealed
environment and lead to corrosion and failure. Even the resistors were
unmarked so that the paint dyes could not leach out.

They didn't have PCBs before 1976? Wow. Phenolic was quite common then
and well known. For hi-rel stuff I really liked alumina. Much better
than perspex posts and so on. You could seal the whole thing, and we
usually did.

Looking at the responses it is clear that E96 resistors are considered
standard in the US. In my experience that is not the case here in the
UK.

E96 is standard here. But only for prototyping and for gear where cost
doesn't matter, or where engineers think it doesn't matter. It always
amazes me when I see a circuit from engineers who aren't great cost
thinkers and then, after re-designing it, cost drops hugely.

 

[Archimedes' Lever]

"Our
Chinese contract manufacturer is asking which of those 5% resistors we
can ease off to 10% or more.

What a bunch of retards.

Sorry, I do not build cheap chinese crap, so I do not need to deal with
a customer that wants to dictate stupid part purchases to pare a penny
off his rip-off priced piece of shit product.

Contract manufacturers are supposed to build to the print (ours did).
If the retards were asking me if they could switch to other values, the
only other value I'd be switching to is a different contract
manufacturer.

 

[Archimedes' Lever]

. That kind of ROI is stunning. Yet none of this
seems to be taught at universities or anywhere else and most people
don't bother to educate themselves about it, probably because it's
perceived as boring.

I know how to economize large volume production. I did not need to
have it taught in school.

I perceive that you thinking the rest of the world doesn't have your
grasp of the industry is pretty fucking boring. Nothing stunning about
that.

 

[Archimedes' Lever]

Someone who has ever designed with a team in Asia (I have) knows the
drill.

Not all makers are turnkey that way. Some MUST and do make what was
designed.

They had reams of computer paper hung on hallway walls, updated
about weekly, with fresh commodity pricing of electronic parts.

Good for them.

And yes,
all the way down to the lowly resistors and diodes.

In the HV power supply industry, the maker builds what we design and
ONLY what we design. We do not need a batch made one way one month, and
then the next batch having entirely different operating characteristics
because some dope decided to make some substitutions.

If we want 104 C caps, that's what we got. If we wanted a particular
brand due to ESR or 'whatever', that is what we want. We do not need
some chump **** trying to cut HIS costs compromising the quality of OUR
design. So NO, there will be NO substitution, including resistors and
diodes.

This wall is what
drove the design process, not elegance or whatever.

Elegance or whatever has nothing to do with it.

 

[Joerg]

Does anyone's "assembly guy" stuff 1K 1% resistors, rather than
P/N 1234567? Why does the "assembly guy" even care if it's a
resistor?

It does help if assembly folks know what part is what kind. For
temperature profiles and such. The guys rigging the machines don't need
to know as long as they follow proper ESD procedure.

 

[krw]

It does help if assembly folks know what part is what kind. For
temperature profiles and such. The guys rigging the machines don't need
to know as long as they follow proper ESD procedure.

Our "assembly guys" (mostly women, actually) know what process to use
on which products and how to profile them. They have no need to know
what's on the boards, other than inventory numbers. The "assembly
guy" doesn't decide which profile to use. The people doing rework
(sometimes the same people) need to know a little more, perhaps.

 

[Joerg]

Our "assembly guys" (mostly women, actually) know what process to use
on which products and how to profile them. They have no need to know
what's on the boards, other than inventory numbers. The "assembly
guy" doesn't decide which profile to use. The people doing rework
(sometimes the same people) need to know a little more, perhaps.

Well, I meant the personnel at the assembler, not just the workers on
the floor. The foremen and similar folks do need to know IMHO. I would
not advice a client to use a shop where that wasn't the case.

 

[krw]

Well, I meant the personnel at the assembler, not just the workers on
the floor. The foremen and similar folks do need to know IMHO. I would
not advice a client to use a shop where that wasn't the case.

Ah, you're including the "manufacturing engineering" people in the
"assembly guys" bucket. I was restricting the group to just those who
push the buttons and load the pick-n-place machines.

 

[Joerg]

Ah, you're including the "manufacturing engineering" people in the
"assembly guys" bucket. I was restricting the group to just those who
push the buttons and load the pick-n-place machines.

Not always real engineering. But it does help if the line lead or at
least the foreman knows a thing or two about this stuff. Older ones can
be more knowledgeable than engineers assume. I was once called to a
serious production problem, nearly all boards failed final test. Asked
their engineers whether they had a sit-down with production people.
"Uhm, no, why?". So I had that sit-down. Problem looked like board
warpage. The foreman and I quickly figured out what could be done, for
lunch we headed to a place where there was a large hardware store.
Bought some lumber there, made a few "pre-stretch" frames, sent some
boards through -> all passed.

 

[Jim Thompson]

Not always real engineering. But it does help if the line lead or at
least the foreman knows a thing or two about this stuff. Older ones can
be more knowledgeable than engineers assume. I was once called to a
serious production problem, nearly all boards failed final test. Asked
their engineers whether they had a sit-down with production people.
"Uhm, no, why?". So I had that sit-down. Problem looked like board
warpage. The foreman and I quickly figured out what could be done, for
lunch we headed to a place where there was a large hardware store.
Bought some lumber there, made a few "pre-stretch" frames, sent some
boards through -> all passed.

Sometimes pisses managers off, but I often go around the manager and
talk to the "down-stream" people to sort out what a chip design
_really_ needs to do.

...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 | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine Sometimes I even put it in the food

 

[krw]

Not always real engineering. But it does help if the line lead or at
least the foreman knows a thing or two about this stuff. Older ones can
be more knowledgeable than engineers assume. I was once called to a
serious production problem, nearly all boards failed final test. Asked
their engineers whether they had a sit-down with production people.
"Uhm, no, why?". So I had that sit-down. Problem looked like board
warpage. The foreman and I quickly figured out what could be done, for
lunch we headed to a place where there was a large hardware store.
Bought some lumber there, made a few "pre-stretch" frames, sent some
boards through -> all passed.

Warpage? Pre-stretch? Must be some warped boards to cause failures.
We have some fairly large boards (half-panel) with a lot of heavy
stuff (audio transformers) on them and haven't had too much trouble
with warpage. Certainly no big fallout in assembly.

 

[Joerg]

Sometimes pisses managers off, but I often go around the manager and
talk to the "down-stream" people to sort out what a chip design
_really_ needs to do.

Best place for that chat is often the local tavern after dinner.

 

[Joerg]

[...]

Not always real engineering. But it does help if the line lead or at
least the foreman knows a thing or two about this stuff. Older ones can
be more knowledgeable than engineers assume. I was once called to a
serious production problem, nearly all boards failed final test. Asked
their engineers whether they had a sit-down with production people.
"Uhm, no, why?". So I had that sit-down. Problem looked like board
warpage. The foreman and I quickly figured out what could be done, for
lunch we headed to a place where there was a large hardware store.
Bought some lumber there, made a few "pre-stretch" frames, sent some
boards through -> all passed.

Warpage? Pre-stretch? Must be some warped boards to cause failures.
We have some fairly large boards (half-panel) with a lot of heavy
stuff (audio transformers) on them and haven't had too much trouble
with warpage. Certainly no big fallout in assembly.

This was a design with tons of RF challenges, there was no way to keep
the copper areas even remotely symmetrical to center. Buried
impedance-controlled traces, umpteen channels, dense as heck, size of an
oven pan, early days of SMT manufacturing and this was all SMT. Oh, and
double-sided.

 

[Rich Grise]

Tek's motto used to be, "Committed to excellence."

Now it's "Enabling innovation."

Hmm, OK, but I really think the old one was a stronger statement...

Anyone have a list of company mottos over the years? I would imagine Tek had
more than the two I've listed here, HP must have had a bunch, etc...

No, but I remember some stuff like that, like:
"See the USA, in your Chevrolet"
"A silly millimeter longer" - Chesterfield 101's
"The seven-minute cigarette" - Pall Mall Gold 100's

And who could forget Burma Shave? ;-)

Cheers!
Rich