beads and zero ohm resistors

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Has anyone measured the resistance and tempco of cheap surface-mount
zero-ohm resistors?

Has anyone measured the resistance tempco of surf-mount ferrite beads?

How are those constructed anyhow?

I guess I'll have to get out of my comfy chair and measure some.


--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

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Re: beads and zero ohm resistors
On Wed, 28 Sep 2016 11:38:10 -0700, John Larkin wrote:

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Excuse my ignorance, but aren't these basically just jumpers - and used  
as such?

Re: beads and zero ohm resistors
On Wed, 28 Sep 2016 18:59:01 -0000 (UTC), Cursitor Doom

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Larkin isn't getting enough podium time... thus the stupid question
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                                        ...Jim Thompson
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| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
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Re: beads and zero ohm resistors
On Wed, 28 Sep 2016 12:57:36 -0700, Jim Thompson

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This is an electronics discussion group. It will die if we don't
discuss electronics. Like, if all people like you post is home
woodworking problems and redneck political links.

And neither of my questions are stupid. Both could matter; right now,
to me, both do matter.


--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

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Re: beads and zero ohm resistors
On 9/28/2016 6:17 PM, John Larkin wrote:
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+1



Re: beads and zero ohm resistors
On Wed, 28 Sep 2016 11:38:10 -0700, John Larkin

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The spec sheets I've seen say around 20 milliOhms for the 0805 or 0603
zero Ohm resistors.

I have tended to shy away from using "zero" Ohm resistors as option
jumpers in PCBs because I find that they open up too often.

Need lower resistance than zero Ohms I guess.

boB



Re: beads and zero ohm resistors
On Wed, 28 Sep 2016 14:11:18 -0700, boB

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I grabbed one of the generic 0r 0805 parts from our stock. I had to
run an amp through it to get enough resolution; it measures 5.75
milliohms.

A *very* rough temp test, with freeze spray, came up +3000 PPM/K,
which is consistant with most pure metals, which run around 4000.


--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

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Re: beads and zero ohm resistors
boB wrote...
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 How much current does it take to make them blow?


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 Thanks,
    - Win

Re: beads and zero ohm resistors
On 29 Sep 2016 07:00:52 -0700, Winfield Hill

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I can't remember but it should be easy to test for.
I think our main problem was in the coil lead of a
relay.  I've seen them open up in other applications so
I try not to use them.  Typically I only use them for  
"options" on a PCB anyway.

Another thing regarding small-ish parts like these is
that, for all resistors, say less than a hundred Ohms,
should be "pulse rated"... meaning, they shiould at least
publish the overload specs for the resistors unless there is
just very very low current through them.  It's a rule my
company has adopted though.

It may be that the zero ohm resistors we have used
were not made by Vishay or Stackpole or one of those
companies that specify a decent maximum repetitive
pulse power.

This is especially important for gate drive resistors where
a capacitor is charged and discharged rapidly.

boB
K7IQ



Re: beads and zero ohm resistors
boB wrote...
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 Ditto for SMT resistors with more than say 10V across
 them, and that might experience moderate power surges.

 My technician's front-loading washing machine control
 board (with elegant Analog Devices DSP six-IGBT three-
 phase VFD motor-drive controller) failed when an 0805
 resistor blew in the offline switching-supply circuit.

 My beautiful expensive Casablanca remote-controlled
 multi-speed reversible ceiling fan failed when an
 SMT resistor failed, similar story.

 And etc.


--  
 Thanks,
    - Win

Re: beads and zero ohm resistors
On 29 Sep 2016 14:21:17 -0700, Winfield Hill

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And SMT capacitors can crack, too.  For instance, try not
to place them next to the edge of a board... Place them such
that if the PCB is going to flex, the cap can flex the least.

SMT capacitor size seems to matter also,  Smaller is usually better
we find. 1206 is getting too big at times. At least for stiff ceramic
types like X7R.  Film is better maybe.

Then again, if you don't mind paying a bit more, there are these
semi-flexible SMT caps we heard about but would rather not spend
the extra money if possible.

All these things that are found out over time. We try to learn from
past mistakes and experiences but sometimes we have to learn again.

boB




Re: beads and zero ohm resistors
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IPC recommends 1210 at the largest.  I'll use up to 1812 (or is there any  
1818ish?), but carefully.

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They're not too expensive IIRC, being used in automotive quantities.

Tim

--  
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
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Re: beads and zero ohm resistors
On Fri, 30 Sep 2016 22:18:18 -0500, "Tim Williams"

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I just got a quote for a 1uF 25V cap for about a nickel.  I think it
was for a million a year but I'd have to check that.  I didn't have
too much time to look at it before I left yesterday.

Re: beads and zero ohm resistors
On Fri, 30 Sep 2016 00:45:07 -0700, boB

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There are X7Rs that are designed with some flex and others that are
designed to open, rather than short.
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Yes, in X7Rs, too.  In some uses, we're required to put two caps in
series so in case one shorts the magic smoke doesn't ruin our day.
That's not cheap, either (4x the capacitor).
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That's how the above edicts come about, too.  Strike your thumb with a
hammer and you tend to learn a lesson.



Re: beads and zero ohm resistors
The resistors are just the usual lowish-tempco metal-filled enamel,  
slathered on thick without laser trimming.

Multilayer beads/coils are probably something like Cu/Ag/Pd, applied as a  
ceramic glaze formulation that bakes into mostly-solid metal on heating.  
Noble metal content is needed, otherwise the ferric iron (a required part of  
a _ferri_te) oxidizes it, destroying the contact.  Not to mention making the  
ferrite terrible (too much Fe(II) would probably crystallize as magnetite,  
which sucks).

Caps have the same construction, but they get away with semiprecious metals  
more effectively as they only have to carry displacement current.  The metal  
layers can be very thin indeed.

Tim

--  
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
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Re: beads and zero ohm resistors
On Wednesday, September 28, 2016 at 2:38:21 PM UTC-4, John Larkin wrote:
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I measured a bunch some years ago.  I couldn't find my notes, so I
re-measured a few:

 #1 0805  0.020 ohms
 #2 0603  0.0085
 #3 0808  0.0085
 #4 0603  0.0165

I was considering using them as non-critical current-sense resistors.

Cheers,
James Arthur

Re: beads and zero ohm resistors
On Thursday, September 29, 2016 at 9:17:02 AM UTC-4, snipped-for-privacy@yahoo.com wrote:
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Ooops, s/#3 0808/#3 0805/

These are from separate reels, BTW.

Cheers,
James Arthur

Re: beads and zero ohm resistors
On Wednesday, September 28, 2016 at 2:38:21 PM UTC-4, John Larkin wrote:
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I'm still hoping you'll take a grinder to one and see what's inside.  
(The FB's)  
Well and post pictures too.  

I'm using some of these..
http://www.digikey.com/product-detail/en/laird-signal-integrity-products/28C0236-0EW-10/240-2492-ND/806595

George H.  
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Re: beads and zero ohm resistors
On Thursday, September 29, 2016 at 10:01:14 AM UTC-4, George Herold wrote:
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If you whack an SMD F.B. with a hammer, I've only ever found an
alloy strap inside.

Cheers,
James Arthur

Re: beads and zero ohm resistors
snipped-for-privacy@yahoo.com writes:

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https://www.google.com/search?tbm=isch&q=chip+bead+structure


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John Devereux

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