OT 0805 resistor noise

In our case a heck of a lot of componentts *have* to be through hole.

I can only actually think of 3 parts we use ( DSP, ADC and DAC ) that are only available in SMT.

I don't know anyone with lead-free experience ! Since many key components are still not RoHS compliant you can't even do any meaningful test runs.

I've seen one site using very simple 'homebrew' SMT assembly where the extra temp for lead free that they're experimenting with results in melting some components !

And we do actually outsource btw. Only one of them does full SMT currently though and they're the ones who want the large orders.

Graham

I second that. It makes perfect sense even for a couple hundred.

Depends on the component type. Many only come in SMT nowadays.

Agree here.

Just outsource it, they know the profiles and have plenty experience.

--
Siol
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Or a rude error message,
See these simple words: "File not found."

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 Thanks,
    - Win

which book was that?

Cheers Terry

still not RoHS compliant you

By the time it becomes mandatory or shortly afterwards they will. RoHS is probably a load of crap anyway, but we're stuck with it for now.

Siol

well, to be honest, it depends on the sampling rate, you can get away with 602R as long as you sample at 192KHz. MP3's sound better with a 620 termination

I get mine made by these clever droids

really excellent products. Highly recommended .

martin

I am astonished to find myself in complete agreement with you on this. I have made one-offs on tagboard until recently and only stopped because supplies of the boards dried up.

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There are apparently some shot effects in impure metals, nonmetals, and for resistors too short for phonon smoothing to get going. I didn't think this is usually a practical consideration in real-life circuit design, though.

Might affect tiny nonmetal resistors ICs, though?

John

How short must those be? Pretty damn short!?

Of course it is. It's easy to get above the 50mV dc bias or signal-drop level, where circuit currents don't add shot noise as they perform their task. In these cases the designer has new tools to employ to his advantage, Phil Hobbs' common-base signal-input stages are one example.

They should have the same benefit, as should JFETs I imagine. Anyplace there's a sea of mobile conducting electrons.

--
 Thanks,
    - Win

Here's one ref.

This isn't really my area of interest or expertise (and I don't currently have a related design going) so I don't want to debate it. But there has been some work in this area in the last few years, so there are Google hits.

John

"martin griffith"

** Beware of the realities here:

ALL equal value resistors have the same (ie Johnson only ) noise when there is no or only low DC volts across them.

Only those resistors in a high gain input stage can possibly affect the overall noise level and ONLY if you place lots of DC across them - this means resistors used in typical op-amp audio circuits are never an issue.

For example:

A 10kohm resistor has 1.7 uV of Johnson noise in a 20 kHz bandwidth and 3.8 uV in a 100 kHz one - to get the "excess noise" to become significant requires at least a 30 volts DC bias.

......... Phil

Why not? I thought that shot noise was caused by the quantized nature of (flowing) charge, thus any current should be associated with shot noise.

robert

Some Lying Pommy

** Quit this megolamanic " we" crapology.

Graham Stevenson is an unemployed wannabe.

.......... Phil

Google should be fine, so long as you restrict it to s.e.d., Phil posted in a few threads where I was discussing some of my transimpedance amplifier tricks, and in other threads where the O.P. was asking about wideband transimpedance amplifiers. In a few of those I followed his posts with ASCII drawings detailing what he was talking about.

--
 Thanks,
    - Win

Yep, pretty damn small, certainly well under 0402 or even 0201 size! Looks like it could be an issue for IC designers however.

Here's another paper that I enjoyed reading a few years ago,

Beenakker and his friends get into some wierd stuff, teleportation of electrons, earthly and heavenly electrons, and the quantum- mechanical no-cloning rule, which should please the far right. :>)

--
 Thanks,
    - Win

I farm out all PCB fab and PCB assembly, locally; all is done with SMD parts. Lead free? the shops just run the stuff thru their oven longer; the change in timing for preheat, etc is so simple for them that the price difference to me is zero. Quantities? So far, 20 has been the minimum for automated pick and place. Word of caution, tho..silver plate the PCBs after solder mask (*NO* solder dip), and use SN95Ag5 solder paste (or wire solder if by hand). If you dip the PCbs in solder first, you have the following problems:

1) NOT lead free, by definition. 2) The resulting solder bond after use of the high temp solder, will be an alloy of tin/lead and the tin/silver solders. The net MP of that alloy will be highly variable, depending on the size of the pad and how high the tin/lead "bump" was.

If you are going to work in the lead-free environment, have the PCBs plated with silver, and use Sn95Ag5 solder (available in wire and solder paste). You will find that Sn95Ag5 solder is as easy to work with as the old tin/lead.

If the PCB is run thru a hot air tunnel for reflow both times, there is no residual stress. Case 1: parts so small that no adhesive is needed = the liquid solder's surface tension holds them in place at all times, and the cooling dimensional change is so small that it would seem the stress is more theoretical than a practical "problem". Case 2: larger parts with adhesive = do not move, so zero problem.

Please be so kind as to give some references by Phil Hobbs that i could dig out of the library, etc. Google seems to be useless here...