Surface Mount Resistor in Vacuum Chamber

UHV in that context - outgassing - meant Ultra High Vacuum. You are AlwaysWrong - perhaps not the original, but an interchangeable replacement.

I'd imagine that some other component types, such as can electrolytic capacitors, would have trouble in a vacuum. Cans will expand, and any wet components will evaporate.

(Before anyone jumps in, I /know/ they are not surface mount resistors!)

Thin film wolfram.

f anyone knows of a surface mount resistor material that can be used inside such an environment?

Wolfram is tungsten, a metallic element. Even a single atom thick layer of metal has a resistance of the order of few ohm per square, which makes almo st them useless as resistors - you've got to have a spectacularly serpentin e pattern to get much resistance at all. Thick film inks worked fine for me in a low vacuum environment.

You didn't say what strength vacuum, but assume e-beam stuff in the10-7 to

You are worried about *if* the material [any SMD resistor] can be placed in a vacuum. Technically, yes. But, somtimes you have to worry about outgassing, etc from unexpected spots so you may end up potting stuff, No biggie. What *IS* a biggie is getting heat out of ANY component. Envisioion your vacuum like a thermos ...you will NOT get air convection cooling. How significant? Well our first naive attempts at using some OpAmps in 10-8 to 10-9 torr resulted in the little critters 'unsoldering' themselves, and due to mounting positions, slid off the polyimide PCBs. Note, that's polyimide, NOT polyamide.

We had to add huge metal 'wings' to the mounting areas AND tack those wings down to metal strips that actually touched metal elsewhere. There are several FREE finite element analyses programs that will help you estimate the temp rise/power input, like femm 4.2

Regarding your question of material in a vacuum: Here is a NASA URL listing materials and their outgassing properties:

PS: IMHO rely on your vendors to 'convince' you of the appropriateness of anything in a vacuum. Use their experience and shorten your learning curve.

Good luck.

On Thu, 21 May 2015 22:56:22 -0700 (PDT), Bill Sloman Gave us:

The SMD resistor would fail with the "couple hundred volts" you described WITHOUT any arc-over, idiot.

On Thu, 21 May 2015 23:41:19 -0700 (PDT), Bill Sloman Gave us:

There is zero tolerance of outgassing in space hardware idiot.

In an HV circuit, it would cause a separation between the potting and the parts, which would cause instant failure at that "pressure". AL HV circuits meant for space must be POTTED. Do we need to discuss why? Oh... that's right... we have. You lost. You really are one clueless bastard.

On Fri, 22 May 2015 09:21:37 +0200, David Brown Gave us:

In a "normal vacuum", they survive long enough to bake the circuit dry. In our "UHV" context, they would last for a short period, then fail.

The medium inside is free of air and gassing elements, so they are already well made. i.e. not much if any bloating at all.

And "wet" is a pretty nebulous term, pal. EL caps are not made with water in them.

Water evaporates and "gasses" at far higher pressures than UHV.

On Fri, 22 May 2015 01:20:43 -0700, Robert Baer Gave us:

Do you not mean "Wolfram thin film", as in "Google this or that"?

Wolfram is one of the first apps I bought on my iPad. Way better than google (or wiki) for technical things.

Some surface mount resistors would. A 10M part probably wouldn't.

A volatile material with a vapour pressure of less a couple of millimetres of mercury at the operating temperature wouldn't. It couldn't apply enough mechanical pressure to create any separation, while still being volatile en ough to completely wreck an Ultra High Vacuum environment.

Actually, they only have to be hermetically sealed. Then you can have whate ver environment you want inside the hermetic seal.

You do seem devoted to making the claim, AlwaysWrong. And you do seem to ha ve enough cluelessness for a whole warren of bastards.

And, whoa, those are OPA627 opamps, drawing 7mA. If their supply is +/-10V that's 140mW of power.

On Fri, 22 May 2015 04:59:09 -0700 (PDT), Bill Sloman Gave us:

No, idiot. AN HV circuit in space MUST be potted.

And your pathetic "moniker" is YOUR name, not mine, and it never was.

If you don't care much about the quality of the vacuum (outgassing).. just about any of them, I would think. The materials are pretty benign.

If you need UHV, you can look at some of the special parts designed to be non-magnetic etc. Some of them are spec'd for outgassing, and they claim that some of the competitive parts contain polymers that outgas.

Riedon is one such supplier.

Outgassing can be reduced by baking the assembly in question under vaucuum, and if you get it really cold in operation not much outgassing takes place anyway (and getters and such like can take care of that for quite some time).

As others have indicated you gotta pay attention to how heat gets out of the resistor and maybe to voltage rating. Forget whatever the spec says about power dissipation under ordinary conditions- the conduction and maybe radiation will be how the part gets cooled- in such an un-convectional application.

The SMD resistor "failure" mode at 200V is simply an excessive (reversible) change in resistance. As expected, it's worse for smaller parts, and it's also worse for higher resistances. Data: Looking at the data, one might agree a 10M 0805 resistor fails at 200V, but accept a 100k part.

Isn't that just the quiescent current ? Driving real loads will increase the current ?

Anyway, without a fluid and hence no convection, one has to rely on conductive cooling (e.g. to the PCB), in which the heat transferred is relative to the temperature difference and radiation cooling and radiative cooling.

The heat transfer between the device at T_hot Kelvins and the back radiation from the environment at T_cold Kelvins is proportional to (T_hot^4 - T_cold^4)

For a vacuum chamber T_cold would be about 295-300 K.

A deep space probe might have T_cold as low as 3 K as, as well as the low Earth orbit satellite (LEO) facing away from the Sun and the Earth. A LEO satellite facing the Earth would have T_Cold about 290 K, but a panel facing constantly towards the Sun would have T_cold much higher. Any woblling/rotating satellite with sufficient thermal mass would have a surface temperature about 290 K.

Even if some satellite electronics is able to dump some part of the heat into the PCB an into the satellite surface, the satellite surface must be able to radiate the heat into space, while still being hit by back radiation from various stellar bodies.

Yeah, A lot depends on how hard a vacuum. At UHV the OP may need to think about the solder too. Tin/lead would be a problem.

George H.

e:

Those are for thick film resistors, and refer to a relatively small non-lin earity. It's scarcely a failure mode to be compared with arc-over.

Precisely what's going on is an interesting question. Thick film resistors are chunks of high resistance material embedded in what's essentially glass frit which is fused when the thick film is fired. If memory serves, the re sistive chunks change nature as you move to higher resistance parts, and th e charge carriers don't have to be electrons.

My understanding is that pretty much all SMD resistors are L-trimmed - a co arse cut part-way across the conducting path, followed by a fine-trimming c ut parallel to the conducting direction.

In so far as SMD resistors all have roughly similar aspect ratio, this woul d argue that they all use the same ink for the same value part.

Obviously the three-dimensional aspect ratio is going to change as you go f rom 2512 to 0201, but thick film inks are sold as having a particular resis tance per square, and implying that they are silk-screened into place at a pretty uniform thickness. At one point at Cambridge Instruments we put our own thick-film conducting layer on the inside of a 6mm ID Macor cylinder, a nd the - very clever - technician that did it didn't seem have had any trou ble getting consistent resistance values.

Thick film inks works as random networks of conduction paths. There are goi ng to be fewer of these paths on an 0201 part than on a 2512 part, and each one is going to be shorter, so there are going to be fewer nodes along eac h path and any individual charge-carrier effects are going to be more obvio us, but I haven't a clue what these individual charge-carrier effects might be.

That's Herold with an "e". German descendants, Bavaria. (maybe Heroldsberg?)

The coat of arms looks like he had too much to drink the night before.

George H.