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High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/08/2011 5:47 PM

I am creating a hermetic thermal vacuum chamber. I would like to metallize a ceramic substrate for internal electric routing, most likely alumina. I would like to solder in receptacles that accept roughly .018" dia pin. Does anyone know if there is a high vacuum (10e-7 Torr or so) receptacle material/source that is commonly available for this application?

Have several ideas for this, I am wary about using Brass as it is approaching a very dangerous region for brass usage, I have read Ni plating brass mitigates zinc outgassing to an extent, does anyone know of direct numbers for the reduction based on Ni plating thickness?

I also have a custom solution but its very pricy using TeCu as the contact housing material with BeCu contact?

Any input or experience in this area would be appreciated. Thanks

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#1

Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/08/2011 6:49 PM

Don't know if this helps.

Page 7 Table 4 here:

PHYSICS OF OUTGASSING

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#2

Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/10/2011 2:35 AM

Don't use brass nor solder.

Any ceramic socket intended for high performance electronics will do your job.

Look at the Paschen curve of breakdown voltages versus pressure times distance if you want to use this equipment at intermediate pressures.

If to be used in homebrewed ceramic plate then try the pin and receptable from Amphenol plugs. These come as single items to be inserted. You may snap these in place or solder with PbAg-solder (not too good), or glue with low outgassing glue.

RHABE

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#6
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Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/10/2011 10:00 AM

Can soldering process be overcome by reflow in a vacuum and the proper cleaning/bakeout process?

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#9
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Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/10/2011 10:30 AM

I don't think so, the problem is the material composition. You could try something like Indium/Tin or Indium/Bismuth for solder like they do with CCDs. We use these alloys in vacuum without problems.

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#3

Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/10/2011 6:31 AM

Brass in vacuum is bad, it will outgass even with plating & the zinc will try to coat everything in the chamber. Alumina with deposited gold, chrome or platinum is OK & BeCu contacts will work.

This list from Caltech shows some vacuum compatible materials with outgassing rates.

It would be worth talking to someone who makes vacuum electrical feedthoughs, Lesker is one that comes to mind.

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#5
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Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/10/2011 9:58 AM

Thanks for the Caltech link its very helpful. I have been in touch with several hermetic feedthrough companies about custom feedthrough.

As Rhabe put it this is more of a homebrewed metallized ceramic substrate that I would like to populate. This substrate will serve as a way to electrically route from my hermetic feed through to instrumentation in the chamber, unfortunately the substrate receptacle pattern changes for the various instrumentation and sensors that would be going into this chamber throughout its lifetime. I am hoping to be able to do a large amount of this in house, rather than have a custom hermetic package created for each setup.

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#10
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Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/10/2011 10:45 AM

Ccoon 17,

you may use this ceramic substrate as feedthrough if you match the outer shape to typical KF or CF flange plates.

Ask a supplyer of hybrid electronic circuit boards - fired siver-palladium on alumina is a very good choice.

With this applied by a silk screening process (that can be done by hand-painting too) any high-vacuum performance can be achieved. Metallised via through holes are used conveniantly.

These are often closed (as often remaining open after silk-screen printing and firing) by soldering but in your application I would suggest to plug these with eutectic AgCuIn braze or (for a fast and simple test) glue with high-temperature epoxy a small flat alumina-plate at the high pressure side onto each of the via-holes to be closed.

I used this process and a similar copper on alumina for a similar application but that is requiring a high quality Nitrogen inert atmosphere at firing. Near 15ppm oxygen (including water) is required to give a very slight oxidation - necessary for adhesion of copper to alumina by copper-oxide. If too much oxygen is present then the oxide will grow too thick a layer and crack. If not enough oxygen is present at firing there will not exist enough copper-oxide to give good adhesion so delamination and leakage will be the result. These problems are overcome by using the (much more expensive) AgPd-paste.

Have success

RHABE

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#12
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Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/10/2011 12:09 PM

Rhabe,

Thank you for the input, we have worked with a couple of different hybrid houses in the past and will be using one this time around as well, alumina is my preferred choice, but we may use beryllia. We hope to eventually progress the ceramic substrate into the seal at some point in time, but we are not ready for that just yet. There is actually a hybrid house that fires multiple ceramic layers together creating sort of a multilayer ceramic board, although I have not used it, the idea is very appealling.

I wasn't going to use the current design as my hermetic feedthrough, we are having a company that does that on a regular basis do that for us (still in the quoting phase, but have a few, SRI, tekna seal, hcc, pa&e, that I have been working with).

For say effectively a surface mount part on a substrate in a vacuum, RTD leads, custom Ion gauge leads, we planned to solder them to the ceramic substrate in the vacuum or preferrably solder in sockets and use crimp leads on the instruments. Is there no way to do this with soldering or should I look only at conductive epoxies or press fit connectors or is the brazing technique applicable for that as well?

Thanks again, Regards

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#14
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Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/10/2011 1:55 PM

Ccoon17,

why think about beryllia when alumina is a near perfect choice?

Beryllia dust is quite toxic, so only an urgent need requiring very high thermal conductivity will motivate this choice.

"Is there no way to do this with soldering or should I look only at conductive epoxies or press fit connectors or is the brazing technique applicable for that as well?"

Soldering: first of first: avoid any zinc - very bad in outgassing, second: avoid tin and lead - acceptable if near 20°C, indium and silver are quite good at low temperatures although pure indium may melt (same with gallium - both are good also if liquid). Press-fit: very good, brazing: very good if none of the critical elements are in (special purity required), welding: very good, look for ultrasonic and thermal compression welding, conductive epoxi: I used Epo-Tek H20E with very good results, very likely H20E-175 will be still better (not only with respect to outgassing but the very long potlife will facilitate usage and minimise waste).

Paschen Curve: (Ignition voltage) versus (pressure times distance). Protect your instruments!

RHABE

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#15
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Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/10/2011 2:14 PM

Rhabe,

Thanks very much, I will have to take a little more time researching and looking at your suggestions. Thank you.

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#18
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Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/11/2011 4:34 AM

Indium/Tin gets you to around 70°C, Indium/Bismuth nearer 120°C. Indium/Gold goes higher but I have no experience of that. This list might help.

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#4

Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/10/2011 9:46 AM

Thanks Dave K,

I have been in touch with a handful of companies that do the hermetic feedthroughs using either glass or ceramic insulators. I am in fact planning on using one of the companies to creat the original feedthrough into the chamber. Good to know about the plating, does that hold true for electroless plating as well?

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#7
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Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/10/2011 10:21 AM

From my personal experience if you must plate a surface for use in a high vacuum chamber it will be necessary to do a secondary processing step. Firing the part after plating will densify the material and drive out the unwanted gas. The plated material is highly porous and is a molecular trap for gas. The best method is to vacuum fire the part to out-gas it.

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#8
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Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/10/2011 10:27 AM

Agree with that, we vacuum stove at 900°C any parts that will see hard vacuum.

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#11
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Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/10/2011 11:48 AM

Yeah the ceramic substrate is done by at a very high temperature, I can't remember what the number is off the top of my head but it is up around 1000C. That gets done by a hybrid circuit house, the plan is to then have them drill out vias creating places for us to solder in sockets followed by a vacuum reflow of the solder and a cleaning and bakeout process before it enters the chamber, I will have to look more closely at the solder approach and which solder I choose, my plan was to use a In alloy or silver solder but I have not selected it yet as it has to match with the ceramic metallization I get.

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#13
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Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/10/2011 12:11 PM

Be aware that the indium alloys can attack copper & it's alloys quite aggressively in vacuum.

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#16

Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/10/2011 2:15 PM

On a side note, has anyone ever tried metallizing Macor, I have worked with it in the past, but never looked into metallizing it. I've heard of it being done, I'm just not aware of anyone who does it?

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#17
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Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/10/2011 3:36 PM

Hi,

I did this many times: with gold and nickel in a first primitive sputtering process, with silver (as in screen printing but applied by hand) and platinum, and with a much better sputtering equipment later with aluminum and other metals, also AlN on Al.

Adhesion is pretty good if first a reactive layer is deposited. Surface roughness will be the same as uncoated.

Any contamination will have disastrous effects.

So final finish should be done near the metallisation equipment immediately before entering the vacuum chamber. Only clean-room approved gloves to be used.

Metalization by thick film procedures is much more forgiving and much cheaper to start with. But will result in 20 or so µm thickness that is not very precise. So we had to use sputtering.

Below a photo of the plasma during coating and an Al-AlN multilayer on silicon, crystalline layers are AlN. Bar length is 0.1µm.

RHABE

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#19
In reply to #16

Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/11/2011 4:36 AM

Similar to RHABE, we've deposited gold on to Macor to make shaped electrodes which worked OK but in the end we found a cheaper way to make what we needed.

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#20
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Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/11/2011 5:14 AM

Thank you for the Indium list.

Gold and Macor are both terribly expensive but for a first quick start ok.

RHABE

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#21

Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/13/2011 11:28 AM

I'm not sure exactly what you are looking for. You need a high temperature interconnect that is useful at low pressure. We need to know what temperature the device will operate at in order to provide valid information, In general, you don't want to use brass pins. Nickel or nickel/iron alloys are good in these applications. So is platinum, but I don't think you need to go there. If thermocouple connections are required, the problem changes. I don't particularly care for screened and fired coatings for custom hermetic feedthroughs. There are many multilayer sputtered coatings such as Ti/Pd/Ni/Au that provide outstanding performance and high yield.

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#22
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Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/13/2011 8:53 PM

The device operating temperature will range from 80C to -80C, so nothing too hot. I have a couple different vendors willing to do a CuTe or BeCu instead of a standard brass shell and then the standard nickel/tin or nickel gold combinations of plating over that if desired. See Mill-Max 5522 profile for one of the ideal socket profiles I would like to use:

( http://mill-max.com/pin_rec_catalog/productinfo.cfm?webpartnumber=5522&start=1&leaddiameterrange=.015-.018&pin_or_rec=&PartDescription=Receptacle%20With%20No%20Tail&taildiameter=NONE&tailtype=NONE&mountingfeature=SOLDER&mountinghole=0.040&bodylength=&search=5522&pr=Rec&stagecode=&usersearch=5522 )

At this point I am weighing all the different options for attaching these sockets to a Nickel/Gold or another combination of metallization for a ceramic Alumina substrate. The pins will not be the hermetic feedthrough portion of the electronics I have a feethrough that is being laser welded to a SS 304L chassis. Any input would be very helpful, I am looking at several of the previous suggestions: epoxy, braze, solder, press-fit etc. I have the ability for a high temperature bakeout and rigorous cleaning process before it will enter the final device. Thanks again.

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#23
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Re: High Vacuum Compatible Pin Receptacles, Ni Plated Brass

02/14/2011 6:07 PM

I suggest you contact Stellar Industries. www.stellarind.com for your metallized substrate requirements. A contact there is John Snook.

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