HTSSOP dead bug cooling for high vacuum (Solved)

[mongo]

#1)  Stop making your own boards.  There is no justification for this if you are actually trying to accomplish something other than making your own boards.
#2)  Start using PCB material designed for thermal transfer such as Metal Core or IMS.  Think high wattage LED boards.  Yes it will be expensive, but it's the right tool for the job.
http://www.multi-circuit-boards.eu/en/products/printed-circuit-boards/special-production/metal-core-pcb.html

1) show me someone whom will make small batch vacuum compatible boards and I will, I do not make my own boards outside of single sided which are so trivial to make that it doesn't justify waiting.  To be honest it takes more time to order a board than it takes to mechanically etch one.  While I can understand this advice for someone whom is doing chemical etching it is really easy and fast using normal blanks.

2) my problem is not with the thermal transfer of commercial boards, my problem was with the glues, solder mask and other materials which, in a post rhos world tend to act poorly under vacuum, now that I am planning on a internal pressure vessel I will be using them.

[sarepairman2]

#1)  Stop making your own boards.  There is no justification for this if you are actually trying to accomplish something other than making your own boards.
#2)  Start using PCB material designed for thermal transfer such as Metal Core or IMS.  Think high wattage LED boards.  Yes it will be expensive, but it's the right tool for the job.
http://www.multi-circuit-boards.eu/en/products/printed-circuit-boards/special-production/metal-core-pcb.html

1) read the fucking thread
2) read the fucking thread 
3) my previous post is more useful then yours

perhaps you can dead bug the PCB and solder a large fin radiator to the package that needs cooling

[mongo]

Um...OK...

You linked to a page that listed "immersion tin" as one of the main components, that is a non-starter at HV.


have a good day? 

[sarepairman2]

Um...OK...have a good day? 

perhaps you can dead bug the PCB and solder a large fin radiator to the package that needs cooling

you can dead bug anything, and by fin radiator i mean large outward surface area to dissipate package heat as IR radiation

[mongo]

Um...OK...have a good day? 

perhaps you can dead bug the PCB and solder a large fin radiator to the package that needs cooling

you can dead bug anything, and by fin radiator i mean large outward surface area to dissipate package heat as IR radiation

I have moved way past the need to dead bug anything at this point.

[sarepairman2]

this would allow you to expose the pad on the bottom of the package to attach a large radiator to it (i.e. copper sheet)

a glass PCB is doing precisely dick for you in terms of thermal management.

https://en.wikipedia.org/wiki/Spacecraft_thermal_control

[mongo]

this would allow you to expose the pad on the bottom of the package to attach a large radiator to it (i.e. copper sheet)

a glass PCB is doing precisely dick for you in terms of thermal management.

When I was using glass as a substrate all parts that needed thermal control were in contact with a water jacket, this just wasn't an option on stepper controllers which would drop current/voltage on hold.  But yes I have abandoned that solution.

[sarepairman2]

with a large surface area outwards facing radiator you might be able to use heat pipes for a solution that is fully contained without need for coolant flow, then pour water over the chamber. (intern + garden hose). optimize the geometry of the radiator to get maximum surface area facing the chamber walls. or directly conduct through the chamber using it as a heat sink if you dont need electrical isolation. or a silpad.

you can do this since its high vacuum not cryogenic.

lubricant less motors? magnetic bearings?

[LaserSteve]

Try kovar or Alloy 52 header seals from HCC Industries, Fusite, MPFPI, Vactron,   etc..

  You probably could request a sample or two of a stock product from one of these companies.

 In my application, I furnace brazed a flanged,  octal header "hermetic seal"  into a recess milled in a CF flange...  To save on buying feedthroughs .. which are all over Ebay if you look... I just searched, and there are a few "hermetic seals" on the bay now, after you dig thru two pages of "occult medallions"(Lord Have Mercy!  )  Including a 125 Pin one, although  it has an O-ring..

I've found 306 SS  CF flanges easy to braze with cadmium/silver solders, and then just pump the daylights out of the chamber. If you design it right, the exposed surface area of the braze is minimal..  I know, not optimal to use a hard solder or braze in UHV, but for my app it worked..   If I ever did it again I'd use Indium Corp's  Nanobond component bonding instead of a braze.


Steve

[ConKbot]

Um...OK...

You linked to a page that listed "immersion tin" as one of the main components, that is a non-starter at HV.


have a good day? 

I'm curious,
http://www.powerstream.com/vapor-pressure.htm 
Tins vapor pressure is 10^-8 torr @ 900 Kelvin, I know lead, zinc, and cadmium can be problematic for UHV stuff, but it seems like tin would be stable enough for 10^-8 @100C, is this more of a porsity/adsorption concern than a metal evaporating/sublimating problem? I haven't worked with anything that required more than a rotary vane, so just trying to pick up tidbits where I can.

[mongo]

Um...OK...

You linked to a page that listed "immersion tin" as one of the main components, that is a non-starter at HV.


have a good day? 

I'm curious,
http://www.powerstream.com/vapor-pressure.htm 
Tins vapor pressure is 10^-8 torr @ 900 Kelvin, I know lead, zinc, and cadmium can be problematic for UHV stuff, but it seems like tin would be stable enough for 10^-8 @100C, is this more of a porsity/adsorption concern than a metal evaporating/sublimating problem? I haven't worked with anything that required more than a rotary vane, so just trying to pick up tidbits where I can.

The problem with tin coatings in HV is not off gassing it is whiskers growth especially when immersion tin. I don't think that the full reasons on why they grow is fully known but if you are re-flowing/wave soldering the boards tend to be OK, but in a one off board I have seen fuzziness after just 48 hours back when I was in a "hey lets see what breaks under HV" phase on wire wrap boards.  It is something you could have controlled for a production system but the failure mode under a vacuum, where it actually creates a plasma arc which will pass lots of current from surrounding pins makes it high risk in a one off, super hack setup.  As whiskers are mostly due to stresses IIRC, the cycling also accelerates the growth in a HV environment.

[mongo]

Thanks everyone, I have marked this as "Solved" as I wait for parts and some test gear to show up. I will be back on a better titled thread when I actually have a proper solution engineered vs. trying to get a one off hack to work just enough. I'll make sure to share photos and info on the project at that time.   

[helge]

I'd still be interested in your opinion regarding the packages I suggested on page 1.