OCXO housings - Why copper and not iron/steel?
Hi
Gradients are a really big deal in an OCXO. Thermal mass works against
you if you are after quick warmup ….
Bob
On Oct 30, 2020, at 6:23 PM, Attila Kinali attila@kinali.ch wrote:
On Fri, 30 Oct 2020 17:58:24 -0400
Bob kb8tq kb8tq@n1k.org wrote:
Simple answer: conductivity. You don’t get much heat capacity either way.
Ah.. so it is more important to have less temperature gradients
than having high capacity?
Attila Kinali
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On 10/30/2020 5:05 PM, Bob kb8tq wrote:
Hi
Gradients are a really big deal in an OCXO. Thermal mass works against
you if you are after quick warmup ….
Bob
I'll take this opportunity to plug my 1997 FCS paper:
"The Theory of Zero Gradient Ovens" explaining how
we got thermal gain over 1 million. You better
believe gradients are a really big deal.
Rick N6RK
Not true
The Wiedemann-Franz gives the ratio of the thermal conductivity to electrical conductivity of a metal:
( pi^2 / 3 ) * ( (k/e)^2 ) * T
Bruce
On 31 October 2020 at 12:49 "Dr. David Kirkby" drkirkby@kirkbymicrowave.co.uk wrote:
On Fri, 30 Oct 2020 at 22:17, Luiz Alberto Saba las@intercat.com.br wrote:
My bad... copper is the second, losing only to silver, as a thermal
conductor.
I think you are mistaken. Copper is second to silver for electrical
conductivity, but I doubt that is so for thermal conductivity. I think
diamond, which is a form of carbon, is the best thermal conductor, and
around 5x better than copper.
Dave
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Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@kirkbymicrowave.co.uk
https://www.kirkbymicrowave.co.uk/
Telephone 01621-680100./ +44 1621 680100
Registered in England & Wales, company number 08914892.
Registered office:
Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United
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Also an interesting material when high thermal conductivity is considered
is boron nitride. It is around five times better than copper, comparable
to diamond and can be sintered to a ceramic material.
Of course the Wiedemann-Franz-Lorenz law doesn't apply here as it is a very
good electrical insulator.
A boron nitride OCXO would indeed be interesting! :-)
I use certain kinds of boron nitride at work to increase the the thermal
conductivity of some plastic materials.
Tobias
On Sat., 31 Oct. 2020, 03:57 Bruce Griffiths, bruce.griffiths@xtra.co.nz
wrote:
Not true
The Wiedemann-Franz gives the ratio of the thermal conductivity to
electrical conductivity of a metal:
( pi^2 / 3 ) * ( (k/e)^2 ) * T
Bruce
On 31 October 2020 at 12:49 "Dr. David Kirkby" <
drkirkby@kirkbymicrowave.co.uk> wrote:
On Fri, 30 Oct 2020 at 22:17, Luiz Alberto Saba las@intercat.com.br
wrote:
My bad... copper is the second, losing only to silver, as a thermal
conductor.
I think you are mistaken. Copper is second to silver for electrical
conductivity, but I doubt that is so for thermal conductivity. I think
diamond, which is a form of carbon, is the best thermal conductor, and
around 5x better than copper.
Dave
--
Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@kirkbymicrowave.co.uk
https://www.kirkbymicrowave.co.uk/
Telephone 01621-680100./ +44 1621 680100
Registered in England & Wales, company number 08914892.
Registered office:
Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT,
United
and follow the instructions there.
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Interesting list
https://thermtest.com/thermal-resources/top-10-thermally-conductive-materials
Enviado do meu iPhone
Em 30 de out. de 2020, à(s) 23:57, Bruce Griffiths bruce.griffiths@xtra.co.nz escreveu:
Not true
The Wiedemann-Franz gives the ratio of the thermal conductivity to electrical conductivity of a metal:
( pi^2 / 3 ) * ( (k/e)^2 ) * T
Bruce
On 31 October 2020 at 12:49 "Dr. David Kirkby" drkirkby@kirkbymicrowave.co.uk wrote:
On Fri, 30 Oct 2020 at 22:17, Luiz Alberto Saba las@intercat.com.br wrote:
My bad... copper is the second, losing only to silver, as a thermal
conductor.
I think you are mistaken. Copper is second to silver for electrical
conductivity, but I doubt that is so for thermal conductivity. I think
diamond, which is a form of carbon, is the best thermal conductor, and
around 5x better than copper.
Dave
--
Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@kirkbymicrowave.co.uk
https://www.kirkbymicrowave.co.uk/
Telephone 01621-680100./ +44 1621 680100
Registered in England & Wales, company number 08914892.
Registered office:
Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United
Kingdom
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-----Tobias wrote-----
Also an interesting material when high thermal conductivity is considered
is boron nitride. It is around five times better than copper, comparable to
diamond and can be sintered to a ceramic material.
Of course the Wiedemann-Franz-Lorenz law doesn't apply here as it is a very
good electrical insulator.
A boron nitride OCXO would indeed be interesting! :-)
About 30 years ago, in my previous job as head of TeleQuarz oscillator
division (now Vectron->...Microchip), we had used AlN hybrid substrates
replacing the FR4 PCB in OCXO. We had built up a complete hybrid
manufacturing line for that. Aluminum Nitride has an extremely high thermal
conductivity while being an isolator. The thermal performance was excellent.
However it was nearly impossible to solder on it manually (e.g. to change
components for fine tuning purposes) because the solder literally was
freezing on the substrate and even a special soldering iron with temperature
regulation directly in thee tip (Metcal) was not able to deliver sufficient
heat fast enough. After a few years we stopped this line.
Have a nice Sunday.
Bernd
Hi
….. and of course, there was an OCXO that used a beryllium oxide substrate
in pretty much the same way (inner oven in a double oven). Same basic issues
and not exactly cost effective.
The alumina substrate lives on in a number of miniature oven designs.
Bob
On Nov 1, 2020, at 5:20 AM, Bernd Neubig BNeubig@t-online.de wrote:
-----Tobias wrote-----
Also an interesting material when high thermal conductivity is considered
is boron nitride. It is around five times better than copper, comparable to
diamond and can be sintered to a ceramic material.
Of course the Wiedemann-Franz-Lorenz law doesn't apply here as it is a very
good electrical insulator.
A boron nitride OCXO would indeed be interesting! :-)
About 30 years ago, in my previous job as head of TeleQuarz oscillator
division (now Vectron->...Microchip), we had used AlN hybrid substrates
replacing the FR4 PCB in OCXO. We had built up a complete hybrid
manufacturing line for that. Aluminum Nitride has an extremely high thermal
conductivity while being an isolator. The thermal performance was excellent.
However it was nearly impossible to solder on it manually (e.g. to change
components for fine tuning purposes) because the solder literally was
freezing on the substrate and even a special soldering iron with temperature
regulation directly in thee tip (Metcal) was not able to deliver sufficient
heat fast enough. After a few years we stopped this line.
Have a nice Sunday.
Bernd
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