[time-nuts] Mini ovens packaging

Guillermo Sobreviela Falces Guillermo.Sobreviela at uab.cat
Mon Aug 15 07:07:41 EDT 2016


Hi Attila and Magnus! It is a pleasure to meet again (this time via time-nuts)! :D

Thank you very much Didier and Bob for your feedback (Also Attila and Magnus), I attach some characteristics of the desired oven:

-        Temperature stability of 0.1ºC, what means temperature control included.
-        Inner cavity of 2cm x 2 cm x 1 cm.
-        In addition to the connectors needed for the oven I need 3 pins reserved for the system.
-        The system must be included into the oven via a chip socket, or pasted inside with silver paint and wire bonded to the oven connections.
-        PCB compatible oven

I have been looking for a Peltier junction in order to reduce the oven temperature to 50ºC (Reducing the temperature is good for my system). But the temperature stability is a must and I am not sure of the precision level I can reach with a Peltier junction.

Also, I have been designing a temperature detector based in a power divider using a resistor and a RTD that will trigger an OPAMP (comparator). This OPAMP will activate/deactivate a high power BJT or FET transistor that will warm the oven. In order to reduce the thermal inertia I thought to make an escalated temperature detector as the shown in the attached picture. The main idea is have a fast heating and reduce the warming current when the temperature is approaching the final equilibrium temperature (120ºC).

Another problem is related to the shell of the oven. It should be metallic in order to equilibrate the temperature, but, would it be interesting to use an external shell made of an isolator material in order to reduce thermal loses or will it difficult the thermal stability?

After this discussion, would it be possible to buy a system that meet the characteristics described above? I am not sure about I would be able to design and test this system on time, but I need this kind of oven with this temperature stability as soon as possible (This is why I am looking for a commercial solution).

Greetings and thank you all in advance!


________________________________
De: time-nuts <time-nuts-bounces at febo.com> en nombre de Magnus Danielson <magnus at rubidium.dyndns.org>
Enviado: sábado, 13 de agosto de 2016 15:57
Para: time-nuts at febo.com
Cc: magnus at rubidium.se
Asunto: Re: [time-nuts] Mini ovens packaging

Hi Guillermo!

Nice to see you ask questions here!

(Attila and I met Guillermo at the EFTS and had many nice discussions
and nice time to hang out. He does his PhD in MEMS systems, which Attila
refers to. I also met him at IFCS in New Orleans when he came up to me
and Dr. Rohde and asked questions on phase-noise measurements. I hope he
got that resolved eventually.)

On 08/12/2016 11:59 PM, Attila Kinali wrote:
> Hey Guillermo!
>
> How is it going?
>
> On Thu, 11 Aug 2016 09:05:02 +0000
> Guillermo Sobreviela Falces <Guillermo.Sobreviela at uab.cat> wrote:
>
>> I am currently looking for a temperature compensation system for an IC
>> (Temperature range from -40°C to 120°C and chip area of 1cm x 1cm).
>> This compensation system has to be external to the IC and, as the power
>> consumption is not the main problem, I have been looking for a crystal oven.
>> The ideal solution will be a PCB compatible oven, but it also can be an
>> external element.
>
> I guess this is for one of your MEMS chips?
>
> What is the spec of the board's environment temperature?
> How big may the oven be?
>
> And I would agree with Bob that building your own oven would be
> actually a good idea. It is not that difficult. You need a rough
> estimate of what your thermal mass inside the oven will be, an
> estimate on what the thermal resistance between the inside and
> outside is, then can apply standard control theory to design
> a PI control loop to keep it stable.

I agree with Bob and Attila, try to build your own, to get something
working isn't all that difficult, and I think that in the end you will
benefit from having the knowledge and additional system insight.

A good test for the trimming of the stability is to turn it on while
cold. I learned this the hard way on a sample that a supplier had sent
me, it oscillated wildly on turn-on, which was obvious on the current.
The remaining oscillation caused the ADEV to have a bump, which was the
first feature I discovered.

For crystals, the oven is set to the turn-over point so that the oven
variations has least impact on the frequency. Do you have a suitable
turn-over point?

Another aspect to reflect on, and here I refer to Rick Karlquist's
paper, is the temperature gradient sensitivity. Do your device have
frequency sensitivity to temperature gradients in any directions?

Some crystal devices have achieved better performance by putting the
temperature sensing thermicaly close to the crystal, it's a generic hint
but it can be good to think about how it can be achieved in the long run.

Cheers,
Magnus
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