Hi

To do a good job of actually controlling the IC temperature, you will need to enclose it and the part of the board it
is on inside the oven. Toss in the wide temperature range (oven running at > 130C). That quickly becomes complicated.
You don’t mention a stability requirement. That also needs to be considered.

Have you considered just building your own heater?

Bob

Hey Guillermo!

How is it going?

On Thu, 11 Aug 2016 09:05:02 +0000
Guillermo Sobreviela Falces Guillermo.Sobreviela@uab.cat wrote:

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.

		Attila Kinali

--
Malek's Law:
Any simple idea will be worded in the most complicated way.

If you have to regulate over ambient temperature as high as 120C, you need
an oven that regulates at a higher temperature, maybe 125 at least or 130C.
You will have a lot of issues with long term reliability with something
that operates 24/7 above 120C.
Have you looked at a Peltier junction that would let you regulate at a
lower temperature like maybe 50C or so over the range you describe?
Peltier junctions can heat and cool and are not too difficult to use.
The actual temperature stability you try to achieve will dictate how much
insulation you need from the environment, but if you only need to regulate
within one or 2 C, you may not need a complete enclosure.

On Thu, Aug 11, 2016 at 4:05 AM, Guillermo Sobreviela Falces <
Guillermo.Sobreviela@uab.cat> wrote:

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:

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

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@febo.com en nombre de Magnus Danielson magnus@rubidium.dyndns.org
Enviado: sábado, 13 de agosto de 2016 15:57
Para: time-nuts@febo.com
Cc: magnus@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:

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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HI

To be meaningful, the stability number when run over the entire range needs to be looked at. If the range is still -40 to +125, that is a 165C range.
A stability of 0.1C implies a thermal gain (reduction in change) of 1,650. That is significantly higher than the “few hundred” one might expect out of
evan a fairly good component oven.

If the stability is inclusive of gradients over that cavity size, the task just became more difficult. That goes up a bit more if power is being
dissipated by parts inside that volume.

There are two basic problems with junction based devices:

1. They pump energy poorly. Getting a 160 degree delta likely requires a stack of a large number of devices. The power required goes up with ever level in the stack.

2. All of the power from the stack ultimately needs to be discharged. Water cooling often comes into play.

Building the entire oven into a MEMS is a commonly used solution to this sort of problem.

If the guesses above are correct, this is not a simple oven design. There are a lot of factors that will need to be considered. One not mentioned so far is the number of units you need to produce. That will impact the design as much as anything else.

You need a custom design.

Bob

Hoi Guillermo,

On Mon, 15 Aug 2016 11:07:41 +0000
Guillermo Sobreviela Falces Guillermo.Sobreviela@uab.cat wrote:

As Bob already wrote, this value has little meaning without the temperature
range at which you want to operate the oven. From what you wrote, i guess
it will be some office environment or a place with relatively low temperature
swing? Then it should be easy to get to that level.

That is nice and small. How much space do you have on the outside?
Does it need to fit into something else?

That's easy to acheive. Mechanically, the easiest construction would be
to use a PCB with cut-outs and put some CNC'ed aluminium case through
these cut-outs. The PCB then acts as mounting system and electrical connection.
The thermal conductance of a PCB (without copper) is moderately low.
Maximum temperature for standard PCB's is 80°C, for higher
temperatures you need special base material with higher Tg (at least 20°C
higher than the maximum expected temperature).

I do not get what you mean with this.

For a classical oven, the inner temperature is defined by the maximum ambient
temperature and the minimum required temperature delta. A minimal temperature
difference is needed to keep the loop stable.

Peltier elements have the nice advantage that you can cool directly and
thus are not bound by the temperature difference to ambient. But you need
to be aware that Peltier elements are not symmetric: They are much better
heating elements than cooling elements. This means that you need to design
your loop carefully to prevent oscillation.

Instead of using a bang-bang controller as you have shown, it is better to
use a linear controller, that controls how much current is flowing
through the FET. This eliminates temperature cycling and current spikes
that may disturb your oscillator.

Depends. In theory, it's good to have the oven well isolated. But you need
some way to get the heat out of the oven. And this thermal resistance
must be low enough to keep the loop stable. You need to calculate the
thermal parameters for this. If you are not 100% confident with this,
start with an unisolated oven, see how it performs on a step response,
add isolation (can be something as simple as some pieces of cardboard),
tweak the loop parameters a bit and check the step response again.

It is very unlikely that you will find an off the shelf system that does
what you need. But you can find a company to design you one. Most people
with a decent electrical engineering knowledge should be able to do so.
It is also relatively easy to do it yourself, if you are not out for optimal
performance over an wide range of temperature and are ready to measure
and tweak the system parameters a bit after production.

The simplest is probably to start with a PI controller, which are fairly
easy to keep stable and only have two knobs to turn. Use that as a basis
with some simple mechanical setup. That should get you already to the 0.1°C
in an office environment.

			Attila Kinali

--
Malek's Law:
Any simple idea will be worded in the most complicated way.