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Would electronics survive if the ambient temperature of the environment was between 120 °C (250 °F) and 260 °C (500 °F) and the operating time was between 30 minutes and 2 hours? After this time the electronics would cool back to room temperature.

As others have mentioned, items going through reflow would hit these temperatures, but only for a short period of time.

Of course this would be based on "normal" components, not "space grade" items.

Would some kind of coating help? Something like High Temperature Epoxy Encapsulating & Potting Compound 832HT Technical Data Sheet.

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Not ordinary components, no. There may be some special ones for unique applications (sensors in oil drilling?) but that will get expensive and constrain your choices quickly. Can you insulate well and include an "ice pack" of phase change material (probably not water, potentially even a lump of low melt metal alloy) that will have to be replaced/refrozen before the next use? – Chris Stratton Mar 15 at 16:23
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I can't help but be curious where you are planning to run this.. – Owen Mar 15 at 21:25
    
Processes that produce transistors that will function at 200C+ junction temperatures are cutting edge, Silicon Carbide mosfets that can handle junction temps of up to 240C are commercially available, as for logic and MCU no chance – crasic Mar 16 at 1:04
    
@crasic High-temp SOI can run to 300C, and SiC can definitely exceed that. Definitely in the expensive or experimental regime. – W5VO Mar 16 at 6:34

This is well beyond the ratings of most parts. You can expect outright failures, major departures from guaranteed specs, flaky (eg. partial) operation, huge leakage and so on. Unless you buy qualified parts, you are on your own, so you are looking at major costs, and it may not be possible to thoroughly test some parts without inside information.

Downhole instrumentation can at very high temperatures, but parts that are qualified for that operation are very expensive (eg. Honeywell) and have rather disappointing performance to boot.

It's possible to design an electronics package that will survive an external temperature of 260°C for a substantial period of time, by keeping the internal temperature to something reasonable like <125°C, but that's more of a mechanical engineering problem than an electronic one. For example, by use of good insulation and a phase-change material.

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@Sphero thanks very much for your reply. That's basically what I'm finding. The components themselves won't work, but possibly with the right "protection" it might be possible. Thanks! – Dave Mar 16 at 13:18

We have to mount electronics on the inside of jet engines (the cooler areas) and we use cooling air fed via a pipe. There isn't an option for us - if we want functionality for more than a few seconds we have to cool the electronics.

We use normal temperature rated components. Reflow does create high temperatures but remember the parts are not powered when this occurs.

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good point on the reflow and the parts being off at the time. – Dave Mar 16 at 13:18

"Would electronics survive?" Yes, if the datasheet says so...

Why on earth would the manufacturers do this to you? Why would they jot down such and awful requirement? Because, when the temperature rises the integrated circuits fail.

Why do they fail? From the wiki:

Electrical overstress

Most stress-related semiconductor failures are electrothermal in nature microscopically; locally increased temperatures can lead to immediate failure by melting or vaporising metallisation layers, melting the semiconductor or by changing structures. Diffusion and electromigration tend to be accelerated by high temperatures, shortening the lifetime of the device; damage to junctions not leading to immediate failure may manifest as altered current-voltage characteristics of the junctions. Electrical overstress failures can be classified as thermally-induced, electromigration-related and electric field-related failures

Another reason is humidity, get a little water in a small space and then turn the temperature up, you just made popcorn! Water gets into everything. (unless you actually take some prevention, they don't stick the humidity sensors in the IC packaging for no reason).

I've talked with other engineers with intermittent failures. The conversation is the same, they forgot to do a few key things like:
1) ESD prevention
2) Humidity control
3) Thermal profile control

After they control these things, the intermittent problems go away, if you want to go in the other direction, you will be creating problems for yourself. Would it be acceptable to have a 1% failure rate? What about 0.1% or even 0.001%?

You are more than welcome to try it with the components you have, and you are more than welcome to play russian roulette. But be prepared to deal with the consequences.

Manufacturers know why their chips fail, they have teams of people and equipment to rip of the epoxy layers and look at their ic's and determine why they fail. Then they write requirements, the absolute maximums and the temperature profile for the IC packaging are a bible for ensuring your components don't fail.

Of course you have options, price vs temperature. They make components that can take abuse and have appropriate materials and manufacturing methods to take such abuse.

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Thanks very much for the answer. Some very good information. The 3 reasons for failure is good. I'll be keeping this in mind for sure. – Dave Mar 16 at 13:29

A water jacket will never get hotter than 100°C — at least, until it runs out of water.

You would have to figure out how much heat will flow into the jacket from outside during the operating period (thermal insulation will help reduce it) and make sure you have enough water to absorb that amount of heat.

You'll need a way to vent the steam, as well.

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Having done thermal tests for GPUs, 2-hours is the length of time I would consider steady-state temperature. So I wouldn't think your application is considered short term. If you have to build electronics, here is what I would suggest:

1) Buy components with military temperature ratings. Their temp ranges are wider, but unfortunately their advantage mainly applies to the colder side of things.

2) Minimize the plastic used in connectors. They are what usually fail when reflowing at lead-free (260oC) temperatures.

3) Try using heat shields to increase the time it takes to warm up.

4) Try doing the 'opposite' of good thermal pcb layout. Don't include spokes when soldering a leg to the board. Try to make pads as large as possible. I get frustrated when trying to hand-solder a component whose one end connects directly to the ground plane. The solder iron heat gets transported away from the solder joint so easily, I practically damage the component from applying the iron for 30-seconds. If you try this approach, maybe your component would get to 260oC, but the PCB copper is whisking the heat away.

Edit: just remembered that microcontrollers get damaged at about 115°C. Maybe older chips whose transistor size is not <65nm might withstand the heat better. You may want to have your sensors inside the turbine but your digital circuits remotely located.

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thanks very much for the answer. There are some good ideas in there. From what I've read the shielding and cooling are the best bets I think. The 2hrs would be max, and probably not at that temp either. That is really a worst case scenario, but that's also why I used it in the question. Thanks! – Dave Mar 16 at 13:21

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