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I'm trying to determine the maximum non-operational limits of my system. The operational limits are easy to determine as they are provided in all of the datasheets for each of my components. However, a lot of my passive components do not provide non-operational or storage temperature limits. Currently my approach is to use the operational limits when no non-operational limits are provided. This means that my system is limited by ceramic capacitors (rated to +85ºC), which seems intuitively incorrect.

  1. Ceramics are usually quite resilient to high temperatures
  2. They have to survive soldering, which includes very high temperatures (lowest pre-heat temp I could find is 100ºC)
  3. From what I can see in the datasheets, heat affects capacitance which I don't care about while it's off

There are a lot of capacitors in my system but the ones in question are all ceramic caps rated to +85ºC operational. The following is a datasheet for an actual cap from the system which should be representative: cl03a104kp3nnnc capacitor datasheet

The best answers will be supported with facts and provide a method to determine the maximum non-operational temperature based on known factors (use the provided datasheet for knowns). That said, I would also appreciate a rule of thumb as a bonus. My gut feel is that as long as the solder doesn't melt the cap will be fine but I'd be happy to hear how others feel.

Follow-up: Just to be clear, when I say "non-operational" I mean that the system is assembled and in a real environment but the system is off. This is not shelf storage.

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With material degradation due to over-temperature, you won't find any hard and fast rules. Why? Because the material degradation depends on a curve that increase with temperature. The curve deals with mechanical and chemical changes that happen, most of these effects are known by manufacturers and sometimes they will share this data, but you have to ask. Most users don't need this and so only rated temperatures are provided. Let's dig into what we know about the temperature of the part.

Almost any electronic part (and this cap) can be put through 260C for at least 30sec and follow a reflow profile like this:

enter image description here Source: https://static6.arrow.com/aropdfconversion/7287aad747c6d8a778a4cf32f86caa437f956283/19-cl03a104kp3nnnc.pdf

From this we know that the part can survive 260C, but the manufacturer doesn't want the part to dwell at that temperature for more than 30s.

The temperature of 150C for 1 hr is okay and then the part degrades over it's lifetime for a X5R or less so for an X7R and almost no degradation over lifetime for a C0G.

enter image description here
Source: https://static6.arrow.com/aropdfconversion/7287aad747c6d8a778a4cf32f86caa437f956283/19-cl03a104kp3nnnc.pdf

The manufacturer didn't tell us anything beyond this, so if we wanted to know more, then the capacitors would need to be tested by a cognizant engineer or the manufacturer. The manufacturer may have additional testing information, but they might not. They are trying to guarantee their part under a specific set of conditions so it is unlikely that they would have additional information but it doesn't hurt to ask.

The other disappointing thing is we don't know (from the datasheet) if extending the time spent a 150C further degrades the part (double the degradation over time), only one test is shown.

So from this I would personally surmise that I don't want this part to get to 150C for more than 1hr. Also it should be noted that an X7R or C0G (which generally have higher operating temperature ratings) do not degrade with time and support 125C operating ranges in most cases. So I would go with a higher temperature rated part or contact the manufacturer. If cost is an issue then finding the rating would be a good idea, if cost is not then just go with the X7R or C0G.

Also the application is also worth considering, if this is for a bypass cap, then tolerance does not need to be accounted for in most cases, conversely a filter application (DC DC converter or analog filter does need a high tolerance part).

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  • \$\begingroup\$ Section 2-4-2 seems to be only related to aging, not heat. In fact it claims that the capacitance lost due to aging is recovered after heat treatment, not that heat ages or damages the part. Section 2-5 shows the temperature affects on capacitance but does not cover outside the operational bounds and does not go into whether or not this capacitance is recovered upon cooling. \$\endgroup\$ – Spartacus Oct 5 '20 at 19:55
  • \$\begingroup\$ Yep, we don't know whether it's related to aging, but we do know that they tested the part at 150C 1hr so that would not degrade the part. \$\endgroup\$ – Voltage Spike Oct 5 '20 at 20:05
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A simple practical suggestion would be maybe 100C. I'd expect it to vary with manufacturer, dielectric and construction FWIW. e.g. from AVX (operating temperature) 'Operating Temperature Range (ºC): Phenolic Coated -30... +85 Epoxy Coated -30... +125 So the encapsulation sets the upper limit, not the dielectric.

Do your data sheets not include storage conditions ? I suspect that in storage the main concern is getting damp.

A search shows you're not the first to ask this. Capacitor Storage Temperature vs Rated temperature

Digikey says ... Conventional X7R and X8R type ceramic capacitors are designed for applications up to 125°C and 150°C, respectively. At temperatures above 150°C, these types of capacitors typically suffer from degradation of reliability performance and severe reduction in capacitance, especially under DC bias conditions but this only seems to refer to operational use.

I doubt you'll find a 'fits all' answer never mind one based on 'facts' which may prove elusive !

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