Capacitor Maximum Temperature - Page 1
Forum section: electronics / beginners

author: schwarzrmsu
author_rank: Contributor
timestamp: July 25, 2015, 05:35:21 pm
content: I am currently working on a design that includes a 105C ambient. I have spec'ed in X7R ceramic caps throughout my design which are rated to 125C. I am concerned about board temps in certain areas coming close to or exceeding 125C in a worst case scenario.Does anyone have experience with ceramic caps and teetering on this max temperature line? Is this a failure threshold? Does the capacitance start to vary? Please let me know what to expect for these capacitors when they approach/cross this max temperature threshold.As always. Thank you very much for any help/input. Also if there is a thread which covers this exact topic please simply point me in the right direction and I will delete this thread. Thank you.

author: Zero999
author_rank: Super Contributor
timestamp: July 25, 2015, 06:04:12 pm
content: It will be fine as far as not blowing up but it doesn't mean the circuit will work.Have you considered the voltage coefficient?The capacitance goes down, as the voltage is increased.http://www.edn.com/design/analog/4402049/2/Temperature-and-voltage-variation-of-ceramic-capacitors--or-why-your-4-7--F-capacitor-becomes-a-0-33--F-capacitor

author: schwarzrmsu
author_rank: Contributor
timestamp: July 25, 2015, 06:16:42 pm
content: I tend to spec in caps that have a voltage rating well above the worst case voltage input. Also have a number of input protection devices such as ESD caps, TVS Diodes and MOV's.For example. Our nominal input voltage is from 9-16V and worst case scenario around 24V. Our caps tied to that rail are rated at 50V.

author: Gyro
author_rank: Super Contributor
timestamp: July 25, 2015, 06:33:06 pm
content: Don't X7R and Y5V caps suffer a slow reduction in capacitance as they age, which can be at least partly restored by heating them above their curie point.I wonder if they might actually degrade less at extended high temperature. The curie point appears to be at 125'C according to...http://www.johansondielectrics.com/technical-notes/product-training/basics-of-ceramic-chip-capacitors.htmlEdit: Might be worth further investigating anyway as it is clearly a temperature where 'physical stuff happens'. If I remember correctly, Tantalum is often used for borehole logging instrumentation.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 25, 2015, 11:14:23 pm
content: Note that the combination of temperature and voltage will reduce the capacitor's value by much more than its tolerance value.Yes, they age as well. Aging is logarithmic with time, and for X7R, I believe, within nominal tolerance.I never consider anything of worse tempco than X7R. It's bad enough having to deal with that.C0G is preferred for high energy density, but rarely available in large enough values; and painfully expensive when it is!PPS (film) as well, which I think is rated for higher temperatures. But pricey. If you really need high temperature and reliability/survivability, you may need wet slug tantalums (mil spec, $$$$) or worse.Tim

author: schwarzrmsu
author_rank: Contributor
timestamp: July 27, 2015, 12:44:34 pm
content: Thank you for all of the help,This is what I assumed, but wanted to make sure. Right now my worst case ambient is what it is, and I do not see the potential to upgrade all of my caps to X8R due to price point.Thanks again!