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One of my boards, which contain solely passive components, may be subject to high thermal cycling (up to +/-100°C, but tradeoff down to +/-30°C is possible).

What sort of degradations can they experience from this?

It seems I need hints and leads, keywords (though an explanation for my understanding would be welcome), as I can't seem to find reliable data on that on internet (I only found a graph of the core losses in an inductor over a range of cycles), not even not-so-reliable data.

Context, if required: it's an impedance matching (including balanced/unbalanced conversion) circuit for a 169MHz dipole antenna.

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The characteristics of passive parts will change significantly over the temperature range (perhaps several percent for capacitors and inductors), and the lifetime of parts will tend to be significantly less at high temperatures than at low (rule of thumb is that lifetime halves for every 10 degrees C increase in temperature.

None of that is what you asked specifically about- cycling, which will tend to cause connection (internal and external) failures, particularly if there are many thermal cycles over the product lifetime. You might want to search reliability data from NASA, automotive and similar industries. I recall a case involving power semiconductors where failures were occurring in a matter of months due to themal cycles of a few seconds. The problem was solved by metallurgists, not electrical engineers.

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