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Electrolytic capacitors service time is based on maximum operating temperature, among other things. When they are inside an SMD soldering oven, the temperature increases to over 375°C. Most of the capacitors are rated at 105°C.

Although there is no electricity flowing through the capacitor, will the increased heat reduce its lifetime?

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    \$\begingroup\$ The specified lifetime ought to be if you followed the solder recommendations from the manufacturer. If the manufacturer didn't specify temperatures for soldering, then it's a bad datasheet. Unfortunately the majority of datasheets for these are bad datasheets... I just peeked into a random Panasonic one and it does at least state which characteristics the cap should have after reflow soldering (and cooling). \$\endgroup\$
    – Lundin
    Commented Jan 17, 2023 at 11:36
  • \$\begingroup\$ I believe that capacitors are damaged less when unpowered and hot, and more when powered and hot. \$\endgroup\$
    – rdtsc
    Commented Jan 17, 2023 at 12:53
  • \$\begingroup\$ I think your 375 °C is excessive, reflow ovens should reach around 260 °C maximum during a lead free soldering profile. \$\endgroup\$
    – Arsenal
    Commented Jan 18, 2023 at 9:39
  • \$\begingroup\$ Yes, today I checked. It doesn't reach that much high temperature. \$\endgroup\$
    – Sadat Rafi
    Commented Jan 21, 2023 at 16:37

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Yes, it does degrade, but the capacitor specifications such as lifetime are given when the specific and allowable soldering conditions taken already into account, as you can't really use a capacitor without soldering it to PCB first.

So you will get the rated life time, if you do the soldering within rated temperature limits, within rated time limits, and within rated number of soldering cycles.

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