What causes chip capacitors to change values?
Got any more background that just that?
There are three ways a capacitance can change, and I can see any or all of them happening with age. The electrolyte material could undergo some chemical change, the spacing between the plates could change, and the size of the plates could change. I don’t know which would dominate.
The capacitance value can temporarily change somewhat with temperature. The capacitor can be permanently damaged (and therefore change value) by exceeding its specifications, like over-temperature or over-voltage.
There is no one single type of “chip capacitor” and different materials are used for the dielectric. Some dielectrics age better than others. Some have a better temperature stability as well.
Everything.
For starters, they have a tolerance (e.g. ± 5%). Soldering might permanently shift the capacitance value a couple percent. And capacitance is a function of temperature (“tempco”). There are environmental factors such as humidity, compression/tension, aging, vibration, etc. that can change capacitance. And there are electrical factors such as voltage and frequency that can also change the capacitance.
The sensitivity of a capacitor’s value to these things is highly dependent on the type of capacitor, and how it is used.
A lot of this is going to depend on the type of capacitor. Aluminum caps are suseptible to the electrolytic drying out. They also suffer from the vents being blown (which leads to the loss of electrolytic.)
Ceramic caps sometimes have problems with cracking. The caps get twisted or pressed, and the plates inside them will snap, leading to either incomplete connections or shorts across the plates.
In almost all types of caps, the operating temp will affect the capacitance, as much as 50% between the low and high end of the cap’s designed temp range. 5, 10 and 20% tolerance ranges are all very standard.
All these and ESD damage too.