Ceramic vs Thin Film Capacitors
So I just learned today how much better thin film caps are compared to cermic caps when it comes to temperature stability. I was designing a band pass filter today with a fairly high Q, and I noticed the center frequency kept on shifting if the filter heated up at all. I replaced the cermic caps with thin film and BOOM, problem fixed. The center frequency was rock solid at temperature. Only problem now is since the thin film is much bigger I couldn't use the same SMD foot print for the PCB I made so I am going to have to make another one.
Out of curiosity I heated up each capacitor while measuring their change in capacitance. Below is the drift of a 1uF size 1206 SMD ceramic capacitor heated up to 200F. It changes around .4uF! That's quite a lot.
Now look at the results from the 1uF smd thin film under the same test conditions. Much better right?
I am not going to start using thin film instead of ceramic in all my designs from now on though. Notice in the first picture their difference in size for equivalent values. On a PCB where size is important and the accuracy of the capacitor values isn't, I'd still use a ceramic capacitor over the thin film. Thin film caps are also generally more expensive as well. I'm sure I could write an article on the befits of all the different types of capacitors under the sun, but I will probably leave that for another day.
