Short version: I understand resistor initial tolerance is commonly obtained through sorting process where manufacturer only picks resistor that has resistance within the advertised initial tolerance. Does MLCC manufacturer use similar sorting process to determine initial tolerance for capacitors?
Long story: This question is related to reliability calculation I have been recently doing where RSS method is used. When I try to find the worst case capacitance change, I combine all the random terms based on manufacturer spec sheet. Let's say for example this capacitor from muRata: GCM31CL8EL225KE07L. The specsheet can be found in this link. I have made the following assumptions when doing RSS for random terms:
- Capacitance change due to a random event such as high temp exposure, moisture resistance, thermal shock, etc. falls within the 3-sigma range, i.e. chance of being within stated change is 99.7% under such event (I could be wrong with this too)
- Capacitance change due to initial tolerance is uniformly distributed. For example, if the it is a 10% cap, its one-sigma (std deviation) is 5.77% and its 3-sigma is 17.32%.
I am guessing if manufacturer determines MLCC tolerance like resistor, I should use uniform distribution. But I would like to make things easier and assume this tolerance also follow normal distribution. This means the initial tolerance corresponds to the 3-sigma probability range. In this way I can make the RSS calculation easier without worrying about the square root of 3, simply calculating the squared sum of all random terms including initial tolerance. I couldn't find related information online and hope someone can help me here. If you can explain how you would use these random terms in RSS that's also much appreciated. Thanks in advance!