[sdiy] ceramic capacitor voltage rating

[Daniel Kruszyna]

I've heard the rule of thumb to use twice the expected
voltage rating for decoupling capacitors, but am
wondering how necessary it is. Particularly, I'm working
on a fairly dense surface mount pcb and the voltage
rating determines the minimum package size I can use.

I'm using Panasonic ECJ series parts:
http://www.panasonic.com/industrial/components/pdf/abj0000ce4.pdf

I thought that this spec looks pertinent:

------------------------------------------
  Dielectric
  Withstanding
  Voltage

  No dielectric breakdown and/or damage

  Test voltage : Rated voltage 250 %
  Duration:1 to 5 s.
  Charge / Discharge current: 50 mA max.
------------------------------------------

Should it be okay to use less of a margin than x2?

-- Daniel