SMD NPO Capacitor Visuals

[metrologist]

I have a lot of scrap boards that I want to salvage a good low tempco 1nf capacitor. What do they look like and how can I measure the tempco? I have a DE5000 tester for the measurement. The caps are generally a light tan, brown, creame, orange, purplish, gray, and black. Some are taller than wide and some are wider than tall, and some are square aspects or cubes. 

I tried a brownish 1nF cap using an avr component tester and placing a hot object on the cap then a frozen one (both non-conductive) and I saw 1007 to 1025pF. Is it that simple, 18ppm ~100C?

[T3sl4co1l]

C0G (or in the old scheme, NP0; but not NPO as frequently typoed!) is usually a lighter color, yes, with type 2 (usually X5R and similar) being tan or brown.  (Black is probably a ferrite bead or inductor.  Bright colors may be tantalum or niobium polarized capacitors?)

C0G are rare to find over 1nF or so, or even 220-470pF in the smallest sizes (0402 and below).  That's where the cost advantage of type 2 dielectrics take over.

Yes, a stable value over temperature is a strong indicator that it's C0G.  The value will also be stable over voltage, which can be tested by measuring the rise time of a square wave into an RC filter, varying the average level (DC bias) of the square wave to see if the rise time changes.  (That's, uh, a little hard to do without a signal generator and oscilloscope, but you can just as well measure it directly, by connecting two capacitors in series, biasing the middle node with a large value (many Megs?) resistor, and varying the bias voltage with respect to ground.  Your AVR tester will measure it just fine this way.)

Tim

[wraper]

C0G usually have light color like white, light grey, slightly pink. Brown caps are basically guaranteed to be type II/III ceramic.

[metrologist]

ewe Folks are awesome! Google is not helping me too much lately, especially if you can't get the correct term!  I actually did notice it eventually and results were better, but still covered everything under the sun... I also thought of concentrating on the circuit in which they are placed, as they are often RF related, such as decoupling caps probably are not of much interest here...