Capacitors

What is it with nF that engineers don’t like? I purchased some various smd capacitors from digikey and they really like pF, going up to 10000pF, then switch to .1uF.
I had to think for a second with a microchip I’m playing with, as they have a .1uF capacitor on a VDDIO pin, then call for a 100nF on a VREG pin. :confused:

What am I missing?

Because capacitors are so tiny, there is almost no space at all for marking the value. With through-hole capacitors and hand assembly, you must have the value written on the cap.

So the 2-digits-and-number-of-zeroes system works well on pF and nF capacitors. There's no space to write the p or the n, so the range is continuous, in pF only.

Once you get to uF sized capacitors, there is usually enough space to write the units and more details.

Now that everything is SMD (Yay!) this is less important but the tradition remains.

Ok, I'll go with that. There just isn't any way they are putting any numbers on these smd's, nor could you read them if they did. Still, I'm a bit befuddled why they put ".1uF" right next to a "100nF" on this datasheet. Personally, if one will get messed up it's going to be the "."1uF.

The use of nF as 10 -9 is comparatively recent, before 30 or 40 years ago it was not used.
This is mainly because capacitors were either in the pF range for RF applications or the uF range for timing.

Before that, I remember listening to old timers and reading books that didn't say uF, they said MMF. Yes, all in caps, even. The old timers called them "micky-mikes".

just for kicks - micro-micro Farads !!

tinman13kup:
What is it with nF that engineers don't like? I purchased some various smd capacitors from digikey and they really like pF, going up to 10000pF, then switch to .1uF.
I had to think for a second with a microchip I'm playing with, as they have a .1uF capacitor on a VDDIO pin, then call for a 100nF on a VREG pin. :confused:

What am I missing?

In the old days there was no nano, pico, atto, femto, giga, tera, peta, exa.
There was only milli, micro, kilo, mega.

Capacitors were thus described using micros and micro-micros. µF, µµF
The manufacturers lagged behind everyone else I think. What's more they seemed
to have an aversion to millifarads (note there was never any aversion to milliohms). pF replaced
µµF but for some reason nF wasn't popular, perhaps because there was no pre-existing prefix.

I do recall some controversy of using "m" as a prefix instead of "milli". It was said there were too many issues with m/M and sloppy writing. The whole problem would rear it's head dealing with resistance and troubleshooting circuits and not so much the repair of the same circuit.

In the old days there was no nano, pico, atto, femto, giga, tera, peta, exa.
There was only milli, micro, kilo, mega.
[\quote]

I would say there was no NEED for any of those values at that time.