[sdiy] What's all this decoupling cap business??

[Paul Schreiber]

The 0.01uf decoupling versus 0.1uf decoupling is a "leftover" from about 1982. Before then, caps
were the round, 10mm 'ceramic disc' types. However, about 1981 a company called AVX invented a
technology called "monolythic multi-layer" capacitors. Instead of 2 parallel plates with
dielectric in the middle (ceramic disc), the caps were made like stacking a deck of cards,
alternating plates and dielectric.

The upside was the *physical size* of the caps (in this case, the *height*) was GREATLY reduced.
Since the actual cap was tiny, you could make them *axial* leaded (like a resistor) and, (drum
roll, please)..........use an auto-insertion machine without a special handler! If you were IBM,
AT&T or Tandy, this was a HUGE deal.

Now, AVX had a good thing going, and they chared out the a** for them (the AVX sales rep at Tandy
went from a Chevy to a Mercedes within 8 months), but....and this was a big but......the
capacitance (at THAT time) was limited to 0.022uf.

So, let the battle begin! All the ceramic disc people could do is claim cheaper and larger
capacitance. But, AVX published literally 50 "white papers" showing that 0.01uf was fine. Now,
you don't suppose that had ANYTHING to do with the fact they couldn't produce 0.1uf caps, do you?

However, I still use 0.1uf although MOTM has Kemet caps, not AVX (basic patent has expired, Kemet
cheaper).

Just is little historical perspective, showing how "standard engineering practice" can be
initiated by MARKETING :)

Paul S.