cctalk Digest, Vol 47, Issue 30, message 30, identify a capacitor - test-drb@ccmp.vtda.org

18 Jul 2007

...
  Message: 30
 Date: Tue, 17 Jul 2007 17:16:16 -0600
 From: "Michael B. Brutman" <mbbrutman-cctalk at brutman.com>
 Subject: Re: Help identifying a capacitor 
...
  Some of what I'm reading says put the capacitor
near the power supply,
 and other things are saying get it as close to the chip as possible.

 The board I posted about is not optimal in this regard.  It's an ISA bus
 to PCjr bus adapter, so there is no TTL logic anywhere on the board -
 the individual ISA cards have the TTL (and hopefully bypass capacitors).
  In this application was the designer just trying to 'clean up' the
 voltage sources for the TTL on the cards a little bit?

From some years in pcb design shop. 
Bulk decoupling where the power enters the board 10-100uF + 0.1uF.
Then a 0.01-0.1uF per Ic (for TTL that is).
Keep the traces from the power pins to caps as short and fat as possible.
Powers should ideally be planes or gridded traces.

Newer logic families / packaging (TQFP, PLCC Etc), usually have very 
specific decoupling requirements set my the manufacturer 