I've heard it said both ways. But what is the deal? Well since decoupling caps 
are intended to minimize switching noise, which shows up at the pwr pin, what 
we're trying to do is dump the noise to gnd. This means minimizing noise on 
traces, so vcc trace(s) should be as short as possible. I've seen the Moto book 
too and it confuses the hell out of a lot of people. Does the Moto fact book say
why the caps should be closer to gnd??

Theoretically the multi layer construction would seem to mean that since there 
are no traces, (a surface mount cap does require a trace/via, however short, to 
feed to the plane) the caps are filtering noise all across the board. Does this 
make sense?

Pete Waddell

______________________________ Reply Separator _________________________________
Subject: Re: Placement of bypass caps
Author:  [log in to unmask] at Internet
Date:    4/5/96 4:18 AM


     Mr Brooks
         The old rule of tumb was to set by-passes next to VCC so you did 
     not have a pwr trace running on top of your board the length of your 
     IC.
        How ever today most boards have planes for pwr, gnd So a even 
     matrics of bypasses across the board will do the trick.
     
     All you are doing is decoupling vcc,gnd, if done correctly the board 
     and parts will not make noise.
     
     
     
                           Hope this helps
                           DM PAVONE
                           Micros
     
     
______________________________ Reply Separator _________________________________
Subject: Placement of bypass caps
Author:  [log in to unmask] at SMTPLINK-Micros 
Date:    4/4/96 5:45 PM
     
     
I have several sources (including the Motorola FACT book) that say bypass 
caps should be placed as close as possible to the GROUND pin of the IC (not 
the power pin.) But I have seen few really specific discussions of why this 
is so.
     
Some of my customers insist on having them placed as close as possible to 
the power pin.
     
Can anyone give me a definitive explanation of where they should be placed, 
and why?  Thanks
     
Doug Brooks