[SI-LIST] Buried Capacitance thread comments

My comments on the past/subject exchanges

From Ron Miller
Does anyone have published articles or books that document this use prior
to 1989?

[MLC] Basic capacitance with thin films was of cource used many years prior 
to 1989, but (as one individual pointed out) it's the manufacturing processes 
that are patented. The processes achieved a reliable way to obtain higher 
voltage breakdown using PCB processes.

[MLC] The "4 mil" thickness originally quoted actually refers to an original 
military specification minimum requirement and also to the Bell Core 
specifications prior to 1989. The Zycon (then Hadco, now Sanmina) process was 
subjected to a rigorous qualification process and approved (as reflected in 
the Bell Core specifications) as the only source qualified for use of less 
than 4 mil thick PCB dielectrics. The thickness used by Zycon was indeed 2 
mils.
********
From Chris Cheng
I've used Zycon before thinking they can lower EMI or 
power noise but the reality is they don't and the reasons
are stated above.

[MLC] Sorry, Chris, but ;you are WAY off on this one. Check out the 
literature from 1989-1991 and the electronic "Product of the Year" award 
given to Zycon for the ZBC 2000 product (the original name) for EMI 
reduction. I know you are practicing some good design to achieve Class B 
certification, but good power/ground plane decoupling plays a major part in 
that success.
*********
From Chris Padilla
I use plenty of sub nf caps to help curb emission problems in a lot of my 
systems and they do work just fine and are necessary.

[MLC] 
**********
From Chris Padilla
EMI is a system level phenomenon and the size of your PCB most certainly can 
resonate at 
frequencies well above 100 MHz.
*********
From Chris Cheng
I suggest you do the following experiment (I've done it so
many times to toy with EMC engineers).
Take a system board with your favorite sub nf caps, do an
EMI scan, replace every single sub nf caps with .1uf or
.01uf on the same PCB and redo your scan. Let's see if they
make any difference.
*********
From Lee Ritchey
It's the plane capacitor that does all the work.  Lots of good
reseach that backs this up.
*********
From Chris Cheng
Clarification, its the plane capacitance between
the power/gnd pair that sandwich the signal layer
that provides the return path for the signal image 
current. Nothing to do with Zycon planes. BTDT.
********
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