Well, first of all, I had the oppurtunity of having Doug Smith as a boss.
I learned invaluable lessons from him before he finally decided to break
free from my former company to start his own consulting business.
The second important thing was having a chamber in which to literally
live with a product to get to know it intimately. Or have an area for
somewhat reliable scans. You have to do a detailed analysis of the
board before you can begin to start recommending things.
Also, please understand that there are obviously some that will remain
trade secrets and I make no apologies about not sharing those with anyone.
The understanding was that "all things being equal" change one thing.
This took a lot of work, a lot of scans, of one product. None of this
may have any correlation to your particular product. But it turns out
that much of the results were based on some very simple concepts
and methods.
1. Interference from one interface card to the next as they are lined
up next to each other could be reduced by as much as 15dB by
simply changing the position of the offending card so that the
component side was not facing any other card. In other words,
the board itself could be as much as a 15dB barrier to interference.
2. Starting from a 2-layer board and increasing layers by 2, emissions
from the board could be reduced by approx 10dB with each succesive
2 layers. I.e., if a 2-layer board was emitting at a certain level,
the 4-layer version could be 10dB lower. The 6-layer version could
be 10dB than the 4-layer. Maxing out somewhere around 8 layers.
3. Moating and bridging some output interface on a board could have
as much as 15dB drop in emissions.
4. Ground studs thru the board to the metal chassis in close proximity to
interface connectors could have as much as 30dB drop in emissions.
If you are interested in this type of thing, there's no general checklist
that can be dropped out of the air to fit your particular product to
produce the specific results above. A thorough knowledge of your
product's emissions and sources is absolutely necessary.
Regards, Doug McKean
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