Your PCB designers and engineers need to understand basic antennas and have a few formulas at their disposal. Have them think like an EM wave. Where would you go in the circuit if you were an EM wave? What are the current loops and what is the area? What potential is on the daughter card and how much radiation will this produce. I find that doing this and then modeling in NEC gives me a feel for what is important and what isn't. Dave Cuthbert Micron Technology
From: [email protected] [mailto:[email protected]] On Behalf Of C N Sent: Thursday, March 11, 2004 10:46 PM To: EMC-PSTC Subject: Re: EMC Checklist 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 _____ Get more from the Web. FREE MSN Explorer download : http://explorer.msn.com
