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EMI reduction and PCB stack up related query.

Rani.pohane , 11-16-2016, 01:22 PM
As per my study, to reduce EMI, we should keep the prepreg height less than 10 mil and clearance between tracks greater than or equal to 10 mil with FR4 material which has Dk of around 4.3. Agree with concept that with this arrangement emitting charges will be absorbed in Lower GND plane as the dist between plane is less than that of nearby track, But my Question is....Solder mask has a Dk of around 3.3 which is less than FR4 so will these emitting charges will go through FR4 to GND plane or through solder mask to affect nearby track? Any more detail study points are welcome.
mairomaster , 11-17-2016, 08:33 AM
I don't think you need to worry about the properties of the solder mask with respect to cross-talk. I am quite sure that its contribution to the cross-talk (either positive or negative) is negligible. Even if you don't have solder mask (for the sake of the argument) and you just have air (Dk of 1.0) over your surface tracks, you will still be fine if you have the appropriate spacing between your tracks and distance to the ground plane below.
Rani.pohane, 11-18-2016, 07:23 PM
Hi Mairomaster, Thanks for the reply.Well,that term APPROPRIATE SPACING is the main area of discussion and confusion. So let's take some figures.If we keep 6 mil of CLEARANCE BETWEEN THE TREACKS (As per the IPC 2221 table 6-1, clearance for the tracks with voltage 0-15 is 0.1mm or 4mil) and PREPREG HEIGHT OF 4mil (FR4 with Dk~4.5) between track and GND plane . So do we need to worry about the properties of the solder mask with respect to cross-talk in this case ?Another off the traffic query, I am using IPC2221 standard as a reference for PCB design, is it mostly used standard? or is there any other mostly or widely used standards for PCB Design? Other suggestion are welcome if any.
mairomaster , 11-21-2016, 06:11 AM
To clarify myself - I don't think you need to worry about the solder mask with respect to cross-talk in any case.

I haven't used IPC-2221. For general PCB design I mostly rely on my experience and knowing what works in a particular case, what can be manufactured reliably, etc. For the footprints in my company's libraries I am trying to stick to IPC-7351.
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