In a message dated 2005-08-08 06:18:48 PM Eastern Daylight Time, [EMAIL PROTECTED] writes:
> I have a small dense board with surface mount and through hole on both > sides. > > Because it is so dense I want to add some internal layers to assist in the > signal routing. > > Is there any recommendation for the internal layers (i.e. one is a ground > plane and the other is a signal layer). > > I don't require a power plane. > My experience with such boards has been a mix of digital, very low-level analog, and RF/microwave all on one board. The strategy that has worked best for me is to have one internal layer be a ground plane (common to all three types of grounds). Crosstalk effects are controlled by placement, not by separating the grounds - one very common ground does indeed work best in most cases. Such boards have always been almost completely carpeted with parts on both sides; I work very hard at placement to allow critical signals (and actually as many signals as possible) to run directly pin-to-pin on the surface, with no vias. That leaves that other internal layer for "long lines" (in this context, "long" is anything in excess of about ½"). It takes some planning to avoid needing to cross over traces on the long-lines layer; I have at times had to use a split plane to create a "trace" on the ground layer, but that's best avoided. Parts placement is extremely crucial to such a layout. I may spend two weeks getting the placement right, and do the routing in half a day. Steve Hendrix ____________________________________________________________ You are subscribed to the PEDA discussion forum To Post messages: mailto:[email protected] Unsubscribe and Other Options: http://techservinc.com/mailman/listinfo/peda_techservinc.com Browse or Search Old Archives (2001-2004): http://www.mail-archive.com/[email protected] Browse or Search Current Archives (2004-Current): http://www.mail-archive.com/[email protected]
