Links

DESIGN TOOLS

This is an excellent program for calculating trace impedances, both stripline and microstripline. Recommended by IPC . See the calculator page for free downloads.    http://www.ultracad.com

CAM 350 is an excellent tool for editing gerbers, or updating old designs
for release to manufacuring. You can read Old Gerbers then convert to DXF.
http://www.downstreamtech.com/

GSVIEW, Ghostscript is shareware program for converting Schematic, Gerber,
and Drawings to ADOBE PDF. All you have to do is first print to a
postscript file from Windows. This will also do many sheets, then make one
PDF file for viewing on any computer. Also, one can convert the postscript
file to a JPEG or Bitmap file. Very handy, easy to use and fast.
http://www.cs.wisc.edu/~ghost/

These products are excellent for EMI/EMC control and suppression on PC boards and systems.  http://www.emicatalog.com

This group provides experienced EMI/EMC consulting and training.
http://www.emiguru.com

PCB Magazine includes latest trends, calculators, what's hot in PCB design.
http://www.pcdmag.com/

IPC Institute of Interconnecting and Packaging Electronic Circuits
http://www.ipc.org/

Controlled impedance differential pair field solver
http://www.polarinstruments.com/

Noise, Ringing, Damping, Transmission Lines and Signal Integrity information
http://www.sigcon.com

Here is a program from Agilent & HP which can help one calculate the width of copper traces for controlled impedance transmission lines. For RF, Radio, Fiber optic and high speed digital design applications. You can download it from the following address: 
http://www.hp.woodshot.com/

DLight Photography
http://home.comcast.net/~harrymarsh1/dlight.html

Here is a great design service for thermal analysis on printed circuit boards. See the links to references, articles and newsletters on The Cooling Zone.
http://www.biberthermal.com

Site of the most comprehensive science directory. DirectoryScience.com
PCB Design Directory