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Free Tools for  Board & PCB Designers

Control Impedance  Calculators

PCB TOOLS   FROM  EEWEB

Toolkit of Saturn

http://www.saturnpcb.com/pcb_toolkit.htm

Viewers for PCB Layout Design SoftWare

http://www.cadence.com/products/pcb/Pages/Downloads.aspx

OrCad Light Schematic Capture Tool

http://www.orcad.com/buy/try-orcad-for-free

Gerber Viewer Free Download

http://www.wssi.com/index.php?option=com_content&task=view&id=212&Itemid=213