Controlled Impedance

Controlled Impedance Articles:

Which Impedance Calculator is Right ? Randy Clemmons

What is Characteristic Impedance - Eric Bogatin

The How and Why of Obtaining Accurate Impedance Calculations - Lee Ritchey

Resistive Nickel Losses - AP17 Polar Instruments

Optimizing Impedance Discontinuities of SMD Pads  Altera - AN-530

Online Trace Impedance Calculator Links:

cgi-wcalc - Dan McMahill

EMC LAB INFO

Circuit Sage

Mantaro Impedance Calculators  Java - PCB Related Calculations

Desktop Trace Impedance Calculator Links:

AWR TxLine 2003 (Free) Excellent Tool

Rogers MWI-2014 Software (Free)

Saturn PCB Toolkit (Free) - PCB Design Calculator

UltraCAD Design Inc.  (Free / Buy) - Douglas Brooks
ICD has a Stackup Calculator and Offers a 14 Day Evaluation

VIA Impedance:  

Designing Controlled-impedance Vias  Thomas Neu - Texas Instruments

The Poor Man’s PCB Via Modeling Methodology  Bert Simonovich's Design Notes