When defining the width of signal traces there should be consideration of path resistance, heating effects and also parasitic capacitance. For example, using a 50 thou trace would result in low path resistance and heating but could affect a modules hot switch performance due to the capacitance.

An on-line tool is available that allows the trace geometry to be determined based on various parameters:-

http://circuitcalculator.com/wordpress/?p=25/

When determining the trace width a target for temperature rise should be 10-20°C above ambient but this can be increased depending on the design / product.