1) Thermal and antipad clearances
Considering thermals and antipad clearances on the power &/or ground plane layers of multilayer boards - if layer to layer registration, tolerances for hole size, location, film expansion and registration have not been taken into account then manufacturing will experience high reject rates and increased costs.
Antipads should be 0.010 to 0.020" larger than outer layer pads. For thermal pads the moat should be a minimum of 0.012 ( preferable 0.015) and pads should be equal to or larger than outer layer pads.
Clearances for solder masks around non plated holes should be at least .005"
2)Restrictive tolerances for multilayer board thicknesses
Specifying tolerances that are very tight can result in higher costs, increased time and lower yields. It is suggested to call for restrictive tolerances only when they are critical to your design.
3)Minimum Text Widths Less than 0.0080” on Silkscreen Layers
Providing artwork which requires Text Widths less than 0.0080” requires extra imaging and processor steps which will increase the cost of your project.
4)Specifying hole sizes less than 0.016” if not required
Requires boards to be subjected to additional chemical processing to ensure sizing and clean-outs are complete. These additional steps could add one full day to your processing time along with the associated costs.