3 Oz Copper PCB , 105Micron ( 4.1339 Mil ) , When a design use 3 oz copper , We can call it heavy copper PCB . If base copper is 3oz , then completed copper will be 4 oz, for multi-layer , Inner 3 oz , the final will be 3oz, When do 3 oz PCB manufacturing, We need take care the solder mask , because the thick solder mask will flow .
General Guideline for Min Spacing by Copper Weight
Cu Weight Min Recommended Space between Copper Features
3 OZ 10 mil (0.254 mm)