Introduction:
Heavy Copper PCB are printed circuit boards with 3 or more ounces of finished copper in the inner and/or outer layers.
While there is no standard definition of Heavy Copper, it is generally accepted that if 3 ounces (oz) of copper or more is used on the internal and external layers of a printed circuit board, it is called a heavy copper PCB. Any circuit with a copper thickness of more than 4 oz per square foot (ft2) is also categorized as a heavy copper PCB. Extreme copper means 20 oz per ft2 to 200 oz per ft2.

When the electronic device need high power or current through, Then we need consider heave copper to control the thermal on PCB

The benefits of heavy copper in PCBs:
Reduction of thermal strain
Better current conductivity
Can survive repeated thermal cycling
Smaller PCB size due to layering of copper
Increased connector site strength