Context: The printed circuit board industry defines heavy copper as layers exceeding three ounces of copper, or approximately 0.0042 inches (4.2 mils, 105 μm) thick. PCB designers and fabricators often use heavy copper when design and manufacturing circuit boards in order to increase current-carrying capacity as well as resistance to thermal strains. Heavy copper plated vias transfer heat to external heat sinks. IPC 2152 is a standard for determining current-carrying capacity of printed circuit board traces.

Question: What's the minimum amount of copper a layer in a PCB can have to be considered "heavy copper"?
Answer: three ounces

Question: About how thick would a PCB layer be if it contained three oz. of copper?
Answer: 0.0042 inches

Question: What will a circuit board with heavy copper carry very well?
Answer: current

Question: What would a PCB designer use heavy copper to make their circuit board resist?
Answer: thermal strains

Question: Where does the heat go when it leaves heavy copper-plated vias?
Answer: external heat sinks

Question: The printed circuit board industry defines light copper as what?
Answer: Unanswerable

Question: PCB designers and fabricators often use light copper when?
Answer: Unanswerable

Question: What is the standard for determining current-carrying capacity of printed circuit board trees?
Answer: Unanswerable

Question: IAC 2152 is the standard for what?
Answer: Unanswerable