Meaning
Substrate thickness measurements specify the mass of copper foil distributed across one square foot of printed circuit board area. This measure, termed copper weight, determines the maximum continuous current that a trace can carry before rising in temperature. It directly influences the trace width constraints during board design.
Thermal Management
Power supply tracks require heavy traces to prevent excessive heat buildup. Increasing the copper weight allows designers to use narrower traces while maintaining a low thermal profile across the board surface. This optimization is critical for compact enclosures where ventilation is limited.
Manufacturing Limitation
Etching processes become more difficult as the metal thickness increases. A higher copper weight requires longer exposure to chemical etchants, which can lead to over-etching or undercutting of the trace profiles. This requires wider spacing between traces to avoid electrical shorts during production.
High-frequency boards must balance these thick power planes with very thin signal layers to prevent parasitic capacitance from distorting the digital signals.
Design Calculation
Electrical rules must account for the cross-sectional area of traces to prevent failures under load. Specifying the copper weight is the first step in calculating the impedance and voltage drop across a power plane. These figures are then validated during board testing to ensure compliance with power requirements.
