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How to Calculate Copper Trace Width Ampacity

Certain design considerations are common to just about every piece of electronic equipment. Copper traces on electronic circuit boards must deliver adequate current to each component without excessive voltage drops or overheating. The current-carrying capacity, or ampacity, of a copper trace is dependent on factors that include the copper weight per square foot, the allowable temperature rise of the board in operation and the width of the trace in thousandths of an inch, or mils. The IPC-Association Connecting Electronics Industries defines standards for circuit board design.

Things You'll Need

Circuit board design parameters
Pencil and paper
IPC-2152 reference charts
Ruler

Instructions

- 1
  Check the weight of copper in ounces per square foot and the intended trace width for the board that you are designing. Make a note of these values.
- 2
  Select the cross-sectional area correlation chart. Read down the vertical axis of the chart until you find the trace width value that you noted. Place the ruler horizontally across the chart directly below this value.
- 3
  Find the line on the chart that corresponds to the copper weight that you noted. Mark the point where the ruler intersects this line.
- 4
  Reposition the ruler vertically on the chart so that one edge passes through the point that you marked. Mark the point where this edge of the ruler intersects the horizontal axis.
- 5
  Remove the ruler and read the cross-sectional area value of the point that you marked on the horizontal axis. Note this value, which is the cross-sectional area of the trace in squares mils. For example, if the trace width is 0.03 inches and the copper weight is 1/2 ounce per square foot, the cross-sectional area is 20 square mils.
- 6
  Select the conservative current-carrying capacity chart. Read across the horizontal axis of the chart until you reach the value of the cross-sectional area that you noted. Position the ruler vertically on the chart, with one edge passing through this value.
- 7
  Check the allowable temperature rise in degrees Celsius for the board that you are designing. Mark the point where the corresponding curve on the chart intersects the ruler.
- 8
  Reposition the ruler horizontally across the chart, with one edge passing through the point that you marked. Mark the point where this edge intersects the vertical axis.
- 9
  Remove the ruler and read the current value of the point that you marked on the vertical axis. Note this value, which is your result. For example, if the cross-sectional area is 20 square mils and the allowable temperature rise is 30 C, the current value is 1 ampere.
- 10
  Check each step of your work. Record the result, which is the ampacity in amperes of the copper trace with the width and weight that you intend to use.

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