PCB Trace Width Design


In PCB design, the PCB trace width is related to the performance of the circuit. For simple circuits with a current of less than 1 ampere, the PCB trace width design is simple. As current, voltage rise in the circuit, the PCB trace width becomes crucial. Wrong trace widths at high current/voltage will tend to burn PCB’s severely impacting performance and productivity. Another factor to be considered is the ambient temperature rise as the circuit functions. PCB trace width design depends on Trace width (W), Maximum trace current (Imax), Rise in the temperature (ΔT), Trace thickness (Th). Additional parameters are ambient temperature (Ta) and trace length (L). Trace width also depends on trace resistance at ambient temperature, high temperature (Ta + ΔT) trace resistance, maximum power loss to trace length, and maximum voltage drop. Internal and external layers have different current and temperature readings.

Why is copper used as PCB trace material? The answer is due to properties like high conductivity and high melting point. Though we use copper, it does not mean you should not keep the temperatures low. Properly sized PCB trace width design needs implementation. The temperature rise kept within limits. When working with high voltage, power rail components, and other heat-sensitive areas in the board, the PCB trace width is determined by the standard trace width versus the current table. No controlled impedance routing factoring gets done by the table. Temperature rise determination becomes difficult to predict. This is where the IPC2152 standard comes into the picture. The IPC2152 ensures current-temperature is within operating limits in a controlled impedance environment. The controlled impedance and the routing needs verification in PCB trace width design for high voltage/current applications.

The thumb rule in high voltage/current design is keeping the temperature low and in control. The design and routing determine PCB trace width that keeps device temperature in control to current. Even though copper has a high melting point, the temperature rise needs keeping within 10 degrees centigrade. If trace temperature rises, the components feel the heat and lead to pressure on cooling devices.

IPC2152 standards reference required for trace width design. The formulas calculate the current to temperature rise. PCB trace width versus the current, table is a good start. The substrate mechanical and electrical properties change with temperature. Always design traces to take care of temperature rise to 10 degrees centigrade. Trace thickness depends on copper weight. High current/voltage requires more copper thickness to tackle temperature rise. Use controlled impedance routing. Alternative substrates are ceramic, aluminum core, and high-speed laminate. Higher the thermal conductivity of the substrate, lower the trace temperature. Temperature rise is directly proportional to the thermal conductivity of the substrate. The IC2152 nomograph allows usage of different copper weights and controlled impedance verification to temperature rise and current.

There are many tools available for PCB trace width design for high voltage/current applications with temperature and controlled impedance. Use your judgment and experience to select the right tools. The thumb rule always considers all parameters without leaving any.

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