1. Although the PCB design process can be fascinating and challenging, it is important to take all necessary precautions to ensure correct circuit operation, especially when dealing with high-power PCBs. As the size of electronic equipment continues to decrease, appropriate consideration must be given to design aspects such as power supply and thermal management. This article describes some guidelines designers can follow to design a PCB suitable for supporting high-power applications.
2. Width and thickness of the trace
In principle, the longer the trace, the greater its resistance and heat dissipation. Since the goal is to minimize power losses to ensure high reliability and durability of the circuit, it is recommended to keep the traces that conduct large currents as short as possible. To correctly calculate the width of a trace and determine the maximum current it can carry, designers can rely on the formula contained in the IPC-2221 standard or use an online calculator.
3. As for the trace thickness, the typical value for the inner layer of a standard PCB is 17.5 μm (1/2oz/ft²), and the typical value for the outer layer and adjacent layer is 35 μm (1oz/ft²). High-power PCBs usually employ thicker copper to reduce the trace width for the same current. This decreases the space occupied by wiring on the PCB. Thicker copper ranges in thickness from 35 to 105 μm (1 to 3oz/ft²) and is typically used for currents greater than 10A. While thicker copper incurs additional costs, it saves space on the board due to its higher conductivity, allowing for smaller required trace widths.
4. PCB layout
Board layouts should be considered from the early stages of PCB development. An important rule applicable to any high-power PCB is to determine the path that the power follows. The location and magnitude of power flowing through the circuit are crucial factors in assessing the amount of heat the PCB needs to dissipate. Key factors influencing the layout of printed circuit boards include:
– The power level flowing through the circuit;
– Evaluation of the ambient temperature at which the board operates;
– Influence on the airflow around the board;
– Materials used in PCB manufacturing;
– Component density on the circuit board.
5. Although modern machinery has lessened this necessity, it is advisable to avoid right angles in the case of directional changes, opting instead for 45° angles or curves to mitigate signal integrity issues and facilitate smoother trace routing.Component Placement
1. To ensure optimal performance, the initial step involves determining the PCB locations for high-power components, such as voltage converters or power transistors, which generate substantial heat. It’s imperative to avoid placing these components near the board’s edge to prevent heat accumulation and subsequent temperature spikes. Rather, position them centrally to promote even heat distribution across the board, thereby mitigating temperature rise. Avoid clustering power components together to prevent hot spots; instead, opt for a linear configuration.
2. Commence placement with power equipment, ensuring minimal wiring length and adequate width to curb noise generation and unnecessary grounding loops.
3. Adhere to the following guidelines:
– Identify and minimize current loops, particularly large ones.
– Reduce resistive pressure drops and parasitic effects between components.
– Keep high-power circuits separate from sensitive circuits.
– Implement robust grounding practices.
4. Depending on component size, consider distributing components across multiple boards if feasible.
Thermal Management
5. Effective thermal management is crucial to maintain each component within a safe temperature range, as specified in the manufacturer’s data sheet (typically between +125°C and +175°C for silicon-based devices). Heat generated by components dissipates through packaging and connecting pins. Despite advancements in thermally compatible packages, cooling complexities persist with shrinking integrated circuit sizes.
6. Key techniques for enhancing PCB thermal management include enlarging layers and incorporating thermal conductors. Enlarging layers increases the heat dissipation area, typically connecting these surfaces to upper or lower layers to optimize heat exchange. Alternatively, inner layers can extract power consumed by PCB devices. Heat transfer between layers is facilitated by heat through holes, directing heat from hotspots to other layers.
7. Sensitive components like regulators and converters are susceptible to environmental fluctuations, which can induce signal errors and compromise device reliability. Hence, insulate these components thermally to shield them from board-generated heat.
Resistance Welding Membrane
8. Removing the solder mask exposes underlying copper, enabling additional solder application to increase copper thickness and reduce overall resistance in current-carrying elements. While more a solution than a design rule, this technique enhances PCB wiring capacity without widening traces.
Decoupling Capacitor
9. Active components may induce undesirable effects like ground bouncing and ringing when sharing power lines. To counteract this, deploy decoupling capacitors placed close to component power pins and directly connected to low-impedance layers, minimizing impedance between power lines and ground. Decoupling capacitors act as secondary power sources, alleviating transient effects like voltage ripple or noise.
10. When selecting decoupling capacitors, factors like capacitance value, dielectric material, geometry, and positioning relative to electronic components are critical. Typical decoupling capacitance values range around 0.1μF for ceramics.
Material
11. High-power PCB design necessitates materials with specialized properties, notably thermal conductivity (TC). Traditional materials like FR-4 boast a TC of approximately 0.20W/m/K, whereas specific materials like RogerSRT laminates offer significantly higher TC values, up to 1.44W/m/K, minimizing temperature elevation at high power levels.
12. In addition to low-loss material utilization for power and heat processing, PCBs must exhibit similar coefficients of thermal expansion (CTE) between conductive and thermal materials. This ensures consistent expansion or contraction rates under high power or temperature conditions, mitigating mechanical stress on the material.
2. Width and thickness of the trace
In principle, the longer the trace, the greater its resistance and heat dissipation. Since the goal is to minimize power losses to ensure high reliability and durability of the circuit, it is recommended to keep the traces that conduct large currents as short as possible. To correctly calculate the width of a trace and determine the maximum current it can carry, designers can rely on the formula contained in the IPC-2221 standard or use an online calculator.
3. As for the trace thickness, the typical value for the inner layer of a standard PCB is 17.5 μm (1/2oz/ft²), and the typical value for the outer layer and adjacent layer is 35 μm (1oz/ft²). High-power PCBs usually employ thicker copper to reduce the trace width for the same current. This decreases the space occupied by wiring on the PCB. Thicker copper ranges in thickness from 35 to 105 μm (1 to 3oz/ft²) and is typically used for currents greater than 10A. While thicker copper incurs additional costs, it saves space on the board due to its higher conductivity, allowing for smaller required trace widths.
4. PCB layout
Board layouts should be considered from the early stages of PCB development. An important rule applicable to any high-power PCB is to determine the path that the power follows. The location and magnitude of power flowing through the circuit are crucial factors in assessing the amount of heat the PCB needs to dissipate. Key factors influencing the layout of printed circuit boards include:
– The power level flowing through the circuit;
– Evaluation of the ambient temperature at which the board operates;
– Influence on the airflow around the board;
– Materials used in PCB manufacturing;
– Component density on the circuit board.
5. Although modern machinery has lessened this necessity, it is advisable to avoid right angles in the case of directional changes, opting instead for 45° angles or curves to mitigate signal integrity issues and facilitate smoother trace routing.Component Placement
1. To ensure optimal performance, the initial step involves determining the PCB locations for high-power components, such as voltage converters or power transistors, which generate substantial heat. It’s imperative to avoid placing these components near the board’s edge to prevent heat accumulation and subsequent temperature spikes. Rather, position them centrally to promote even heat distribution across the board, thereby mitigating temperature rise. Avoid clustering power components together to prevent hot spots; instead, opt for a linear configuration.
2. Commence placement with power equipment, ensuring minimal wiring length and adequate width to curb noise generation and unnecessary grounding loops.
3. Adhere to the following guidelines:
– Identify and minimize current loops, particularly large ones.
– Reduce resistive pressure drops and parasitic effects between components.
– Keep high-power circuits separate from sensitive circuits.
– Implement robust grounding practices.
4. Depending on component size, consider distributing components across multiple boards if feasible.
Thermal Management
5. Effective thermal management is crucial to maintain each component within a safe temperature range, as specified in the manufacturer’s data sheet (typically between +125°C and +175°C for silicon-based devices). Heat generated by components dissipates through packaging and connecting pins. Despite advancements in thermally compatible packages, cooling complexities persist with shrinking integrated circuit sizes.
6. Key techniques for enhancing PCB thermal management include enlarging layers and incorporating thermal conductors. Enlarging layers increases the heat dissipation area, typically connecting these surfaces to upper or lower layers to optimize heat exchange. Alternatively, inner layers can extract power consumed by PCB devices. Heat transfer between layers is facilitated by heat through holes, directing heat from hotspots to other layers.
7. Sensitive components like regulators and converters are susceptible to environmental fluctuations, which can induce signal errors and compromise device reliability. Hence, insulate these components thermally to shield them from board-generated heat.
Resistance Welding Membrane
8. Removing the solder mask exposes underlying copper, enabling additional solder application to increase copper thickness and reduce overall resistance in current-carrying elements. While more a solution than a design rule, this technique enhances PCB wiring capacity without widening traces.
Decoupling Capacitor
9. Active components may induce undesirable effects like ground bouncing and ringing when sharing power lines. To counteract this, deploy decoupling capacitors placed close to component power pins and directly connected to low-impedance layers, minimizing impedance between power lines and ground. Decoupling capacitors act as secondary power sources, alleviating transient effects like voltage ripple or noise.
10. When selecting decoupling capacitors, factors like capacitance value, dielectric material, geometry, and positioning relative to electronic components are critical. Typical decoupling capacitance values range around 0.1μF for ceramics.
Material
11. High-power PCB design necessitates materials with specialized properties, notably thermal conductivity (TC). Traditional materials like FR-4 boast a TC of approximately 0.20W/m/K, whereas specific materials like RogerSRT laminates offer significantly higher TC values, up to 1.44W/m/K, minimizing temperature elevation at high power levels.
12. In addition to low-loss material utilization for power and heat processing, PCBs must exhibit similar coefficients of thermal expansion (CTE) between conductive and thermal materials. This ensures consistent expansion or contraction rates under high power or temperature conditions, mitigating mechanical stress on the material.
