B. Thermal Design
With regards to heat dissipation, it is best for the printed board to be installed upright with a distance of at least 2cm between two boards, and the arrangement of devices on the printed board should adhere to specific guidelines.
●For equipment utilizing free convection air cooling, it is advisable to align integrated circuits (or other devices) longitudinally. For equipment utilizing forced air cooling, it is preferable to arrange integrated circuits (or other devices) horizontally.
●Devices on the same printed board should be arranged based on their heat output and heat dissipation capabilities. Devices with lower heat output or lower heat resistance (such as small signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) should be positioned at the top of the airflow, while devices with higher heat output or better heat resistance (such as power transistors, large-scale integrated circuits, etc.) should be placed at the downstream end of the cooling airflow.
●In the horizontal direction, high-power devices should be positioned near the edge of the printed board to reduce the heat transfer path. In the vertical direction, high-power devices should be placed near the top of the printed board to minimize the impact on other devices’ temperature during operation.
●Temperature-sensitive devices should be located in cooler areas (e.g. the bottom of the device) and should never be placed directly above heat-generating devices. It is best to stagger multiple devices on the same horizontal plane.
●The heat dissipation of the printed board relies heavily on airflow, so airflow paths should be considered during the design process and devices or printed circuit boards should be configured accordingly. Airflow tends to follow paths with low resistance, so when arranging devices on a printed circuit board, avoid leaving large gaps in certain areas. The configuration of multiple printed circuit boards within the entire equipment should also take this into account.
C. Electromagnetic Compatibility Design
Electromagnetic compatibility ensures electronic equipment functions effectively in various electromagnetic environments. The design aims to suppress external interference, enabling equipment to work in specific electromagnetic conditions while reducing interference to other electronic devices.
1. Optimal Wire Width Selection
To minimize impact interference caused by transient current on printed lines (due to wire inductance), wire inductance should be minimized. Inductance is directly proportional to wire length and inversely proportional to wire width, hence short and wide wires help in interference suppression. Signal lines carrying high transient currents (e.g. clock leads, drivers) should be kept short. For discrete component circuits, a wire width around 1.5mm meets requirements, while for integrated circuits, a width between 0.2~1.0mm is suitable.
2. Effective Wiring Strategy
Equal routing reduces wire inductance but increases mutual inductance and distributed capacitance. If feasible, utilize a grid-like wiring structure with horizontal wiring on one side and vertical on the other, connected by metallized holes at intersections. To reduce crosstalk, avoid long-distance equal wiring, increase wire separation, and avoid signal lines crossing ground/power lines. Adding a grounded printed line between sensitive signal lines can suppress crosstalk.
3. Reflection Interference Suppression
To mitigate reflection interference at printed line terminals, shorten line length, use slower circuits, and implement terminal matching if necessary. Terminal matching includes adding a matching resistor of equal resistance at the end of the transmission line to ground and power. For faster TTL circuits, apply terminal matching for lines exceeding 10cm, with resistor value based on maximum output and absorption current of integrated circuits.
With regards to heat dissipation, it is best for the printed board to be installed upright with a distance of at least 2cm between two boards, and the arrangement of devices on the printed board should adhere to specific guidelines.
●For equipment utilizing free convection air cooling, it is advisable to align integrated circuits (or other devices) longitudinally. For equipment utilizing forced air cooling, it is preferable to arrange integrated circuits (or other devices) horizontally.
●Devices on the same printed board should be arranged based on their heat output and heat dissipation capabilities. Devices with lower heat output or lower heat resistance (such as small signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) should be positioned at the top of the airflow, while devices with higher heat output or better heat resistance (such as power transistors, large-scale integrated circuits, etc.) should be placed at the downstream end of the cooling airflow.
●In the horizontal direction, high-power devices should be positioned near the edge of the printed board to reduce the heat transfer path. In the vertical direction, high-power devices should be placed near the top of the printed board to minimize the impact on other devices’ temperature during operation.
●Temperature-sensitive devices should be located in cooler areas (e.g. the bottom of the device) and should never be placed directly above heat-generating devices. It is best to stagger multiple devices on the same horizontal plane.
●The heat dissipation of the printed board relies heavily on airflow, so airflow paths should be considered during the design process and devices or printed circuit boards should be configured accordingly. Airflow tends to follow paths with low resistance, so when arranging devices on a printed circuit board, avoid leaving large gaps in certain areas. The configuration of multiple printed circuit boards within the entire equipment should also take this into account.
C. Electromagnetic Compatibility Design
Electromagnetic compatibility ensures electronic equipment functions effectively in various electromagnetic environments. The design aims to suppress external interference, enabling equipment to work in specific electromagnetic conditions while reducing interference to other electronic devices.
1. Optimal Wire Width Selection
To minimize impact interference caused by transient current on printed lines (due to wire inductance), wire inductance should be minimized. Inductance is directly proportional to wire length and inversely proportional to wire width, hence short and wide wires help in interference suppression. Signal lines carrying high transient currents (e.g. clock leads, drivers) should be kept short. For discrete component circuits, a wire width around 1.5mm meets requirements, while for integrated circuits, a width between 0.2~1.0mm is suitable.
2. Effective Wiring Strategy
Equal routing reduces wire inductance but increases mutual inductance and distributed capacitance. If feasible, utilize a grid-like wiring structure with horizontal wiring on one side and vertical on the other, connected by metallized holes at intersections. To reduce crosstalk, avoid long-distance equal wiring, increase wire separation, and avoid signal lines crossing ground/power lines. Adding a grounded printed line between sensitive signal lines can suppress crosstalk.
3. Reflection Interference Suppression
To mitigate reflection interference at printed line terminals, shorten line length, use slower circuits, and implement terminal matching if necessary. Terminal matching includes adding a matching resistor of equal resistance at the end of the transmission line to ground and power. For faster TTL circuits, apply terminal matching for lines exceeding 10cm, with resistor value based on maximum output and absorption current of integrated circuits.
