**The Importance of Thermal Design**
The heat dissipation of PCB circuit boards is a crucial aspect. So, what is the heat dissipation technology used in PCB circuit boards?
For electronic equipment, during operation, a certain amount of heat is generated, causing a rapid rise in temperature. If this heat is not dissipated promptly, the equipment will continue to overheat. Excessive heat can reduce the reliability of the equipment. Therefore, effective heat dissipation from circuit boards is essential.
**Factors Contributing to PCB Temperature Rise**
The primary reason for the temperature increase in printed boards is the power consumption of circuit devices, which fluctuates with varying loads.
There are two main phenomena regarding temperature rise on printed boards:
(1) Localized temperature rise versus widespread temperature rise.
(2) Short-term versus long-term temperature rise. When analyzing thermal characteristics of PCBs, several aspects are typically considered:
**Power Consumption**
(1) Assess the power consumption per unit area.
(2) Examine the power consumption distribution across the PCB.
**Structure of the Printed Board**
(1) Dimensions of the printed board.
(2) Materials used for printed circuit boards.
**Installation of Printed Boards**
(1) Installation methods (such as vertical mounting, etc.).
(2) The distance between the seal and the housing.
**2.4 Thermal Radiation**
(1) Emissivity of the printed board surface.
(2) Temperature difference between the printed board and the adjacent surface, along with its absolute temperature.
**2.5 Heat Transfer**
Install the heat sink (1)(1).
(2) Transmission through other installation structures.
**2.6 Thermal Convection**
First, natural convection.
Second, forced cooling convection.
Analyzing the above PCB factors is an effective approach to addressing the temperature rise of printed boards. These factors often correlate with dependencies in products and systems. Most should be evaluated based on actual conditions; only under specific scenarios can temperature rise and power consumption be accurately calculated or estimated.
**Three PCB Thermal Design Methods**
1. Heat dissipation through the PCB itself.
2. Radiator heat conduction plate for high-heat equipment.
For a limited number of PCB devices with higher heating capacity (less than 3), if temperatures do not decrease, a heat sink with a fan can enhance heat dissipation. When heating devices exceed three, a large heat dissipation cover (board) is recommended. This special heat sink, tailored to the position and level of heating elements on the PCB, is fastened to the component surfaces to facilitate heat transfer. Due to the high consistency of components, heat dissipation may be suboptimal, often necessitating the addition of a soft thermal phase change pad on component surfaces to enhance performance.
For free convection air cooling equipment, arranging integrated circuits (or other components) horizontally is advisable.
4. Implement a reasonable wiring design to enable heat dissipation.
Given the poor thermal conductivity of the resin in the board, copper foil wires and holes act as thermal conductors, increasing the efficiency of copper foil and enhancing thermal conductivity through holes.
**Four Conclusions**
(1) The temperature rise of printed board wires due to current should not exceed 125°C (a commonly used typical value). The selected board may vary. As components are mounted on the board, some heat will influence operating temperatures. When selecting materials and printed boards, ensure that hot spot temperatures remain below 125°C, and opt for thicker copper foil.
(2) In special cases, thermal resistance plates, such as aluminum-based ceramic substrates, may be utilized.
(3) Multi-layer board structures facilitate PCB thermal design.
3.2 Ensure unobstructed heat dissipation channels.
Utilize technologies such as copper skin, window openings, and heat dissipation holes to establish effective low-heat barrier channels, ensuring smooth heat discharge from the PCB.
The design of heat dissipation holes can enhance dissipation area, reduce thermal resistance, and increase circuit board power density. For instance, a via hole on the pad of an LCC device allows solder to rapidly propagate through holes or blind holes to the metal heat dissipation layer or copper pad on the back, improving thermal conductivity. Special heat dissipation materials may also be employed, particularly in module power supply printed boards.
To reduce thermal resistance in the heat conduction process, thermally conductive materials should be applied at contact surfaces between high power devices and substrates.
To enhance heat dissipation, consider adding a small amount of copper to solder paste. Post-soldering, the solder joints under equipment create a gap, increasing convective heat dissipation.
3.3 Component Layout Requirements
(1) Use software thermal analysis for PCB design to control internal maximum temperature rises.
(2) Consider mounting high-radiation components on the printed board.
(3) Ensure uniform distribution of board heat capacity; avoid concentrating high power consumption equipment upstream of airflow, and ensure sufficient cooling air circulates through concentrated heat zones.
(4) Minimize heat transfer path length.
(5) Maximize heat transfer cross-section.
(6) Component layout should account for heat radiation effects on surrounding components. Heat-sensitive parts (including semiconductors) should be distanced from heat sources or isolated.
It is advisable to keep capacitors (7) away from heat sources.
(8) Pay attention to forced and natural ventilation.
(9) Ensure the air duct of additional daughter board equipment aligns with ventilation direction.
(10) Maintain sufficient distance between intake and exhaust.
(11) Position heating equipment above the product whenever possible to enter the airflow channel.
(12) Avoid placing high heat or high current parts in board corners; install them on the radiator, distanced from other equipment, ensuring an unobstructed heat dissipation channel.
(13) Peripheral equipment of small signal amplifiers should minimize temperature drift.
(14) Consider using metal chassis for effective heat dissipation.
**3.4 Wiring Requirements**
(1) Select steel plates for reasonable printed board structure design.
(2) Adhere to PCB wiring rules.
(3) Plan minimum channel width based on equipment current density; pay special attention to wiring at seams.
(4) Keep large current lines as surface-mounted as possible; if not feasible, consider bus bars.
(5) Minimize contact surface thermal resistance by increasing heat conduction area, ensuring smooth contact surfaces, and applying thermally conductive silicone grease if necessary.
(6) Consider stress balance and increase thermal stress point thickness.
(7) Employ heat dissipation stress window methods for copper skin and correctly open heat dissipation solder masks.
(8) Utilize large-area copper foil on the surface where appropriate.
(9) Ground mounting holes on the circuit board should have larger pads, maximizing the use of mounting bolts and copper foil on the printed board for effective heat dissipation.
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