How to solve the heat dissipation problem in PCB circuit board design

　　The heat dissipation issue in PCB circuit board design is crucial and directly affects the performance, stability, and lifespan of electronic products. To solve the heat dissipation problem, a systematic design needs to be carried out from three aspects: "reducing heat generation at the source", "efficient heat conduction in the path", and "strengthening heat dissipation on the surface". Here is a detailed set of solutions and methods:

　　1、 Source optimization: reduce heat generation

　　This is the fundamental method.

　　Device selection

　　Prioritize the selection of low-power and high-efficiency chips and devices while meeting performance requirements (such as using DC-DC instead of LDO and choosing low Rds (on) MOSFETs).

　　For switching devices, choose a model with a good balance between switching speed and loss.

　　Circuit design and working point optimization:

　　Optimize the power supply voltage and signal level to avoid unnecessary power loss.

　　For digital circuits, techniques such as clock gating and dynamic voltage frequency regulation are used to reduce dynamic power consumption.

　　Reasonably set the driving capability to avoid excessive driving leading to increased switch losses.

　　2、 Path design: Efficient thermal conductivity and uniform temperature

　　This is the core of PCB layout and stack design, with the goal of establishing a low thermal resistance path from the heat source to the heat dissipation surface.

　　Layout strategy:

　　Heat source dispersion: Try to avoid placing multiple high heating devices in a concentrated manner, and distribute them evenly on the board to prevent the formation of local "hot spots".

　　Thermal sensitive device isolation: Keep temperature sensitive devices such as crystal oscillators, sensors, and precision reference sources away from high heat sources (such as CPUs, power inductors, and power chips).

　　Air circulation considerations: According to the direction of the air duct inside the chassis, place the heating devices upstream of the airflow or in a well ventilated location.

　　PCB Stacking and Thermal Holes:

　　Inner ground/power copper layer utilization: There should be a complete grounding copper layer or power layer as much as possible below high heating devices. Large area copper foil is an excellent thermal conductive surface.

　　Heat dissipation via array: A series of thermal conductive vias are densely drilled below or around the solder pads of the heating device. This is one of the key means.

　　Function: Quickly transfer heat from the top layer to the inner and bottom copper planes.

　　Design points: The through-hole diameter should be small (such as 0.3mm), the spacing should be dense (1-1.5mm), and arranged in a grid like pattern. Tin or copper filling through holes to maximize thermal conductivity.

　　Copper foil area and shape:

　　Expanding solder pads and copper cladding: For SMD devices that generate heat (such as SOIC, QFN), increase the copper foil area on the PCB side of their exposed pads and connect multiple rows of vias.

　　Using thick copper foil: For power boards with high current and high heat generation, 2oz (70 μ m) or thicker copper foil can be used, which can not only carry high current but also significantly improve thermal conductivity.

　　Copper foil shape: Using a mesh or spoke shaped copper-clad connection pad, it can provide electrical connection and mechanical strength, and avoid "standing monument" or poor welding caused by uneven thermal expansion during reflow soldering.

　　3、 Surface strengthening: enhances heat dissipation capability

　　When the thermal conductivity of the PCB itself is insufficient, additional heat dissipation measures are required.

　　Heat sink:

　　Adhesive heatsink: directly attached or clipped onto the chip package (such as TO-220, D ² PAK). Ensure a smooth contact surface and fill the micro gaps with thermal conductive silicone grease to reduce contact thermal resistance.

　　PCB mounted heat sink: designed with through holes or card slots, fixed on the PCB and in contact with the top of the chip.

　　Heat dissipation pad/thermal conductive material:

　　Thermal conductive silicone pad: used to fill the gaps between heating devices and chassis, heat sinks, or other structural components, transferring heat to larger metal shells for heat dissipation.

　　PCB as heat sink:

　　For packages with exposed solder pads (such as QFN, DFN), the bottom solder pads are well soldered to the heat dissipation solder pads on the PCB. The heat dissipation pad is connected to a large area of copper through a via, and the entire PCB becomes an extended heat dissipation surface.

　　4、 System level and process considerations

　　Shell and air duct design:

　　The chassis is designed with heat dissipation holes (inlet and outlet) to form effective air ducts.

　　Design heat dissipation teeth at the corresponding positions of the key heating components on the casing or directly contact them with the metal casing (through thermal pads).

　　Using a fan to force convection is one of the effective methods to solve the problem of medium to high power dissipation.

　　Material selection:

　　High thermal conductivity substrate: In exceptional cases, metal substrates (aluminum substrates, copper substrates) or ceramic substrates can be considered. Their thermal conductivity is much better than FR-4, but their cost is high and they are mostly used for LED lighting and high-power power modules.

　　High thermal conductivity solder: Some special solder pastes have higher thermal conductivity.

　　Welding process:

　　Ensure that the heat dissipation pads of the heating device (especially the bottom pads of QFN) are fully soldered and have a low void rate. Excessive voids can greatly increase thermal resistance. It can be improved by optimizing the opening of the steel mesh (increasing the area ratio, grid segmentation) and the reflux curve.

　　5、 Design inspection and simulation

　　Hot Design Checklist:

　　Is there a grounding copper layer and a heat dissipation via array below the high heat generating device?

　　Is the thermistor device far away from the heat source?

　　Is the heat dissipation path continuous and low resistance?

　　Is there space to install additional heat sinks or fans?

　　Thermal simulation:

　　For complex or high-power products, it is strongly recommended to use thermal simulation software (such as ANSYS Icepak, FloTHERM, Simcenter Flotherm, etc.) during the PCB design phase.

　　Simulation can predict temperature distribution, locate hotspots, and evaluate the effectiveness of different heat dissipation schemes, thereby avoiding thermal problems in the early design stage and saving expensive board modification costs in the later stage.

　　Summary: An effective heat dissipation design process

　　Assessment: Estimating or measuring the power consumption of critical components.

　　Layout: Following the principle of thermal layout, dispersing heat sources and isolating sensitive components.

　　Copper laying and punching: Establish a golden thermal conductivity path of "heat dissipation pad → via array → internal copper plane" for each heat source.

　　Enhancement: Determine whether a heat sink, thermal pad, or fan needs to be added.

　　Verification: Verify and iterate through thermal simulation or physical prototype temperature measurement.

　　Remember, heat dissipation is a system engineering that requires collaborative consideration from chip level, board level to system level. The primary task of PCB designers is to create an "unobstructed escape route" for heat during the layout and wiring stages.