Heat Dissipation of the Motor-Through-Hole

Hot through-hole: use as much as possible

Through holes are small electroplated holes typically used to thread a wire from one layer to another. Although hot through holes are made in the same way, they are used to transfer heat from one layer to another. Proper use of hot through-holes is crucial for PCB heat dissipation, but several process related issues must be considered.

The through-hole has thermal resistance, which means that when heat flows through the through-hole, there will be some temperature drop between the through-holes, measured in ℃/W. To minimize this thermal resistance and improve the efficiency of heat transfer through holes, large through holes should be used, and the holes should contain as much copper area as possible.

A large through-hole should be used (the figure shows the cross-section of the through-hole), and the hole should contain as much copper area as possible to minimize thermal resistance.

Although large through-holes can be used in the open area of a PCB, through-holes are often placed within the IC board area to directly transfer heat from the IC packaging. In this case, it is not possible to use a large through-hole. This is because large electroplating through-holes may lead to "tin infiltration", where the solder used to connect IC and PCB flows downwards into the through-hole, resulting in poor quality of the solder joints.

There are several ways to reduce tin penetration. One way is to use very small through holes to reduce the amount of solder that penetrates into the holes. However, the thermal resistance of small through-holes is higher, so more through-holes are required to achieve the same thermal performance.

Another technique is to set up a tent for through holes on the back of the board. This requires removing the gap in the solder mask layer on the back of the board to cover the through-hole with the solder mask material. If the through-hole is small, the solder mask layer will plug the through-hole; Therefore, solder cannot penetrate the PCB.

However, this may lead to another issue: flux accumulation. After the through-hole is blocked, flux (a component of solder paste) may accumulate in the through-hole. Some flux formulations may be corrosive, and if not removed over time, it can lead to reliability issues. However, most modern cleaning free flux processes are not corrosive and do not cause problems.

Please note that hot air pads must not be used for hot through holes, they must be directly connected to the copper area.

The hot through hole should be directly connected to the copper area on the PCB.

It is recommended that PCB designers and surface mount technology (SMT) process engineers inspect PCB assemblies together to select the optimal through-hole size and structure suitable for the assembly process, especially when the hot through-hole is placed within the IC board area.

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