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PCB Design
29Nov

# Interpret PCB design high current path setting

The current usually does not exceed 10A, or even 5A. Especially in household and consumer electronICs, the continuous working current on the PCB usuallydoes not exceed 2A. However, recently we need to design power wiring for the product. The continuous current can reach about 80A. Considering the instantaneous current and the margin for the whole system, the continuous current of power wiring should be able to withstand more than 100A. Then the problem arises. What kind of PCB can withstand 100A current?

To understand the over-current capability of PCB, we first start with PCB structure. Take the double-layer PCB as an example. This kind of circuit board usually has a three-layer structure: copper sheet, board, and copper sheet. The copper sheet is the path through which the current and signal in the PCB will pass. According to the physics knowLEDge in middle school, we can know that the resistance of an object is related to material, cross-sectional area and length. Since our current flows on the copper sheet, the resistivity is fixed. The cross-sectional area can be regarded as the thickness of the copper sheet, that is, the copper thickness in PCB processing options. Generally, the copper thickness is expressed in OZ. The copper thickness of 1OZ is 35um, that of 2OZ is 70um, and so on. It can be easily concluded that when high current is to be passed on a PCB, the wiring must be short and thick, and the thicker the copper on the PCB, the better.

In practice, there is no strict standard for the length of. In engineering, three indicators, copper thickness/temperature rise/wire diameter, are usually used to measure the current carrying capacity of PCB.

From the table, it can be known that a circuit board with 1Oz copper thickness can pass 4.5A current with a wire of 100mil (2.5mm) width at 10 ° temperature rise. And with the increase of the width, the current carrying capacity of PCB does not increase strictly in a linear way, but decreases slowly, which is consistent with the situation in the actual project. If the temperature rise is increased, the current carrying capacity of the conductor can also be improved.

Through these two tables, we can get PCB wiring experience that increasing copper thickness, widening wire diameter, and improving PCB heat dissipation can enhance the current carrying capacity of PCB.

If I want to use 100A current, I can choose 4Oz copper thickness, set the wiring width to 15mm, double sided wiring, and add heat dissipation devices to reduce the temperature rise of PCB and improve stability.

In addition to wiring on PCB, wiring can also be done in the way of terminal.

Fix several terminals capable of withstanding 100A on PCB or product shell, such as surface nut, PCB terminal, copper column, etc. Then connect the wire that can withstand 100A to the terminal with copper nose and other terminal blocks. In this way, the large current can pass through the wire.

Even copper bars can be customized. It is a common practice in PCB industry to use copper to drive high current. For example, transformers, server cabinets and other applications use copper to drive high current.

In addition, there are some special PCB processes, which may not be available in China. Infineon has a kind of PCB, which is designed with three copper layers. The top and bottom layers are signal wiring layers, and the middle layer is a copper layer with a thickness of 1.5mm. It is specially used to arrange power supplies. This kind of PCB can easily achieve a SMAll volume over-current of more than 100A.

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