Generally, the design current of PCB will not exceed 10A or even 5A. Especially in household and consumer electronics, the continuous working current on PCB usually does not exceed 2A. Recently, however, the company’s products should be designed with a power line, and the continuous current can reach about 80A. Considering the instantaneous current and leaving a margin for the whole system, the continuous current of the power line should be able to withstand more than 100A.
Then the question comes, what kind of PCB can withstand the current of 100 A?
Method 1: wiring on PCB
To find out the overcurrent capability of PCB, we should first start with the PCB structure.
Take the double-layer PCB as an example. This kind of circuit board usually has a three-layer structure: copper skin, plate and copper skin.
Copper is the path through which current and signal in PCB should pass.
According to middle school physics knowledge, we can know that the resistance of an object is related to material, cross-sectional area and length.
Because our current is on the copper skin, the resistivity is fixed. The cross-sectional area can be regarded as the thickness of copper skin, which is the thickness of copper in PCB processing options.
Usually, the copper thickness is expressed in OZ. The copper thickness of 1OZ is converted to 35 um, that of 2OZ is 70um, and so on.
Then it can be easily concluded that when a large current passes through the PCB, the wiring should be short and thick, and the thicker the copper thickness of the PCB, the better.
In practice, there is no strict standard for the length of wiring. In engineering, copper thickness/temperature rise/wire diameter are usually used to measure the current carrying capacity of PCB.
The following two tables can be referred to:
It can be known from the table that a circuit board with a thickness of 1OZ copper can pass a current of 4.5A with a width of 100mil (2.5mm) when the temperature rises at 10℃.
Moreover, with the increase of the width, the current carrying capacity of PCB does not increase strictly linearly, but the increasing range decreases slowly, which is also consistent with the actual project.
If the temperature rise is increased, the current carrying capacity of the wire can also be improved.
From these two tables, we can get the experience of PCB wiring: increasing the copper thickness, widening the wire diameter and improving the heat dissipation of PCB can enhance the current carrying capacity of PCB.
Then, if you want to run a current of 100A, you can choose a copper thickness of 4OZ, a wiring width of 15mm, double-sided wiring, and add heat dissipation devices to reduce the temperature rise of PCB and improve its stability.
Method 2: terminal post
In addition to wiring on the PCB, wiring can also be done by means of terminals.
Fix several terminals that can withstand 100A on the PCB or the product shell, such as surface-mounted nuts, PCB terminals, copper posts, etc.
Then use copper nose and other terminals to connect the conductor that can withstand 100A to the terminal post.
In this way, a large current can go through the wire.
Method 3: Custom-made copper platoon
You can even make custom-made copper bars.
It is a common practice in industry to use copper bars to run high current, for example, transformers, server cabinets and other applications all use copper bars to run high current.
Attached copper bus current carrying capacity table:
