Printed circuit boards for high current densities and efficient thermal management (1)

Thick copper, Iceberg® and HSMtec® are three different technologies for high current PCBs. The article compares the three technologies and explains the design possibilities, current carrying capacity and heat dissipation of the power semiconductors.

Engine control adjusts speed, power and torque to demand and operating conditions and plays a major role in the energy efficiency of industrial engines and vehicles. There are around 30 motors in a vehicle alone, e.g. for the blower, engine cooling, water and oil pump, window regulator, front and rear wiper.

On the hardware side, users and system manufacturers are demanding innovation in the components for signal acquisition, signal conversion and signal conditioning. The producers of printed circuit boards and connection technology have also adapted to this market: Manufacturing processes, materials and designs are optimized for the special requirements of current carrying capacity, thermal management and reliability.

From the point of view of the printed circuit board, the specifications of the drive electronics can be summarised in five points:
1. High integration density,
2. reliability of the electronic assembly,
3. Fast heat dissipation,
4. High currents combined with control electronics,
5. reduce system costs, e.g. by switching to SMD components, fewer components or assembly processes.

A smart solution is to combine the requirements for the power section and control electronics, load circuits and control on one PCB instead of on two PCBs – large conductor cross-sections and large insulation distances for the high-current conductors and fine conductor structures for the control. This eliminates connectors, cables and busbars, assembly steps and risks that limit reliability. This in turn saves space and increases reliability and economy.

The optimal PCB design for power electronics or high current applications is determined by five essential aspects:

1. the knowledge of the technical possibilities of the process, which specifies special design rules.

2. the dimensioning of the high-current conductors and insulation clearances.

3. The selection, combination and maximum utilization of materials.

4. the layer structure, which is also decisive for the current carrying capacity and heat dissipation.

5. a thermally optimized printed circuit board design.

PCB specialist KSG offers three technologies that are used in these applications: Thick copper technology, Iceberg® and HSMtec® technology. The standard base material FR4 can be used in all three applications.

Thick copper circuit boards distribute the power losses horizontally

The printed circuit board industry generally refers to thick copper as copper structures of more than 105 µm. With up to four inner layers of 400 µm copper each, a current carrying capacity of several hundred amperes is possible. Ideally, the thick copper conductors are located in the inner layers.

The advantages of the thick copper PCB include flexibility in the event of layout changes, its compact design, simple processing/assembly and comparatively low modification costs, as well as the standard processes of the PCB industry. Due to the strong undercutting, only relatively coarse structures can be created.

Important to know: FR4 laminates with a base copper lamination >105 µm are not inexpensive due to the high copper content. Compared with a standard 18 µm laminate laminated on both sides, the factor is around 1:8 to 1:10 in terms of material costs.21

 

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