PCB connection technology keeps pace with power demands

by Georg Grunenberg, Product Marketing, Business Unit, Device Connectors, and James Dunbar, Product Marketing Manager, Printed Circuit Board Connectors, Phoenix Contact

As power electronics devices become more compact, it is up to PCB connector manufacturers to fit within these space constraints while helping to increase efficiency.

Power electronics — as used in drive technology or photovoltaics—play a role in many areas of our everyday life. They are currently growing in importance thanks to the rising demand for energy efficiency. For instance, 40% of today’s global electrical power consumption goes into electrical drives. Complex power electronics ensure optimal use of electrical power behind the scenes, as in the complexity of baggage handling in airports.

Most manufacturers of frequency converters and inverters are currently engaged in an international competition to build more compact, powerful and economical solutions. The development of semiconductors for power electronics enables increased efficiency and allows for more compact converter dimensions. Some current devices can reach efficiencies of 96% or higher.

Less space, more power
With these higher demands and space constraints come design challenges for connection technology. Converter manufacturers need optimal and fitting PCB and feed-through terminal blocks to stay on top of the game. One challenge is that there is less and less space inside the device itself for connecting and transporting electrical power. However, the conductance of economically feasible conductor materials is physically set and, therefore, limited.

It is common to use copper or even copper alloys. For weight and economical reasons, the use of aluminum is also possible in some cases. Generally, however, the use of aluminum is limited to certain externally connected cables, depending on the application.

Therefore, the required cross-section of the conductor materials for external connection, as well as for the transport of electrical power within the frequency converter, is largely predetermined. Almost in contradiction to this, the connection space should still be large enough to enable comfortable cable connection of suitably large cross-sections. The cable cross-section of copper cables remains unchanged for the same current and cannot be reduced. Even larger cross-sections tend to be used in the installation environment to avoid line losses. When considering the system from an economic point of view, a right-fit design makes sense in most cases.

Compact connection technology increases cost-effectiveness
Newer wave-solderable PCB terminal blocks have much higher power than in the past, representing a viable solution. Some are available with a rated current of 200 A according to UL. Where an expensive copper busbar installation was previously needed, the device manufacturer can now use a simple solderable solution, which no longer requires separate operations during production. A standard PCB with multilayer technology carries the high current. Bolts, nuts and special busbars are no longer needed.

Another advantage to this solution is a smaller space requirement. In addition, there are no potential sources of error during installation. Furthermore, the PCB terminal block can be processed using common soldering profiles. The forces required for the cable connection up to 3/0 with or without ferrules are accomplished by equipping the screws with a Torx drive. The pitch is a compact 20 mm, and based on the vibration test according to DIN EN 60068-2-6, the user is safe from an electrical and mechanical
point of view.

Manufacturers of frequency converters and inverters can now consistently use PCB terminal blocks to terminate wire from 16 AWG to 3/0. In this way, end users receive an integrated cable connection up to 200 A based on an identical operating philosophy.

External connection is necessary
The external cable connection of devices should be as easy and self-explanatory as possible. Engineers have little time on site when installing photovoltaic inverters, so the connection should be simple and robust.

One feasible method would be a screw connection. Operators are familiar with screw connection for terminal blocks, and this technology is internationally accepted. Some screw-type terminals are also vibration-tested and fitted with self-locking screws. In addition, the screws are integrated in the terminal to prevent their loss; the screw must be tightened with the required torque as a matter of principle.

Terminals with a lever clamp make this task even easier. This enables the correct contact force automatically and continuously through the spring. The user also has visual control with the lever position—and the lever operation, too, is self-explanatory.

The advantages of fast connections
External device connections require easier operation and even more compact design. However, device-internal PCB connections often take place in industrial large-scale production under controlled conditions. In addition, trained personnel typically perform the wiring and installation.

Prefabricated cables with ferrules are often used, enabling high-speed installation. Saving time during production makes it easier to reach a higher level of economic efficiency. The use of fast connection technology also has clear advantages.

The prefabricated cable is pushed into the clamping area in the case of fast connection technology based on the push-in principle, making permanent and secure contact. This operation only takes a few seconds.

Newer PCB terminal blocks feature a fast connection with a wire of 2 AWG. This means that 101 A and 600 V, according to UL, can be connected in a matter of seconds.

Reflow solderable without insulation housing
A cost-efficient device design is possible today thanks to compact and flexible connection technology, as well as by avoiding different manufacturing processes. New reflow-solderable terminal blocks are designed for up to 41 A. This allows the terminal blocks to be processed with the other components in one soldering process. A compact spring connector without insulation housing makes this possible. The developer can set the reachable voltage level by means of trace spacing on the PCB. These new terminal blocks allow for horizontal cable connection and are available with an open- or closed-spring connector. The closed version can be populated with the pick-and-place method using a vacuum pipette. Certain versions even support a vertical flat conductor connection.

A final review of demands
The demands placed on power electronics devices are constantly increasing. An innovative connection technology offers device manufacturers the desired level of compact design and economy without forcing them to make compromises to quality. The main demands of device manufacturers usually refer to the following aspects:

• connection technology
• angle of cable entry
• operating direction
• manufacturing process
• external shape/dimensions

In addition, in large-scale production there is often the desire to match the color of external connectors to a superordinate or corporate design. Marketable PCB terminal blocks must fulfill all of these manufacturer demands.

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