Unlike signal connectors, which continue to shrink despite offering higher transmission speeds, power connectors require a certain amount of conductive material to carry a given current or amperage. There's no special design secret that allows smaller power contacts to carry larger currents. While progress is being made in refining low-interference interfaces, the space required for higher-amperage interconnects increases as power demands grow.
In this article, we will examine the key factors that design engineers must evaluate in the early stages of the design process. Furthermore, we will explore how connector innovations and clear engineering principles for power integrity can not only drive smarter designs but also help ensure that specified interconnection solutions will deliver optimal electrical performance and superior levels of long-term safety and reliability.
Although new system designs often require power current to pass through a limited space, several factors still affect a design's density and its effective power handling capacity. A clear understanding of each of these elements is critical to successfully designing systems with a robust and safe power supply, which will contribute to optimizing the entire design process. These key factors are:
Balancing Space and Power:
First, it's necessary to determine how much space is required for a power interconnect compared to the available space allocated in the finished product design. While space savings are a high priority for most original equipment manufacturers (OEMs), the height, width, and length of the connector, and especially its copper content, will directly impact the achievable current density. System architects always want to pack more power into the same space, which presents a challenge for connector manufacturers.
However, leading global connector manufacturers continue to develop new and innovative designs that utilize higher conductivity materials and make more creative use of available space to improve power delivery and electrical performance, thus requiring no additional space. For example, in some cases, a lower-profile connector would be preferable to maximize cooling airflow. In other cases, a larger connector offering more stable contact would be the appropriate solution to effectively handle the amount of current generated in the confined space of a circuit board's edge. The key is finding the optimal balance between power, and its resulting thermal effects on the printed circuit board, and the space requirements for design to ensure the safety and performance of the final product.
Thermal Management:
Thermal problems caused by contact or pinch resistance and insufficient airflow are always a concern and deserve careful consideration from the outset. The copper content of the printed circuit board (PCB) is one such element. Too little copper can restrict current flow and cause pinch resistance. An appropriate size of the copper traces decreases bulk resistance, allowing for lower temperatures and fewer losses. Otherwise, that heat can dissipate to the connector interface and compromise its reliability. Power supply manufacturers are very creative in incorporating additional features into the PCB structure that mitigate thermal and pinch problems.
Given the trend toward housing systems in smaller packages with more components, it is essential to ensure good airflow management around connectors positioned at points of intersection (for example, between a power supply and the server) that can obstruct airflow. Ample airflow around and through the connector helps cool the power contact, allowing for increased current and/or providing a greater safety margin. Connectors are also sometimes located at critical points where they block airflow. Connector cooling is not a top priority for designers when considering airflow.
Considering operational safety, the designer must examine the entire system—from end to end—including its power architecture, to understand potential areas of constriction and voltage drops that could negatively impact thermal and electrical performance. Typically, a maximum voltage drop of 30 mV defines the threshold for thermal stability for a power contact. Beyond this threshold, thermal instability increases significantly.
Leading companies specializing in innovative connector designs are working with their customers to develop improved power interconnect solutions that ensure safe operation and reliable performance in smaller spaces at higher temperatures throughout the product's lifecycle. The new designs incorporate novel alloys, molded resins, metallization, and enhanced contact technology, all aimed at increasing current density without compromising safety or reliability.
Risk Mitigation:
Connector manufacturers typically base the electrical performance ratings of their products on tests conducted under optimal conditions. While these published values are accurate in what they measure, they don't tell the whole story because they don't account for the varied conditions and interactions that will affect the environment in which the connector will actually operate.
As a result, a common practice among OEMs has been to subtract some of the connectors' capacity to provide a thermal safety margin relative to the product ratings published in the connector manufacturers' documentation. Many use a simple method: start testing with a small number of circuits and gradually increase the number, recording the temperature rise in relation to the current. This demonstrates that the current-carrying capacity decreases as the number of circuits increases. Some customers arbitrarily apply a certain percentage: for example, a product rated at 100 amps by the connector supplier. In this case, the user would automatically subtract 30% to ensure a built-in safety margin that protects against potential overheating.
Today's leading connector suppliers know this and will work closely with OEMs and their design teams to tailor their range of connectors to the specific application, based on scientific testing and performance analysis under real-world usage conditions.
To provide accurate values, leading manufacturers conduct large-scale testing and create predictive models, such as finite element analysis (FEA) with Joule heating and computational fluid dynamics (CFD) software, using inputs related to connector, PCB geometry, material properties, current, contact resistances (actual test data), and airflow. This allows them to estimate the performance of each of their interconnect products and reliably advise customers on which products would best suit their application requirements. While simulating and/or testing every possible environment is impractical, these models and analyses guide designers in making smarter decisions faster. This is an important criterion given the rapid design cycles required in the electronics industry.
Better Results Through Power Integration Planning
In today's highly competitive, trend-driven technology market—where compact form factor, transmission speed, and signal and power integrity are paramount—it is simply impossible to overstate the advantages of proactive power integrity engineering. The increasing demand for computing power drives the need for higher raw power output. Meanwhile, product design cycles are getting shorter and shorter, leaving power engineers with less time to make critical decisions.
As we have seen, clearly understanding all requirements in the initial design phase, before specifying interconnect components, can help make the right decisions and avoid costly mistakes. More importantly, high-quality engineering for power integrity empowers OEMs and their product designers to maximize the performance, reliability, and safety of their products, contributing to increased sales and customer satisfaction.
Author:
Ken Stead, manager and head of new food product development for the global market at Molex.
