Connector system removes the need for a midplane in high performance systems

4 mins read

High performance computing systems by necessity pack as many boards in an enclosure as possible. But the fact they are high performance means they generate a lot of heat. Cooling them becomes an important design issue.

But that's only one issue facing those designing high performance computing systems. Because these systems are moving data around at multigigabit rates, far closer attention needs to be paid to the electrical characteristics. Impedance control, for example, becomes important, as do other factors, such as trace length. And the performance of the connector is fundamental to system performance. In a traditional architecture, boards plug into a backplane – so called because it resides at the back of the enclosure. This not only links all boards in the system, it also provides physical support. But as datarates increase, the distance which signals have to travel between boards becomes a concern. In a move to overcome these limitations, the midplane architecture was developed, an approach in which boards can be plugged in on both sides, rather than one. Because the midplane sits in the middle of an enclosure, it can affect airflow and hence impact cooling efficiency; it may require front and back cooling systems, for example. The industry has developed a solution to this problem in the shape of the orthogonal director connector architecture. Ralf Semmeling, regional product manager with connector developer Molex, said: "Speed and heat go together. When speed increases, cooling becomes a challenge. Orthogonal direct connection enables designers to have simpler cooling mechanisms because there is no midplane, which would block airflow. It's an approach which is taking off in high performance computing systems and in datacomms." Molex has recently launched the Impact 100? orthogonal direct connector system, which has been designed to enable direct connection of pcbs using the same daughtercard. With a choice of three to six pairs – providing from 18 to 72 differential pairs – the Impact orthogonal direct technology supports data rates of up to 25Gbit/s, while mitigating airflow, crosstalk, and capacitance constraints in high speed channels, factors that can be introduced in backplane and midplane laminates. Pete Soupir, Molex' new product development manager, noted: "The direct connector solution benefits from the density, signal integrity and high speed of Molex' Impact technology without added cost and press fit assembly. The space saving combination of the direct right angle male connector and daughtercard simplifies component management and enhances performance in data, telecommunications, medical, networking and other high speed devices." According to Molex, Impact orthogonal direct connectors feature two compliant pin attach options and 18 to 72 differential pairs per orthogonal node. The configurations – the parts are available with three to six pairs – also include a range of options for the pcb and mating interface. The system is said to take advantage of the low mating force of the Impact connectors and of patented compliant pin technology to provide design flexibility and balance. Soupir noted: "Orthogonal connectors are being used more and more because they shorten the channel requirement and enable designers to increase board density. Designers can also use this system to upgrade existing systems without having to change the infrastructure. If they want to move from 12G to 25G, they don't have to change the chassis; just pull the cards, insert the upgrade and they're up and running." Soupir added that the orthogonal connector approach can reduce overall trace length in a system by some 50% compared to a traditional backplane approach. Kevin O'Connor, Molex' manager of new product development, pointed out another benefit of the approach. "Orthogonal design architecture incorporates a cost cutting angle for OEMs and their design teams," he said, "because it allows the continued use of standard pcb materials, rather than higher end, more expensive materials. Using more traditional pcbs means signal length is shorter and signal integrity is improved. This greater density also allows for smaller packaging, which directly addresses customer need for smaller and more environmentally friendly solutions." Over the last few years, growth in demand for high speed broadband networks has seen signal integrity become a more important issue. O'Connor said: "High speed networks typically require closely coupled high speed links, which can introduce noise, cross talk and signal degradation. This is because data transmission and signal integrity issues become magnified over longer links in backplanes, cables and pcb materials. "Since signal integrity is paramount for reliable product performance, it is imperative for designers of communication system components and equipment and smart devices to find effective solutions to overcome these challenges." The orthogonal connector architecture also improves performance, enabling high speed channel bandwidth, low insertion loss and cross talk and minimal channel performance variation across every differential pair within the system. This is due to design improvements, such as the inclusion of smaller compliant pins that provide a better signal launch off the pcb, as well as lower mating force. A simple 2.15 x 1.35mm grid on both the backplane and the daughtercard is said to reduce pcb routing complexity and costs, while also providing routing flexibility. "Smaller compliant pins serve to reduce the 'stub' effect and allow for smaller diameter drilled holes in the board," said O'Connor. "This, in turn, improves capacitance and impedance. With smaller holes that are not as close together, crosstalk performance is similarly improved." The Impact orthogonal direct right angle male connector is supplied with a plastic locking latch on one side of the daughtercard, allowing it to mate securely with the standard orthogonal daughtercard connector. This creates an orthogonal direct right angle to right angle connector solution. Concluding, O'Connor said: "High speed backplane connectors continue to be in great demand in supporting next generation product development in the telecommunication, data networking, data storage, medical diagnostics and other market sectors. With data rates trending ever upwards, electronic design engineers are seeking new ways to push the speed and density envelope of backplane interconnects, while neither busting the budget nor negatively impacting signal integrity and product reliability. Orthogonal connectors are available in a variety of configurations, offer great flexibility and allow for a matrix of communication channels." Benefits * Improves airflow and reduces board space constraints, compared to backplane and midplane connector systems * Simplifies component management * Reduces midplane thickness and enhances high speed performance * Allows for more overall robust signal channels * Provides flexibility to optimise designs for mechanical and electrical performance * Higher density, lower crosstalk, low insertion loss and minimal performance variation across all channels * A range of options for the pcb and mating interface * Supports system performance upgrades * Reduces pcb routing complexity and costs * Provides pcb routing flexibility * Ensures end to end channel performance compliance