Addressing embedded systems interconnect challenges

This article originally appeared in the October'24 magazine issue of Electronic Specifier Design – see ES's Magazine Archives for more featured publications.

Connectors for embedded systems

Demands for embedded systems to deliver ever-higher and more robust performance in smaller and lighter platforms makes the selection of connectors – typically the largest and heaviest components in the design – more critical than ever, with careful consideration given to everything from data throughput and power handling ability to form factor, pitch density, size, weight, and long-term reliability. And while the majority of applications will need connectors that interface to the outside world (for example for audio, video, power transfer, and connections to other systems and sub-assemblies) for many designers a key challenge is finding the best connectors to deploy within the system itself.

Take, for example, the board-to-board connectors that provide the cable-free interfaces between printed circuit boards. These connectors come in a variety of types including pin headers, mezzanine connectors that allow stacking of parallel printed circuit boards, edge card connectors and backplane connectors and demand is growing rapidly as designers look to accommodate more and more PCBs in ever-smaller form factors.

Board-to-board connectors

Among the key factors to consider when selecting board-to-board connectors will be connector performance, pitch density, size, and weight. 

Board-to-board connectors include pin headers, mezzanine connectors, edge card connectors, and backplane connectors

Some of the latest high-density board-to-board connectors for industrial and embedded applications, for example, have pitches down to just 0.5mm yet are capable of supporting data rates up to 24Gbps. This is the case for Harwin’s Archer family of compact, high-speed, high-pin-count mezzanine connectors. Available with pitches of 0.80 and 0.50mm supporting respective data rates of 12GHz/24Gbs and 8GHz/16Gbps, this range offers up to 120 contacts in a double-row layout, making it ideal for mezzanine daughterboard to motherboard signal transfer applications that need high contact density.

Many embedded systems, in particular those employed in industrial applications, are expected to have long operating lives, making reliability another key criteria. The good news is that connector manufacturers have developed flexible, rugged and space-saving board-to-board connectors specifically designed to withstand the rigorous demands of applications ranging from factory automation systems to hand-held equipment. Products such as Harwin’s Kontrol family of 1.27mm pitch connectors that support data rates up to 3Gbps, deliver reliable, space-saving connections for edge-to-edge and motherboard-to-daughterboard designs and offer board-to-board mating from fully mated to 1.5mm separation – giving a full range of mating heights from 8 to 20mm. 

Addressing the automated manufacturing challenge

Another challenge facing embedded systems engineers is how to best ‘design for manufacture’. As well as meeting the performance, size, weight, and reliability criteria of a given application, the chosen connector may need to be compatible with the production process, which is increasingly likely to be partially or fully automated. The Kontrol connectors mentioned, for example, not only incorporate polarisation but have the ability to tolerate some mis-alignment to ensure fault-free assembly during automated pick-and-place operations.

Indeed, the issue of connector misalignment is critical and is particularly acute when two or more connectors are to be mated between the same two PCBs. This is because the level of precision placement needed is often outside the parameters of even the best modern manufacturing processes. Unfortunately, misalignment by even sub-millimetre distances can put undue stress (such as excessive side-loading) on or damage to board-to-board interfaces. This not only leads to quality and yield issues during manufacture but also has the potential to degrade performance in the field.

To mitigate misalignment problems, engineers can choose ‘floating connectors’. These devices use a novel contact type capable of flexing, typically in the male half of the connector pair. Combined with housings that are suspended by the contacts, this leads to a spring-like action that allows floating connectors to maintain connection integrity while accommodating a difference in position across multiple axes – effectively ‘floating’ the contact areas both along and across the connector to absorb the difference. Because of this, floating connectors tolerate the small misalignments that can occur during automated manufacture, allowing pick-and-place processes to be deployed for boards with multiple connectors where the sum of misalignments might, otherwise, present challenges for high-speed, high-precision mating.

By reducing the limitations on the number of connectors that can be deployed, floating connectors also give system developers far greater design flexibility. The need for filtering, for example, can be reduced by choosing to separate noisy digital, sensitive analog and power signals. For complex boards, smaller connectors can be placed in multiple locations, eliminating the need for running long traces to a single connector.

The spring-based ‘suspension’ mechanism inherent in floating connectors also contributes to connection integrity during operation. For example, floating connectors can mitigate the possibility of performance degradation or failure from ‘fretting’ – a situation that occurs when long-term vibration causes the plating to wear from rigid mating pins, exposing the underlying alloy to potential oxidation.

Additional support

Creating optimised interconnects is not always a core competence for embedded system designers whose primary expertise is more likely to lie in processing hardware and embedded software. As a result, many engineers look to connector manufacturers and their distributors to provide support that goes beyond the straightforward supply of components and datasheets.