FEATURE INTERCONNECTION
Getting the right angle
Words by Wendy Jane Preston, marketing engineer, Harwin I
f you ask any electronic designer, they are likely to tell you that PCB real estate is in very short supply. The problem is not just in two-dimensions, as space above the board is also shrinking. The combination of these two space problems presents a major challenge to a cross section of industry sectors, including robotics, autosport, aeronautics and factory automation systems. A key example is in satellite construction, especially in relation to ultra-compact CubeSats. Here, the design’s external dimensions must be kept to an absolute minimum, so that they won’t take up too much of the payload capacity during the launch. Each cubic unit (U) of one of these satellites equates to 10cm x 10cm x 10cm, with multiple units making up the total volume. Popular sizes of CubeSats consist of 1U, 2U, 3U and 6U-size formats. By increasing the number of PCBs contained within the CubeSat framework, greater functionality can be achieved. Engineers need to stack these boards as closely as possible. However, narrowing the distance between boards has serious implications for the component parts populating them, and their accompanying cabling. As a result, low profile component options need to be specified, and the layout of cable harnessing must be approached differently. The example of the CubeSat problem is equally true in many other contexts, like unmanned aerial vehicles (UAVs) or single-seater racecars. When considering the PCB headroom issue, the effect on overall system reliability must also be taken into account. Cables exiting a PCB connection vertically will need a tight bend before making contact with the next PCB in the stack. This puts strain on both the cable and the board connector, and increases the risk of interconnect failure. As the minimum bend radius of a cable increases with wire diameter, then
18 APRIL 2020 | ELECTRONICS
thicker wires (for higher signal current or power) will need more space to accommodate the larger bend. This additional height of board connector, plus mating cable connector, can also cause other issues. The cable bend will be more prone to wear, especially if it is located in contact with other devices or the next PCB. Air flow around and across each board will need consideration for thermal management, both during assembly and when subjected to heat cycles in space. Assembly will also be more complicated during initial build, and additional cable management devices may be required.
connector and harness off the edge of the PCB, rather than taking up space between the PCBs. As the attached cables do not need to be bent by the same amount, they are placed under less strain once they are installed. An extra advantage is that the connectors are now more accessible, making cabling simpler to assemble and replace. Cabling can now be done as a single operation after the stack is constructed, rather than having to alternate between adding cables and PCBs to the stack.
Harwin’s Gecko series of connectors specifically target high-reliability (Hi- Rel) applications, with their compact form factors. The spatial constraints introduced in these applications raises demand for an interconnect solution like the Gecko Screw-Lok (SL) series. Building on the existing advantages of light weight and small size, these latest Gecko-SL connectors take things one step further. The new right-angle configuration means that the mating face of the male connector is at a 90-degree angle to the board itself. This reduces the mated height-above- board significantly, by routing the cable
Harwin’s Gecko-SL connectors with their right-angle configuration
Horizontal Gecko-SL connectors meet the same 2.8A current rating and 1.25mm pitch as the existing range, and are fully compatible with female cable and PCB connectors. Robust and corrosion-resistant stainless steel jackscrews ensure long-term mating integrity. Screw-loks are designed to be Mate-Before-Lock, where the screws are not tightened until the connectors are mated together. Mating and securing all connectors is simple and fast as a result. These connectors are resilient to both shock (50G) and vibration (20G at up to 2kHz, for a six hour period), plus an extensive -65 to +150 degrees Celsius working temperature range. They also possess low outgassing properties, which appeal to space applications. Faced with having to implement more densely packed electronic systems, with very little room to manoeuvre, engineers must be able to specify connectors that can cope with space-constrained environments. By using alternative orientations for mated connectors, PCB heights can be reduced; more electronics or other devices can be given more space for other purposes; production operations can be simplified and made more accessible. The design, overall, can be functional and have low assembly costs.
Harwin
www.harwin.com / ELECTRONICS
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