There’s a lot of truth to the old maxim that a cable assembly is a potential source of trouble connecting two other potential sources of trouble. How many times have you found that the problem with a system is not in the electronics themselves, but the interconnect that links boards, modules, or enclosures? The reliability and intermittent challenge is especially difficult with “user-facing” connectors, which are repeatedly connected, disconnected, abused, pulled on, mis-aligned on forced insertion, stepped on … you get the picture.
The problem is aggravated by the increasing emphasis on smaller and lighter for many consumer products. In general, connectors and cable reliability are related to size and mass: the more, the better. But physically small, low-mass connectors such as those in the widely used USB family offer minimal retention force and contact area. Frankly, it’s amazing and impressive that these connectors work as well as they do.
Still, that’s not good enough for many non-consumer applications which would like to leverage the many advantages of using USB 3.0 (Figure 1), so vendors are introducing ruggedized versions of this connector. For example, L-com/Infinite Electronics International, Inc recently released a family of USB 3.0 connectors that has an optional provision for adding locking thumbscrews to firmly attach the connector to its mating half, which can be on a cable or chassis (Figure 2).
Figure 1 The USB 3.0 connector and cable offers speed and other performance virtues but lacks the ruggedness many applications require. Source: Wikipedia
Figure 2 L-com offers a broad line of ruggedized USB 3.0 cables, including a cable with A male to B male connectors with die-cast shells (left) plus optional thumbscrews (right). Source: L-com
There’s nothing new about locking screws, of course, as they were – and still are – often used on the once-ubiquitous RS-232 D-shaped connectors (Figure 3). Known as jackscrews, they could be tightened into matching jackposts using your fingers or a small screwdriver. The latter was often needed as there was not enough clearance for finger access around a jackscrew due to neighboring cables.
Figure 3 Many of the widely used RS-232 D-shaped connectors came with jackscrews that locked them solidly to the mating chassis-mount or cable-attached connector. Source: BH Photo
Jackscrews are not the only retention option. The near-obsolete Centronics-printer connector (Figure 4) and the IEEE-488 connector use metal bails, shaped wires that could be snapped on retaining clips. These are easier to use than jackscrews but can be inadvertently flipped open to their unlocked position, so they are a better fit for fixed-in-place arrangements, but less secure where there is a chance of inadvertently being brushed against.
Figure 4 Some connectors, such as this one for a Centronics printer, used wire bails that could easily be flipped to lock/unlock instead of jackscrews. Source: Pacific Cable
The need for cable and connector ruggedness is not limited to the ones cited above. The standard RJ-45 connector used for wired Ethernet relies on a slim, easier to install/release plastic tab, but that convenience also results in a lack of physical strength and physical protection; the same concern applies to the smaller RJ-11 modular telephone connector. The weakness of the RJ-45 connector for some applications is addressed by a variety of solutions, including circular sealed ones from TTI/TE Connectivity (Figure 5).
Figure 5 Circular, sealed connector enclosures are available for the otherwise unprotected RJ-45 Ethernet connector. Source: TTI/TE Connectivity
There are even ruggedized receptacles for the increasingly popular, yet relatively flimsy, USB-C connector, such as the MUSBR series from Amphenol ICC. Despite its modest appearance, this receptacle even meets the IP67 standard for resistance to water ingress (Figure 6).
Figure 6 The MUSBR series provides some ruggedization for the USB-C connector, including an IP67 water-ingress rating. Source: Amphenol ICC
While mechanical retention is certainly a critical factor in ensuring a reliable cable connection, it’s not the only one. Most connections are specified for only 50 to 100 insertion/removal cycles, as the microinch plating on their contacts wears down with every such cycle. Once that plating (usually gold) is worn, the contacts are subject to fretting, corrosion, and other subtle sources of intermittent connection issues.
Have you wasted precious time troubleshooting a project by looking for sophisticated faults, only to find it was an intermittent connector pair? Have you ever had to retroactively upgrade a design to include a better connector assembly with improved mechanical retention?
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