White Paper. Lightweight Connectors for Demanding Applications. June by Brad Taras Product Manager Cinch Connectivity Solutions

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1 White Paper Lightweight Connectors for Demanding Applications June 2018 by Brad Taras Product Manager Cinch Connectivity Solutions

2 Phenomenal levels of integration are being achieved in modern electronics and there will always be a need for physical connections between circuit boards, panels, ICs or to external wire harnesses. It is an increasing challenge to achieve this in a reliable way, particularly in applications such as aerospace and UAVs where demand is for reliable connectors that are lightweight and small. When we think of high-reliability connectors, perhaps big circular bayonet types come to mind. While these certainly do still have their place, there are many applications where size and weight, along with the ability to operate in harsh environments, is increasingly important. Typical examples might be UAVs (Unmanned Aerial Vehicles) and electric vehicles, where every ounce or gram saved translates into extra operational time for each battery cycle. Aerospace is also an application area where weight is crucial; the increasingly popular CubeSats, for example, are limited to a mass of no more than 1.33 kilograms per 10cm3 unit. Connector specifications Making an electrical connector is more complex than it may seem; a connector comes with specifications for DC current handling, voltage rating, insulation resistance, contact resistance, insertion loss up to a specified frequency, cross-talk between conductors, connection inductance, mutual capacitance and inductance between conductors, a well as insertion/withdrawal force. There s also a whole range of environmental specifications including temperature, humidity, shock and vibration, operating altitude, chemical resistance and more. As connector sizes decrease, design and manufacturing techniques are challenged to keep many of these parameters optimized and consistent for signal and power integrity. Connectors that pass 20 GHz signals, for example, benefit from the low inductance that comes with small form factors, but even a variation of just 0.5 nh between conductors would change differential impedance by more than 60 Ω. Similarly, at DC, mω variations in contact resistance can make a significant difference to voltage drop and temperature rise when carrying just a few amps of current. Clearly a simple sprung terminal with a singlepoint friction contact is not a good solution in these cases. What meets the challenge? Connector manufacturers have long realized that an ideal arrangement is to use multiple points of contact with a degree of mechanical compliance so the connection is maintained under deformation, shock and vibration conditions, while also keeping contact resistance and inductance low. Ideally the connector should provide a contact interface that gives an absolute minimum of physical and electrical discontinuity to prevent a hot-spot at DC, and an impedance mismatch or loss at high frequency. Over the years various techniques have been presented as solutions but as connector sizes reduce, miniaturizing these has been a challenge. Some elegant but simple designs have emerged, though. An example aimed at relatively low frequency signalling and power is the Twist-Pin technology from Cinch used in many styles of their Dura-Con TM connectors (Figure 1)[1]. A bundle of seven strands of gold plated berylliumcopper wire is welded at its tip then mechanically expanded to form a cage which provides seven points of contact inside the periphery of a mating female pin.

Figure 1. Cinch Twist Pin Contact Technology The Twist Pin is the contact used in all the Cinch Dura-Con line of rectangular connectors, which includes the Micro-D (Mil-DTL-83513).

3 Figure 1. Cinch Twist Pin Contact Technology The Twist Pin is the contact used in all the Cinch Dura-Con line of rectangular connectors, which includes the Micro-D (Mil-DTL-83513). When used in their minimal space and weight configured strip connector product, Cinch achieves up to 60 in-line connections with a pitch down to 0.05 inch (1.27 mm). Insertion tends to expand the cage with a positive wiping action, while the withdrawal force needed remains low, as the cage contracts a nice feature that avoids putting potential stress on the wiring to the connector. Figure 2. Cinch Dura-Con Strip Connectors with Color Coded Wire Leads and Polarizing Pin Another solution from Cinch is their CIN::APSE compression technology (Figure 3)[2]. This continues the approach of providing multiple connections but through a discrete bundle of gold plated molybdenum wire randomly bundled

4 so that seven to eleven points of contact are made at each end, against a mating pad on a rigid or flexible PCB or semiconductor device. Figure 3. Cinch CIN::APSE Contact for Solderless Compression Technology The bundle is inserted into a patented hourglass shaped aperture in the insulating liquid crystal polymer connector body, protruding each side. The targeted application for the technology is to provide a connector interface between PCBs or from PCB to Land Grid Array (LGA) devices (such as ASICs and CPUs). Using the technology, I/O pin counts can exceed 7000 at pitches down to 0.03 inch (0.8 mm). Figure 4. Cinch CIN::APSE Connectors for ASICs, Interposers and RF Interposers

5 How the connectors perform The Dura-Con TM Twist-Pin contacts are rated at -55 C to +135 C and each contact is rated at 3 A and 600 VAC at sea level. Contact resistance is 8 mω maximum. Insertion and withdrawal forces have a more than 10:1 ratio, at 6.0 and 0.4 ounce maximum respectively, showing the effect of the expansion and contraction of the cage. The Twist- Pin contact can be used in applications where a controlled differential impedance is necessary, matching associated cabling for high signal integrity. Pseudorandom Binary Sequence (PRBS) tests at 1.25 Gbps data rate prove the performance along with Time Domain Reflectometry (TDR) measurements confirming 100 Ω differential impedance. The CIN::APSE compression contact is rated at 3 A 6 A at 0.02 inch spacing and up to 10 A at 0.04 inch. Its dielectric withstand is 500 VDC at sea level and operating temperature range is from -60 C to +105 C with a shock rating of 100 G. In particular customer applications, shock tests have reached 22,000 G with a temperature withstand as low as -200 C. Useable frequency range is up to an impressive 50 GHz with an insertion loss of -0.2 db at 10 GHz and just -1.2 db at 20 GHz. A typical performance graph is shown in Figure 5 for a single APSE contact with a height of inch in a coaxial arrangement, with an aerated Teflon insulator. Figure 5. Insertion Loss of the CIN::APSE Contact Coaxial Arrangement Crosstalk between contacts is less than -25dB and return loss -19dB at 10 GHz. Contact resistance is less than 10 mω, while inductance is less than 0.5 nh.

6 To get the best performance from the CIN::APSE technology, a compression system needs to be used which provides uniform pressure over the array of contacts. This can be a simple arrangement of clamps and screws, perhaps used for terminating a flexible circuit to a PCB, to a typical LGA system of a top heatsink and bottom bolster plate between LGA device and PCB, fixed together with controlled-stop screws and springs with defined rate to give uniform pressure distribution. The CIN::APSE contact itself is available with a mated height of inch (0.8 mm) but the effective length can be extended with a variety of options of spacers and plungers integrated into the length of the connector contact. In this way, distances of up to 1 inch (25.4 mm) can be spanned. When the CIN::APSE contact is embedded between two plungers (Figure 6), it is also mechanically protected against any possible handling damage. Figure 6. CIN::APSE Contact Embedded Between Plungers With more than 2 billion contacts shipped in more than 50 configurations, Cinch is confident in the performance of the product in demanding applications such as defense, aerospace, industrial instrumentation and data centers. Custom versions can be configured to match customers exact footprint requirements along with complete compression system design. Summary For applications demanding small size, high density and reliable interconnections, simple friction-fit connectors are simply not up to the job and a hi-tech but elegant solution of a multi-contact terminal is needed to provide an optimum solution, from DC to 50 GHz. Cinch offers two product ranges, Dura-Con TM and CIN::APSE, that meet many of these requirements. References

7 ABOUT THE AUTHOR Brad Taras Cinch Connectivity Solutions Product Manager for C-ENX TM, Dura-Con TM, and Cin::APSE product lines. He has a Master's in Business Administration from the University of Illinois at Chicago and a Bachelor's Degree in Material Science and Engineering from University of Illinois - Urbana/Champaign. Brad has been a product manager in the connector industry for over a decade after starting in the industry as a design/manufacturing engineer. Brad s experience as an engineer in the military industry goes back to Contact Information O E brad.taras@us.cinch.com

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CIN::APSE Compression Technology Enabling technology for the most demanding interconnect applications

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