A New Solder-less, Spring-Loaded Coax Connector Revolutionizes RF Connectivity
The landscape of high-speed radio frequency (RF) interconnects is continuously evolving, driven by the need for enhanced performance, simplified assembly, and improved durability. For decades, the Subminiature Push-On (SMP) connector has been a staple in many RF applications. However, a new, solder-less, spring-loaded solution, EZiCoax, offers significant advantages over traditional SMP contacts, particularly in complex, board-to-board architectures.
The Traditional Subminiature Push-On (SMP) connector
The traditional SMP connector was first developed in the 1980s and initially marketed as GPO. Today, numerous manufacturers offer compatible SMP connectors used across a variety of applications. SMPs are typically a three-piece system, featuring two male connectors, referred to as shrouds, which are designed to be surface mount or through-hole soldered to Printed Circuit Boards (PCBs) and come in two types: Detent and Smooth Bore. The third piece, a female connector, is referred to as Bullet and completes the mating of the two male connectors located on adjacent PCBs.
Traditional SMPs are usually robust RF contacts capable of operating from DC to 40 GHz with low insertion loss. They are designed for a nominal 50 Ohms impedance, operate between −65∘C and 165∘C and exhibit good leakage characteristics, offering better than −60 dB rejection.
While SMPs can be blind-mated, this often presents challenges due to the potential for misalignment and the high forces required. Mating a single SMP connector can require up to 9 lbs of force. For a PCB assembly with, for instance, 32 connectors, the total mating force would exceed 280 lbs.
Introducing EZiCoax: A Solder-less Solution
Smiths Interconnect has introduced EZiCoax, a new single-piece, spring-loaded coaxial connector designed for high-speed RF applications. EZiCoax features a double-ended design with a spring-loaded signal and ground contact, fully encapsulated within the assembly. It mates between two PCBs by compression, eliminating the need for any soldering.
EZiCoax is designed to be supplied in an interposer—a frame that aligns the contacts precisely to the PCB. A significant benefit is that interposers can be highly customised and can incorporate both digital and power contacts alongside the coax, providing a comprehensive solution for mixed-signal applications. The smallest coax offers a low profile, with a 3.30mm board-to-board distance and can be used on a pitch as small as 3mm.
Performance and Qualification
EZiCoax is a 50 Ohm RF contact that performs out to 40 GHz. Its performance characteristics are exceptional:
• Insertion Loss: Better than −1 dB through 40 GHz.
• Return Loss: better than −15 dB through 40 GHz.
• Crosstalk: near and far-end crosstalk is better than −60 dB through 40 GHz.
• Environmental and Electrical: working temperature range is −65∘C to 165∘C.
• Electrical: the signal pin current capacity is 1 Amp, and the dielectric withstanding voltage is 500 V DC.
EZiCoax has been qualified to ESCC 3402 ESA Space qualification. Key qualification highlights include:
• Random vibration of 53.79 Gs.
• Mechanical shock of 100 Gs half sine.
Both shock and vibration tests were repeated three times in all three axes.
Misalignment Tolerance
With traditional SMP-style connectors, board-to-board tolerances and shroud placement can lead to three types of misalignments:
Radial Misalignment: This occurs when the shrouds are offset from true centre in the X, Y, or both directions.
Axial Misalignment: This is the distance variation (in the Z-direction) between the two PCBs.
Angular Misalignment: A product of both radial and axial misalignment, causing the bullet to sit at an angle within the shroud.
EZiCoax exhibits remarkable performance under misalignment, which is critical for system reliability. The performance is optimized by designing the PCB to the recommended pad layout, which specifies a 26mil signal pad with a 41mil anti-pad.
EZiCoax has been tested under Axial Misalignment: the performance remains strong, with insertion loss at the maximum working height of 0.138 inches (3.5 mm) dropping only to about −1.1dB of attenuation.
With Radial Misalignment, performance also remains highly stable. There is less than a half dB shift in insertion loss with a mismatch of ±10 mils (0.25 mm) in the X and Y directions.
Angular Misalignment: since interposers are designed to ensure the PCBs are flush-mounted and parallel, angular misalignment is minimized. If it does occur, the design allows for up to 2.5 degrees of displacement with less than −1 dB of loss.
Interposer Solutions and Applications
An interposer is an electrical interface that routes connections between one socket/connection and another, essentially bridging two opposing sides of a PCB. The housings are typically made of engineered plastics like TECAPEEK or Ultem, though other materials may be used for specific environmental or electrical needs.
Interposer designs can incorporate various features: dowel pins or bosses for precise alignment, thru-holes and hardware for securing the assembly as wells as custom features like cutouts to avoid existing system components and the ability to integrate environmental or electromagnetic interference (EMI) gasketing.
EZiCoax is an improved alternative to older methods of passing RF signals in interposers, with arrays that typically require a grounded housing and take up considerably more space on the board.
EZiCoax primarily targets Space and Military applications which notably demand high performance and ruggedness while benefiting significantly from increased ease of installation and system reworkability.
In Applications like Satellites, Deep Space Probes/Rovers, HTCS antennas, launch vehicle avionics, telemetry modules, as well as the Active Electronically Scanning Arrays (AESA) radar systems used in defence, EZiCoax is well suited to replace current RF interconnects offering the possibility of 90% weight saving, easier assembly, extremely reliable performance with an overall lower cost of ownership.
By providing a robust, solder-less, and highly tolerant solution, EZiCoax simplifies assembly and enhances the reliability of high-frequency board-to-board connections across critical industries.
Features and Benefits of EZiCoax
In conclusion, the EZiCoax spring-loaded coax connector offers a significant leap forward compared to traditional soldered SMP contacts, primarily by delivering a substantially lower cost of ownership. This advantage stems from the stark differences in assembly and handling. Unlike SMP, which requires a complex, multi-step process involving soldering of the shrouds, specialized tools for installation/removal, post-soldering flux cleaning and, finally, costly maintenance plans requiring regular inspection of the soldered joints, EZiCoax simplifies the process immensely. It utilizes compression mounting and alignment via the interposer features, making assembly quick and the connection reliable.
Furthermore, the spring-loaded technology within EZiCoax dramatically improves product life and reworkability; it requires only a low mating force and no extraction force for de-mating, allowing the interposer to be assembled and removed repeatedly without the risk of PCB damage associated with the high forces of SMPs.
Finally, EZiCoax provides by design superior reliability by absorbing greater misalignment, tolerating up to 0.25 mm of axial and 0.33 mm of radial misalignments.
Get in touch for orders or any queries: sales@rfdesign.co.za / +27 21 555 8400
Courtesy of Smiths Interconnect
