Spring probe contact systems can ensure high performance in critical-care applications.
BY MURTAZA FIDAALI AND TED WORROLL
When designing high reliability (hi-rel) connectors for medical applications, it all comes down to shielding and, in turn, EMI/RFI protection.
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Increasingly, manufacturers of medical equipment are placing an emphasis on shielding and low insertion losses due to greater demands for higher resolution imaging, viewing and displays. The same connector technologies used in military and aerospace applications for EMI/RFI requirements are critical for diagnostic equipment, such as X-ray machines and ultrasound equipment, and even robotic surgery equipment. In fact, any medical application that utilizes imaging is susceptible to the effects of EMI/RFI disruption.
Materials as well as filtering of the connector both play a key role in shielding to meet EMI/RFI requirements. Nickel-plating the connector shell and gold-plating the ball spring are just a couple of ways in which insertion loss and resolution requirements are met. Connector manufacturers are also increasingly using plating on beryllium copper and stainless steel, since both materials feature excellent insertion loss characteristics.
Absorbing the impact
Overmolding the connector cable is also imperative for producing a hi-rel connector, and is often accomplished by attaching the stainless steel shield over the shell (the shielding lies between the wires and the connector jacket), and then pre-molding/ overmolding the end of the cable to the connector. In this instance, when EMI/RFI hits the connector, the overmolded cable absorbs the impact, thus minimizing insertion loss and any electrical variation.
It is particularly important that specific applications, such as pace- makers and patient monitoring systems, be resistant to EMI/RFI. Signal noise can affect the operation of a pacemaker and can corrupt collected and transmitted data within patient monitoring devices.
While RF connectors are often employed in medical applications, it is paramount that they feature non-magnetic materials, since magnetic emissions affect image clarity and increase signal noise. As a result, connector manufacturers are using stainless steel, alloys, and brasses because they offer non- or low-magnetic fields that keep electromagnetic and radio frequency signals from interfering with the performance of the medical equipment. EMI shielding effectiveness allows some connector manufacturers to offer EMI performance of greater than 85 dB at frequencies from 40 MHz to 10 GHz.
Filter connector designs
While traditionally considered an excellent means of suppressing surge spikes, filter connectors also play a critical role in managing and controlling the effects of EMI and RFI on system performance. In some connector designs, standard filtering capabilities are provided, including individual isolated pin filtering of high-frequency noise, built-in ground plane barriers in the connector inserts, and filtering at the face of system boxes.
Filtering enhancements
A more effective connector signal barrier further enhances these traditional filter attributes. This filter-design approach offers the system designer complete flexibility in defining or changing individual circuit capacitance, ground, and electro-magnetic pulse (EMP) performance during the design and development phase. Many connector designs also incorporate shield cans placed on the PC board to protect the circuitry from signal interference.
Filtering effects can be further enhanced through a spring probe pin/pad contact system. The contact system is comprised of the spring probe pin in the plug connector configuration, and can be implemented across multiple sizes. Some manufacturers use an internal clip mechanism to ensure uninterrupted contact with the contact itself. The spring probe design helps reduce electrical resistance while addressing misalignment issues, making the contact system much more forgiving. Along with the high durability of mating cycles possible with the spring probe design, the contact system offers higher performance in harsh or critical environments.
 FIGURE 2. ITT says its Breakaway connectors feature EMI performance characteristics of greater than 85dB. |
A spring probe system houses individual touch pad contact areas, which enables an effective electrical engagement point of contact. Further, the individual touch pad contacts incorporate no crevices in which contaminants can accumulate–a desirable feature in critical medical field conditions. For all these reasons, spring probe contact systems can be a superior solution for ensuring high performance in critical operations requiring hi-rel connectors.
Connectors designed with shielding and EMI gaskets can typically satisfy any EMI requirement. Electromag- netic interference is also reduced through the connector’s capacitance value. Connectors with capacitance values ranging to 50,000pF significantly reduce signal noise traveling through the device, thus directly and positively affecting the performance of the end unit.
Smaller and lighter
Today’s ever-increasing need for electronic systems that perform in extreme and critical environments is further challenged with growing demand for smaller and lighter electronic systems where space and weight are at a premium (such as portable and at-home medical equipment). Not only must designers ensure that their system modules (LRM) and boxes perform in critical situations, they must guarantee that the interconnect links for their systems survive and maintain signal fidelity.
These requirements can be accomplished with breakaway connectors that provide complete cable termination solutions (discrete wires, flex circuits, and composite cables) with a high-performance, EMI-shielding/grounding electronics cable assembly. The designs allow for shell-to-shell grounding at less than 10 mΩ as well as EMI performance of greater than 85 dB at frequencies from 40 MHz to 10 GHz. Perfor- mance is further enhanced by termination processes that allow for 360° shield/connector coverage.
Complex EMI/RFI electronic issues have driven connector manufacturers to develop higher-performance and more cost-effective EMI suppression filter solutions, including advanced technology such as a spring probe contact system with a Chip-on-Flex (CoF) filter solution. CoF technology features a flex circuit that incorporates individual chip capacitors surface-mounted to a pad on the feed-through contact. This new system approach replaces the traditional planar array block capacitor while providing a hi-rel filter solution, and also promises cost-effective thermal shock and vibration performance.
Design options
Today’s medical equipment applications requiring reliable connector components because of EMI/RFI, shock/vibration, or harsh environment conditions have more design options than ever before. From material analysis and selection, to specific contact design and creative filtering solutions, innovative connector suppliers continue to provide medical OEMs with the performance they need. CS
MURTAZA FIDAALI is director of business development/medical and industrial markets, and TED WORRELL is product manager at ITT Interconnect Solutions (www.ittcannon.com).
Medical Connectors & Support
36-POSITION SMT
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Mezza-pede SMT connectors are now available with 36 positions. Designed for 1-mm pitch micro board-to-board and flex cable-to-board applications, this connector’s patented pin and lead frame design is surface mountable and features brass/copper alloy screw-machined terminals with multi-finger beryllium copper contacts. An overmolded lead frame seals the surface-mount pins to prevent solder wicking and helps ensure a solid solder joint at the PCB level.
Key specifications:
- Mating force– 2.5 lbs.
- Extraction force– 2.2 lbs.
- Durability– 100 cycles
- Contact resistance– 10 mΩ max. change after testing
- Current carrying capacity– 1.1 amps @ 80° C ambient
- Operating temperature range– -55° to 125° C
Applications:
- High-rel medical and military mezzanine board-to-board
ADVANCED INTERCONNECTIONS CORP., W. WARWICK, RI
www.advanced.com
HI-REL RECTANGULAR SOLUTIONS
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The MDM Series micro-D, MDMA Series rectangular micro miniature, and MTB1 Series single in-line microminiature connectors feature a high-rel twist-pin contact system designed to provide a secure base for the contact and improved electrical and mechanical characteristics compared to traditional machined or stamped contacts. These connectors employ non-outgassing and non-magnetic materials to eliminate distortion in imaging equipment.
Key specifications:
- Sizes– 9, 15, 21, 25, 31, and 37-way
- Removable contacts; twist-pin contact technology
- Wire sizes– Insulated AWG 26 and 28
- Distance between 2 adjacent contacts– 1.27 mm
- Distance between contact rows– 1.09 mm
- Operating temperature range– -270° to 200° C
Applications:
- Cryogenic process, medical imaging equipment
C&K COMPONENTS, NEWTON, MA
www.ck-components.com
MINI MEDICAL TEST DEVICES
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Now with metric thread options, the ME001 Series is designed for mounting and media connection flexibility in leak testing infusion and drug delivery devices. Its pneumatic actuation is suited for soft-touch control of delicate components. The design is also suited for automated processes for ergonomics or high production testing. Connectors are chemically cleaned and double-bagged.
Key specifications:
- FDA-approved seals and lubricant
- Capable of sealing outside diameters (OD) down to 0.38 mm (0.015”)
- Size– 21.3 millimeter OD (0.84”)
- Operational pressure range– Vacuum to 500 psi
- Sealing capacity– Up to 12.95 m OD (0.510”)
- Housing– Aluminum, stainless steel
Applications:
- Testing medical devices, secure sealing of ultra-thin hypodermic and catheter tubing.
FASTEST INC., ROSEVILLE, MN
www.fastestinc.com
MODULAR 2-MM SYSTEM
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Tempus 2-mm modular CBC 20 is a 2-part plug and receptacle connector system designed to provide headroom to expand as design requirements change. Contacts are laid out in four or five rows on a 2-mm pitch rather than in three rows on a 0.1-inch pitch. Available in 4- and 5-row versions, the cable receptacles include all components needed to assemble finished cable ends.
Key specifications:
- Compatible with IEC 61076-4-104 backplane connectors
- Wire size– AWG 24 to 30
- Contacts– 4-row versions, 4x6 and 4x12 contacts; 5-row versions, 5x6 and 5x12 contacts
- Application tooling support– Manual and pneumatic crimping
Applications:
- Medical, instrumentation, telecommunications, industrial
ITT CANNON, SANTA ANA, CA
www.ittcannon.com
RIGHT-ANGLE BNC
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These 4-, 6- and 8-port right-angle BNC connectors are available in filtered and unfiltered versions, and 50- or 75-Ω impedances. With a through-hole/PC-mount configuration, the connectors have solderable mounting tabs designed for strength and connectivity, and feature phosphor bronze contacts and a tin plating-over-brass mounting post.
Key specifications:
- Dielectric withstanding voltage–1500 volts AC, one minute
- Operating voltage–500 volts RMS
- Insulation resistance–5,000 MΩ min.
- Contact resistance–3.0 mΩ max.
- Frequency range–0 to 1 GHz
- Operating temperature– -55° to 85° C
Applications:
- Medical devices, video switcher and distribution banks, communications and recording studio equipment, matrix switchers, and video surveillance systems.
REGAL ELECTRONICS, SUNNYVALE, CA
www.regalusa.com
PCB-MOUNT POWER ENTRY MODULE
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Pre-wired between the inlet and fuse holder, the DA22 series power entry module features built-in overload protection, maximum high power density, and EMC filter performance. All functions are integrated in a compact component, designed specifically for PCB mounting. Overload protection is provided by a 1- or 2-pole shock-safe fuse holder for 5x20-mm fuses. Optimal EMC performance is achieved by incorporating the filter and shielding directly at the point of entry.
Key specifications:
- IEC ratings–Up to 10A @ 125/250 volts AC; 50 Hz
- UL/CSA ratings–15A @ 250 volts AC; 60 Hz
- Dielectric strength– >2.5 kV AC between L-N; >3 kV AC between L/N-PE (1 min./50 Hz)
- Terminal–Quick-connect, 6.3 x 0.8 mm
- Panel thickness–Snap-in 1.5, 2, 2.5 mm
- Housing–Black thermoplastic
- Temperature range– -25° to 60° C
Applications:
- Mid-profile design enclosures with a height of 1.5 or 2U, including medical and laboratory equipment, telecom and IT infrastructure equipment, power supplies, and test and measurement equipment.
SCHURTER ELECTRONIC COMPONENTS, SANTA ROSA, CA
www.schurter.com
