High-reliability, robust designs, peak performance, and simple assembly are some of the most critical connectivity requirements for high-vibration medical equipment.
Alfred Lee, Business Development Manager at Hirose Electric
Engineers must take many factors into consideration when designing connectors for medical equipment in high-vibration environments. From stationary high-vibration equipment, like computed tomography (CT) scanners, to portable electronic patient monitoring and in-home care equipment, medical connectors need to offer high-reliability in the form of resistance to shock, bumps, drops, jolts, and more. In addition to reliable performance, medical connectors are tasked with simplifying OEM designs, delivering higher densities, and supporting higher speeds — and all in an ever-smaller and lighter package.
Medical imaging equipment, including MRI, CT, X-ray machines, offer detailed pictures of the various structures inside of the human body. Physicians utilize medical imaging technology for diagnosing, staging, and evaluating treatments for patients. Product innovations in medical imaging technology are primarily aimed at improving image resolution and reducing equipment and procedural costs. By developing better detectors, enhancing image reconstruction, increasing the efficiency of image acquisition, and reducing the size of the equipment, medical imaging equipment will be able to deliver more accurate and detailed information to medical professionals and patients.
These various imaging techniques produce images in very different ways; however, each technology utilizes equipment that spins rapidly, creating significant shock and vibration. Connectors that are unable to handle these vibrations can cause in-field failures and lead to costly downtime and maintenance.
The miniaturization of connectors has enabled the medical industry to develop advanced mobile monitoring stations and in-home care equipment. Some mobile equipment, such as ventilators, moves around with individual patients as they amble throughout their environment, while other equipment, like diagnostic equipment, travels from room to room to support many different patients. The movement of such mobile equipment inevitably leads to bumps and dings along the way, and can even lead to the loosening of critical board-to-board solder joints and, ultimately, to machine failure.
Board-to-board connectors typically utilize leaf contacts, which only offer one point of contact per position and, as such, are not robust enough for high-vibration environments. Medical equipment subject to high shock and vibration is better served by board-to-board connectors with a dual-beam contact structure. Dual-beam designs provide two points of contact per pin, ensuring rugged connectivity and high-reliability performance, and can even be constructed so that each contact beam has a different vibration characteristic and a different contact force. This widens the frequency range and reduces resonance while simultaneously improving shock and vibration resistance. Connectors that employ this unique dual-beam design can feature a 0.5N contact force on the first beam and a 0.35N contact force on the second beam.
Hybrid power and signal board-to-board connectors that combine high-speed transmission capabilities with built-in power contacts also offer significant design advantages. Combining signal and power in a single connector saves PCB space, and can often eliminate the need for an additional power connector, further reducing both the PCB footprint and overall component count. These hybrid structures also reduce the total number of pins required. Hybrid signal and power connectors, like the FX23 Series from Hirose’s FunctionMax product family, can offer high-speed transmission up to 8Gb/s and feature four built-in power contacts located on each side of the connector housing to provide a power rating of up to 3A per pin.
Figure 1: Hirose’s FX23 Series board-to-board hybrid power and signal connectors
Hybrid connectors support high-speed applications with a specialized contact structure that utilizes a ground contact between adjacent differential pairs to reduce crosstalk, as well as provides superior impedance matching and low insertion loss, even with short rise times. In addition, non-magnetic versions are available for use in MRI applications.
Board-to-board connectors that feature a floating contact mechanism offer a degree of play between the contacts during mating in order to simplify the assembly of medical equipment. Board-to-board connectors with these highly-reliable floating contacts effectively eliminate mating alignment issues by allowing the connectors to absorb alignment errors up to ±0.6mm in the X- and Y-axis directions. By self-centering in both the X and Y directions, floating contact structures ensure safe and correct mating, reduce the stress on mounted parts, mitigate solder cracking, and improve reliability. This unique floating contact structure is also particularly convenient when mating multiple connectors on the same PCB, as it saves significant assembly time and associated costs.
Figure 2: The internal structure of Hirose’s FX23 Series connectors.
Additionally, pin-in-hole intrusive reflow can be applied to board-to-board connectors with floating contacts to reduce the manual soldering process of the metal posts. This soldering process, combined with the floating contacts, solves the problem of solder joints coming loose in portable medical equipment subject to shock and vibration.
Out with the Old
Much like hard metric connectors, which are commonly used in medical imaging equipment, floating contact board-to-board connectors are available with 20–120 standard positions at various stack heights, and compared to the through-hole parts, SMT parts, like the FX23, can assist in streamlining the manufacturing process. However, most hard metric connectors only offer transmission speeds up to 3Gb/s, which makes them less attractive solutions as medical imaging equipment continues to evolve and demand higher speeds.
Medical imaging equipment requirements continue to drive connector technology to enable high-quality images to be generated faster and with superior resolution. Further, as medical equipment continues to become more portable for use in environments ranging from hospitals to small clinics and mobile care units to homes, the connectors they rely on must be proven safe, simple, effective, and reliable. Combining floating contact mechanisms with hybrid signal and power connector technology delivers extremely functional solutions suitable for use in demanding, high-vibration medical applications.