Medical Electronics

Connectors in medical electronics: When reliability and mating cycle life are key

By Tom Kannally, medical and industrial connector product specialist at Smiths Interconnect


s increasingly sophisticated electronics are now being designed into medical applications, the need for high reliability interconnect solutions is being recognized as a critically important requirement. Connectors used in harsh medical environments typically need to be able to handle fluids, withstand various chemicals, perform electrically and mechanically after many mating cycles with the utmost reliability, offer EMI/RFI protection, and be resistant to shock and vibration. In addition, applications such as operating room equipment need to use inert materials that withstand various sterilisation methods, such as autoclaving and EtO (Ethylene Oxide). In medical equipment, connectors are continually mated and un-mated even in cases where disposable parts are used. The connector on the patient side is typically discarded along with a single-use probe, however, at the instrument side, the connector is fixed and will need to offer a high cycle life with various disposable mates. Certainly, cost is also an issue in medical electronics and it is important to note that field maintenance is a specialist occupation and is inherently expensive. Consequently, reliability and long life would alleviate the effects of maintenance on cost-of-ownership.

Many of the benefits offered by a hyperboloid- shaped wire basket contact make connectors based on this technology ideal for demanding medical applications. Key to the design is a socket constructed from a series of beryllium copper spring wires. When the pin is inserted into the socket, the wires stretch and wrap themselves around it. The design addresses the main operational and performance requirements for connectors in medical environments of reliability and high-mating cycle life.

The key factor ensuring high reliability is the multiple points of contact, inherently provided by the unique hyperboloid contact technology, around the pin by each wire. In a possibly harsh environment that can subject the connectors to ingress from bodily fluids or chemicals along with rigorous mechanical duress, these multiple contact lines ensure that signal integrity is maintained under the worst conditions, especially in hospital or ambulance applications.

16 May 2020

The smooth and light wiping action inherent in the contact design also produces little wear of the contact surfaces, making connectors incorporating Hypertac contacts suitable for applications that require long life with high numbers of mating cycles. Such contacts have been tested to ensure very high insertion and extraction cycles with minimal wear and no loss in functionality or specified electrical performance, contributing to reduced costs in downtime and repairs. In addition, the smooth wiping action also makes the contacts ‘self- cleaning’ as they are mated and un-mated.

Sensitive electronics require low contact resistance

The multiple lines of contact in Smiths Interconnect’s Hypertac sockets deliver a much greater contact area than other types of contacts of comparable size, resulting in about half the contact resistance of conventional contact designs which is a critical advantage for design engineers. This is a useful attribute when dealing with sensitive signals from sensors and transducers where power consumption and heat generation of a connector must be kept to a minimum for the equipment to function with reliability, as specified.

Furthermore, the contact resistance of the connector should be constant and not vary when under stress, whether this is due to vibration or any other external influence. A circuit “seeing” a variable contact resistance due to an unreliable connector could result in erroneous readings on the instrument or, in the case of sophisticated medical equipment such as defibrillators, could even be life threatening.

Contact resistance is typically dependent on the size of the contact, dropping with increasing contact size due to the contact surface area available for the current path. Thus, there is a trade-off between contact resistance and the ability to miniaturise the connector, a potential problem that is alleviated with the low resistance Hypertac technology.

Other advantages include low insertion and extraction forces, immunity to shock and vibration, and the ability to easily customise the design. Since these contacts offer significantly lower insertion and extraction

Components in Electronics

forces, they allow for higher densities than conventional contacts and can be easily mated with dozens of contacts in a single connector. Hypertac hyperboloid contacts are capable of withstanding extreme levels of shock and vibration while maintaining signal integrity, and this is one of the main reasons that they are used widely in industrial and aerospace environments as well as in medical applications. Shock and vibration often result in an intermittent loss of contact, which becomes important when dealing with high data rates. Due to the hyperboloid socket design, specifically the 360º wrap provided by the spring wires, immunity to high levels of shock and vibration provides signal continuity even when measured as low as 5ns.

Cost of ownership and perceived risk When factoring in the reliability of Hypertac contact technology, the overall cost over the lifetime of the equipment can be considerably lower than conventional connectors. This is especially pertinent if a failure is caused by a relatively low-cost component, such as a connector, with respect to the overall equipment price tag.

In medical environments, if a connector fails, not only does this incur expensive specialised repair costs, but the downtime of the equipment could seriously compromise medical services, and potentially placing a patient’s health at risk. Doctors and technicians are reluctant to use devices that they see as being unreliable. Typical connector problems might include difficulties in mating and un-mating, intermittent connection due to shock and vibration in mobile medical applications such as

air or road ambulances, failure or intermittent connection due to fluid ingress, and damage from rough usage.

Designing for medical applications Historically, Hypertac contacts proved themselves in many application environments where vibration was a key concern. The proven performance and benefits of the contact became increasingly apparent to the medical community. HyperGrip from Smiths Interconnect is a highly reliable and proven circular connector that embodies all the features, benefits and capabilities of the Hypertac hyperboloid contact technology and is designed to deliver excellent performance in real-world medical applications. It embeds a wide range of specific benefits, including user- configurability, colour-coding and customer keying, while also providing sealing and shielding options. Sealed connectors deliver up to IP65 protection when mated and EMI/RFI shielding protects against signal interference in electrically noisy environments. Materials used in connector designs, specifically for medical applications include polyetherimide, liquid crystal polymer, and silicone rubber, all of which enable the connector to handle autoclaving, EtO and other sterilisation protocols. The materials are flame retardant (UL 94V-0, self-extinguishing) and withstand cleaning and working chemicals found in medical environments. Medical connectors based on the Hypertac hyperboloid contact incorporate all these requirements while delivering a flexible design that is easily customised for a specific application or offered as a standard product.

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