Healthcare connectors for medical electronics

Paul Boughton
Healthcare devices and systems rely on the robust design and performance of their electronics. Serge Buechli reports.

When designing new equipment, electrical and mechanical engineers need to make sure that the user interface is unquestionably reliable. Cable connections, switches, LCD touch screens need to withstand repeated handling and wear. Particularly important are the connectors and cables that will need to withstand repetitive handling by patients or medical staff.

In addition to these first requirements, systems used in medical environments sometimes need to be repeatedly sterilised. Sterilisation is quite harsh on plastic material and electrical devices; it either involves high temperature, for instance autoclave (121°C to 134°C in a pressure chamber for over 15minutes) or chemical solutions. Chemical solutions such as Ethylene oxide (EtO), Sterrad or Steris Cidex enable killing microorganisms including spores, but sometimes require long cycle time, may leave toxic residuals and can be costly. Finally, medical device designing also goes through selecting materials that are 'health friendly', or that are for instance FDA approved.

The requirements for new interconnects are essentially high number of mating cycles (guaranteed extensive product life), high density and fail-safe connections. While the devices become more complex and smaller, the density of the interconnections increases, in other words the connectors have to perform better in less space. With higher density, the assembly of small connectors becomes more difficult when soldering the multiple small cables and wires.

Soldering is recommended for small volumes, it requires less equipment (just a soldering iron), but each wire assembly requires more time. It is ideal to use crimping tools when assembling large volumes and high density connectors. Another advantage to crimping: no heat is required to make the assembly in the assembly house or on the customer's end. By crimping the wire, the equipment can be later used in a higher temperature environment. Crimping requires more tooling such as hand crimping tool and contact positioners that will help crimping the contact in an exact position. The crimp contact's barrel (location where the wires are inserted) is annealed. During production, an electrical coil is used to rapidly heat the contact (induction process). The process has to be very fast, it lasts just a few milliseconds as each contact requires to be individually annealed.

LEMO and its associated brand REDEL now offer the new REDEL XP connector, a connector with new features including high density contacts. The connector is available with up to 22 contacts, in an ergonomic shell that includes a sculpted shell with thumb grip location.

These circular plastic connectors are especially adapted for applications such as medical electronics, including catheters, surgical power instruments, endoscopes, ultrasound ablation equipment, sleep apnea monitoring, as well as test and measurement equipment. With an operating temperature ranging between -50°C and 170°C, the materials used in the design make them adapted to sterilisation in saturated steam. A PEEK insulator offers high electrical insulating properties and mechanical resistance throughout operating temperature ranges. Gold-plated contacts ensure low contact resistance and therefore signal integrity. This range of connector is ideally suited for cable diameter ranging from 2.5 to 7.5mm.

The XP series offer additional features: the patented latch sleeve is recessed into the connector body ensuring greater resistance to shock and repeated sterilisation cycles. The complete connector can be assembled from spare parts (even the contact configuration), therefore good flexibility in stock keeping is possible. A large choice of bend reliefs is available in different colours and sizes. The bend relief increases the lifespan of the cable-connector assembly by limiting the wear and strain on the vulnerable point of the cord. LEMO recommends using Vibra-Tite VTSC-6 Clear or Threebond 1401 adhesives and sealants as thread locker to secure the connector nuts.

LEMO has been designing precision connectors for six decades. Today, manufacturing plants exist in Switzerland, Hungary, and the United States. Manufacturing capacity has been significantly increased primarily in Switzerland, resulting in reduced lead times.

As a highly vertically integrated corporation, LEMO also controls the vast majority of its manufacturing process from procuring raw materials, through tool making to production, plating, final assembly, and testing.

Total control over these processes allows LEMO to react much more quickly to special or high volume customers' needs. Each of the manufacturing sites specialises in its own discipline - turning of large volume products, low volume special products, plastic parts, plating, and assembly.

The continuous and rigorous application of strict quality standards guarantees the consistent production of high quality connectors that exceed customers' expectations year-after-year. All LEMO facilities are ISO9001:2008 certified.

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Serge Buechli is product manager, LEMO SA, Switzerland.

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