Originally Published MPMN June 2001

Connectors Offer New Twists on the Mating Ritual

Suppliers focus on size and cost reductions to keep device OEMs satisfied.

Whether intending to attach cables to electronic devices or to create a link between two different sizes of tubing, medical device manufacturers must consider several factors when choosing their connectors. A chief concern is cost: designers want to trim down expenses as much as possible but without compromising the quality of their finished products. Size is also important, as some devices require multiple components and run the risk of becoming too bulky and heavy if their parts aren't as compact as possible. Other important factors include assembly time and cost, chemical resistance, and EMI and heat reduction. In an effort to meet these challenges, suppliers have developed a range of connectors to suit varied requirements. Read on for examples of new developments in connector technology.

Feedthrough minimizes overheating and electromagnetic coupling

Manufacturers requiring metal connectors for electronic devices seek components that help to prevent overheating and resulting power loss. Ceramaseal has designed an RF feedthrough that brings cooling water close to the seal at the conductor-insulator interface to control heat without complex cooling jackets. The ceramic-to-metal feedthrough is suitable for a variety of RF applications including sputtering, plasma generation, and induction heating. "Metal components of RF feedthroughs usually will heat up and negatively affect the efficiency of the system as well as damage their own hermetic seals," says design engineer Rich Combs. "Ceramaseal's RF feedthroughs keep all metal components at a proper distance, place the hermetic seal at the joint to improve reliability, and utilize a dual conductor design with one piece of ceramic so that no metal flange resides between conductors." The feedthroughs have a 100-kHz to 13.56-MHz frequency range and a -55°–350°C temperature range. They handle currents up to 800 A and voltages up to 10 kV. Standard feedthroughs are available as weldable and flange-mounted units. Custom configurations include additional coolant lines, custom coolant flow paths, solid conductors on the vacuum side, large flanges, coils, and other accessories. The <1-in.-diam single-conductor version can fit into a specially designed O-ring seal and is available with compression fittings.

Stamped and formed contacts cut costs

Metal connectors used on medical devices can add significant weight to the end product. In addition, the labor required to make a cable termination can cost as much as the connector itself. To address these concerns, Odu-USA Inc. has developed the Minisnap PC, which can be used in handheld instruments and portable equipment. The connector weighs only 15 g, providing a significant weight reduction. This plastic cylindrical push-pull connector requires minimal panel space, can be blind mated, and clearly indicates whether it is mated or unmated. The connector is made of temperature and chemically resistant polyethylenimine that allows it to be used in mechanically demanding applications. Its exterior is made of all plastic parts, which enables users to touch it even in high-voltage applications. A nonmagnetic connector makes the Minisnap PC suitable for MRI machines and other applications that cannot tolerate EMI. According to the company's CEO Ralf Eberlein, the most innovative feature of the Minisnap PC is "the stamped and formed contact that can be produced for only a few cents, offering a tremendous cost advantage over machined contacts that can cost as much as 60 cents." In addition, the contacts can be terminated on automated crimping machines, reducing the cost of connector assemblies. The connector is autoclavable when used with PEEK inserts and can be produced in a shielded version with metallized internal surfaces.

Heat-seal connectors attach by hot bar bonding

Manufacturers integrating displays into their portable devices may have difficulties attaching them safely without creating excess bulk. This problem is eliminated when heat-seal connectors are used to connect glass or plastic flat-panel displays to PC boards without solder or clamps. Elform Inc. offers ultrafine-pitch monostropic heat-seal connectors that have an integral conductive adhesive system that attaches by hot bar bonding. The company uses graphite-based adhesive inks that offer 35-W/sq in. resistance in lieu of amorphous carbon, which provides 100-W/sq in. of resistance. Synthetic rubber used in the graphite ink formula makes connector traces flexible at any pitch: the connectors may be repeatedly hard creased without compromising performance. The monostropic construction involves screen printing the ink on 23-µm PET-based film at a pitch as fine as 0.18 mm. A second layer of ink is loaded with gold-plated nickel particles to ensure low contact resistance, and is screened over the first layer. The part is then covered with a thermoset adhesive that is loaded with titanium dioxide and yellow pigments to simplify part inspection. Monostropic construction allows fine pitches, high yields, and low bonding rework rates without the risk of particle cross talk or shorting.

Circular connectors offer snap-in screwless assembly

To enhance connection options and reduce assembly time, a line of miniature circular connectors features snap-in application, screwless assembly, and a nonthreaded, self-activating, push-pull locking system. The newest additions to the series, the Neutricon and Nanocon from Neutrik USA, offer a chuck-style relief that accepts 3- to 7-mm cable diameters and flat ribbon cables. The Neutricon is a modular system of one- to eight-pin cable connectors and panel receptacles that can be used for medical instrumentation in nonsterile applications. "The miniaturization of this connector does not jeopardize its quality or reliability," says product applications manager Fred Besnoff. "In fact, this connector is extremely versatile and can withstand high-traffic areas." The system includes mechanically protected gold crimp, solder, or vertical PCB contacts. Nickel or black chrome-plated receptacle or cable end housings absorb vibration and protect loaded inserts. Splashproof cable shells are standard.

Like the Neutricon, the Nanocon has gold-plated contacts that are suitable for hardwired soldering. It is a three-pole subminiature connector that measures only 0.19 x 1.22 in. The Nanocon offers a selective load of one to three contacts in mating cable ends, PCB vertical or horizontal male and female receptacles, or male and female solder termination receptacles. Panel receptacles with blank inserts, mating cable ends with interchangeable inserts, and fully loaded PCB receptacles are available. "The spacing between the contacts allows the Nanocon to be selectively loaded with the precise amount of contacts required," says Besnoff.

PEEK luers are cost-effective and chemically resistant

Medical-grade polyetheretherketone (PEEK) barbed male and female luers have been developed to provide OEMs with connectors that can withstand various types of sterilization. Supplied by Value Plastics Inc., these components accommodate tube sizes from 1/16 to ¼ in. The luers integrate the company's 500-series single-barb design that uses blended radii for enhanced versatility with various tubing sizes and types. Compared with compression fitting techniques, the luers require fewer components to make a tubing connection and are more cost-effective. PEEK luers offer high-temperature performance, chemical resistance, and hydrolysis resistance in steam or high-pressure water environments. PEEK can retain its properties even after repeated autoclave cycles and can be EtO, gamma, or E-beam sterilized. "PEEK luers were developed in response to the industry's need for a material that would not lose its properties after repeated sterilizations, yet it still costs less than brass or stainless steel," says sales manager Dave Splett. "While polysulfone is a good material for the medical industry, it is not as chemically resistant as PEEK."

Katherine Sweeny