PRODUCT UPDATE
Connectors and Interconnects:
In the Beginning, Consider The End-Use Environment
Gabriel Spera
Metal or plastic? Cost shouldn't be the only consideration when you're specifying a connector, say experts. You should also factor in the user's needs and habits, the method of sterilization that is likely to be used, and how critical electromagnetic compatibility will be to the application.
In specifying a connector for a medical device, designers need to consider more than just conductor size, panel space, and contact configuration. Both the end-use environment and the target market will have a significant impact on the final selection. For example, manufacturers must weigh the benefits of using low-cost lightweight plastic connectors instead of metal connectors, which are generally more reliable, provide better electromagnetic compatibility, and present a higher-quality image. Designers must also address the needs of users, who might be accustomed to a particular push-pull connector or need something that can be easily handled with gloves. EU hospitals currently have much lower patient throughput than US hospitals, and something that works here might prove inadequate in the US, where it will be used three times as often--particularly in surgical applications.
Sterilization and disinfection place exceptional demands on device components. Although the connectors themselves don't need to be sterilized, the devices they're attached to usually do. Hospitals disinfect devices by soaking them in solutions such as Cidex or putting them through an autoclave. The composition of Cidex can be extremely harmful to connectors, and an autoclave is a rather nasty environment to put anything in. Moreover, many EU manufacturers are just now becoming aware of newer options such as Steris and Sterrad, and they are evaluating the impact these products may have on their devices, particularly those that are destined for the US market.
EMC is also critical. A connector that carries signals from an endoscope to a TV monitor, for example, has to maintain extremely high resolution. The surgeon has to watch what he or she is doing by seeing it on the monitor, rather than by looking at the patient, so signal integrity is important.
Cost can also play a significant role in connector selection. While ultrasound and surgical devices might necessitate a high-end component, patient-monitoring and catheterization equipment might permit more flexibility, allowing designers to consider unit price. EU suppliers have traditionally offered lower prices than their US counterparts (the strong dollar is also helping), and this is reflected in relatively stronger sales by EU suppliers.
Designers looking for an appropriate connector might begin by contacting one of the suppliers profiled in this section. All of them share a strong commitment to the medical marketplace.
ODU Steckverbindungssysteme-GmbH & Co. KG
"Over 50 years ago," says Ralf Eberlein, "Otto Dunkel invented the spring-wire contact, which has a special feature that allows it to withstand hundreds of thousands of mating cycles." Today, ODU (Mühldorf/Inn, Germany) makes metal cylindrical connectors with standard or spring-wire contacts as well as custom units involving special shapes and materials.
The company's Mini-Snap connectors, with push-pull locking, are easy to mate even in hard-to-reach places. The plugs have latching fingers that hook into a groove inside the receptacle, making unintentional separation nearly impossible. Available in four sizes down to 10 mm in diameter, the connectors can be specified with solder contacts, crimp contacts, or PCB pins. An internal EMI ring, together with a closed metal housing, protects against EMI. ODU connectors can be supplied in standard and autoclavable versions designed to survive 1500 autoclave cycles, according to Eberlein.
ODU is also investigating the demand for disposable connectors. As Eberlein explains, "Many handpieces that come in contact with patients are used only once and then disposed of. So cost is a concern." The solution, he says, is to make an inexpensive connector--a sort of hybrid--with a disposable component on one end and a reliable metal component on the other.
Precision Interconnect
Specializing in ultrasound, electrosurgery devices, and surgical video systems, Precision Interconnect (Portland, OR, USA) provides complete cable assemblies and offers capabilities in the integrated design and manufacture of microminiature cables, high-density terminations, and molded flex reliefs. "We provide the complete interconnect system," says Mary McNamara. "We have experts who look at the entire system--the cable, the interface, the connectors." This comprehensive approach, she says, "improves the design and reduces the number of suppliers that manufacturers have to work with."
The company is attentive to the special demands of sterilization and disinfection. As Homer Fairley explains, "For ultrasound this is a significant problem, because the traditional Cannon DL connector has no sealing mechanism at all. Precision Interconnect will soon announce a solution that allows this favored connector to be used by designing our assemblies to allow full sealing." For surgical applications, he says, Lemo and Fischer connectors are more commonly used, but if they are not designed for use in the operating room, they generally won't be sealed against the effects of sterilization processes. Although these connectors can be modified to give some degree of protection, primarily by potting, Fairley notes, "Success of this process is highly variable." Precision Interconnect, he says, "has mastered the technique and, as a result, has become a leading supplier of assemblies for surgical devices."
W.W. Fischer Inc.
The main strength at W.W. Fischer (Atlanta, GA, USA), according to Dawn Brown, is the ability to make hermetically sealed connectors. Recent product introductions include the plastic-shelled 405-series connector, which can hold up to 27 gold-plated contacts in a body measuring 18 mm in diameter.
The medical industry represents an important market for the company, says Brown, and Fischer connectors are designed to meet strict requirements concerning safety and reliability. The 405-series connector, for example, maintains reliable operation even after 5000 mating cycles. All external body components are made from a lightweight USP Class VI plastic, which reduces overall connector weight by 60% compared to similar metal-shelled versions. Highly resistant to chemicals, the unit withstands operating temperatures up to 200°C and can tolerate thousands of sterilization cycles via autoclave or liquid germicide. What's more, says Brown, "with the plastic-shelled body, there's little risk of shocks or sparks." The 405-series connector is available with or without integral shielding for EMI/ RFI protection and meets current EMC standards. The unit can be mated with Fischer's metal-shelled models as well, giving designers even more flexibility.
Teknek Electronics
"Our main strength," says Lindsey Kelly of Teknek Electronics (Bridge of Weir, Renfrewshire, UK), "is short runs and prototypes. We're happy to do one-offs and small runs as well as larger runs. We also can supply unusual designs rather than just a plain strip connector--we have such a wide variety of options."
On the board level, Kelly notes a trend toward increased miniaturization: "Everything is trying to get thinner and smaller. Manufacturers are looking almost for a single thread." The challenge is to create a connector that's both thin enough and strong enough for the job.
For connecting miniaturized subassemblies in electronic circuits, Teknek offers heat-seal connectors, a low-cost alternative to flexi-rigid PCBs. The flexible interconnects are bonded to each subassembly using heat and pressure, allowing connection from PCB to PCB or PCB to LCD. "You can bond our flexible connector strips without the use of a physical connector," Kelly explains. "By eliminating the connector, you can have the smaller area you need to work with," which is crucial for miniaturization. Heat-seal connectors unite screen-printed conductors and an anisotropic conductive adhesive on a flexible film base ready for bonding. Kelly describes the components as "incredibly flexible" and "particularly useful in confined spaces." Heat-seal connectors are custom made and can be created in any shape, allowing designers to accommodate for components and other obstacles.
Lemo S.A.
What distinguishes Lemo from other suppliers, says Karen Dias at Lemo S.A. (Ecublens, Switzerland), is quality, service, and the willingness to create custom designs. Typically, she says, a company will go to a supplier looking for a particular connector. If it's not on the shelf, they're out of luck. "Then they can come to us," she says, "and whether it's 1, 100, or 1000 pieces, we have the ability to make them."
Lemo's line of self-latching circular connectors includes the Redel family of plastic connectors, which can be modified to include from 2 to 14 gold-plated contacts in one compact housing. As a result, a single connector can be used in place of several. Contacts can be specified in solder, crimp, or PCB termination styles to accommodate requirements ranging from 20 to 28 AWG and cables with outer diameters from 2.7 to 6.5 mm. Shell materials include PSU and autoclavable PEI. The connectors will endure 1000 mating cycles without significant deterioration of electrical signals.
