You might think some designers almost take pleasure making oddball requests that put connector manufacturers between a rock and a hard place. “Trends in connector design, for instance, are toward hotter temperatures, greater mechanical performance, and the need for higher dielectric strength,” says Hal Kent, CEO of Medconx Inc., Santa Clara, Calif., (medconx.com). “And then as the markets mature, the client needs even lower costs.” Asking for more performance at lower costs can drive any designer to their wit's end.

Of course, a customized connector may be necessary when the one you need does not appear in catalogs. Before the call, however, you might sketch out a few particulars. Otherwise, manufacturers say they have to pelt you with pages of questions, and it would be easier on all concerned if the basic answers were readily available. Here's what they'll likely ask.

The big question

What are the environmental conditions? Obviously there will be an operating temperature range. The sterilization method governs material selection for medical connectors. “Moisture calls for other considerations,” says Kent. “And whether it is used in a surgical suite or a doctor's office makes a difference. Once you have those answers, you can dial in the material properties.”

Kent goes so far as to say it is usually not appropriate for engineers to pick connector materials because it makes follow-on design work more difficult. “In the connector world, Design for Manufacturing and Design for Cost involves expertise in materials, injection molding, stamping, plating, and chemistry.” So selecting materials before hand severely limits downstream options.

“Connector design can be a collaboration between OEM engineer and the connector design team,” says Tom Kannally, Medical Industry Market Manager for Hudson, MA based Hypertronics Corp., (hypertronics.com). “The OEM outlines the performance requirements, which can drive the material selection for the connector. If the materials are to be used outside the body, there is some leeway, but there is always the question of how the connectors will be sterilized.” Be aware, he cautions: “Not all typical connector materials are autoclavable.”

When a connector will be used several times, the design must account for cleaning chemicals, or temperatures, or both in the autoclave, and this governs material selection. Gamma and ETO sterilization are often used on connectors in disposable applications and devices that will not come in contact with body fluids. If they have, autoclaving is often preferred for reusable devices. Hypertronics designed a connector for one recent device, intended for autoclave cleaning, which has no crevices or corners that could trap contaminants. This is not the case on all connectors.

Will it be used around MRIs? If so, material selection is even more limited. “There can be no ferrous metals used around MRI equipment,” says Arnie Feinberg, Medical Industry Manager for Imaging Applications with Hypertronics. This becomes even more important as Tesla ratings (magnetic fields) increase in newer machines to generate clearer pictures.

“Part of the connector problem is how to get highly reliable insertions repeatedly from nonferrous metals while generating a clear MRI image. Copper would be an ideal contact material from an electrical and magnetic standpoint, but it does not have the mechanical properties needed for high connector reliability,” says Feinberg. “Alloying materials added for strength, usually ruin its nonmagnetic properties. Copper alloy materials necessary to get the high cycle life in contacts are available but material stocks are limited or must be custom ordered. Alloying plating materials for ultra high cycle life are magnetic. However, nonmagnetic plating materials are available to meet MRI high cycle life applications.”

How many pins? “It's surprising how difficult it is to get a handle on how many signals are needed, mostly because of signal creep,” says Medconx's Kent. “The design might start out at 50 pins, but before you know it they need 65. So expect to need more room, regardless of what the first design concept suggests.”

One way of adding signals without pins is to multiplex signals. “You can multiplex thermocouples, detectors, and sensors,” says Kent. “Multiplexing lets one wire carry up to 10 signals, although there is no fixed limit,” he adds.

Pin counts inside pacemakers and other implantables also seems headed up. “The more sophisticated implantables get, the more interconnects they need,” says Anthony Kalaijakis, Hypertronics Global Medical Industry Director.

A connector inside a pacemaker would obviously have to be small, reliable, and shaped to fit in its allotted space. These connectors are often used to aid assembly and allow wider material selection. In these cases, designers like to know size, pin count, shape, and mating force, an essential figure, especially when assembly is done under a microscope with tweezers.

Shielded connectors are needed to ensure signal integrity and guard against EMI/RFI. It is typically needed for devices using digital data transfers. A grounded shielding uses stainless-steel or plated shells made from a variety of materials.

Contact resistance in non-signal applications directly affects connector performance. “High contact resistance between mated connectors can generate heat as current levels increase,” says Kannally. “Tests must check for a temperature rise even though as much as a 30°C increase is typical and should not damage contacts at the usual ambient conditions. We like to put a high factor of safety on that characteristic. We have 4A contacts with a heat rise of only 5°C. It's a good idea to have less than a 30° rise, especially for devices in which the proximity of the connector to the patients could make them uncomfortable with too much heat.”

“You have to know the voltages and loads on the connector. If it handles a signal current that is low voltage and amperage, your choice of contacts is greater. However if there is significant current through the pin, make sure to use low-resistance contacts that are rated for the load,” he says.

Disposable connectors are another trend. Liability concerns lead to making sure items are sterilized properly. Even though a device is disposable and will be thrown away, it has to work perfectly that one time. “A connector with an RFID tag can be used so the device knows what's being plugged into it, and refuse to connect if misapplied,” says Kannally. “In developing countries, they might not be inclined to throw away a device, even if it's labeled for single use. They may clean it to some degree and reuse it to save money, and therein lies a serious hazard of infection. RFID can give connectors an ID or profile so that once it has been used, it won't work again,” he says.

Will it work?

Product testing validates connector designs, and manufacturers can test for almost any characteristic. Feinberg says his company can test for cycle life, that is, mating and unmating connectors, while verifying and testing for electrical characteristics to assure the product meets specifications.

Manufacturers say they can design for almost any reasonable cycle count. A conventional stamped and formed contact can survive 50 mating cycles. But specs often call for up to 25,000 cycles. “Our standard connector contacts have been tested to over 100,000 cycles,” says Feinberg.

He also tells of a test in which an OEM engineer dipped a connector pin in blood, let it dry and then connected it to a Hypertronics female contact to make sure it still worked. It did, he says. “That probably won't make it into the ISO specs, but it shows how concerned some engineers are that the devices work in demanding conditions.”

Another half-serious experiment is referred to as the oatmeal test in honor of the breakfast cereal's propensity to stick to just about anything. “If a patient gets something with the consistency of oatmeal on the connector will the connector still work and can it be easily wiped clean? Cleaning is a very important consideration in a hospital environment and the oatmeal test is a tough test to pass,” Hypertronics' Kalaijakis added. It's a good idea, he says, to consider just about anything that might happen to the connector.

Building a better disposable connector

It's no surprise that one priority of disposable devices in minimally invasive surgery is to keep their costs as low as possible. This goal also comes with the almost opposite requirement of making sure the device meets the high quality needed for surgical devices.

Until recently, few options existed to solve the low cost, high-quality connector conundrum. “Engineers either over-designed the disposable handpiece by using a high-cost plug to mate with a high-cost receptacle on the console, or under-designed the capital equipment with low-cost receptacles to mate with a low-cost plug on the handpiece,” says David Bastable, director of engineering at Fischer Connectors, Alpharetta, Ga. (fischerconnectors.com). “Choices were limited regardless of whether the application was a relatively simple catheter or a high-tech tool.”

In response, says Bastable, his company developed the Limited Use Connector (L.U.C.). “It provides reliable mating with our high-cycle life, medical-grade receptacles. Four basic L.U.C. configurations come with standard contact configurations and include a two-piece shell, a one-piece shell, an over moldable plug, and a snap-in plug. Although all versions are relatively inexpensive, the two-piece shell is the most complex and customizable, with the snap-in plug being the simplest,” he adds.

Another trend is toward more cable choices. “The industry's idea of a disposable product has typically included a long section of cable hardwired to a handpiece, whereby the handpiece, cable, and plug are all thrown away after one use,” he adds.

The move towards disposables gives designers a second choice: a much shorter cable and a disposable plug that connects to a reusable intermediate cable instead of directly to the console. The intermediate cable uses standard male and female high-mating-cycle connectors to hook up to the console.

The third choice also uses an intermediate cable with standard connectors to complete the console connection. There is no disposable cable hardwired to the single-use handpiece. Instead, the disposable connector mounts directly to the handpiece using a snap-in design.

Low-profile connector ready for small packages

A manufacturer of connectors and interconnects has developed a 0.3-mm pitch, low-profile ZIF connector for small mobile devices, digital cameras, and displays. The YLL Series, from FCI, Etters, Pa., (fciconnect.com) comes in two flavors: with down-side contacts and upper-side contacts. “This is one of the lowest profile 0.3 mm connectors available,” says FCI Manager Sean Riley. He says both series provides 0.3-mm spacing, 13 to 45 contact positions, and a maximum height of 1.05 mm.

Design-it-yourself custom connectors

The ODU USA Web site (odu-usa.com) lets viewers select features they want in a Medi-Snap medical connector. In six-steps, viewers select details such as a receptacle, contact diameter and type, and a housing material, while the software builds the part number.

The connectors tolerate temperatures from -50 to 120C and up to 140C as would be needed in autoclaves. The PEI housing material handles autoclaving and steam sterilization, and is good for more than 2,000 mating cycles.