Medical Device Link.

DESIGN

Solutions for speed

Rapid product evolution in the medical electronics sector presents designers with many challenges, not least of which is finding suitable connectors for use in their equipment. Major trends in connector technology include the use of higher speed data connectors and higher current power connectors in diagnostic imaging machines and the need for smaller fine-pitch and docking connectors in handheld therapeutic devices.

Much of modern medical electronic equipment is concerned with imaging, examples include magnetic resonance imaging scanners and ultrasound machines. Producing and manipulating images, especially in real time, involves handling large amounts of data rapidly. It is not uncommon, therefore, to find equipment in which the backplane and input/output (I/O) connector speeds in the image processing sections are 5Gb/s or even higher. Connectors specifically designed to offer good performance at these speeds are essential and shielding must be of impeccable quality. Backplane connectors need to be able to handle a multitude of high-speed signals, which makes high connection density with minimal crosstalk important. This has been addressed in the latest connectors by designing integral shielding that provides earth continuity. This eliminates the need for ground pins and allows every pole of the connector to be used for signals.

Manufacturers are also starting to adopt more industry standard data I/O interfaces such as RJ45 Ethernet, USB, DVI, HDMI, Serial ATA, Serial Attached SCSI, PCI Express and Infiniband* to ensure secure routing of data signals for their internal and external interfaces. Signal integrity at these speeds is critical and designers should strive to work with suppliers who can supply connector and cable-assembly solutions and offer experience gained in the data or telecom industries.

Large current handling

A consequence of increasing the processing capacity required in medical electronic equipment is that devices need more electrical power. Where once it was unusual for electronic systems to involve currents of more than a few amps, today currents in the tens of amps range are commonplace, and currents of a hundred amps or more are not unknown. Producing compact connectors to reliably handle these large currents is by no means a trivial task and equipment designers need to exercise care in making their selections if dependable results are to be obtained.

Recent innovations include wire-to-board and board-to-board connectors that successfully combine small dimensions with durability and a current carrying capacity of 40A per pole. These connectors can, if required, handle power and signal connections thereby simplifying equipment design, construction and maintenance.

Size reduction in 3D

Another significant driving force in the medical electronics industry is the desire to treat patients as often as possible outside hospitals. A wide variety of electronic products, including insulin pumps, glucometers and sophisticated monitoring devices are being used to make this extra-mural treatment practical and safe. The effect of this on new product development is that devices should have a compact construction, a trend that extends to much of the portable equipment used in hospitals. The size of the connectors used in this equipment is critical, but what really matters is overall three-dimensional size. In compact designs, space above and around the printed circuit board (PCB) is almost always just as valuable as space on the PCB.

One way in which this need for miniaturisation is being addressed is with back-flip wire-to-board connectors for flat flex cables (FFC). These combine zero insertion force with a lever-operated latch that ensures secure cable clamping, yet versions of 0.9 mm high are available. Similarly, manufacturers are developing smaller board-to-board connectors with pitches of 0.4 mm, which combine high retention forces with the need for small PCB space. In the latest versions, the housing is seated over the solder pads on the board and thus occupies a minimum of board space.

However, FFC cables are not suitable for all applications in miniaturised equipment. They are insufficiently flexible, for example, to be used with the flip-out-and-rotate display panels, which are increasingly popular. In these cases, a common solution is to use a bundle of ultra-fine co-axial cables, which combine flexibility with efficient screening. Even the smallest types, which today have a pitch of 0.4 mm, provide excellent screening and uniform impedance, and ensure reliable operation even with the high data rates used in modern equipment.

Connectivity

Data collection and generation are important in much of the larger electronic equipment used in medicine. To make the collected data available to external devices, appropriate connectivity is required. In many cases, this takes the form of a shielded docking cradle connector. Convenient for the user, these cradles make particular demands on the connectors employed. Docking forces are often high and frequent docking/undocking can be expected, thus designers need to consider the mating force and cycling properties of the connector they select. In addition, the device being inserted into the cradle will invariably block the view of the connector during mating; therefore, types that provide positive guidance to aid blind mating must be used.

There will still be a need to save space and fine-pitch connectors are required with sufficient capacity to carry the current needed to recharge the battery in the portable device. Typical of the latest connectors developed specifically for use in docking cradles are types with a 0.5-mm pitch, a current carrying capacity of 0.5A, full shielding and a life of 10000 or more mating cycles. Suppliers with strong design capabilities can develop custom solutions that meet the unique requirements of the medical industry.

Explore the possibilities

Electronic equipment is playing an increasingly important role in virtually every aspect of modern medicine and the growth in the sophistication of that equipment continues unabated. Sophisticated systems, however, depend on sophisticated connections for their success. This article, has described just a few of the connection solutions on offer and many more are available. The key to finding out about them and to obtaining more information on the types of applications discussed here is to enlist the aid of a dependable connector supplier, preferably at the earliest possible stage in the equipment design process. Choose that supplier with care. The best suppliers are those that have proven experience in every aspect of the medical sector, an international reputation and an outstanding track record in connector innovation.

*Glossary

USB: Universal Serial Bus
DVI: Digital Visual Interface
HDMI: High Definition Multimedia Interface
ATA: Advanced Technology Attachment
SCSI: Small Computer Systems Interface
PCI: Peripheral Component Interface Infiniband Registered trademark of the InfiniBand Trade Association

Dermot Byrne is Industry Marketing Manager – Medical at Molex Interconnect GmbH, Luchthavenweg 38, NL-5657 EB Eindhoven, The Netherlands, e-mail: dermot.byrne@molex.com.

For product information, Mark Taylor, Applications Support Coordinator, Molex UK, Molex House, Millennium Centre, Farnham GU9 7XX, UK, tel. +44 1252 720 753, e-mail: mark.taylor@molex.com www.molex.com