Cables and harnesses are often the last components to be designed into medical equipment. Yet, in order to properly address functionality, quality, and time to market, cables and harness considerations need to be an upfront part of the design effort. When outsourcing these products to electronics manufacturing services (EMS) providers, the following need to be addressed.

Early involvement

This is critical because adequate upfront time provides the best opportunity for an EMS provider to suggest alternative materials and product features that lower cost and improve manufacturability. Nortech Systems' involvement with a power cable assembly project for a piece of medical diagnostic equipment began almost two years ahead of a planned product introduction, when the OEM provided a concept drawing. The assembly required numerous splice points and breakouts, the consolidation of multiple cables, and the provision of 100% shielding against radio-frequency and electromagnetic interference. Early involvement enabled the production process, tooling, and fixturing to be designed concurrently with the actual product.

Design assistance

Once product requirements are established, an EMS provider can assist in writing the specifications, keeping in mind compatibility and manufacturability issues. While Albert Einstein never designed a cable assembly, his cautionary words apply: “Everything should be made as simple as possible, but not simpler.”

An EMS provider/OEM team approach today usually includes sharing 3-D models throughout the design process. Model-sharing and design discussions with the previously mentioned equipment OEM led to Nortech developing a cable junction design that incorporates a harness-mounting point by creating a simple channel in the overmold. This solution improved manufacturability for the OEM by eliminating the need for extra cable ties, fasteners, or mounting brackets. And because the collaborative process began early, adding this feature was easy and incurred only minimal cost.

A common cable design feature that is often overlooked by OEMs is adding strain relief to a molded connection; the EMS provider can catch this omission early when designs and ideas are shared. While essential for new products, such cooperation is equally important with product enhancements, which is a core competency many OEMs value in EMS providers. At any stage in the product's life cycle, the EMS provider's knowledge base includes familiarity with product documentation procedures, offering validation and verification that the OEM's design intent is met.

Broad experience

Medical OEMs can benefit from partnering with EMS providers able to leverage their experience across numerous industries. For example, Nortech applied its expertise in producing ruggedized combo d-sub connectors for military customers to meet a design challenge for this OEM on a different type of medical diagnostic equipment. Because off-the-shelf solutions were inadequate and unreliable, a new production process was developed - building precision alignment fixtures to ensure proper pin alignment and mating under even high-stress conditions. The overmolding process and tooling development encompassed more than 45 connector families. The tooling evolved into a three-step process: epoxy, premold, and overmold. It also incorporated shielding.

Prototyping partnership

During the prototype stage, OEMs and EMS providers exchange working models of the assembly. The prototyping method selected should be based on the stage of the project, the goals, and the timeline. Clear communication of objectives will determine whether the EMS provider builds a prototype for simple functional testing - fit and form - or full verification. Three common engineering tools for cable assemblies include rapid prototyping, machining, and soft (aluminum) overmold tooling. High-volume production utilizes hardened (steel) overmold tooling. Rapid prototyping is becoming more common. When speed to market is critical, OEMs should allow EMS providers to substitute equivalent components or risk delays.

For this OEM, the first prototype of this particular power cable assembly featured epoxied junctions wrapped in electrical tape, to determine proper fit inside the diagnostic equipment. The finished assembly features hundreds of wires going into many separate splices, with hundreds of sockets to optimize signaling; the total length is nearly 10 ft. The first premolding material selected failed dielectric testing because the heat shrink melted under high temperatures. Switching to a premold material with more paraffin solved this particular problem.

Quality testing

Along with their own internal quality systems, EMS providers should match process controls, inspection, and testing to the customer's specific product and regulatory requirements.

As interconnect technologies continue to get smaller and more precise, leading-edge product design often introduces workmanship challenges that can be eliminated by process controls and strengthened test procedures. EMS providers often use TDR (time delay reflectometer) equipment because of its versatility and ability to eliminate the variability of test equipment and interface cables.

For this OEM's power cable assembly, the test strategy included determining the true resistance across all splice junctions through Kelvin contact-resistance testing. The customer requested a custom test fixture that simulates the installation's requirements and static positioning of the assembly within the diagnostic equipment. This test fixture also served as an audit board to ensure tolerances were met without any cable strain.

As performance requirements increase and the size of electronics decrease, the margin for error is also shrinking. Many OEMs are now asking the EMS partner's entire supply chain to provide accurate FMEA (failure mode effect analysis) data to help refine their designs.

Low-profile copper cable for QSFP assemblies

Low-profile copper cable by W. L. Gore & Associates, Inc, Newark, DE (gore.com) fulfills the needs of dense, higher-port-count switch installations while providing a reliable interconnect for high-performance computing (HPC). This cable was provided to major switch vendors and computing OEMs for testing over the last six to eight months and was tested for compliance and interoperability in spring 2009. With a diameter of 0.170 in. for a 4x channel, 8-pair cable, the cross-section savings are significant. The low-profile cable is targeted at high-performance computing applications, where a large percentage of high-density port-count interconnects are two meters or less.

Cable, wiring, and tubing solution

Alpha Wire, Elizabeth, NJ, (alphawire.com) has created a cable, wire, and tubing solution set for the medical device market. This portfolio of products is for medical manufacturers of diagnostic equipment such as MRI and CAT scanners, laboratory equipment, adjustable beds, and other non-invasive testing and treatment equipment.

“Hospitals and other medical facilities present challenging electrical environments where mistakes caused by electrical noise or worn cables can adversely affect patient outcomes,” says Mike Dugar, senior marketing communications manager at Alpha Wire. “For noninvasive cabling needs, our medical devices solution set provides medical device designers with maximum reliability and flexibility to decrease time-to-market and ensure long-lasting performance.”

The company's products for medical devices are Xtra-Guard high-performance cable for imaging and diagnostic devices, dialysis and blood centrifuge machines, and EEG/EKG devices; Xtra-Guard Flex for adjustable hospital beds, scanners, and medical robots; hook-up wire in a variety of insulations to meet requirements for temperature and electrical performance, as well as provide the ability to withstand wear and abrasion; and FIT heat-shrink tubing in a range of shrink ratios and materials for protection, organization, strain relief, and repair of cables.