DigiKey-emag-MedTech-Vol-12

Five considerations when specifying connectors for medical applications

more elastic than brass and less susceptible to stresses that limit the cycle life of bronze contacts.

Figure 1: NRZ has a single eye (left) and transmits 1 bit of information per signal interval. PAM4 is a multilevel signal modulation format with three eyes (right) and has a throughput of 2 bits per interval. Image source: Samtec

IEC 60601, ISO 80369-1, and ISO 13485 There are numerous application- specific industry standards for various medical systems and devices. Three of the more general standards that need to be considered in all designs are: ■ ISO 80369-1: this focuses on the design methodology to reduce the risk of misconnections between medical devices, or between accessories for different applications ■ IEC 60601 focuses on the general requirements for basic safety and essential performance including electromagnetic interference (EMI) and electromagnetic compatibility (EMC) ■ ISO 13485 focuses on the quality systems needed for tracking the components and processes used in the manufacturing process. It is related to ISO-9001 Testing beyond industry standards Severe Environment Testing (SET) is a suite of tests developed by Samtec that extend beyond typical industry standards and specifications and includes: ■ 250 mating cycles with 100% humidity

Written by Jeff Shepard

Designers of medical devices and systems need connectors that will help them address increasing complexity and smaller form factors, while at the same time ensuring high levels of reliability and performance under various usage models. Some connectors are inaccessible within the system making reliability critical. Other connectors are regularly used by surgeons, physicians, nurses, or technicians, so ease of use, and a high number of mating cycles are also important. Depending on the application, connectors for medical devices and systems must comply with standards such as IEC 60601, ISO 80369-1, and ISO 13485, and may require severe environmental testing beyond typical industry standards and specifications. Along with a usable model and specific standards, designers need to consider technical tradeoffs between non-return-to-zero (NRZ), also called pulse amplitude modulation 2-level (PAM2), and pulse amplitude modulation 4-level (PAM4) connector technologies to arrive at the optimal cost and performance for a specific use case.

Designers have a broad range of connector types to consider when identifying the best solution. To assist in the process, this article begins by briefly reviewing five important factors to keep in mind

in high-speed links such as multi- gigabit communications.

terminations are being supplanted by surface mount terminations in a growing number of applications. Paste-in-hole connectors are mounted in holes that do not completely penetrate the pc board. To be used for surface- mount or paste-in-hole designs, the connector body material must be able to withstand solder reflow temperatures, and they need to have horizontal and vertical clearance around the leads to accommodate the required quantity of solder paste.

in applications where connectors need to be regularly mated and unmated. The lower the contact resistance, the less power that is lost through the connector. A low mating/unmating force can contribute to ease of use, as long as the contact resistance remains low enough to meet electrical requirements. Connectors have limited mating/unmating cycle specifications, ranging from tens of cycles to many thousands of cycles. The cycle life of the connector must be matched to the needs of the application. When connector contacts are mated, the contact is displaced, and the metal is flexed. The flexing is important and determines the force needed to mate and unmate the connector, and the contact resistance. Flexing also causes stresses in the contacts that results in both the mating/unmating force decreasing and the contact resistance increasing over time. Replacing the brass base metal commonly used in connector contacts with more expensive phosphor bronze will increase the cycle life. Phosphor bronze is

Mechanical considerations

Mechanical considerations when selecting connectors include contact pitch, mating type, termination style, and size (Figure 2). Pitch measures the center-to- center spacing of the contacts. It can be more than one number; the pitch between contacts in each row and the pitch between rows can be the same or different. Connectors on printed circuit boards (pc boards) can use horizontal, vertical, or right-angle mating. Retention force is another consideration that measures how easily the connector can be removed. Common termination styles include through-hole, surface- mount, paste-in-hole, and press fit. Through-hole contacts pass through a hole in the pc board and provide strong connections between the pc board layers. Surface-mount connectors mount on the surface of the pc board and don’t require holes to be drilled. They can have smaller pitch spacings compared with through- hole connectors. Though-hole

when specifying connectors for medical devices. It then

presents examples of connector options from Samtec and closes with an overview of application considerations when integrating connectors in high-speed systems.

NRZ versus PAM4

NRZ transmits 1 bit of information per signal interval. PAM4 is a multilevel signal modulation format with a throughput of 2 bits per interval. In the NRZ eye, the top represents “1” and the bottom represents “0”, while the PAM4 signal consists of three stacked eyes formed using four voltage levels; 00, 01, 10, and 11 (Figure 1). The height of the eyes is an important consideration. The greater eye height of the NRZ signal results in better signal quality. NRZ is simpler to implement, has lower reflections, a better signal-to-noise ratio (SNR), and is lower in cost compared with PAM4. However, PAM4 is inherently faster and used

Press fit terminations are solderless and lower in cost but require special tooling for

installation. They are pressed into a hole on the pc board and held in place by compressive forces. Less common termination styles include land grid arrays, ball grid arrays, wire wrapping, crimping, and screw terminations.

Ease of use

Contact resistance, mating cycles, and mating/unmating force contribute to connector ease of use

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