Five considerations when specifying connectors for medical applications
■ Misalignment can be a significant problem on pc boards with multiple connectors. Closely follow the manufacturer’s recommended termination connection specifications and keep alignment pin hole diameter tolerances to ±0.002 inches (0.05mm) ■ EMI is not just a pc board problem. Board-to-board connectors can contribute to EMI concerns and need to be considered from the beginning as part of the overall design
Figure 2: A small selection of the variety of available contact pitches, terminations, and sizes. Image source: Samtec
Figure 4: SEARAY 1.27mm high- density open-pin field-press-fit arrays are available in vertical and right-angle (shown
High-density, high-speed connectors Applications that need high speed and high density can use Samtec’s SEARAY 1.27 mm open-pin field- press-fit arrays. These connectors have up to 500 contacts optimized for signal integrity and are available in vertical or right-angle mounting options (Figure 4). This system features up to 10 rows and 50 contacts per row to enable grounding and routing flexibility; a choice of 7mm, 8mm, 8.5mm, and 9.5mm stack heights; and can handle signals up to 28 gigabits per second (Gbits/s). For example, part number SEAFP-40-05.0-S-06 is a vertical mount design with 240 contacts and through-hole terminations. Connectors for PAM4 or NRZ Applications that need higher contact densities and more than 28Gbits/s speed can use the 56 Gbit/s SEARAY series. Their 0.8mm pitch delivers twice the contact density of connectors with 1.27
above) options. Image source: Samtec
to Samtec’s TFM and SFM series , members of the company’s Tiger Eye interconnect system. These connectors are designed for micro, rugged, high-reliability, high-cycle applications, and are available in three pitches; 0.80, 1.27, and 2.00 millimeters (mm). These connectors have heat-treated, beryllium copper (BeCu) multi- finger contacts optimized for high- cycle applications and are designed for rugged environments (Figure 3). For example, the model TFM-105- 01-S-D-A is a 10-position header with 1.27mm pitch contacts. The smooth contact mating surface does not stress the plating, providing lower contact resistance, longer plating life and longer cycle life. Solder can easily penetrate the micro slot on the tail providing greater solder joint strength. These connectors are polarized to guarantee proper mating, and optional friction locks improve connection security.
■ Intense shock and vibration based on low-level contact resistance (LLCR) and event detection ■ LLCR testing using 40 times the standard gravitational force (g) peak, 11 milliseconds (ms), half sine and 12g RMS, 5 – 2000 Hertz (Hz), 1 hour/axis ■ Event detection according to EIA-364-87, EIA-364-27 and EIA-364-28 using the same test procedure as the LLCR testing ■ 500 temperature cycles ■ Non-operating-class temperature testing where the connector is LLCR tested, exposed to -55 to 105°C for 100 cycles, then tested for LLCR again; exposed to -65 to 125°C for 100 cycles, and tested
mm pitches, are available with 7mm and 10mm stack heights, and can handle PAM4 or NRZ communications. Configurations are available with up to 12 rows of 60 contacts for a total of 720. These open-pin-field arrays provide maximum grounding and routing flexibility including differential signal pairs, single-ended signal transmission and power delivery (Figure 5). Part number SEAF8-20- 05.0-S-04-2-K features 80 gold- plated contacts and surface-mount terminations. These connectors are SET qualified.
in medical applications, there are numerous factors that designers need to consider related to signal integrity and EMI, a few of these considerations include: ■ Shorter is better. Shorter connectors deliver better signal quality. The shorter the connector, the shorter the time available for reflections and crosstalk to occur ■ The signal-to-ground ratio is important. In most instances, a ratio of 1:1 is optimal, but for connectors with large pin counts, a ratio of less than 1:1 may be needed for reliable high-speed, single-ended operation ■ Ground shielding of contact pairs is recommended for differential connectors carrying signals of 2.5Gbits/s or faster
Conclusion
Selecting connectors for medical systems is an important and complex activity. Connectors need to be optimized to meet the mechanical durability, reliability, and ease of use requirements, in addition to meeting the electrical specifications and supporting communications protocols such as NRZ and PAM4. Adhering to relevant industry standards is important, but testing beyond the industry norms, such as with the Samtec devices mentioned here, is often needed to ensure the high levels of performance expected from connectors in medical devices and systems.
High-speed connector application considerations
for LLCR again; the connector must maintain a change of ≤5 milliohms (mΩ) in LLCR to pass ■ Dielectric withstanding voltage at an altitude of 70,000 feet ■ Electrostatic discharge (ESD) testing is not usually performed on connectors but is included in SET Connectors that handle 10,000 mating cycles Designers that need up to 10,000 mating cycles can turn
When using high-speed connectors
Figure 3: Tiger Eye interconnects (left) are available in a variety of formats and sizes and provide a rugged contact system rated to 10,000+ mating cycles. The TFM-105-01-S-D-A (right) is a 10-position header with 1.27mm pitch contacts. Image source: Samtec
Figure 5: SEARAY high-density open-pin- field arrays provide maximum grounding and routing flexibility including differential signal pairs, single-ended signal transmission and power delivery. Image: Samtec
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