ATCA switch advances

Selecting the right device is integral for server safety and cooling functionality

BY DAVID WEBBER
C&K Components
Newton, MA
http://www.ck-components.com

Switches are integral in ATCA applications such as telecommunications and computer servers. Implemented on the server blade as a safety mechanism to guarantee that the blade is powered down (processing) and to ensure that no data are lost, network devices often have as many as ten detect switches within each server.

Magnetic switches are used to signal the powering of fans in rack and panel systems.

While detect switches have been specified for such applications for quite some time, ATCA and Advanced Mezzanine Card (AMC) usage is growing in popularity and expanding into the medical and military arenas. As a result, switch manufacturers are expanding their offerings and enhancing switch technology to meet the needs of these applications as well.

In the server room

In ATCA applications, the primary function of a detect switch is to interact with the handle mechanism to tell the server to stop functioning when the handle is removed. Conversely, when the server blade is reinserted, the switch lets the handle mechanism — and subsequently the server — know it’s safe to begin running again.

The safety and security of the server blades, as well as the technician removing the blades, is imperative. Because detect switches can be actuated for a prolonged period of time, they are ideal for this type of application.

While most detect switches for ATCA applications are through-hole devices, it is a common misconception that the solder joint on a through-hole switch is more stable than that of a SMT component. Both through-hole and standard SMT detects provide comparable stability when used on networking equipment.

Due to the extensive number of components on process boards, components must be highly flexible for ease of use and compatibility. OEMs are taking many different approaches to solving their detect needs, from through-hole switches that are riveted to the panel and use wire leads and a connector, to a standard through-hole device, or a SMT solution.

Typically, the OEM evaluates the volume and constraints in their application to dictate the solution. SMT switches offer an advantage as they are pick and placeable and suit high-volume production-line processes. Some engineers still feel more comfortable with a through-hole solution in the handle mechanism engagement.

Many design engineers are requesting that switches have no alignment posts at the base of the switch. Often the hole on the PCB is larger than the alignment post, negating the retention value intended. Additionally, an alignment post dictates where a trace can be run on a PCB.

Military and medical markets

ATCA and AMCs are growing in popularity in the military and medical arenas, forcing switch manufacturers to alter detect switch designs to conform to environmental changes, such as expanded temperature ranges and vibration requirements. Within the military market, ATCA and AMCs are being utilized in the form of a black box for battlefield logistics and in combat vehicles for tracking, to download data, and for analysis.

In the medical field, mezzanine cards perform similar functions for gathering data, serving as a type of flash memory to remove and review data for high-end ultrasound equipment. The shift in industry has forced temperature ranges of switches to be expanded from a typical operation and storage temperature of 20 to 70C to 40 to 85C. Testing must be done to ensure no electrical or mechanical drop-off in the expanded temperature environments.

Due to the new environments, switch materials are being altered to withstand the higher temperatures. Upgrading the plastic material to withstand high-temperature processing not only allows for implementation into harsh-environment applications, but the switches can now be put through RoHS-compliant and compatible processing. The high-temperature plastics also enable the development of more reliable through-hole devices.

More than detects

Increasingly, detects or magnetic solutions are used to ensure that a fan is powered down before the blade is accessed by a user. Magnetic switches are typically implemented in the cabinets of rack and panel systems, with access to the fan, server, and daughter card via a door or latch.

Magnetic reed switches are implemented to sense when the cabinet doors are closed, which in turn signals the fan to begin operating. With some magnetic switches featuring life cycles of 10 million actuations, the rugged devices are capable of withstanding door slams and misalignment. ■