5
ENVIRONMENTAL PROTECTIONS FOR THE TACTICAL EDGE
Rugged Packaging and Cooling Technologies
mrcy.com
AIR FLOW-THROUGH
(ANSI/VITA 48.8) — High Performance
Air Flow-Through similarly uses an air management cooling
approach. Instead of defining the airflow at the component
level, Air Flow-Through channels the air over fabricated
fins that are placed within a cavity in the middle of the
module. Although lacking the precision of Air Flow-By, this
approach is efficient and well suited to cooling mezzanine
cards that reside close to the center of the module (Figure
3). Mezzanines, when used within the Air Flow-Through
architecture, necessitate an increase in the standard
1-inch OpenVPX module width to 1.2 or 1.4-inches, giving
room to both the fins and mezzanines. As such, Air Flow-
By has a SWaP advantage if mezzanines are used, as the
architecture does not require an increase in module width.
Mercury has conducted various performance tests
between VITA air-cooling architectures (tech brief entitled
"Comparison of high performance OpenVPX forced air-cooling
architectures") and concluded that Air Flow-Through is
generally marginally more efficient for 3U and that Air Flow-
By is generally more efficient for 6U and larger systems.
LIQUID FLOW-BY
Dual/Redundant Liquid/Air-Cooling
Although not a current VITA standard, Liquid Flow-By™ is
interoperable with the overarching VITA 46 standard and
exceeds REDI requirements. Liquid Flow-By is the logical
next step to a truly agnostic approach to OpenVPX cooling
as it combines the best attributes of Air Flow-By (VITA
48.7) and Liquid Flow-Through (VITA 48.4) into a single
entity enabling dual/redundant cooling. Mission-critical
and large payloads that are subject to wide variations
in environmental conditions benefit greatly from this
approach. An airborne payload, for example, may be air
cooled during ground-level pre-flight preparation and liquid
cooled (fuel) during a high-altitude (limited air) mission.
Figure 4: 6U OpenVPX Liquid Flow-By module
Figure 5: Agnostic Air Flow-By extreme air-cooling technology applied to rugged
3U and 6U OpenVPX and ATCA server blades – all may be conformal coated.
Figure 3: 3U OpenVPX Air Flow-Through (ANSI/VITA 48.8) module construction
Mezzanine
cover
Mezzanine
card
Primary
heatsink
Secondary
cover
CONFORMAL COATINGS
Conformal coats protect circuits from moisture and abrasion
and act as a barrier to tin whisker growth. Mercury protects
electronics with specialty coating, including acrylic or
parylene, that supplements our baseline Mil-I-46058C
and IPC-CC-830-compliant urethane coating. Mercury
complies with the Government Electronics and Information
Technology Association (GEIA) GEIA-STD-0005-2, Level
2B: standard for mitigating the effects of tin whiskers in
aerospace and high-performance electronic systems.
