WHITE PAPER
Enhance product performance under extreme environmental conditions
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The defense electronics market encompasses a significant
range of environments — touching every corner of the globe
and the atmosphere's edge — from fixed installations with
conditioned air environments, to mobile deployment in extreme
temperature environments. Attempting to create a "one-
size-fits-all" approach for the full environmental spectrum
is impractical — operations with little concern regarding
SWaP constraints or ruggedization pay for unnecessary
features, whereas more constrained deployments may
not receive the optimized solution they require.
For this reason, Mercury produces various form factors:
rackmount servers and ATCA-based architectures for
less-constrained environments, and OpenVPX (3U and 6U)
for rugged deployment optimization. Within the rugged
OpenVPX solution space, the most demanding durability
requirements include the ability to withstand extreme
temperature cycles, multiple patterns of shock and
vibration, and resistance to fretting, corrosion, and tin
whiskers that go beyond the baseline military standards.
In response to this need, Mercury has developed a modified
off-the-shelf (MOTS) service offering that includes a set of
baseline product design requirements and manufacturing
operations to provide extreme durability. Each Mercury
OpenVPX product uses a base design that includes built-
in hooks for the MOTS process. This gives customers the
freedom to select the appropriate durability options for
their application without a required product redesign
or re-spin. The resulting MOTS-enhanced products
are able to withstand the most extreme conditions,
including wide-ranging temperature cycles.
Many DoD programs have already benefited from the
application of MOTS to meet their durability requirements.
MOTS offerings also can help future programs meet their
reliability-related requirements with significantly reduced
technical and schedule risk. Mercury has managed a wide
breadth of program requirements from a diverse set of
customers: system integrators, prime contractors and
government agencies. Applying learned best practices,
Mercury 's MOTS service is a comprehensive solution
that spans multiple engineering and manufacturing
disciplines to deliver long-term durability.
MOTS MECHANICAL ATTACHMENT AND
SOLDER JOINT INTEGRITY
One of the critical elements of a MOTS solution is a ball grid
array (BGA) mechanical attachment. Due to regulations
that limit lead content, most BGA manufacturers no longer
offer components with lead balls. Where lead solder forms
a strong joint between different metals, less-rugged
lead-free solder balls are rigid, fragile and do not bond
well with other metals. They are prone to cracking from
repeated thermal cycling that can result in critical failure.
Unfortunately, thermal cycling is a common occurrence
in many deployed programs. Consider an aircraft that
has been sitting on a desert runway rapidly transitioning
from the ground to tens of thousands of feet in the air.
This paper describes Mercury's approach to building products for enhanced durability
under extreme environmental conditions, including repeated temperature cycling over
wide temperature ranges. Requirements and best practices have been accumulated over
dozens of military and avionics programs, resulting in a best-in-class set of design rules and
manufacturing process called modified off-the-shelf (MOTS).
