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Advantages of Mercury's Modified Off-The-Shelf (MOTS) Product Approach

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www.mrcy.com INNOVATION THAT MATTERS ™ Corporate Headquarters 50 Minuteman Road • Andover, MA 01810 USA (978) 967-1401 • (866) 627-6951 • Fax (978) 256-3599 europe - MerCury systeMs, Ltd Unit 1 - Easter Park, Benyon Road, Silchester, Reading RG7 2PQ United Kingdom + 44 0 1189 702050 • Fax + 44 0 1189 702321 Mercury Systems and Innovation That Matters are trademarks of Mercury Systems, Inc. Other products mentioned may be trademarks or registered trademarks of their respective holders. Mercury Systems, Inc. believes this information is accurate as of its publication date and is not responsible for any inadvertent errors. The information contained herein is subject to change without notice. Copyright © 2017 Mercury Systems, Inc. 3354.00E-1017-wp-cots-mots care must be paid to situations where space between contacts is too small (less than 0.010 inches) as in Figure 3, and tin whiskers may bridge the gap even with conformal coat in place. In most cases however, the tight spaces can prevent conformal coat material from fully encapsulating gull-wing leads, with the interior leg of the lead being exposed and unprotected. For this reason, Mercury's MOTS products minimize the use of fine pitch com- ponents, and when required, tin-lead solder dip fine pitch lead-free devices. To prevent tenting and provide a better adhesion surface, Mercury is in- vesting in the capability to RF Plasma process PCB assemblies prior to con- formal coating. Figure 3: Fine Pitch Leads on Components Another area where traditional mitigations might not be applicable is with press-fit connectors. With these connectors, conformal coat is often unable to penetrate and cover any exposed leads due to the design of the connector itself. For this reason, Mercury's MOTS product apply underfill to these con- nectors to provide the same benefits as if the coat could have been applied. DFN/QFN packages DFN/QFN packages, while convenient for many applications, bring chal- lenges when dealing with highly rugged environments with long-term ex- posure. Primarily, the low height of the package when soldered is problem- atic. These packages are very low profile, and the solder is correspondingly reduced in height. Because there is less solder available to absorb move- ment resulting from thermal expansion/contraction, the stress of this ex- pansion is almost entirely expressed as shear. The risk of long-term shear- ing to the integrity of the electronics is too high, and so Mercury MOTS compliant designs avoid these packages in favor of gull wing alternatives. Figure 4: Convert DFN/QFN Packages to Gull Wing Packages Management of Vented Packages Many large BGA flip-chip packages are vented – that is, there is an open vent from the inside of the package to the outside. This prevents issues when unwanted air or contaminants expand within the package, causing damage over time. Vented packages, however, carry their own challenges. Moisture from wash downs should not remain inside vented packages af- ter conformal coat, so a significant and measured baking cycle is required prior to coating. As with BGA solder, die attach (when not wire bond) is preferred to be ac- complished with leaded solder – but in many cases, lead-free solder is used internal to the package as well. Some device manufacturers will produce a more rugged variant with leaded solder used inside as well. In these cases, however, Mercury will re-scan the device to ensure that height changes have not resulted, as in many cases the packages have been seen to grow or shrink when process changes internal to the package have occurred. Conclusion Mercury has invested significantly to create a combination of design re- quirements and manufacturing processes that can be applied to standard off-the-shelf product lines to enhance durability. This Modified Off-The- Shelf (MOTS) approach is based on our extensive experience with the requirements from system integrators, major prime contractors, and gov- ernment agencies when Mercury delivers subsystems – and as such, rep- resents the best and most complete set of requirements in the industry. To ensure that these enhancements can be applied regardless of product se- lection, Mercury implements the baseline module design in a manner that allows the application of the MOTS process to deliver these enhancements without the need for a module redesign. This is a significant risk reduction for programs, both in terms of technical risk and schedule risk. Should a particular customer or program require divergences or enhancements from Mercury's baseline MOTS approach, a customized MOTS+ service can eas- ily be applied to meet that customer's needs. Mercury's goal is to produce processing product lines that deliver the high- est performance in the most rugged of environments. Mercury's MOTS service is designed to ensure the long-term durability of these products in these environments. Through the combination of product design consider- ations, and enhanced manufacturing processes, products with the MOTS services applied meet the broadest set of durability requirements across the industry.

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