White Paper

w w w. m r c y. c o m WHITE PAPER 2 repeated thermal cycling. Unfortunately, thermal cycling is a common occurrence in many deployed programs. Consider an aircraft sitting on a desert runway, called into service and rapidly transitioning from the ground to tens of thousands of feet in the air. This cycling occurs many times in the life of deployed electronics equipment such as radar or EO/ IR processors. Using a non-eutectic solder under such conditions can result in cracks in the solder joints, as shown in Figure 1, and is simply not an option for these systems. Figure 1: 84 Ball COTS SDRAM (lead-free): solder joint crack after 250 thermal cycles To mitigate this concern, Mercury's MOTS service chooses BGAs with eutectic tin-lead (Sn/Pb) solder spheres whenever commercially avail- able. (Ceramic BGAs may have 90%Pb /10%Sn non-collapsing solder spheres). For BGAs available only with SAC solder spheres, Mercury sends the BGAs in question to an approved contractor for re-balling. As a result, the solder joints can withstand many hundreds of extreme tem- perature cycles, as shown in Figure 2. Any Land Grid Array (LGA) compo- nents (such as Intel Xeon EP or SP processors) are consistently converted to BGAs in all Mercury products, and only leaded solder is selected for this LGA conversion. Conversion of LGAs to BGAs also greatly improves tolerance to vibration by eliminating the socket. Figure 2: 84 Ball MOTS SDRAM (tin-lead solder): solder joints after 750 thermal cycles Abstract This white paper describes Mercury's approach to building products for enhanced durability under extreme environmental conditions, including repeated temperature cycling over wide temperature ranges. Require- ments 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 call Modified Off-The-Shelf (MOTS). The baseline hooks for the MOTS process are built into each new Mercury ensemble boards and subsystem components so that customers can choose the enhanced durability options for any of those products without requir- ing a redesign or respin. The resulting MOTS-enhanced subsystems are designed to withstand extreme conditions, such as over 1000 wide tem- perature cycles. Introduction The defense electronics market encompasses a significant range of en- vironments – from fixed installations with conditioned environments, to mobile deployment in extreme temperature environments, from under the sea to the edge of the atmosphere. Attempting to create a "one size fits all" approach to the full environmental spectrum makes little economic sense –less rugged and size/weight/power (SWaP) constrained environ- ments would end up paying the rugged tax, and the more constrained deployments may not end up with the optimized solution they demand. For this reason, Mercury has broken its product line into various form factors – rack servers and ATCA-based architectures for less constrained environments, and OpenVPX (3U and 6U) for rugged optimization. Within the rugged OpenVPX solution space, the most demanding deployments require additional manufacturing and packaging technology and tech- niques to deliver the ruggedness, durability, and reliable long-term oper- ation required in the harshest of environments. In response to this need, Mercury has developed a set of design requirements and manufacturing operations to provide extreme durability, resulting in Mercury's Modi- fied Off-The-Shelf (MOTS) service offering. Many DoD programs have already benefited from the application of MOTS to meet their durability requirements, and MOTS offerings can help future avionics programs meet their reliability-related safety requirements. Mercury's ability to integrate requirements from system integrators, prime contractors, and government agencies, sourced across a wide breadth of program requirements and commercial best practices, results in a comprehensive solution that spans multiple disciplines and delivers the required level of long-term durability to meet program requirements. This paper examines the various mechanical and electrical modifications that go into a MOTS design, and describes the benefits that result from the application of these cross-program requirements across multiple technology deployments. MOTS Mechanical Attachment One of the critical elements of a MOTS solution is the method of Ball Grid Array (BGA) mechanical attachment. Due to the application of regu- lations that limit lead content, most BGA manufacturers no longer offer their components with lead balls. The most critical failure that can result from these less rugged solder balls is cracking and opens as a result of

• Cover