Abstract:

Communications hardware for high reliability systems are starting to include modern low profile parts such as Quad Flat Pack No-lead (QFN) and Land Grid Array (LGA) packages to take advantage of their size and weight. In these parts, heat sinks often provide a conductive thermal dissipation path. Printed circuit assemblies with these parts will still need to meet the industry specific qualification requirements for thermal and vibration testing.

It is beneficial to identify if the equipment will be able to meet the qualification test requirements during the design phase particularly when new technology insertions are being made. In this design, various surface mount packages like LGAs, QFNs and so on were used in a printed circuit board which included two stiffening layers with non-standard laminates.

calcePWA is a simulation software which estimates the cycles to failure of components under various loading conditions using Physics of Failure (PoF). The cycles to failure simulation of this design using calcePWA software identified the critical interconnects that are at risk for failure under non operational test conditions. The design was also evaluated under a long haul aircraft profile, with the assembly in operational state. In operational state simulation, the effectiveness of thermal shunts in reducing board to component thermal differentials was evaluated. Effects of degradations of the thermal shunts with time were used in the evaluation. Results showed that the vibration and shock reliability were less of a concern than thermal cycling for this board layout. Risk mitigation methods for thermal cycling durability were identified and recommended to be used in the system redesign.

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