A highly accurate prediction of hermeticity lifetime is made for eutectic 63Sn37Pb and 80Au20Sn alloy solder sealed optical fiber-Kovar™ nosetube feedthroughs subjected to repetitive thermal cycling. Thermal fatigue fracture of the Sn-Pb solder/Kovar™ interface develops when cracks, initially generated from creep deformation of the solder, propagate gradually through the junction in the axial direction. A nonlinear axisymmetric finite element analysis of the 63Sn37Pb fiber feedthrough seal is performed using a thermo-elastic creep constitutive equation, and solder joint fatigue based on accumulated strain energy associated with solder creep imposed by temperature cycling is analyzed. Additionally, thermal effective stress and plastic strain is studied for alternative 80Au20Sn solder by the finite element method with results indicating significant increase in useful life as compared to 63Sn37Pb. SEM/EDX metallurgical analysis of the solder/Ni-Au plated Kovar™ nosetube interface indicates that AuSn 4 intermetallic formed during soldering with 63Sn37Pb also contributes to joint weakening, whereas no brittle intermetallic is observed for 80Au20Sn. Hermetic carbon coated optical fibers metallized with Ni,P-Ni underplate and electrolytic Au overplating exhibit correspondingly similar metallurgy at the solder/fiber interface. Combined hermeticity testing and metallurgical analysis carried out on 63Sn37Pb and 80Au20Sn alloy solder sealed optical fiber feedthroughs after repetitive temperature cycling between 65 and +150 C, and 40 and +125 C validated the analytical approach.Index Terms-80Au20Sn, FEM, fiber-optic, helium leak, hermetic feedthrough, intermetallic, Kovar™, SEM/EDX, 63Sn37Pb, solder.
The Boeing 777 is the first commercial jetliner to utilize fiber-optic local area network (LAN) technology for onboard data communication. Design specifications, technology constraints, manufacturing methods, test equipment, installation processes, and airplane repair processes all were determined, produced, and finally incorporated into the 777 Optical LAN design. The tremendous success of the 777 Optical LAN demonstrates the viability of fiber-optic technology for aerospacelavionics applications. Since its initial introduction on the Boeing 777, fiber-optic LAN technology has proven to be an excellent alternative to traditional copper based airborne network interconnect solutions.
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