Publications

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The SA1358-10 and SA2052-4 circular JT Type plug connectors are used on a number of nuclear weapons and Joint Test Assembly (JTA) systems. Prototype units were evaluated for the following specific defects associated with the 95Sn-5Sb (Sn-Sb, wt.%) solder joint used to attach the beryllium-copper (BeCu) spring fingers to the aluminum (Al) connector shell: (1) extended cracking within the fillet; (2) remelting of the solder joint during the follow-on, soldering step that attached the EMR adapter ring to the connector shell (and/or soldering the EMR shell to the adapter ring) that used the lower melting temperature 63Sn-37Pb (Sn-Pb) alloy; and (3) spalling of the Cd (Cr) layer overplating layer from the fillet surface. Several pedigrees of connectors were evaluated, which represented older fielded units as well as those assemblies that were recently constructed at Kansas City Plant. The solder joints were evaluated that were in place on connectors made with the current soldering process as well as an alternative induction soldering process for attaching the EMR adapter ring to the shell. Very similar observations were made, which crossed the different pedigrees of parts and processes. The extent of cracking in the top side fillets varied between the different connector samples and likely the EMR adapter ring to the shell. Very similar observations were made, which crossed the different pedigrees of parts and processes. The extent of cracking in the top side fillets varied between the different connector samples and likely reflected the different extents to which the connector was mated to its counterpart assembly. In all cases, the spring finger solder joints on the SA1358-10 connectors were remelted as a result of the subsequent EMR adapter ring attachment process. Spalling of the Cd (Cr) overplating layer was also observed for these connectors, which was a consequence of the remelting activity. On the other hand, the SA2052-4 connector did not exhibit evidence of remelting of the spring finger solder joint. The Cd (Cr) layer did not show signs of spalling. These results suggested that, due to the size of the SA1358-10 connector, any of the former or current soldering processes used to attach the EMR adapter ring and/or EMR shell to the connector shell, requires a level of heat energy that will always result in the remelting of the spring finger solder joint attached with either the Sn-Ag or the Sn-Sb alloy. Lastly, it was construed that the induction soldering process, which is used to attach the EMR adapter ring onto the shell, was more likely to have caused the remelting event rather than the more localized heat source of the hand soldering iron used to attach the EMR shell to the adapter ring.

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Cadmium plating on metal surfaces is commonly used for corrosion protection and to achieve good solderability on the 304L stainless steel shell of the MC4636 lightning arrestor connector (LAC) for the W76-1 system. This study examined the use of zinc as a potential substitute for the cadmium protective surface finish. Tests were performed with an R and RMA flux and test temperatures of 230 C, 245 C, and 260 C. Contact angle, {theta}{sub c}, served as the generalized solderability metric. The wetting rate and wetting time parameters were also collected. The solderability ({theta}{sub c}) of the Erie Plating Cd/Ni coatings was better than that of similar Amphenol coatings. Although the {theta}{sub c} data indicated that both Cd/Ni platings would provide adequate solderability, the wetting rate and wetting time data showed the Amphenol coatings to have better performance. The Zn/Ni coatings exhibited non-wetting under all flux and temperature conditions. Based on the results of these tests, it has been demonstrated that zinc plating is not a viable alternate to cadmium plating for the LAC connectors.

Low temperature, Sn-based Pb-free solders were developed by making alloy additions to the starting material, 96.5Sn-3.5Ag (mass%). The melting behavior was determined using Differential Scanning Calorimetry (DSC). The solder microstructure was evaluated by optical microscopy and electron probe microanalysis (EPMA). Shear strength measurements, hardness tests, intermetallic compound (IMC) layer growth measurements, and solderability tests were performed on selected alloys. Three promising ternary alloy compositions and respective solidus temperatures were: 91.84Sn-3.33Ag-4.83Bi, 212 C; 87.5Sn-7.5Au-5.0Bi, 200 C; and 86.4Sn-5.1 Ag-8.5Au, 205 C. A quaternary alloy had the composition 86.8Sn-3.2Ag-5.0Bi-5.0Au and solidus temperature of 194 C The shear strength of this quaternary alloy was nearly twice that of the eutectic Sn-Pb solder. The 66Sn-5.0Ag-10Bi-5.0Au-101n-4.0Cu alloy had a solidus temperature of 178 C and good solderability on Cu. The lowest solidus temperature of 159 C was realized with the alloy 62Sn-5.0Ag-10Bi-4.0Au-101n-4.0Cu-5.0Ga. The contributing factor towards the melting point depression was the composition of the solid solution, Sn-based matrix phase of each solder.

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Legislative and marketing forces both abroad and in the US are causing the electronics industry to consider the use of Pb-free solders in place of traditional Sn-Pb alloys. Previous case studies have demonstrated the satisfactory manufacturability and reliability of several Pb-free compositions for printed circuit board applications. Those data, together with the results of fundamental studies on Pb-free solder materials, have indicated the general feasibility of their use in the broader range of present-day, electrical and electronic components.