Electrical Resistance of the Solder Connections for the Consolidation of the LHC Main Interconnection Splices

For the consolidation of the LHC 13 kA main interconnection splices, shunts will be soldered onto each of the 10 170 splices. The solder alloy selected for this purpose is Sn60Pb40. In this context the electrical resistance of shunt to busbar lap splices has been measured in the temperature range from RT to 20 K. A cryocooler set-up has been adapted such that a test current of 150 A could be injected for accurate resistance measurements in the low nΩ range. To study the influence of the solder bulk resistivity on the overall splice resistance, connections produced with Sn96Ag4 and Sn77.2In20Ag2.8 have been studied as well. The influence of the Sn60Pb40 solder resistance is negligible when measuring the splice resistance in a longitudinal configuration over a length of 6 cm. In a transverse measurement configuration, the splice resistance is significantly influenced by the solder. The connections prepared with Sn77.2In20Ag2.8 show significantly higher resistance values, as expected from the relatively high solder resistivity at cryogenic temperatures. The experimental results are complemented by simulations with Comsol multiphysics, showing the contribution of each splice component on the overall splice resistance.