Electrical resistance of the solder connections for the consolidation of the LHC main interconnection splices

For the consolidation of the LHC main interconnection splices it is planned to solder shunts onto each of the 10,170 splices. The solder that has been selected for this purpose is Sn60Pb40. In this context the electrical resistance of the shunt to busbar lap splices has been measured in the temperature range from RT to 20 K. A cryocooler setup has been adapted such that a test current of 150 A can be injected for accurate resistance measurements in the low nΩ range. In order to study the influence of the solder bulk resistivity on the overall splice resistance, solder connections produced with Sn96Ag4 and Sn77.2In20Ag2.8 solder 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.