Brief Investigation of Splices, Solders and Flux: A Quick and Dirty Approach. Steve Krave, Rodger Bossert 1/13/2013

Solders and Flux Not necessarily related… Higher temperature solders require a higher temperature flux, but there is some working room. LHC uses Kester 135 flux and 96/4 Tin/Silver solder (or similar for NbTi). –Additional challenge of reacted cable. Read dirty! Poor wetting of tin/silver with LHC flux (Kester 135) on reacted cable Fermilab has always used 60/40 Lead/Tin and Kester 1544 flux for Nb3Sn splices. –Highly aggressive flux and forgiving solder 2

Things working against LHC Specification LHC Spec uses Tin-Silver Solder –High(er) melting point –High wetting angle (doesn’t wet as well as lead tin) –Lead Free… LHC Spec is Kester 135 Flux –Classified as type R (ROL0) Very weak and halide free. No-clean Chloride free… This spec does not appear to be suitable for Nb3Sn as there is a “heavy” oxide layer formed on cable during reaction and this flux/solder combination is extremely “gentle” 3

Some Pictures Tried different fluxes and cable treatments. Simply used a large solder iron to head Brushed flux on beforehand. No mechanical cleaning(can’t scrub inside cable) 4

Dirty Reacted Cable with 135 5

With Overnight Soak in Vinegar and 135 Mild acid strips some oxide, clearly enough to allow wetting. Still chloride free 6

Kester 1544 Extremely easy and fast soldering Could we just use a flux cleaner? Type RA (ROM1) 7

Fresh NbTi and 135 Very fast and easy 8

So what about flux… B rookhaven has been using Nokorode Paste Flux, A rosin flux.(ROL0) –Used for splicing –Nb3Sn leads still tinned with activated flux. –Nearly chloride free, but more aggressive than Kester 135 –Probably also could be considered RMA –Seems to be reasonably successful CERN is using MOB 39 rosin paste Flux (ROL0) –Similar to the above –Probably RMA equivilant. –Published <0.05% Cl 9

Preliminary Conclusions 96/4 Tin Silver with Kester 135 flux is most likely not suitable for Nb3Sn splices with current methods. –It may be a workable solution if some sort of chemical or mechanical cleaning is applied. What is acceptable? –Lead solder and less aggressive flux? –Lead-free solder and more aggressive flux? –Pre-treatment and cleaning? Brookhaven and CERN have had similar troubles and have switched to a slightly more aggressive flux. 10