Hello,

For reference, I have attached a list of all solder joints in the TM2 Source Tray, and the alloys used for the most recent build (as per ITA6144).   I have also provided data sheets for the alloys, and PDF copies of all the drawings calling out the joints.

Certanium 34 C (222 deg C melt point) was used for all low-temperature solder applications, except for the steel inserts in the water blocks.  Previous revisions of the Source Tray drawings called out a higher-temperature McMaster lead-based solder (304 deg C melt point).  The change to Certanium 34 C on the prints was made in Bevan's era, during the transitional update of the source tray drawings between the TM1 and TM3 source tray projects, just before I took over updating the drawing packages.  I believe Bevan made this change on general advice from Guy Stanford, who stated that Certanium 34 C is a much easier solder to work with and makes a more mechanically reliable joint.  However, the change really should have had more review and validation testing before being implemented.

This said, we now have a source tray that uses Certanium 34 C, and rework of every joint would set us back too far in the schedule to meet the deadline, so we will have to run with it as it is.

Of particular concern are the joints on the target oven and coil heating blocks, which are now using a lower temperature solder (222 deg C melt vs 304 deg C melt).  We have experienced a coil block failure on TM4 due to a failed solder joint, although the failure mode is not known for certain.  We also had two recent failures on the test stand of a coil joint soldered with Certanium 34 C, but this was due to an error in the connection of cooling water to the joints (i.e. the joints had no coolant flow and the solder melted... this is expected!).

Anders and I have performed independent thermal analysis on the joints due to the radiative and electric heating from the target, and have concluded that even with a lower temperature solder, there is a lot of margin, so the risk seems to be low.  This work will be published in a separate report to be circulated later.

Thank you and regards,

Grant