Welding, Brazing, Joining to PCB

Hello all,

I need to somehow join a small diameter copper tube (.063 inch OD) to a copper pad on a circuit board. The board experiences high temperatures (> 250° C) so solder connections melt, even with higher temperature silver solder. I have been experimenting with a micro TIG welder, but it blows holes in the copper pad down to the PCB substrate. Have had similar issues, though not as severe, with laser welding. Have not tried brazing yet, but am concerned with it damaging the PCB or substrate. Any ideas on how to make a reliable connection (both electrical and structural)?