Soldering pure nickel foil

Hi Everyone! I would like to solder pure nickel foil to a base metal.
I don�t know the best choice of solder or base metal for this task.
Does anyone have a suggestion or have tried something similar? The
materials I plan to use are�

Nickel foil (99% pure), 100mm square, 0.05mm thick Base metal plate,
100mm square, 1.5mm thick

The base metal will have been lapped to global flatness of 0.002mm.
After joining the foil to the base metal, it would be ideal if the
flatness was maintained.

Any leads to companies that can bond nickel foil to other metals
would also be very helpful.

Thank you,
Jeff