A method for bonding thermally-mismatched elements of a traveling wave tube employs a metallic plate of undulating character. The plate is located at the region of the interface between tube elements formed of materials of materially-differing thermal character such as the ceramic termination piece and an adjacent sever pole piece of copper. Through either a brazing or a sintering process, pluralities of bonds are formed at points of tangency between the plate and the two elements of differing thermal expansion coefficients. As a result, a good heat flow path, accompanied by a more stable r.f. interface, is formed between the materials that is not subject to fracture as are prior art diffusion bonds.