Patent ID: 8348139

Claim:
A method of bonding, comprising: placing a composite preform foil between two pieces to be bonded to create an assembly; and reflow soldering the assembly with an appropriate reflow profile sufficient to cause the composite preform foil to undergo isothermal solidification to form a solder joint having a composite structure comprising a top intermetallic layer, a bottom intermetallic layer, and a center ductile metal or metal alloy layer between the top and bottom intermetallic layers; wherein the composite preform foil comprises a core metal layer comprising a metal selected from the group consisting of Ag, Au, Pd, Pt, Cu, Ni, Co, Fe, Mn Mg, Ti, Zr, or alloys thereof, the core metal layer having a solidus temperature greater than 280° C.; a first solder layer joined to the core metal layer, the first solder layer comprising a Sn-based solder or an In-based solder, and the first solder layer having a thickness equal to or greater than 5 μm; and a second solder layer joined to the core metal layer, the second solder layer comprising a Sn-based solder or an In-based solder, and the second solder layer having a thickness equal to or greater than 5 μm; wherein the core metal layer has a sufficient thickness such that a layer of the metal remains after isothermal solidification in reflow soldering.