Diffusion soldering preform with varying surface profile

A method of soldering a semiconductor device, the method comprising:

• providing a substrate comprising a first metal joining surface;
• providing a semiconductor die comprising a second metal joining surface;
• providing a solder preform that comprises a first interface surface and a second interface surface opposite the first interface surface;
• arranging the solder preform in between the substrate and the semiconductor die such that the first interface surface faces the first metal joining surface and such that the second interface surface faces the second metal joining surface;
• placing the arrangement of the solder preform in between the substrate and the semiconductor die in a soldering furnace;
• performing one or more pre-soldering steps in the soldering furnace below a reflow temperature of the solder preform with the arrangement of the solder preform contained in the soldering furnace;
• increasing the temperature of the soldering furnace to reach a melting temperature of the solder preform such that the solder preform melts and reacts with the first and second metal joining surfaces to form intermetallic phases in a soldered joint without applying mechanical pressure to the arrangement,
• wherein during the pre-soldering steps the arrangement of the solder preform in between the substrate and the semiconductor die comprises channels between the solder preform and one or both of the substrate and the semiconductor die, and
• wherein the channels permit ingress and egress of ambient atmosphere within the soldering furnace.