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 ; and performing a mechanical pressure-free diffusion soldering process that forms a soldered joint between the substrate and the semiconductor die by melting the solder preform and forming intermetallic phases in the soldered joint; wherein both of the first interface surface and the second interface surface have a varying surface profile that creates voids between the solder preform and both of the substrate and the semiconductor die before the melting of the solder preform , wherein the varying surface profile comprises a plurality of ridges and channels that are disposed between immediately adjacent ones of the ridges , and wherein the channels create the voids in the arrangement of the solder preform in between the substrate and the semiconductor die , wherein the ridges and channels have an undulating profile along a cross-section of the solder preform that is orthogonal to the ridges , and wherein both of the first interface surface and the second interface surface have the same undulating profile, and wherein the solder preform has a substantially uniform thickness (T) along the cross-section of the solder preform that is orthogonal to the ridges . 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 ; and performing a mechanical pressure-free diffusion soldering process that forms a soldered joint between the substrate and the semiconductor die by melting the solder preform and forming intermetallic phases in the soldered joint; wherein both of the first interface surface and the second interface surface have a varying surface profile that creates voids between the solder preform and both of the substrate and the semiconductor die before the melting of the solder preform , wherein the varying surface profile comprises a plurality of ridges and channels that are disposed between immediately adjacent ones of the ridges , and wherein the channels create the voids in the arrangement of the solder preform in between the substrate and the semiconductor die , wherein the ridges and channels have an undulating profile along a cross-section of the solder preform that is orthogonal to the ridges , and wherein both of the first interface surface and the second interface surface have the same undulating profile, and wherein the solder preform has a substantially uniform thickness (T) along the cross-section of the solder preform that is orthogonal to the ridges . <EOS>