The invention relates to method for copper-to-copper direct bonding comprising the steps:



a) providing a first substrate comprising a first pure copper deposit having a bonding surface;
b) providing a second substrate comprising a second pure copper deposit having a bonding surface;
c) connecting the bonding surface of the first deposit with the bonding surface of the second deposit and obtaining a connected deposit; and
d) converting the first deposit and the second deposit of the connected deposit into a connected and converted deposit,
wherein the first deposit and the second deposit are formed by an electrochemical copper deposition step and having copper grains with a grain size which is smaller than a grain size after the converting in step d),
wherein the connected and converted deposit is having grains with a grain size which is larger than the grain size of the first deposit and the second deposit before the converting in step d); and to an assembly and a device produced by the method. (FIG. 1)