Copper (Cu)-to-Cu bonding techniques for high bandwidth interconnects on a bridge chip attached to chips which are further attached to a packaging substrate are provided. In one aspect, a method of forming an interconnect structure is provided. The method includes: bonding individual chips to at least one bridge chip via Cu-to-Cu bonding to form a multi-chip structure; and bonding the multi-chip structure to a packaging substrate via solder bonding, after the Cu-to-Cu bonding has been performed, to form the interconnect structure including the individual chips bonded to the at least one bridge chip and to the packaging substrate. A structure formed by the method is also provided.