Solder edge conductor bonding, as its name suggests, is a process where vertical interconnections between ICs are performed by soldering along the edge of an IC stack - the I/O of each die is rerouted to a conductor deposited on the edges. There are three variants of this method as follows:
Figure: Three variants of the solder edge conductors vertical interconnections. (a) Solder edge contacts. (b) Solder filled via. (c) Stacked PCB leadframes.