An integrated circuit chip stack and a method for forming the same in which bond pads of an interposer are directly bonded to bond pads of a package substrate using only pre-solder. The interposer can have a bond pad pitch of less than 150 micrometers. The interposer can be an organic interposer. The pro-solder can be melted to make contact with the bond pads of the package substrate and the interposer. After solidifying, the pre-solder can form an electrical connection between a bond pad of the interposer and a bond pad of the package substrate.