Patent ID: 8847387

Claim:
An integrated circuit structure comprising: a first work piece comprising: an under bump metallurgy (UBM) at a main surface of the first work piece; a copper bump over the UBM and having a first dimension in a first plane parallel to the main surface of the first work piece; and a nickel-containing barrier layer over and adjoining the copper bump; a second work piece bonded to the first work piece and comprising: a bond pad at a main surface of the second work piece; and a solder mask at the main surface of the second work piece and having a solder resist opening with a second dimension exposing a portion of the bond pad, wherein the second dimension is measured in a second plane parallel to the main surface of the second work piece, and wherein a ratio of the first dimension to the second dimension is greater than about 1; and a solder region electrically connecting the copper bump to the bond pad, wherein the solder region contacts a surface of the nickel-containing barrier layer facing the second work piece to form an interface, and substantially does not contact sidewalls of the copper bump, wherein the interface has a dimension substantially equal to the first dimension.