A semiconductor package assembly comprises a first conductive pad on a semiconductor substrate; a second conductive pad on a package substrate; a bump physically coupled between the first conductive pad and the second conductive pad, wherein the bump is substantially lead-free or high-lead-containing; the bump has a first interface with the first conductive pad, the first interface having a first linear dimension; the bump has a second interface with the second conductive pad, the second interface having a second linear dimension; and wherein the ratio of the first linear dimension and the second linear dimension is between about 0.7 and about 1.7.