A semiconductor device includes a first passivation layer over a substrate. The semiconductor device further includes at least two post passivation interconnect (PPI) lines over the first passivation layer, wherein a top portion of each of the at least two PPI lines has a rounded shape. The semiconductor device further includes a second passivation layer configured to stress the at least two PPI lines. The semiconductor device further includes a polymer material over the second passivation layer and filling a trench between adjacent PPI lines of the at least two PPI lines.