A package includes a corner, a device die having a front side and a backside, and a molding material molding the device die therein. A plurality of redistribution lines is on the backside of the device die. The plurality of redistribution lines includes a plurality of metal pads. A polymer layer contacts the plurality of metal pads. A plurality of openings is formed in the polymer layer, with the plurality of metal pads aligned to and exposed to the plurality of openings. The plurality of openings includes a corner opening that is elongated and an additional opening farther away from the corner than the corner opening. The additional opening is non-elongated.