A semiconductor device has a semiconductor die with composite bump structures over a surface of the semiconductor die. A conductive layer is formed over a substrate. A patterning layer is formed over the substrate. A first portion of the patterning layer is removed to form an opening to expose the substrate and conductive layer. A second portion of the patterning layer is removed to form a sloped surface in the patterning layer extending from a surface of the patterning layer down to the substrate. The sloped surface in the patterning layer can be linear, concave, or convex. The die is mounted to the substrate with the composite bump structures electrically connected to the conductive layer. An underfill material is deposited over the surface of the patterning layer. The sloped surface in the patterning layer aids with the flow of underfill material to cover an area between the die and substrate.