Methods of fabricating semiconductor chip solder structures

Various semiconductor chip solder bump and underbump metallization (UBM) structures and methods of making the same are disclosed. In one aspect, a method is provided that includes depositing a layer of a first metallic material on a semiconductor chip. The first layer has a first physical quantity. A layer of a second metallic material is deposited on the layer of the first metallic material. The second layer has a second physical quantity. The first and second layers are reflowed to form a solder structure with a desired ratio of the first metallic material to the second metallic material.