Patent ID: 8828860

Claim:
A method comprising: providing a substrate having a plurality of electrically conductive contact pads; positioning a first flexible mask on the substrate, the first flexible mask including a plurality of first holes, the first mask being positioned such that the plurality of first holes are aligned with the plurality of contact pads; injecting a molten first solder having a first melting point into the first holes; allowing the first solder to solidify, whereby the first solder adheres to the contact pads and forms a plurality of first solder bumps; removing the first mask from the substrate; positioning a second mask on the substrate, the second mask including a plurality of second holes, the second mask being positioned such that the second holes are aligned with the plurality of first solder bumps; injecting a molten second solder having a second melting point lower than the first melting point into the second holes and covering the first solder bumps, the first solder bumps remaining solid during the injection of the molten second solder, and causing the second solder to solidify to form second solder bumps, each comprising the first and second solders, the second solder adhering to and forming layers respectively covering each of the first solder bumps.