The development of balling technologies for wafer level devices with pitches down to 400µm pitch

Solder bumping usually represents the final stage in the WLP assembly process prior to dicing. Standard solder paste print & reflow techniques can be utilised but the resultant bumps invariably fall below specifications due to process limitations. More commonly, dedicated equipment sets that place pre-formed solder spheres onto the wafer are used. This paper details work undertaken to combine the benefits of standard stencil printer technology with that of solid solder sphere placement to enable the development of a low cost, flexible system for the bumping of wafer level packages.