Issues with fine pitch bumping and assembly

One of the primary areas of research at MCNC is fine pitch (100 /spl mu/m or smaller) solder bumping on existing I/O patterns and on redistributed connection footprints. The bumping process is based on an electroplating method that provides flexibility with respect to bump size, pitch, and solders. Significant progress has been made in reducing the bump size and pitch by means of innovative process modifications. The reduction in pitch and bump size leads to a small standoff between the chip and the substrate after assembly. This small gap inhibits flux cleaning between the chip and substrate and requires unique approaches for fluxing and assembly. MCNC's PADS (Plasma Assisted Dry Soldering) process enables fluxless/no-clean soldering by means of a dry pretreatment step, which allows solder reflow and joining. Conventional soldering tools can be used by including a PADS pretreatment step and eliminating the flux dispense and cleaning steps. A review of the plating procedures, assembly, and application studies for fine pitch bumping is presented.