CIRRUS: FINE PITCH FLIP CHIP INTERCONNECT

摘要

As part of the European Project "Cirrus", an ultra thin IC package has been developed. The package, in the shape of a "cavity-down" Ultra Thin EGA, has 168 IOs and measures 9*9 mm. The interposer is 50 μm thick polyimide flex provided with a fan-out build with a Cu/Ni/Au stack. For the present design an IC of 5*5 mm has been used with a bondpad pitch of 100 μm. The package has a standardised board interface with ball pitch of 0.5 mm. The ultimate height reduction has been achieved through the use of a thinned die (150 μm) with low flip chip bumps (20 micron) in combination with anisotropic conductive adhesives. The resulting height after solder reflow on the motherboard is limited to 300 μm. In the paper the design, process investigations for first level and coplanarity requirements for the second level interconnect will be treated. Further work is aimed at realising the chip connection to the foil using a lead-free solder and on reducing the flip chip pitch down to 40 μm, in line with future enhanced capabilities in wirebonding technolo