Redistribution and bumping of a high I/O device for flip chip assembly

Redistribution and bumping of a high I/O device has been successfully achieved at Motorola´s Interconnect Prototype Lab using a combination of photosensitive benzocyclobutene (BCB), electroless nickel underbump metallurgy, and photoresist defined solder printing technique. To take full advantage of flip chip packaging technology, redistribution is necessary to rewire bondpads to an area array. BCB was chosen as the interlayer dielectric between the redistributed metal traces and device circuitry. Advantages of BCB include high level of planarization, low moisture uptake, rapid thermal curing, high thermal stability, high solvent resistance, and a low dielectric constant. We successfully optimized many steps in the process flow to redistribute the bondpads. The BCB residue in vias was cleaned with a plasma descum comprised of an Ar/SF₆ mixture. BCB to BCB adhesion was improved by optimizing the curing time. The shear strength of the bumps was increased 80% by sputter-roughening of the BCB/Al interface. Sematech ATC04-2 functional wafers with 1004 bumps/die and a minimum pitch of 8 mils were successfully redistributed to a 10 mil and 16 mil mixed array pitch and solder bumped using a photodefined squeegee bump technology