Development of fluxless flip chip bonding to a thin film multichip module substrate

Motorola SPS has developed an assembly process for a three-chip multichip module using a fluxless bonding technique. The substrate is a 25 mm×25 mm glass that containing two layers of electroplated metallization with vias connecting the two layers and dielectric layer separating them. A test substrate is designed to characterize the continuity and leakage of the assembled modules. One of the chips has two staggered rows of 384 total bumps on the periphery with 80 μm pitch and 45 μm bump size. The other two chips have three staggered rows, 222 bumps on each chip, 210 μm pitch and 100 μm bump size. The bump composition is Pb-Sn with low Sn content. All three chips are bonded to the substrate using a fluxless plasma process followed by reflow in a nitrogen furnace. A high precision robot is used for placement and tacking of the chips on the substrate. After the bonding, the chips are underfilled with a proprietary underfill epoxy, and tested for reliability. All the reliability criteria for the specific application of this module have been met. Physical design and assembly process of this multichip module will be presented