Embedding technology-a chip-first approach using BCB

With the current trend to ever faster clock rates the propagation delays between the chips constitute a significant portion of the clock cycle. Mounting both active and passive devices as closely together as possible will therefore boost system´s performance. Although flip-chipped devices have good performance, design constraints may prevent the placement of pads to comply with flip chip design rules. An additional advantage of the embedding technology is the possibility to employ 3-D stacking, the highest package density. Bare dice and standard passive components were embedded into a ceramic substrate to achieve a common, planar surface. Hence by employing thin-film processing all components can be directly interconnected to the copper routing of the module. Benzocylobutene (BCB) with its low curing temperature is preferred as dielectrical polymer for the embedding technology. Application of bonding or soldering techniques which might limit the reliability is avoided. This offers excellent electrical properties of the wiring system. By planarizing the reverse side of the MCM a low thermal resistance between heat sink and dice can be accomplished simultaneously for all embedded components. An SRAM MCM and a Thermotest MCM demonstrate the facibility of the embedding technology