AT&T spl mu/Surface Mount Assembly: A New Technology for the Large Volume Fabrication of Cost Effective Flip-Chip MCMs

The realization of a high speed, high-yield flip-chip assembly capability is essential to the development of a practical, cost effective MCM technology because it supports large volume, relatively inexpensive product applications in which equipment costs per unit can be minimized. This paper describes a novel assembly technique for flip-chip silicon-on-silicon Multi-Chip Module (MCM-D) tiles which readily meets the above criteria. This new hybrid technique, which is called AT&T /spl mu/SMT, involves stencil printing a custom AT&T ultra-fine pitch solder paste directly onto a silicon fabric wafer which is then populated with bare die and reflowed, much as surface mount packaged components would be assembled onto a circuit board. This approach is capable of achieving higher component and interconnection densities than can be achieved with any fine-pitch SMT design - and at a lower unit cost at large production volumes than can be achieved with any other MCM assembly technology.