Flexible beam-leaded substrates

Early in the search for an effective replacement for the chip and wire bonding method for interconnecting large numbers of integrated circuit chips in a single package, the idea of a beam-leaded substrate was suggested. This technique utilizes substrates with apertures to accommodate the integrated circuit chips. The interconnections on the substrate terminate in integral beam leads which overhand the chip apertures. The beam leads are eventually bonded directly to the pads of the integrated circuits. The more significant advantages of beam-leaded substrates over other alternatives to chip and wire bonding (e.g. beam-leaded devices and flip chip devices) are excellent heat sinking since the chips and substrate can be mounted on a suitable heat sink, a virtually unlimited selection of chips since devices of all types of terminal metallurgy can be utilized by choosing the appropriate beam-lead material, and a planar bonding surface for easy bond inspection and incapsulation. In addition, the beam-leaded substrate approach, along with the beam-leaded device and the flip-chip device, reduces the number of bonds by a factor of two in comparison with the chip and wire method of chip interconnection.