High-leadcount, single- and multi-metal-layer TAB: design considerations

It is suggested that high-leadcount, single- and multi-metal-layer TAB (tape automated bonding) can offer a viable, longer-term power distribution alternative. High-leadcount, single-metal-layer TAB will soon provide in excess of 1000 I/O at an inner lead bond pitch of 0.002". The overall size of the TAB package, or its outer lead bond (OLB) footprint, can be minimized by reducing a 2* fanout to zero-fanout. This shortens the line length, which improves the electrical performance characteristics of the device, provides drastic reductions in inductance, and takes up much less area. As board-mounted device speeds exceed 50 MHz, critical parameters can best be optimized by the use of multi-metal-layer TAB. The addition of a ground plane in close proximity to the signal plane also allows for reduced inductance, thus lowering simultaneous switching noise. The three-metal-layer design approach offers even lower simultaneous switching noise by further reducing inductance. Area array TAB, which uses a three-metal-layer construction, offers a more powerful interconnection solution. This approach enables design engineers to locate power and ground planes directly over the active area of the die.<>