Reverse engineering obsolete devices

In our work on resurrecting really old and obsolete devices using bipolar technology, some designed using rubylith techniques, we found an interesting evolutionary trend from the oldest to the older. The layout techniques and the basic designs were dictated by the availablity of or non-availability of CAD tools. The earliest designs tend to have the very simplest layouts for the individual devices such as: simple epi-tub, base and emitter rectangular diffusions. Large contact areas of every shape and description and very broad isolation and device to device spacings starting at almost 10 mils and coming down to about a mil for the older devices. Devices are layed out almost as one would layout a PCB using discrete devices. Active devices occupy their own tubs, resistors occupy their tubs and there is a general absence of capacitors. For the relatively newer obsolete devices the layout style changes to active devices, resistors sometimes occupying a single tub with very unique shapes and geometries. As the the CAD tools become better, circular geometries become more and more prevalent and we see lateral pnps and smaller npns with circular emitters. On chip capacitors make their appearance using the emitter diffusion, oxide /nitride and metal sandwiches. The line widths shrink down to sub mil sizes and device densities per chip increase. Interestingly bondpad sizes seem to be consistent for a long period of time ( around 100 um X 100 um). Scribe lines appear to also hold on to widths. ( Around 100 to 150 um wide). All in all the art of reverse engineering these devices, including the electrical characteristics as deduced from the layout and ancient specifications form a most interesting activity for those interested in the art. Interested parties may contact SPG for reverse engineering of obsolete parts via our website at http://www.sinalpro.biz