Hi David, A technique I had set up succesfully in a large corporation about 15 years ago had very good results, recovering over 70% of multilayer boards with internal (power/ground) shorts. First problem is in locating the short, as you essentially have large, complex parallel circuits to isolate a single point. We had used a "low ohms" meter (capable of measuring micro ohms) and left one probe stationary, searching for the lowest resistance with the other probe moving about the board. We could "zero in" on a single pin, usually a signal thru hole shorted to an internal plane. Once the suspect area was isolated, visual inspection was performed by backlighting the pcb with a halogen microscope light. The FR4 is transparent enough to project a reasonable image through the clearance ring of the plane to see a darkened area where a short (usually an underetch whisker) was present. We then would take a photomicrograph of the image before the next step. We would then begin to "excavate" the site using "micro-abrasive" equipment. I recall (it was a LONG time ago) we experimented with different materials such as sodium bicarbonate (very sharp) and crushed walnut shell (very dull) and found certain abrasives would remove FR4 and not disturb the Cu, and others would be more aggressive to the Cu, and less aggressive to the FR4. Once the site of the short was exposed, we would again take a photomicrograph, this time top-lighted with the same hallogen light. We'd then remove the short with the micro-abrasive, clean it thoroughly with IPA, then backfill it with 2 part epoxy. We'd then take the photomicrogaphs, log them together with a time sheet, and bill back the PCB supplier for the rework at burdened rate. From a business standpoint, the repair was a "profit center" (billing back to the supplier), so cost justifying the equipment and training to execute was recovered in a short time, as well as recovering all the labor and materials already in the assembly at that time, which would have ended up scrap. The one drawback at that time, which now I'm led to believe there is a viable solution, was ESD. The micro-abrasive action created enormous charges which are unnacceptable. I spoke briefly with one of the micro-abrasive equipment suppliers several Nepcon's ago, and they claim this is no longer an issue if ionized air is employed. Sorry if I got a bit "long winded", folks, but sometimes I just can't help myself! If you would like to discuss this "offline" please feel free to contact me at (714) 364-6614 Regards, and have a great weekend! Ed Popielarski QTA Machine ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ##############################################################