grits to go straight through the row your interested in. Using hot pressure setting mounting compound helps fill the vias. We use the same method for flip chip joints as well. If you are trying to section a specific via, then you just have to go very carefully. The amount of material removed by the 5 micron diamond paste for example becomes significant. If anyone is using equipment or jigging to help hit the right spot on these small features I'd be interested to hear. J Drake Celestica Ltd Kidsgrove Stoke on Trent England