Gregg: The simple answer to your question is that the holes will be within .0085" DTP, or +/-.003" linearly from the intended location. This is on finished product. Bringing in the hole-to-pad issue is another animal. The relationship of the hole to its pad involves multiple disciplines: drilling (hole location) imaging (artwork location) etching (pad size reduction) material movement tooling system Since we can't assume that everything wrong will happen to the same hole and pad, we use something akin to the "root mean square" to calculate worst case scenarios. In order to make 100% of your product fit our manufacturing window in volume, the following formula is used at HADCO to calculate the minimum pad size needed to sustain a customer's annular ring requirements: Drill Size* + Mfg. Allowance# + (2 X annular ring req'd) * Drill size is nominal finished hole size + .005" # Allowance for inner layers = .014"; outer layers = .012" The mfg. allowance captures the multiple disciplines listed above. For example: .039" finished hole diameter; .001" annular ring INNER LAYER: .044" + .014" + .002" = .060" min. pad size OUTER LAYER: .044" + .012" + .002" = .058" min. pad size Using these formulae, 100% of your boards will meet your requirements in our volume environment. Not every hole will be located in exactly the same spot on every pad. That is why we need a manufacturing allowance. Regards, Tom Coyle Field Services Engineer HADCO Corporation *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************