Hi all, I am trying to update the hole/pad chart that our designers use for their CAD tools. To do this I have been looking at the IPC-2221 calculation (paragraph 9.1.1) which has the age old formula: Land size min = a + 2b + c What is different from what I remember is "a" is now the maximum diameter of the finished hole. In the past I used the drilled hole diameter. Since the internal annular ring is measured from the effective drilled hole to the edge of the foil pad this equation seems to have something missing. It seems like 2x the plating thickness needs to be added to the formula for internal pads to guarantee that the annular ring requirement will be met in the final product. This formula looks like it will allow no annular ring, or a hole tangent to the edge of the pad, when taken to its extreme. Since external pads are measured from the plating the formula looks fine for external pads. Any comments? Bill Dieffenbacher, Technical Leader Product Design Engineering Lockheed Martin Control Systems @ Johnson City, NY Tel (607)770-2961 Fax -2056 MARCALL 8*255 [log in to unmask] ############################################################## 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. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################