LaVern, In the C rev of SM-840, we went away from the usual class 1,2,3 of IPC convention and went to a class H (for high reliability) and class T (for telecommunications). T - Telecommunications (includeds computers, telecommunication equipment, sophisticated business machines, instruments, and certain non-critical military applications). Solder mask on boards in this class is suitable for high performance commercial and industrial products in which extended performance life is required, but for which interrupted service is not life threatening. H - High Reliability / Military (includes that equipment where continued performance is critical, equipment down-time cannot be tolerated and / or the equipment is a life support item). Solder mask on boards of this class is suitable for applications where high levels of assurance are required and uninterrupted service is essential. Note: Class Designations - Previous versions of this specification, and other IPC documents, make reference to Class 1, Class 2, and Class 3. For all practical purposes, there is no Class 1 solder mask. Class 2 is equivalent to Class T. Class 3 is the equivalent of Class H. If you would like more information, please contact me. Doug Pauls Vice-Chair Solder Mask Task Grou CSL [log in to unmask] *************************************************************************** * 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. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************