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]

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