Mark,
I was just reviewing the IPC-SM-840 standard, and came across section
3.4.7, "Visual Requirements". This section gives requirements for allowance
of surface imperfections for solder mask. (Touch-up is certainly
allowed...)  Table 2 gives the "Maximum Number of Allowable Imperfections"
for each class.  Class 2 is 3 imperfections per 6.5cm2 (1 sq.in., and Class
3 is 1 imperfection per 6.5 cm2 (1 sq.in.).
(It must be Monday... where did my weekend go?!?)

Best Regards,
Roger M. Stoops
Trimble Navigation Ltd.

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