Nancy 

The ionic contamination number of 10.06 micrograms/in. sq. or 1.56 mictograms
per cm.sq. is pretty universal around the industry.  IPC-RB-276, IPC-6012,
J-STD-001, MIL-P-55110 and MIL-PRF-31032 all list this number as the max. for
cleanliness measurement and has been the value for a long time.  I am not
sure where the 6 micrograms/in.sq. or 0.96 micrograms/cm.sq. came from or on
what it is based, but it is not one of the more common callouts. As chairman
of the 276 task group, I found that our discussions alway led to retaining
the higher number which appear to be working for us.  If anybody has any
input into the 6 micrograms number or why it is used or needed, I would like
to hear from you.

Thanks
Phil HInton 
Hinton Engiineering 
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