Nancy,

Fab requirements are probably getting tighter (we spec 6.45 micrograms/in2 NaCl 
for PCBs which is/was Bellcore) because assembly outgoing requirement per 
J-STD-001A 8.3.2 is 1.56 micrograms/cm2 NaCl (or 10.06 micrograms/in2 NaCl) 
ionic residues, same as IPC-RB-276.  

Specifying a tighter cleanliness standard for PCBs gives the assemblers
a guardband.  PCB suppliers should not have a problem meeting the tighter 
cleanliness spec if the PCBs go through a final cleaning prior to packaging and 
shipping.  We've been at 6.4 for years without having any complaints from our 
suppliers, our PCBs typically come in the 2 - 4 microgram/in2 NaCl.  

My opinion of checking prior to Entek coating is that it's not necessary.  A 
cleaning and microetch is part of the standard Entek process, so any residual 
contaminants on a PCB should be cleaned off in the Entek process.  Others might 
have a different opinion.

Tracy Tennant
Micron Technology
[log in to unmask]

                                                       30-JUL-1996 09:49:48.21
>From:   [log in to unmask] 
>To:     [log in to unmask],[log in to unmask],STHUMMEL,TTENNANT,MIKEPARRY
>Subj:   Fab-Ionic Contamination
>
>Dear Technet,
>
>I have a question about the ionic contamination limits stated in
>the IPC-RB-276.
>
>Reference to IPC-RB-276 Section 3.13.3, it is specified the
>resistivity shall not be less than 10.06 micrograms/sq.inch of
>sodium chloride.
>
>I have discovered that many OEM's are requiring this to be 6
>micrograms/sg. inch.
>
>Is this left over from the Mil-Spec days?
>
>Also
>
>Should boards that are checked before Entek Application be
>required to be 6 micrograms per sq/inch as well?
>
>
>Thanks,
>
>
>Nancy Nelson
>Dell Computer
>[log in to unmask]
>
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