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July 1997

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Fri, 18 Jul 1997 12:40:29 -0400 (EDT)
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IPC and pink ring 

IPC 6012 and IPC-RB-276 states that pink ring is acceptable: however, wedge
voids are not as described in the circufirmential void criteria.  As we all
know you can have pink ring and not have wedge voids.  Many, many boards that
I look at have pink ring to various degrees and do not have wedge voids.  And
I have seen boards with wedge voids that did not have pink ring, it does not
always follow that they are coincidental.
It has also been voiced by many that the permanganate dsmear method is a
great pink ring enhancer and may also produce wedge voids when another
desmear method such as plasma may not.  The permanganate method apparently
works it way into the  microfractures in the oxide and oxide/prepreg
interface and does what it is designed to do, remove exposed resins.  The
neutralizers and other acid do the rest.  But with thin and reduced oxides
and some limits on acids dips, a pink ring or a visible circumferential ring
on the reduced oxide surface on the land encircling the hole does not cause a
 wedge voids which is the only defect per the IPC specifications.  It is also
noted that some of the direct metallization products fill the microcracks and
even some large cracks and the wedge void does not appear.  Again, this is
acceptable per the IPC specifications which have tried to eliminate cosmetic
appearances from the non-acceptable criteria.

Phil Hinton 

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