I am with Patty, it has been around for a long time.  I saw my first pink
ring in 1965 when we switched from bare copper to oxide treat to improve
adhesion.  Of course, I did not see it by looking at the board because it was
not on the the layer you saw when looking into the board.  You had to make a
horizontal microsection from the inside of the board in order to see it. Pink
ring to various degrees existed on most boards from the 60 until the 1980's
and someone decided to use a new process called "cap foil" and pink ring
became apparent to the casual observer.   Seaching for a something to call
this newly discovered defect, we called it "delamination" and were able to
scrap a good many circuit board for this reason.  Then the Thermal Zone
concept came into existence and a delamination in Zone A was acceptable.  How
can we scrap the board using the Zone concept, a big problem!!  So the
argument goes on.  To my best knowledge there has been no studies or reports
that show that pink ring without wedge voids causes any functional problem or
that it will cause delamination.
There are many reports that show that pink ring without wedge voids is a
benign defect and even though it looks ugly, it is not a functional defect.
 Perhaps to settle the argument, we should go back to hiding the oxide layer
or always use reduced oxide to satisfy the purists.  Invisible pink ring
often occurs on reduced oxide, but appears only as a circular stain around
the hole and is not visible from the surface.  You must make a careful
horizontal microsection in order to detect it, so it is acceptable. 

I heartily agree with Patty that the processes used in lamination, drillling,
oxiding etc. will increase/decrease pink ring, but did we improve the board
or its reliability..  Maybe the next 30 years will tell.

Phil Hinton

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