Hard to believe that pink ring is making the news again.  When the oxide
post dip (DMAB) chemistries hit the market most shops made it go away on
both direct connect vias and thermally relieved vias.

Is it a functional defect?  All of the past reports said that no one ever
experienced a field failure associated with pink ring.

It was definitely an aesthetic defect and therefore a lot of customers
rejected product back to a lot of board shops.  

The main tie-in between direct connect vias and thermally relieved vias
is associated with the epoxy bond.  An epoxy-epoxy bond (on the thermally
relieved vias) is stronger than an epoxy-oxide bond on a direct connect
via.  Merix succeeded in getting rid of pink ring on both types of vias
through process changes/control in lamination, drilling, plating, and 
finally oxide (including the addition of an oxide post-dip).

If chemistry gained access to the oxide layer it would discolor it (usually
a pink color) in a flower shaped pattern.  Severe cases of pink ring could
also occur on a thermally relieved via, but it was less common.  The people
that claimed it was no issue supported the case by the claim that it was
just a discoloration.  The people that claimed it was an issue supported the
case by saying that a path for the chemistry was present.

Instead of resolving that debate, Hitachi developed a DMAB dip that reduced
copper oxide to copper metal and improved the epoxy-oxide bond.  That
solved the problem at Merix and many other shops.

Glenn Heath
Account Manager
Merix Corporation
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