In a message dated 12/14/00 8:22:48 PM Eastern Standard Time,
[log in to unmask] writes:

<< 1)  Uncured prepreg
 2)  Too much resin "squeezed out" of the prepreg
 3)  Drilling feeds and speeds not optimized (usually indicated by the
 presence of nailheading)
 4)  Too aggressive of a desmear or etchback chemistry
 5)  Adhesion promoting properties of the inner layer foil being attacked more
 aggessively by the desmear or etchback chemistries >>

Mr/Ms Yeo -
I would like to amplify Susan Mansilla's response above.  "Wedge Void" is the
discriptive term for a hole wall plating failure where something has been
removed from the hole barrel through chemical attack. It is selective at the
B stage to copper conductor interface. The cross section of the missing area
is a "wedge" showing preferential chemical removal of either the resin or the
copper.  Removal of resin indicates undercure or too agressive desmear, but
is not as common as copper "wedge voids".

Some copper is removed by the microetch in either the plated-through-hole
line, or in the preplate to copper electroplating.  Copper and copper oxide
are both available to the microetch solution, and copper oxide (if thick) is
removed faster.  Hence, you see the attack travelling back along the
conductor/cured B stage interface, forming the "wedge".  Drill fracture can
cause this, as well as poor control of the copper oxide process at inner
layer manufacture.

Extra care is taken with direct metallization systems, as the copper
oxide/cured B stage line is avialable for attack at both through hole
processing and electroplating.  This interface is inherently covered during
electroplating when using electroless copper through hole processes.

Dennis Fritz
MacDermid

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