We have been delivered a printed circuit board which
is causing a great deal of concern at my company.
It is a 12 layer blind via card with three drill
cycles. 1-6, 7-12, and 1-12. The pwb is constructed
of Polyimide and has LPI solder mask over bare cu.
The concern is over cu flakes visible in the blind
via holes. These flakes are embedded in the LPI
soldermask which fills the holes. At first it was
thought that these flakes were caused by a dull
drill, left over burrs. However, the vendor says they
are caused by the dual cu platting process and is a
common occurrence.
The vendor explains that two six layer pwbs are
constructed, drilled and plated. They are then
joined together by the polyimide resin and re-drilled
and plated. At this second plating process, the cu is
attempting to plate the polyimide nodules formed in
the blind vias. Some of these are not sticking and
float up until they are captured by the solder mask.
They were designed / built iaw IPC-D-275 CLASS 2/IPC-RB-276 Class 2.
They will be thermo-cycled and need to perform over time.

Has anyone seen this before?
Is it really normal?
Is there any risk in using these pwbs?

Thanks for any help

Tom Obarski
Harris Corp,
Melbourne Fla.

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