Subject: Random nail heading.

As we all know the causes of nail heading are many,  and may be the result of
drills, drill machines, operational practices, materials of construction,
construction of laminate and prepreg, cure state, copper foil type, thickness
and processing.  A detailed list comes up with about 40 contibutors.

Unfortunately, nail heading is what is called a non-defect defect; requests
for any data on nailheading caused defects in 1989 came up with none.  Only
responses were "An indiction of poor quality control" and similar.  Many
smart guys have learned to control the pre-electroless-copper-etch to
etch-off and eliminate a reportable nailhead defect.

The Industry Spec IPC-RB-276 dropped the nailheading requirement in 1992 and
the military counterpart, MIL-PRF-31032 also dropped the requirement at its
issuance in 1995.  MIL-P-55110E still carries the requirement, but I
understand that its replacement will also not mention the subject.

The nail heading requirement was installed in the early 1960's in the
military spec by some of us guys who worked for large companies that could
afford good drill equipment and did not use resharps, mainly. to prevent
competion from the fabricator who couldn't       

Today many company specs. are a slightly modified copy of the military
specification and nail heading continues to appear because no one knows how
to evaluate and many have the belief that its a part of the process control
system.

So every year many tons of boards are discarded because of this supposed
defect which has no revelency to board performance.

Phil Hinton 
Hinton PWB Engineering 
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