Good morning everyone!

We are currently investigating a failure mode that has happened on a few of
our customer's assemblies.

The problem is as follows (a little background):

We have three confirmed occurrences in which a through-hole clinched
resistor lead has shorted out with a non-common conductor on the "solder
side" of the board.  All the conductors are coated with soldermask, however,
after about four (4) months in the field (in which the unit had been working
properly) the resistor lead had penetrated or pierced through the soldermask
and "shorted" out with the adjacent conductor.  The cause of the penetration
is unknown at this time.  We gently pulled the resistor lead slightly away
from the adjacent conductor and the unit began working properly again (short
was gone).  We inspected the soldermask at 40X but did not see any copper
exposure.

IPC-A-610C (Section 5.2.7.2) states that "The lead is clinched toward an
electrically non-common conductor, violating minimum electrical clearance"
is a defect (all three classes).  Our Auto-insertion machines are set up for
a 45 degree angle clinch.  (However, in these cases the clinch was below 45
degrees...so it did appear the clinch was much tighter to the board than we
would like)

So....The issue we have are the following:

The design of the board is such that the clinched resistor lead will always
overlap the adjacent non-common conductor.  Our detection for this condition
has always been ICT and Functional Testing (which it will detect if the
condition exists immediately).  But unfortunately the failure did not occur
until the unit was in the field for awhile.  Has anyone else ever
experienced this problem?  If so, what steps were taken to resolve it?  How
was is verified? Did you have to rely on visual inspection of the clinch
over soldermask?

Help!!!!

Thanks

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