I have seen the same error in our facility. It's something very soft ,
black color and it can be very long and thin. The location is always under
the conductor of the laminate.
  I have seen the problem in two laminates suppliers and in thin (0,25 mm)
and thick  (1,6 mm) FR4 material.
  I think that the spots are in the treated side of the cooper foil,but I'm
not sure.

Xavier Angel    LAB CIRCUITS,S.A.
  [log in to unmask]

----------
> De: Eltek Ltd. - Process Engineering <[log in to unmask]>
> A: [log in to unmask]
> Asunto: [TN] High resistance internal shorts
> Fecha: martes 5 de mayo de 1998 9:04
>
> Hi Technetters !
> During the past period we made a lot of improvements in our production to
> reduce the scrap due to internal shorts .  At this moment 90% of internal
> shorts are " isolation shorts " , it mean high resisitivity .
> Some of this shorts were located and we found  unidentificed spots in the
> laminates . The spots are located under the conductors ( laminate side )
,
> they  have irregular shapes and are very thin . Such spots are bridging
two
> adjacent conductors . Such spots are not result of unetched copper since
> they are running deep into the laminate ( more than 25 microns ) .
> I will appreciate comments on this problem via technet or to my private
e-mail .
> Best regards
>
>
> Edward Szpruch
> Eltek Ltd - Israel
> Tel  972 3 9395050
> Fax 972 3 9309581
> E-mail :  [log in to unmask]
>
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