Hi Thomas.
    Thieving (on the external layers) is used as a "robber" for plating.  By this I mean that it
allows for a more consistent distribution of the plating material.  If a circuit is Isolate, it
will "absorb" the plating at a faster rate, resulting in a heavier plating finish in the isolated
area.  Results of this could be a) overplating resulting in shorts due to the plating resist
becoming entrapped under the plating, b) undersize holes due to the relationship of this to other
areas, c) poor ductility/elongation (potential cracking) due to the larger grain size of the
copper plating, d) thinning of soldermask at this area due to the increased height of the circuit
, and e) in the event of an impedance control line, you will notice a "dip" in the wave sine in
this area and subsequent timing changes in the circuit speed.
    Plating thief is used by the manufacturer to help in racking during the plating operation as
well as a handling region for other equiptment points.  It is also used by the manufacturer to
incorporate certain "coupons" for drilling and such.  The innerlayer operation uses this real
estate for "damming".  Damming gives the panel an area to pull the volatiles/moisture from the
prepreg and a flow path for the resin during its gelling/curing cycle.  It also gives a "buffer"
area to insure thickness consistancy during the lamination stage.
    There are a couple of other uses, but these are the most common in regards to the
manufacturer.  When you design, take a hard look at your circuit density/distribution. In the
event that a manufacturer is requesting internal thieving, it is probably due to unbalanced
circuit design.  If they are asking about panel size, it is due to the need for the plating
thieving around the edge of the panel.  Some circuit sizes may require an oversize panel (poor
panel real estate utilization) due to the need for stepping (unless scoring), and plating thief
or test coupons.
    I hope you are still awake after this.  If I can offer any other information, please Email
me.  Thanks JOHN WAITE
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Tomas A. Gutierrez wrote:

>      Can anyone out there explain the process of thieving during pcb
>      fabrication.
>
>      thanks in anvance,
>
>      Tomas
>
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