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May 1997

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From:
[log in to unmask] (Mark R Ford)
Date:
Thu, 8 May 1997 15:02:34 PST
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In response to drilbert's drill wander reply:

Having worked with the largest PCB manufacture in the US for 6 years, I
tend to use them as a "barometer" for what does and does not work
effectively in producing printed circuits.  I have a great deal of
confidence in the Cpk values for DTP using an aluminum clad entries
(Cpk: 1.80 to 3.50).  I would be very interested in what kind of Cpk
values you achieve with melamine cladded entries over 2500 hits with a
#80 in a three high .062" 6 layer board with 1.0 oz inners.

My biggest concern with using melamine entry is abrasion.  melamine is
one tough customer to drill (that's why we like to use it for counter
tops in our kitchens).  Regardless of whose tools you use, they tend to
abraid faster and, more importantly, farther down the margin of the tool
creating a detrimental front taper condition.  This equates to reduced
hit counts, more stock removal at repoint, fewer repoints and
ultimately, higher drilling cost.  However, the entry that I originally
spoke of was solid phenolic or melamine (.008 to .024 thick) which are
being used by some PCB manufactures.

And lastly, not to beat this subject to death, penetrating a "hard entry
quickly" can be misinterpreted as utilizing unconventional chip loads. 
There are tool geometries available that allow for extremely "high" chip
loads but, this does in fact cause drill wander - no if's, and's, or
but's.  If the goal is to reduce drill wander, chip loads have to be
carefully scrutinized to assure that you are not penetrating the work
piece too rapidly.  

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