Is melamine more abrasive than e-glass?
Actually, I have not found any difference, in terms of front
taper/margin land wear, between aluminum clad entry/backer vs.
melamine clad entry/backer.
Whereas, with a spec limit of .003" TPR, in a 3 high stack of .062"
and using a .0145" tool at 2000 hits, we saw CpK values for top panel
accuracy of .99 and 1.03 for aluminum clad and melamine products,
respectively. CpK's for bottom panel accuracy were, .76 and .85.
(These findings were substantiated in a study previously conducted by
a lEading drill mach. manf.)
I'm not sure that enough holes were measured to capture the effect of
alum. galled on the point of the tools... But, that's something else
to consider.
These two materials were the better performers in a group of 8
different products studied. So, I too, would be interested to know
more details of how these CpK values were derived.
______________________________ Reply Separator _________________________________
Subject: RE: FAB: Drill Wander
Author: [log in to unmask] at INTERNET
Date: 05/08/97 2:16
Mark,
I was reading your response and become curious about the stated CpK =
values. What was the true position used to calculate the CpK and what =
type of drill machine were used?
Ed Cosper
Graphic Electronics
=20
----------
From: Mark R Ford[SMTP:[log in to unmask]]
Sent: Thursday, May 08, 1997 6:03 PM
To: [log in to unmask]
Subject: Re: FAB: Drill Wander
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.=20
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. =20
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