In a message dated 01/06/2000 11:01:22 PM Central Standard Time,
[log in to unmask] writes:

<< Dear fab folks ;
 could you give me indication of "standard" No. of cycles on small via holes
 drill sizes, on carbide and steel bits please, and would there be a
difference of
 utilization habits between say US and SEA/CHINA/SOB regions ?

 Facing patches of cracked vias , suspecting blunt drills > uneven barrel
 plate.>>

Hi ya' Paul!

I'm not a fab guy, but I've picked-up a little knowledge about fabs since
I've been out here in Oklahoma...we've experienced some fab problems that got
me looking into the whys of some of the problems that we'e had. A lot of my
references come from the "Printed Circuits Handbook" by Clyde F. Coombs Jr.
(A GREAT reference book!)

There's a whole chapter (about 30 pages) on nothing but drilling. From what I
read, it's kinda' difficult to make a general statement about how many hits a
drill bit can take before it doesn't give you good hole quality, there's so
many variables that will affect drill life, such as the design of the bit
itself (point angles and flute designs), what kind of drill entry and back-up
materials are being used, the laminate make-up itself, harder and thicker
copper will shorten the life of the drill as will a higher glass to resin
ratio laminate. Feeds and speeds if wrong, can also cause hole quality
problems as well.

That being said, there is however, a statement in the chapter when talking
about qualifying entry and back-up materials; "The number of hits varies
depending on the abrasive characteristics of the laminate and the wear
characteristics of the drill's carbide. Normally, the number of hits to show
significant wear beyond normal usage is 1500 to 2000 for #80 (.0135") drill
bits and 2500 to 3000 for #76 (.020") drill bits."

So I would guess it would be at or below the lower numbers above (but only
for those drill diameters).

But like what was stated earlier, it really depends on a lot of other
variables...did I confuse you enough? I confused myself....hehehe.

-Steve Gregory-

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