You wrote:
>
>We are currently experiencing drilling tears in a 12 layer part.  The
part
>has 12 layers FR4 all layers are 2oz.  Pre-Preg style is 1080.  Tears
are
>in both pre-preg and original substrate layers.  We have tried
reducing hit
>counts, some attempts at pecking.
>
>Has anyone experienced this problem or can anyone suggest a fix.
>
>Best Regards
>Ian Giddings
>
Ian,

A few questions to try and help you out.

1. What size drill?  When drilling through 10 - 2oz layers (internals)
the bit is going through a lot of copper and may become hot..If you are
using drills smaller than .021 or so you may have a real problem. I
would definitely reduce the hit count on your bits and I might reduce
the chip load and maybe the stack height.

2.  How is the lamination?  With all that copper you need a lot more
heat to flow that resin well.. are you getting good fill? Are you
drilling through dry glass because all the resin ran to the layers?...
I would look at the cure..you may not be advancing the Tg of the
material due to all the heat needed to get the 20 ozs of copper up to
temp for enough time.

3. By tears..do you mean gauges at the bundles?  This would be a result
of a worn dull bit or a lack of resin in the bundle.

I would look at these issues and try to optimise the package. can the
signal layers be 1 oz?  Can the dead pads be removed from the signal
layers to reduce wear on the bits? Can you go to more B-stage to
improve the resin to glass ratio between layers?...like replace 2 plys
of 1080 with 3 plys of 106?

Hope these suggestions help

Douglas Jefery
Electrotek, Inc.
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