In message <[log in to unmask]>, drilbert
<[log in to unmask]> writes
>My best exit location results were with a paper core with melamine
>facing entry product. I tried three different vendors of alum clad entry
>and my results were all over the map.  Pure alum results were middle of
>the pack. I think results are greatly affected by material grade,
>thickness, and vendor process variation.  "Hard" is not always bad if
>the drill can quickly pierce the melamine facing.
>Mark R Ford wrote:
>> 
I agree with what Mark says. We use a phenolic paper with a smooth shiny
surface and achieve good results. The key point is to allow the drill to
penetrate the entry material without any deflection due to the surface
hardness or roughness. Problems have occurred in the past when our
supplier changed their method of manufacture to produce a rough surface
on one side which tended to deflect the drill slightly on entry. Also,
there can be hard particles embedded in the material which cause drill
breakage. Quality of the material supplied is therefore very important
and it is not just a question of getting a generic type of entry
material. I believe that aluminium suffers from a micro rough surface
due to brushing which can deflect the drill but you will need an SEM to
see the grooves.

A 1 degree deflection will produce a 5 thou" error on the bottom side of
4 x 0.062" laminate with 0.31" entry material. This is a minimum figure
as it assumes the drill follows a straight path which it probably does
not.
-- 
Paul Gould
[log in to unmask]
Isle of Wight,UK

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To subscribe/unsubscribe send a message <to: [log in to unmask]>   *
* with <subject: subscribe/unsubscribe> and no text in the body.          *
***************************************************************************
* If you are having a problem with the IPC TechNet forum please contact   *
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *
***************************************************************************