Dusty, the most obvious method to monitor the effect of extending the cure
cycle has on the product, is to perform 'out of press' Tg determination
using DSC. You should find that by continually extending the cure cycle, the
initial Tg will eventually start to decline. When the Tg does indeed start
to decline, you may have reached a point where thermal degredation of the
resin has started. Take care though, this analysis should be limited to only
one specific lot of prepreg since the natural lot-to-lot variation between
prepreg lots will confound your measurements.

It wouldn't hurt to ask your material supplier for assistance on this... I'm
sure that they would help.

By the way, out of curiousity, what is your metric for 'small hole quality',
is it position? hole wall roughness? gouging? can you clarify?

hope this helps

Dave Rooke
Circo Craft - Pointe Claire
_____________________________
>TechNetties,
>We have been experimenting with extended cure times in the press for 
>improved small hole quality. We are working with standard multifunctional 
>materials and with some of the newer high temp stuff (180 Tg Etc.) We have 
>achieved much improved quality in vias of 10 mils by holding in the press 
>for 90 minutes at cure temperature (350 - 360 F)with various rise 
>rates versus the recommended 60 minutes. My question is this, how much 
>further can we go with this extended cure cycle before we can expect to see 
>some degradation of the materials? I think we're getting into a grey area 
>here and if anyone has some information I would love hearing from you.
>Thanks,
>Dusty
>
>
>+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
> Dusty Van Iderstine                                 Direct 408-954-5784
> Engineering Manager                                    FAX 408-954-5780
> Quick Turn Divisions                                
>
> [log in to unmask]
> [log in to unmask]
> [log in to unmask]
>+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+

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