Steve,
The thinest core or prepreg material available usually resembles a 106 glass
style type coming in at about .0015" thick, not .015". The 52 layer board,
of course, did not use any single ply constructions. It's primary dielectric
thickness was .006". You can't build high layer count boards with
thin/juicey (high resin per cent ratio) materials. Dimensional stability
would suffer too much both during relamination and after. Still, certain
electrical performance requirements demand thin core stuff to satisfy
impedance control, etc.
See my forthcoming article in the SMT Express next month. It explains much
of what you ask concerning multilayer constructions for laminate integrity,
dimensional stability, and electrical performance.
I would add all layers do not start out as double sided copper. Often inner
layers are single sided, depending on requirements. Outer layers on more
sophisticated types start out with only prepreg and are "foil" laminated as
thin metal, copper or otherwise, foil is added to the MLB "book" before
relamination. Therefore, anything is possible.
Earl
----- Original Message -----
From: Stephen R. Gregory <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, August 27, 1999 5:33 PM
Subject: Re: [TN] In Circuit Test
> In a message dated 8/27/99 6:26:31 PM Central Daylight Time,
> [log in to unmask] writes:
>
> > interesting , how thick is 52 ? (just curious) .
> > Earl we have the layers cost dilemma here :
> > What would be ratios of yields and costs from simple double sided FR4 ;
> > to 4 layers, 6, 8, >>> etc. ?
> >
> > And why even's only ; no odd layers ever ?
> >
> > thanks paul
>
> Hey Paul!
>
> What you doing sending a email on your Saturday? Workin' a week-end or
> something? I'm just answering you just to test what little I've learned
about
> PCB fabs ( I need to learn a lot more!) So all you teachers out there,
> correct me if I'm wrong.
>
> All layers start out as a double-sided copper-coated laminate, thus the
even
> number. The technology is advancing all the time (what's new?) but the
> smallest core I've heard of is .014". So at that dimension, a 52-layer
would
> work out to .728" at the minimum...but there has to be some resin between
the
> layers, so I would think that it would be some VERY THICK BOARDS. (I've
never
> seen a 52-layer board! 18-layers is the most I've ever seen!)
>
> The problem that I see with that many layers (and why Earl's boards are
big
> bucks!) is the registration between all these layers when making the fab!
We
> think we have problems putting some components on boards like this and
> reflowing them, I'd hate to have the job of putting this FAB together!
>
> I've gone to the dogpile and looked around, found some stuff about resin
> coated copper, but it was listed as a "product in development" so maybe
you
> might see some odd numbered layers soon...boy, I'm I dumb about this
stuff!
>
> -Steve Gregory-
>
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