On Thu, 23 Aug 2001 11:14:19 +0200, Florian Finsterbusch wrote:
>i have just seen your new layer-stackup for your 8-layer PCB.
>But i'm wondering about the numbers of prepregs.
>I think when you put 4 cores with copper on both sides together, you need
>only 3 prepregs.
Not so simple.
I believe the most common process for making double sided PCBs goes as
follows:-
Drill the holes
Apply the tracking artwork in negative resist
Selectively copper then tin plate including plating through holes
Etch using the tin plate as resist.
When you make a multilayer you can use the same process for the final stage
but only if you use prepreg and foil for the two outer layers. If you want
to use a core on the outside then you have to somehow etch the 'inside'
side of it leaving the outside intact so you still have electrical
continuity for plating through the holes after the stackup has been
assembled and drilled.
So for an 8 layer board I believe most houses would use 3 cores (which
could have buried vias) and 2 foils on the outside.
Cheers, Terry.
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