Genny

It sounds like your PCB was built with two B stages with FR4 between the copper layers and the prepreg
between layers 2-3.


Similar to this               Most 4-layers

1- cu                            1- cu
     FR-4                            pre-preg
2- cu                            2- cu
    pre-preg                        Filler FR-4
3- cu                            3 - cu
    FR-4                              pre-preg
4- cu                            4 - cu





Genny Gibbard wrote:

> Hi,
> We just received a new rev of a PWB in house.  It has not been populated
> yet.  It looks like it has been built correctly - the right layer order,
> connections, etc - but it looks different than the rest of our 4 layer
> boards.  Normally the traces on the inner layer that is closest to the
> surface appear dark in colour and the deeper layer appears lighter.  This
> board is the opposite.  The layer closest to the surface is light in colour
> and the deeper layer is dark.  Also, the FR4 seems much easier to see
> through than usual.
>
> Any thoughts or explanations for this?
> Thanks for your time.
>
> Genny Gibbard (mailto:[log in to unmask])
>
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