Mike,

I should know better than to say such foolish things as you can't, etc.
Sometimes you can, and someone will do it. I should have said 12 and 14
layer .062" thick boards offer particular challenges.

When fabricating a 12 layer board .062" thick, lots of 5 core, and a little
4 core stuff, along with lots of 5 mil preg must be used. The 4 core and 4
mil preg is ideal if used throughout as it should be single ply 2113
material with a near ideal resin to glass ratio meaning it has enough glass
to make the structure highly dimensionally stable and enough resin to
provide lots of laminate integrity. 5 mil stuff often is composed of two
plies of 1080 material with very high resin content, really juicy and
sticky, making it not dimensionally stable but having very high inner
laminar bond strength.

This could go on forever so I'll just say if you use all 4 mil dielectrics,
you will be on the low side of .062 when using .5 oz copper throughout. You
will have a great board however. If you use all 5 mil stuff with the same
copper weights, you will have a monster slipping and sliding in the press
board with little chance of having pads line up for drilling - and on it
goes.

Of course, you could use all 1 oz copper foil with 4 mil dielectrics and
nearly get to the desired thickness.

Hell, this is too much even for me. It's just that there are too many
compromises involved to effect really high yields for 12 and 14 layer 62 mil
thick boards. Therefore, you pay more for the thickness and you may not get
your impedance requirements, and you may wish for a thicker or thinner board
to make it all go away. If you're really happy, then this is a waste of
time. I think I wasted words anyway so enjoy your boards as they are.

Earl

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