In message <[log in to unmask]>,
[log in to unmask] writes
>We are experincing a reaccuring problem with our lamination process on 10 
>layer projects with the following stackup: 
>
>1.  1 oz copper on all 5 FR4 5 mil sheets;
>2.  3 sheets of PGFK1080 2.5mil prepreg in each gap (total of 7.5mils each 
>gap); 
>3.  Grain of prepreg is in the same direction;
>4.  finished thickness 69 mils;
>5.  layers 2-4 & 7-9 are signal layers; 
>6.  layers 5&6 are ground/VCC planes.
>
>Problem:  We are consistently seeing layers 2 and 9 shift 3-4 mils more than 
>the other layers (3:4, 5:6, & 7:8).  Layers 3:4, 5:6, & 7:8 all align well 
>with each other and the outermost sheets are shifted to the right by this 3-4 
>mils.  Once layers 1 and 10 are imaged onto the drilled panel, they also line 
>up well with the innermost layers (3:4, 5:6, & 7:8).  We are losing panels due 
>to annualar rings less than 2 mils on layers 2 & 9 (Mil-P-55110).

It seems you are getting good alignment with the inner panels and only
the outer ones are shifted so the more common technique of using copper
foil for the outer layers should solve your problem. Four double sided
panels will make your inner 8 layers with pre-preg and copper foil on
the outside and you should also find it cheaper to produce this way.

I can't explain why you are getting this slippage unless your platens
are not quite parallel and the tooling pins are unable to stop some of
the slip.

If you have buried vias or other reasons for the construction, then
consider single sided panels for layers 2 & 9 and use foil for the outer
layers. Don't use single sided laminate but etch off one side to get the
best bond strength.

Good luck.
Paul Gould
Teknacron Circuits Ltd

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