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).

We would appreciate any suggestions from those who have seen similar 
occurances.

Patty Causey / Marty W. Sheppard
Process Engineering Section
email address:  [log in to unmask] / 
[log in to unmask]
Phone: (912) 926-9473(9632)

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