Patsy,

Is your multilayer construction such that layers 1/ 2 and  9 / 10 are on the same core or are you using foil lamination for the outerlayers. The situation you are describing sounds like you are not using foil lamination. If this is the case, what you are seeing is not unexpected. The outermost cores will have solid copper on one side. If this is the case, then what you are seeing is not movement of layers 2 and 9 but rather all the other layers are "shrinking" while layers 2 and 9 are relatively stable due to the copper on layer 1 and 10. 

If you are using foil lamination, then I would suggest that you recheck the front to back registration of the artwork on layers 2 / 3 and 8 /9 .

Hope this helps.

Ed Cosper
Director Quality Assurance and Engineering
Graphic Electronics, Inc.
Tulsa, OK  

----------
From:  [log in to unmask][SMTP:[log in to unmask]]
Sent:  Thursday, March 20, 1997 10:11 AM
To:  [log in to unmask]
Subject:  FAB(Shifting Layers)

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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