Bob, I've been very interested in the dialogue pertinent to film
compensation (aka shrinkage factors). At Circo we developed several years
ago, a modelling system that is empirically derived from a slightly
different theoretical model. The results however are excellent, our defect
rate for misregistration is extremely low and the factors used are
essentially the same key factors as is used by your theoretical model. I
would be interested in comparing movement predictions of a specific
construction to your predictions and perhaps this would lead to additional
insights.

As far as 100 ppm target for accuracy, are you sure that this is attainable
with the lot to lot variations of raw materials ( ie prepreg resin content,
resin formulation , glass cloth consistency etc..)?

Dave Rooke
Circo Craft
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_______________ reply separator ___________________

>Lou Hart asked the attached question on film compensation for innerlayer 
>lamination shrinkage.
>
>**********
>
>I gave a paper at the last IPC expo in which I discussed a model for 
>compensation factors.  This paper will be updated with a few more details and 
>some concrete examples at the IPC Fabworks this Fall in Naples.  In a 
>nutshell, the model says that innerlayer shrinkage is equal to the thermal 
>expansion difference between a clad innerlayer and a finished MLB. The  TCE of
>a clad innerlayer is less than a MLB due to the effect of the copper.  Things 
>that reduces the innerlayer TCE such as low resin content, heavy glass or 
>thick copper increase lamination shrinkage.  However the very same factors 
>reduce the MLB TCE decreasing innerlayer lamination shrinkage.  The result is 
>a balance between these two effects and is design and process dependent. 
>
>I also plan to address the second question at the Fall IPC Fabworks. In this 
>paper I will try to show the relative importance of various factors that 
>affect internal registration yield.  The bottom line on compensation factors 
>is that an accuracy of 100 ppm (0.1 mil/inch) is needed.  There is little gain
>for better compensation factors by you lose nearly a mil of registration 
>tolerance for every additional 100ppm increase in compensation error.
>
>R. R. Holmes
>Lucent Technology
>[log in to unmask]
>  
>
------------- Begin Original Message -------------
>Here's a question for TechNet that may be vague and imprecise, but I 
>will ask it any way.  It has to do with film compensation for inner layers.
>
>Our plant compensates inner layer films according to simple rules:  add 
>0.5 mils/inch and 0.3 mils/inch for ground planes in the grain and 
>non-grain directions, respectively;  add 0.6 mils/inch and 0.4 mils/inch 
>for signal planes in the grain and non-grain directions.  
>
>The engineering team believes that these rules, made 4 or more years ago, are 
>too simple.Some factors that, we believe, should affect compensation are
>
>- layup pattern, location of ground and signal planes in the board stack
>
>- weight of copper (could be many variations here)
>
>- number of layers
>
>- trace density
>
>- orientation of traces with respect to grain
>
>- prepreg styles used (many variations seem possible here)
>
>- supplier of prepreg
>
>- type of material (polyimide, epoxy formulation).
>
>Anyone have any ideas of the relative importance of these factors?  
>Anything we have overlooked?
>
>
>How important is it to be concerned about compensation?
>
>Lou Hart	Compunetics
>
>
>
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>
>
D. Rooke
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