-- [ From: Doug Jeffery * EMC.Ver #2.10P ] --

Lou,

You have hit on all valid factors, I would add only 1 -- core
thickness. the cores vary as much as the pattern of copper on them.  We
started out with a single standard factor and have been adjusting ever
since.  We now have 9 standards for cores and I don't know how many
part numbers have been customized.   

The good thing about our system is the feedback loop we set up.. Based
on a standard coupon (fixed drill to pad ratio) we xray each drill
setup...A process engineer reviews the setup xrays each day and
feedsback to preproduction engineering adjustments when needed.   This
has really dialed in the registration..especially on ultra thin cores
and wild patterns.   

Another factor that may influence the scale factor is your press cycle.
If you have more than one press cycle make sure you evaluate the
shrinkage with that in mind.

Doug Jeffery
Electrotek


-------- REPLY, Original message follows --------

> Date: Monday, 05-Aug-96 03:47 PM
> 
> From: [log in to unmask]       \ Internet:    ([log in to unmask])
> To:   Doug Jeffery             \ PRODIGY:     (TCGE34A)
> 
> Subject: FAB:  Film compensation
> 
> 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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-------- REPLY, End of original message --------


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