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

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to:           *
* [log in to unmask] with <subject: unsubscribe> and no text.        *
***************************************************************************