As a board manufacturer, I would be reluctant to agree to a 0.7% (.007in/in)
flatness requirement without first reviewing the design of the circuitry in
question. It is absolutely imperative that the board design is optimized for
board flatness before any  control can be achieved. I often state that the
top five causes for non-flatness in todays products are, in order of
significance:

1) board design
2) board design
3) board design
4) board design
5) all other factors

Dave Rooke
Viasystems Canada
= = = = =
>Hello, TechNetters,
>
>I was wondering what others are calling out for flatness requirements on
>double sided boards with surface mount components.  IPC-A-600 calls out
>1.5% but with a caveat that automated assembly and surface mount may
>require more stringent requirements, and refers to IPC-D-275.  The most
>stringent callout in D-275 for a 0.062" double sided board is 0.9%, and
>this is classed "reduced producibility".  If we have, say, an 8.5"x11"
>board with 0.9% bow or twist, I know we'll have difficulty running it down
>our lines.  What are others calling out, and how have your fabricators
>responded?  Some of mine are balking at 0.7%, saying it can't be held
>(would have to be sorted, possibly increasing cost) because of variability
>in the base material.  I think 0.7% is met most of the time, but every once
>in a while...
>
>Thanks for any input.
>
>*****************************
>* Pat Bailey                *
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