Pat,

Our drawings routinely call out "maximum bow & twist of panel [or board]
shall be .3%".  Most of our boards come in meeting this spec, but
occasionally some have to be rejected and replaced by the vendor.  I am
not familiar with any objections from our board fabricators to this
specification.  The fact that they are producing for military and thus
are used to different specifications may be part of that.

Steven Lustig
Process Engineer
EMS Technologies, Inc.
Norcross, GA
(770) 263-9200 x4714
[log in to unmask]
>----------
>From:  Pat Bailey[SMTP:[log in to unmask]]
>Sent:  Monday, December 15, 1997 5:48 PM
>To:    [log in to unmask]
>Subject:       [TN] Board Flatness
>
>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                *
>* Supplier Quality Engineer *
>* Zytec Corporation         *
>* 1425 E. Bridge Street     *
>* Redwood Falls, MN  56283  *
>*                           *
>* phone 507 637-2966 x355   *
>* fax   507 644-3720        *
>* e-mail [log in to unmask]     *
>*****************************
>
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