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Subject:	Re: Board Bow and Twist
From:	Earl Moon <[log in to unmask]>
Reply To:	TechNet E-Mail Forum.
Date:	Thu, 14 Mar 2002 10:07:06 -0600
Content-Type:	text/plain
Parts/Attachments:	text/plain (40 lines)

Now this is starting to get interesting. The first comment about DFM, how
about that?

Taking it a step farther, as part of my stiring the pot response way
earlier, we need to get sensible. You acceptance experts easily find the
right IPC thing and test method. Well ain't that great.

The whole point of this incredible exercise is about designing - not
accepting after the damn thing does or does not work for BGA's or whatever
needing minimal bow and twist.

You hot shot designers out there have to be thinking about what you need. If
you have a board needing .75% then design your board accordingly. As I said
before, panelization is very important in this case. You must not design a
two up panel when you know it will not be possible to meet the requirement.

Board shops know most of this but designers must get on top of it. We all
know about balanced constructions but few realize how designing a board's
size and thickness on a panel will make or break you.

If you're on the edge of being two up, and have a critical need, make sure
it's done on a one up. If you have critical requirements, keep it simple
stupid while realizing what design considerations you make will affect Ken
Carlile's boards. His designers certainly did not think about it and look
what he's bitching about now notwithstanding poor supplier selection.

MoonStraightMan

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