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June 2000

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Subject:
From:
Dwight Mattix <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 1 Jun 2000 08:52:45 -0700
Content-Type:
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We score many designs.  It's a really useful process to optimize panel
utilization and sometimes assy tooling/depaneling tradeoffs.  However, our
experience here shows your concerns are valid.  I suggest the even bigger
concern should be the risk of latent defects that will pass through all
your tests and into the field.

We've seen the risk to be with ceramic chip components (chip caps et al)
within .1 - .2" of the score.  The mode is latent ceramic cracking leading
to leakages or outright device failure.  Either way the end result is the
same -- field infant mortality.

As a result of our experience (read scar tissue -- and some crude long
forgotten rel experiments way back in the early 90's dark ages -- Phil
Bavaro may have better memory of that) our design rules don't allow scoring
if chip components are within 0.200" of the score. The exception to the
rule we sometimes make is when the assembly has shields soldered out to
board edge effectively making a box beam that stops/reduces flex of the pwb.

I'd be real interested to hear what others have learned and design rules
they maintain -- esp if there's been some science applied to their
establishing their rules.

Dwight

At 11:01 AM 6/1/00 -0400, Ed Holton wrote:
>We have recently started using boards with V-score for the panelization and
>we have a debate raging here.  There is a concern about separating the
>boards before versus after the incircuit test and whether there is the
>possibility that there is imparted stress to the board that could create a
>failure mechanism that might have been caught at the ICT and not at the
>functional test, thus the requirement to singulate before versus after ICT.
>I have read various articles, but am wondering what people have found in
>the real world.
>
>Thanks
>
>Ed Holton
>Manufacturing Engineer and Group Leader
>Hella Electronics
>Telephone (734) 414-0944
>Fax (734) 414-0941
>
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