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July 2013

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Subject:
From:
Reuven Rokah <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Reuven Rokah <[log in to unmask]>
Date:
Wed, 10 Jul 2013 08:29:44 +0300
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Hi Phil,

I recommend to add a detail for each of the 3 technologies with tolerances
and keep-out from components and traces.
Its better than 1000 words.
Reuven

On Wed, Jul 10, 2013 at 2:51 AM, Phil Bavaro <[log in to unmask]>wrote:

> I have been asked to determine what the best practice is for depaneling
> PWAs from an array (more than one PWA per panel run down the assembly
> line), or in other words...
>
> ....how should we be depanelizing PWAs, a) v-score, b) pin router, or c)
> mouse bite/punch.
>
> I do have a personal opinion (listed below), but my experience was with
> commercial Class 2 and not Hi-rel Class 3 hardware.  I am looking for input
> from others that have years of experience in the Hi-rel arena:
>
> a) V-scoring was always the easiest but required that the score go all the
> way across the panel.  The result was that there were a few glass bundles
> (.012" approx) which were sheared left over while the area of the v-score
> was smoothly finished by the original router.  The mechanical stress, if
> performed using the round blade to shear while supporting the v-score from
> the bottom, in minimal.  The solder joints keep away is a minimum of .080"
> away from the top edge of the V, but ceramic caps might need further
> distances and special orientation.  Proper singulation method is important
> so this is not a high volume production type method.  I have always
> discouraged jump scoring.
>
> b) The pin router method results in a nicely milled edge but it requires
> ESD controls (ionized air) as well as excellent FOD controls (vacuum for
> the dust) to control the process.  The resultant board edge is identical to
> what a PWB fabricator would supply and one advantage is that the copper to
> board edge pull back area is less than with a v-score.  We don't have room
> for tooling pins to hold the boards so vacuum hold down is a requirement
> and that applies mechanical stress to the PWA as well.  This method is
> suited well to high volume.
>
> c) The mouse bite punch method leaves the entire board edge thickness
> exposed for glass bundles and is the least desired due to this.  If the
> mouse bites are not spaced optimally, the punch or nipping process can
> impart the highest stresses of all of these methods.  The edge copper pull
> back is from the edge of the mouse bite holes which is close to the amount
> needed for v-scoring.  The other drawback is that some people tend to want
> to flex the mouse bites to failure and that causes unknown but excessive
> stresses.
>
> Please feel free to respond with your preferences as well as point out any
> disagreements you might have given that this process needs to be used with
> hi-rel hardware (non-space, but definitely airborne).
>
>
> Thanks in advance,
>
> Phil
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-- 

Best Regards,

*Reuven Rokah*

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