Martin,

  After 3 or 4 problems like this, we established an "internal" standard.
     All smt at least .125" from score line!!!
   Never had a problem in 3 years since.
  No testing or studies to back it up, just real world experience.
  And a zero incidence of problems from the singulation process.

  The designers hate the restriction, but it WORKS.

  My .02 worth.

  Ralph Garvin
   Dir. of New Product Development
    Westport Research, Inc.


-----Original Message-----
From: Martin Christie <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Friday, April 07, 2000 7:25 AM
Subject: [TN] De-panellisation guidelines


>Hi Technetters,
>
>I have a problem with cracked surface mount resistor network. The cracking
>occurs after de-panelisation. I have confirmed this electrically and
>visually (at up to x35 mag). The current fallout is about 5%. The board is
>0..070" (1.8mm) thick and v-scored from both sides. De-panelisation is by
>means of a "bacon slicer" (rolling v-shaped blade approx 4" diameter). The
>network is located 0.032" (0.8mm) away from the v-groove.
>
>
>_____________________________________________________  V-score edge
>                                           ____________________
>                                           |        /               \
> |
>                                           |____/                  \____|
>
>                                                  |                    |
>                                           ____|                    |____
>                                           |
> |
>
>Resistor network with diagonal cracks from stress points
>
>
>The question I have is: does anyone know of any guidelines with respect to
>minimum component mounting distance away from the v-groove in a situation
>like this?
>
>Also, is there an algorithm anywhere that can be used to calculate stress
>involved?
>
>Thanks
>
>
>Martin Christie
>ACW Technology Ltd.,
>Hylton Road,
>Petersfield,
>Hants.
>GU32 3XX
>Tel: 01730 300000 ext 146
>Fax: 01730 266045
>e-mail: [log in to unmask]
>
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