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September 3, 2014

V - Scoring PCB Question

I am considering scoring a PCB with a 90 degree scoring blade after SMT placement and reflow to create a card edge connector on a PCB. I would score deep enough to bevel and depanelize in 1 step.

Is there a precedence for doing this? Are there any horror stories of failures?

B.S.

Experts Comments

I've not heard of anyone doing the scoring after SMT, though Iím sure it has been done. I canít think of any show stoppers... there are, however, some risks that need to be addressed. Here are the ones I can think of:
  • Support of the board needs to eliminate possibility of bending stresses in the PWB that may damage components or joints near the edge. This should not be a real issue because you will need very solid support in order to control score depth
  • Damage to the metallization at the edge of the score may necessitate a post-score inspection and burr removal. Blades need to be tailored to avoid severe damage, e.g. lifting of the edge of the copper from the laminate
  • Conductive debris will be created by scoring through the metal, and this will need to be controlled/removed so that it does not result in an electrical failure
  • Broken glass fibers resulting from breaking along the score line could become a risk to contact reliability, and should be removed after breaking at the score.
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Fritz Byle
Process Engineer
Astronautics
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.
You will generate post-assembly dust that will include metal (copper) particulates. Otherwise, going sufficiently deep to depanel with a 90-degree cutter will produce a moderately wide bevel. Other issues depend on actual PCB substrate and v-score process control.
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Robert "Bob" Lazzara
President
Circuit Connect, Inc.
Bob has been in PCB design and fabrication since 1976. He has held elected positions with the SMTA, is a member of the MSD Council, has served as a committee member for various IPC standards and is a Certified IPC Trainer.
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