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Ask the Experts

September 3, 2014 - Updated
August 26, 2014 - Originally Posted

V - Scoring PCB Question

I am considering scoring a PCB with a 90 degreescoring blade after SMT placement and reflow to create a card edge connector ona 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.

Expert Panel Responses

I'venot heard of anyone doing the scoring after SMT, though I�m sure it has beendone. I can�t think of any show stoppers... there are, however, some risks thatneed to be addressed. Here are the ones I can think of:

Support of the board needs to eliminate possibility of bendingstresses in the PWB that may damage components or joints near the edge. Thisshould not be a real issue because you will need very solid support in order tocontrol score depth
Damage to the metallization at the edge of the score maynecessitate a post-score inspection and burr removal. Blades need to betailored to avoid severe damage, e.g. lifting of the edge of the copper fromthe 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 anelectrical failure
Broken glass fibers resulting from breaking along the score linecould become a risk to contact reliability, and should be removed afterbreaking at the score.

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 generatepost-assembly dust that will include metal (copper) particulates. Otherwise,going sufficiently deep to depanel with a 90-degree cutter will produce amoderately wide bevel. Other issues depend on actual PCB substrate and v-scoreprocess control.

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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