Thank you Boston Brad, this is some great information. My engineer
seems to only be thinking on the level of what the flex manufacturer
capabilities are and not actual usage of the part. This will help
me in my arguments against his will to go as small as the shops are
boasting because he can.
Thank you,
Dee Stover [log in to unmask]
Associate Technician Design
National Optical Astronomy Observatory
950 N Cherry Ave
Tucson, AZ 85719
www.noao.edu
520-318-8489
FAX 520-318-8303
At 09:43 AM 7/12/2002 -0400, you wrote:
Dee,
Trace width is a function of risk. A happy face button with
blinking eyes; 2mil line. A Defense Missile; 8 mil line. The
2mil very short distance like <.2 inch, the 8mil, on flex, about 8
inches. The length on the 2mil is function of PCB process wherein
the 8 is more end configuration/usage of part.
Many, many more complexities come to the table; dielectric callouts,
robust design, Supplier selection, and the like. Personally I still
believe it comes down to annular ring for the process and limiting the
number of flexures prior to install. The number of flex layers also
plays a large roll in reliability.
I have done sub .005 widths on flex. It is flex-flex not rigid-flex
and for short distance, even the cable itself is small and limited
layers. To predict your situation: based on 5mil in the flex,
the designer didn't have correct input and the vias are to close to the
rigid flex area, you have a less than optimum stack up, probably a
thickness issue and the pad to PTH size combined with a >90 degree
flexure is giving you some intermittent opens.
I would look at the entire configuration from a systems approach
perspective, it is probably not one item.
Good luck,
Boston Brad
Bradford Saunders
Packaging Consultant
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