Speaking from experience, life on the edge...edge of a facility's
manufacturing capability is not a fun edge on which to teeter. There is a
cliff on one side of that edge and an unpleasant fall when pushed over that
edge by unpredictable yields, low yields, deviations requiring engineering
time to determine acceptability and flat out non-delivery. Do your company
a favor and take as many steps back from that edge as you can.
Best Regards,
Jana Carraway
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Dee Stover
Sent: Friday, July 19, 2002 6:50 AM
To: [log in to unmask]
Subject: Re: [TN] flex circuit line and space
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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