I guess I'll ask the next obvious question: When are the joints failing? Are
they not making it through initial inspection, or are they coming back from
the field with failures? If the first, look at your solder pad
design...maybe you need a larger pad area, or maybe you're getting cold
solder joints from the flex acting as a heat sink. If the second, I'd look
into shock and vibration analysis. The second problem could be solved with
something as simple as a strain relief on the flex to isolate the solder
joint from shock and vibe waves travelling along the flex. The solder joints
might be on the receiving end of a "crack the whip" effect from the movement
of the flex.

Michael Hiteshew
Lockheed Martin NE&SS Marine Systems
410-682-1259

> ----------
> From:         Brooks,Bill[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.;Brooks,Bill
> Sent:         Friday, July 13, 2001 4:00 PM
> To:   [log in to unmask]
> Subject:      Re: [TN] FLEX CIRCUIT FAILURE
>
> I guess I will be the one to ask the obvious question.... Have you looked
> into a Rigid/Flex design where the 2 boards are integrated into one board?
> an example can be found at this link:
> http://www.dyconex.co.uk/prod02Flexrigid.htm
>
> Bill Brooks
> PCB Design Engineer
> DATRON WORLD COMMUNICATIONS INC.
> 3030 Enterprise Court
> Vista, CA 92083
> Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510
> mailto:[log in to unmask]
> IPC Designers Council, San Diego Chapter
> http://www.ipc.org/SanDiego/
> http://home.fda.net/bbrooks/pca/pca.htm
>
>
>
> -----Original Message-----
> From: Joseph Keary [mailto:[log in to unmask]]
> Sent: Friday, July 13, 2001 11:56 AM
> To: [log in to unmask]
> Subject: [TN] FLEX CIRCUIT FAILURE
>
>
> HELLO TECHNETERS
>
> GOOD FRIDAY TO YOU ALL
>
> I HAVE A PROBLEM THAT I AM HOPING SOMEBODY CAN HELP WITH. I HAVE A FLEX
> CIRCUIT BEING HOTBAR SOLDERED TO A PCB. THERE ARE COMPONENTS UNDER THE
> FLEX
> CIRCUIT. THIS CAUSES THE FLEX TO EXIT THE SOLDER JOINT AT ABOUT A 30
> DEGREE
> ANGLE. WE ARE PRESENTLY HAVING FAILURES IN THE SOLDER JOINTS OF THE FLEX
> TO
> PCB. THE COMPONENTS UNDER THE FLEX STRIP ARE WELL PLACED (FILTER CAPS).
> MOVING THESE PARTS COULD CAUSE THE PCB NOT TO PASS EMC TEST. THESE
> ASSEMBLIES GO INTO AN  ENVIROMENT THAT HAS A LOT OF VIBRATION INVOLVED.
>
> 1) IS THIS 30 DEGREE ANGLE A REAL PROBLEM ?
>
> 2)IS THERE POSSIBLY MORE THAT I SHOULD BE LOOKING AT?
>
> 3)IS THERE A WAY OF SOLVING THIS PROBLEM WITHOUT MOVING THE COMPONENTS
>
>
>
>
>   ALL COMMENTS GREATLY APPRECIATED
>
>
>
>    THANKYOU
>    JOE KEARY
>   SR. PCB DESIGNER
>   SYSTRON AND DONNER
>
>

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