The 30 degree angle shouldn't in itself be a problem. Are the leaads
pre-formed to this angle? If they're not, then there could be a leverage
effect from the flex being forced up over the components. How much
unsupported flex is there? i.e. do you have a long run of flex after the
solder joints before it either terminates again or passes through a
securing tie/clip.

Pre-formed flexis perform pretty well in my experience, while flexis that
are forced into a shape they're not pre-fomed for can have numerous
problems. Talk to your flex manufacturer about the problems you're having
and the design that the flexi is part of see what they suggest. An
alternative (though I'm reluctant to suggest it, as it seems like a
backward step) is to have the terminations made as through-hole and wave
solder the thing.

Pete Duncan




                    Joseph Keary
                    <jkeary@SYSTR        To:     [log in to unmask]
                    ON.COM>              cc:     (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
                    Sent by:             Subject:     [TN] FLEX CIRCUIT FAILURE
                    TechNet
                    <[log in to unmask]
                    ORG>


                    07/14/01
                    02:55 AM
                    Please
                    respond to
                    "TechNet
                    E-Mail
                    Forum.";
                    Please
                    respond to
                    Joseph Keary






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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