Hi there,
The problem you describe is a very common one and taxes the minds of us
tooling designers. The short answer is that there are a number of solutions
depending upon the nature of the board. The main variable which has
greatest bearing on the solution is the thickness of the flex, and whether
or not tooling pins and/or a pin with a tensioning device can be used (most
tooling companys worth their salt, have some sort of device, simple or
complicated. We have a simple but very effective tensioning device). If the
flex is too thin for this type of device, or is a very awkward shape which
will not flatten when tension is applied, then Kapton tape can be used to
good effect. Alignment of the flex can then be a problem. We have a
solution for that too. I would be happy to discuss this with you, as it
takes too long to explain it in writing!

Regards,
Chris Chapman
Managing Director
Datum Dynamics USA
(401) 683 5300
[log in to unmask]
www.datumdynamics.com


-----Original Message-----
From:   Narayana Vishy-CVN002 [SMTP:[log in to unmask]]
Sent:   Friday, March 12, 1999 2:15 AM
To:     [log in to unmask]
Subject:        [TN] Flex circuit flatness  - Is  the solution out there ?

Hi Technet pals :

Flexible circuits have this natural tendency to be flexible . They tend to
springup , bend ,kink & warp due to natural flexibility & handling .

This behaviour is a major headache for the manufacturing engineers during
the assembly process of these circuits - Defects & more defects !
The non-flat nature of these circuits is the root cause of numerous defects
like misaligned , unflush and unsoldered  components . Processes such as
solder paste printing,component placement & reflow oven are not very
resistant to such flexible , warped & bent surfaces . Keeping these ciruits
perfectly flat (like a PCB  ) during these processes is key to eliminating
many of the defects mentioned.

Not to mention that much of conventional automation strategies are not
easily applicable on flex ciruit assembly manufacturing - For example,
automated vision isnpection is an entirely different ball game when it
comes
to flexible circuits.

Now the questions :

1) Is there anybody out there who knows techniques of holding the flexible
circuits down real flat ?
2) Are there technologies/vendors in the market who have adhesives
(sheets/sprays/liquids) which can :
        a.      hold down flexible circuit panels flat on a solid pallet
(carrier)
        b.      withstand the reflow oven temperature (max 290 deg
centigrade)
        c.      be peelable/detachable from the flexible circuit panel w/o
causing cosmetic defects on the flex circuit after the reflow process .

Any clues ?


Thanks in advance,
Vishy.

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