Vishy, we manufacture a fixture that can hold the flex circuit flat through
out the entire SMT process. We utilize a below surface tension device that
aligns itself with tooling holes in the circuit and fixed pins on one side.
The below surface tension device will then slide forward and make contact
with other tooling holes in the circuit. It is then released under tension.
Holding it stable through the screen, P&P and reflow. This device can be
used for single sided flex, mixed tech. flex and circuits that contain
connectors. If you would like more information, please contact me off line.
Eric Miller
S.P.P.I.
800-725-5388

-----Original Message-----
From:   Narayana Vishy-CVN002 [SMTP:[log in to unmask]]
Sent:   Thursday, March 11, 1999 11:15 PM
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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