One of the biggest problem in the assembly of boards with flex
attachments is the inline cleaner. Its chains tears off so many board
attachments it is not funny. We used to place those boards in cages. Of
course there are more than one way to send those boards through the
cleaner. Another issues is operator training. Operators need to be much
more careful in handling these parts.
	Regards,
	Ramon
 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Thursday, February 22, 2007 8:54 AM
To: [log in to unmask]
Subject: Re: [TN] Disconnections in transition zone in rigid-flex boards

Anna-

That's a very high stress point, and there are a whole bunch of factors
which come into account. 

Obviously, you can place some stiff RTV at that point to make the bend
radius larger.  Hot melt glue might work for some apps.  This can be a
sloppy process and adds time.

Alternatively, you can introduce a separate forming process, which bends
the flex section as a very controlled process.  Following this the
assembly would be placed in a fixture to prevent inadvertent extra
bending during assembly.

The circuit board production process can also probably be re-engineered
to improve the crack resistance of the conductors.  For example, is the
metal on the flex Rolled Annealed?  Is the roll direction controlled to
be in line with the conductors?  How thick is the metal?  Can the
dielectric within the flex layer be increased in thickness to help
control the bend radius?  Can the metal thickness on the flex be reduced
to make it less likely to crack?  Is the metal on the flex
electro-plated during the manufacturing process (this vastly reduces
crack resistance)?

I have seen most products move from rigid/flex constructions to separate
rigid and flex boards.  This is made possible because of cheap,
dependable flex connectors which mount on the rigid boards.  With
independent flex construction its a lot easier to control stiffness as
well as problems with the assembly process.

Wayne Thayer

>>> [log in to unmask] 2/22/2007 6:55:25 am >>>

Hello Techneters,

We have some boards disconnected in transition zone: between rigid and
flex segments. This happens during an assembly process. What is
recommended to add to manufacture process in order to strengthen the
area. 

Thank you, 

Anna Seredovaya

Kodak IL Ltd.

 

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