Hi Jeffrey-

After reviewing the design guidelines from NCAB Group (it appears to be a
franchise-structured international agglomeration), and checking out their
website, this is not an example of classical rigid/flex. Using a controlled
depth router, they have experimented with several varieties of FR4 and have
found one that can withstand a pretty tight bend radius if it is thinned
enough. The router bit they finish with leaves a reverse inside radius in
the bottom of the cut. This avoids a hard point when the assembly is bent.
They are suggesting it as an inexpensive way to do a "bend once for
installation" type of rigid/flex. The bend radii appear amazingly tight:
5mm for a single conductor layer which has been routed down to an overall
thickness of 0.25mm. Naturally the conductors are on the outside of the
bend, which is preferably an outer layer of the circuit board.

If you are counting on getting within a factor of two of their suggested
minimum bend radii, I would insist on getting reliability data.

Wayne Thayer





On Wed, May 27, 2020 at 6:57 AM McGlaughlin, Jeffrey A <
[log in to unmask]> wrote:

> NCAB Group list flex outer layers as a preferred stack-up. (See attached
> .pdf, I know this will be deleted on the tech net copy.) This was new to me
> when I was reviewing their guides for technology fit for a new design.
>
>
> Thank you,
> Jeffrey
>
> Jeffrey McGlaughlin, C.I.D.
> Engineering Designer
> ST RE SMD&P(SF)
> Office: 614.424.7582| Fax: 614.458.7582
> [log in to unmask]
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> -----Original Message-----
> From: TechNet <[log in to unmask]> On Behalf Of [log in to unmask]
> Sent: Wednesday, May 27, 2020 9:17 AM
> To: [log in to unmask]
> Subject: [TN] IPC-2223D, Rigid Flex Technology
>
> Message received from outside the Battelle network. Carefully examine it
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> Fellow TechNetters:
>
>     Does the flex applique in a Rigid Flex Technology CONSTRUCTION always
> has the be sandwich between rigid laminate material?
> Can the flex portion be on the TOP or BOTTOM side of a Rigid Flex PWB?
>
> Victor,
>