Hi Nigel,
1) ZIF¹s require the flex to be usually .008 or .012 plus tolerance in
thickness so in most cases a .010 thick stiffener unless it is a single
layer flex is too thick
2) ZIF¹s come in a large variety of clamping mechanisms so you need to
review this carefully- some are more friendly than others
3) In most cases the issue is handling - accidentally bending in the ZIF
area or over the stiffener during assembly is usually the issue- the
clamping of the ZIF onto the ENIG is not an issue

Regards Steve Kelly

-- 






On 2016-04-06, 8:42 AM, "TechNet on behalf of Stadem, Richard D."
<[log in to unmask] on behalf of [log in to unmask]> wrote:

>There you go! Thanks, Guy!
>Odin
>
>From: Guy Ramsey [mailto:[log in to unmask]]
>Sent: Wednesday, April 06, 2016 7:08 AM
>To: TechNet E-Mail Forum; Stadem, Richard D.
>Subject: Re: [TN] ENIG on flexi PCBs
>
>IPC 6013 is the Qualification and. Performance Specification.
>IPC2223 is the  Sectional Design Standard.
>
>On 4/6/2016 7:51 AM, Stadem, Richard D. wrote:
>
>Hi, Nigel
>
>Typically, connectors on flex that see any stress at all from
>connect/reconnect forces should have a stiffener applied on the opposite
>side of the flex. The larger the connector, the more important this
>becomes.
>
>It does not take much; even a .010" thick FR-4 stiffener can reduce the
>stresses on the solder joints significantly.
>
>I have learned that the thinner the stiffener that you can get away with,
>the better. If the stiffener has a good modulus of elasticity, it reduces
>the chances of trading one problem for another, that of inner-layer trace
>fracture at the point where the flex comes away from the stiffener.
>
>There is an IPC standard that covers all this in great detail, but I
>cannot remember the number. I know it is similar to IPC 6012, but for
>flex circuit and design. I know there is information there regarding
>connectors on flex. Check it out.
>
>dean
>
>-----Original Message-----
>
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Nigel Burtt
>
>Sent: Wednesday, April 06, 2016 4:10 AM
>
>To: [log in to unmask]<mailto:[log in to unmask]>
>
>Subject: [TN] ENIG on flexi PCBs
>
>
>
>IPC-4552 requires 3-6um nickel, but does not appear to distinguish
>between rigid FR4 PCBs and flexible PCBs.
>
>
>
>A flexible interconnect PCB using ENIG with ZIF end connectors has been
>shown to be prone to track cracking near the ZIF ends. The supplier has
>suggested a lower thickness of nickel 1-3um rather than the IPC spec to
>would be beneficial to resolve this and tests on samples seem to bear
>this out.
>
>
>
>Does anyone have any experience of such a suggested modification of ENIG
>spec and that thinner nickel improves the resistance to stress-cracking
>for flexi tracks?
>
>
>
>In this specific application as there are no component soldering
>requirements so the thinner nickel under the gold does not lead to
>solderability concerns, but what would be the likely consequence on other
>flexi/flex-rigid designs with flexi ZIF connector ends and SMT components
>if a 1-3um thickness was imposed more generally? Increased likelihood of
>black-pad type defects?
>
>
>
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