There have been some valid points made as to the possible cause; Surface finish plating thickness and type of nickel, Type of copper used (Grain direction of RA copper should also be considered) and the amount of bending the flex sees. All of these items could be contributors.

There are also other items that could contribute; shape of copper trace as it exits the coverlay, copper thickness (and therefore tensile strength) the stiffener edge (generally a Polyimide stiffener is need to build flex up to ZIF connector spec thickness) on back side of flex in relation to coverlay opening edge, etc.

Based on the many possible contributors, the trick is to find out which ones apply to this application.

I would be curious to see a picture of the ZIF area that is cracked. If the picture includes the end of the flex, and the beginning portion of the coverlay and stiffener, One can many times determine the cause based on what the picture shows.



Mike Lehmicke
Project Engineer
Printed Circuit Products
Molex Incorporated
22 Empire Drive
St. Paul, MN 55103
651-846-7728
[log in to unmask]




Warning - Information included in this email and /or in any attachments herein may be subject to the EAR (15 CFR 730-774) and/or ITAR (22 CFR 120-130) Regulations.

The recipient acknowledges their responsibility for compliance with all Export Administration Regulations & ITAR regulations regarding the handling and/or export of any Molex products and technical information; including the disclosure to any Foreign Nationals.



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Wednesday, April 06, 2016 9:25 AM
To: [log in to unmask]
Subject: Re: [TN] ENIG on flexi PCBs

-- Sent by an external Sender --

Based on the emails below, it sounds like the ZIF connector is incompatible with any flex application where it will be mated more than once.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David Hillman
Sent: Wednesday, April 06, 2016 9:22 AM
To: [log in to unmask]
Subject: Re: [TN] ENIG on flexi PCBs

Hi team - a data point for the conversation: the EN plating has 1%-3% elongation so its not very robust to bending stresses.

Dave

On Wed, Apr 6, 2016 at 10:19 AM, Vladimir <[log in to unmask]>
wrote:

> According to the best flex‎ guru I know any bending with ENIG is excessive.
>
> Regards,
>
> Vladimir
>
> SENTEC
>
> Sent from my BlackBerry 10 smartphone on the Rogers network.
>   Original Message
> From: Stadem, Richard D.
> Sent: Wednesday, April 6, 2016 10:13
> To: TechNet E-Mail Forum; Vladimir
> Subject: RE: [TN] ENIG on flexi PCBs
>
> What is the limit, and how do you define that?
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Vladimir
> Sent: Wednesday, April 06, 2016 9:10 AM
> To: [log in to unmask]
> Subject: Re: [TN] ENIG on flexi PCBs
>
> I don't think E-Ni thickness has anything to do with the issue. Most
> probably the flex was bend over the limit. That's what we normally see
> from our customers.
>
> Regards,
>
> Vladimir
>
> ‎SENTEC
>
> Sent from my BlackBerry 10 smartphone on the Rogers network.
>   Original Message
> From: Mumtaz Bora
> Sent: Wednesday, April 6, 2016 10:05
> To: [log in to unmask]
> Reply To: TechNet E-Mail Forum
> Subject: Re: [TN] ENIG on flexi PCBs
>
> Hello Nigel, Cracking issues in flex can also occur based on the type
> of copper used for the traces. Is your supplier using rolled annealed
> copper or ED( electro deposited ) copper. Rolled annealed copper is
> preferred for flex circuits.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Nigel Burtt
> Sent: Wednesday, April 06, 2016 2:10 AM
> To: [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?
> CONFIDENTIALITY NOTE: The information transmitted, including
> attachments, is intended only for the person(s) or entity to which it
> is addressed and may contain confidential and/or privileged material.
> Any review, retransmission, dissemination or other use of, or taking
> of any action in reliance upon this information by persons or entities
> other than the intended recipient is prohibited. If you received this
> in error, please contact the sender and destroy any copies of this information.
>
> ______________________________________________________________________
> This email has been scanned by the Symantec Email Security.cloud service.
> For more information please contact helpdesk at x2960 or
> [log in to unmask]
> ______________________________________________________________________
>
> ______________________________________________________________________
> This email has been scanned by the Symantec Email Security.cloud service.
> For more information please contact helpdesk at x2960 or
> [log in to unmask]
> ______________________________________________________________________
>
> ______________________________________________________________________
> This email has been scanned by the Symantec Email Security.cloud service.
> For more information please contact helpdesk at x2960 or
> [log in to unmask]
> ______________________________________________________________________
>

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________

________________________________



CONFIDENTIALITY NOTICE: This message (including any attachments) may contain Molex confidential information, protected by law. If this message is confidential, forwarding it to individuals, other than those with a need to know, without the permission of the sender, is prohibited.

This message is also intended for a specific individual. If you are not the intended recipient, you should delete this message and are hereby notified that any disclosure, copying, or distribution of this message or taking of any action based upon it, is strictly prohibited.

English | Chinese | Japanese
www.molex.com/confidentiality.html

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________