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

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  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?
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