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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