IPC-2223, section 5.2.3.3
How did you deduce the Au *and* Ni were cracking first? Likely the
cracking is initiated in the Ni layer, as electroless nickel is not as
ductile as copper. Also (per earlier email form esteemed TechNetter)
check to see that grain of copper is in same direction as bend.
Otherwise, ask flex vendor for most ductile copper available.
Is this flex using adhesive-based or adhesiveless copper/baselayer? The
adhesiveless allows for tighter bend radii.
FYI, hopefully the "bend" is not being done close to the point where the
coverlayer ends, as this would put undue strain upon flex area just
beyond end of flex.
Curious as to how thick the base layer is, and if there is an adhesive
layer and what thickness it would be.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of [log in to unmask]
Sent: Friday, May 09, 2008 10:22 AM
To: [log in to unmask]
Subject: Re: [TN] Fw: [TN] Brittle FPC Tracks
Still looking for answers to this problem...
Can anyone tell me if there is an IPC standard which covers requirements
for FPCs i.e. how much they should be able to bend before cracking.
It appears that it is the Au and Ni which are cracking first. The
plating is ENIG.
Also I own a copy of Soldering in Electronics (Wassink) - can anyone
recommend a similar comprehensive text for PCB (PWB) manufacturing
including details on flexies...
Thanks,Neil>----Original Message----> From: [log in to unmask]>
Date: May 2, 2008 1:05:53 PM> To: [log in to unmask],
[log in to unmask]> Subj: Re: [TN] Fw: [TN] Brittle FPC Tracks> >
>OK - I don't know much about this FPC - it is 3-4 suppliers back in
the chain, still working my way back...
>I do now know that there is actually a Ni Layer (3microns thick)
with 3microns of Au on top. The copper is 34microns and the crack on
one part (as I have received it) goes through the Ni and about 25% of
the way through the Cu.
>I will try to get a photo to Steve.
>Neil>>>----Original Message---->> From:
[log in to unmask]>> Date: May 2, 2008 11:41:12 AM>> To:
[log in to unmask], [log in to unmask]>> Subj: Re: [TN] Fw: [TN]
Brittle FPC Tracks>> >> Hi Neil,>> Indeed, Au over Ni
will result in diffusion. However, while AuSn IMC is indeed brittle and
weak and weakens the solder structure, I do not know whether Cu-Au is
particularly brittle. it would also be very thin. Ni barrier would stop
the Au diffusion, but brings with it a whole new set of problems, among
which are a thicker possibly equally brittle Ni layer, Black Pad with
too muc P, Ni 'hyper-galvanic' corrosion with too little P, etc.>>
My question about your problem is-have you determined whether the Cu is
not brittle itself. If you use un-annealed rolled Cu, it will be brittle
in the cross-rolling direction.>> >> >> >>
Werner>> >>>>>>**************>>Wondering
what's for Dinner Tonight? Get new twists on family favorites at AOL
Food.>>
(http://food.aol.com/dinner-tonight?NCID=aolfod00030000000001) >
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