I have another flex on the same product with a Au finish - I can bend this
in half with a pair of pliers and no crack!
I assume this is a different type of Au finish...? It is alos not soldered
at all as it is bonded to an LCD - the one that is cracking has LEDs
soldered to it...
Sorry I have so little information - like I said previously, the supplier is
a sub-sub-sub supplier to a wee bit difficult getting info at the moment.
At least this problem got me back into the world of Technet... Every cloud
has a Ag lining!
-----Original Message-----
From: John Burke [mailto:[log in to unmask]]
Sent: 09 May 2008 15:44
To: [log in to unmask]; [log in to unmask]
Subject: RE: [TN] Fw: [TN] Brittle FPC Tracks
You should never (ever) finish a flex in ENIG that is needed to bend in the
plated area it will crack - there is no spec for this combination of board
and finish= if flexed it will crack - period.
I presume you have full body enig.
Change the specification to a different finish
John Burke
(408) 515 4992
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of [log in to unmask]
Sent: Friday, May 09, 2008 7:22 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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