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May 2008

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Fri, 9 May 2008 14:21:41 +0000
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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&gt;----Original Message----&gt; From: [log in to unmask]&gt; Date: May 2, 2008 1:05:53 PM&gt; To: [log in to unmask], [log in to unmask]&gt; Subj: Re: [TN] Fw: [TN] Brittle FPC Tracks&gt; &gt; 
&gt;OK - I don't know much about this FPC - it is 3-4 suppliers back in the chain, still working my way back...
&gt;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.
&gt;I will try to get a photo to Steve.
&gt;Neil&gt;&gt;&gt;----Original Message----&gt;&gt; From: [log in to unmask]&gt;&gt; Date: May 2, 2008 11:41:12 AM&gt;&gt; To: [log in to unmask], [log in to unmask]&gt;&gt; Subj: Re: [TN] Fw: [TN] Brittle FPC Tracks&gt;&gt; &gt;&gt; Hi Neil,&gt;&gt; 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.&gt;&gt; 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.&gt;&gt; &gt;&gt; &gt;&gt; &gt;&gt; Werner&gt;&gt; &gt;&gt;&gt;&gt;&gt;&gt;**************&gt;&gt;Wondering what's for Dinner Tonight? Get new twists on family favorites at AOL Food.&gt;&gt; (http://food.aol.com/dinner-tonight?NCID=aolfod00030000000001) &gt;

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