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May 2000

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Subject:
From:
Glenn Pelkey <[log in to unmask]>
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Date:
Thu, 25 May 2000 17:35:20 PDT
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Hi all,

        What would you recommend as a minimum thickness for Nickel plating on
a flex circuit?

        We have specified 150 uin followed by 30 uin gold on top and sides of
conductors to prevent copper electrochemical migration.  This has worked.
However, we may have to reduce this requirement to meet a supplier's
capability.  I looked up the specification information in IPC-6013 and got min
40 uin (Class 1), 50 uin (Class 2 and 3).  Same thing in IPC-2221 except
there's a statement in para 4.4.5 that says "...It is an effective barrier
layer (when its thickness exceeds 2.5 um) which prevents the diffusion of
copper into gold."
        I calculate the 2.5 um to be approx. 100 uin, which is what many have
said in searching the archives.  My thoughts are along the line if copper can
migrate into the gold, than it can reach the surface and have the potential of
creating the dendritic short.
        So, now I'm stuck.  Would you say 100 uin Ni is O.K.?  What about 70,
or 50?

Thanks for your help.

Glenn

P.S.  I don't have IPC-2223.  Would somebody mind checking the numbers there
for me?

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