Have to agree with 2221, Glenn ,
2.5 um would be just about a practical minimum (we have internal 5.0 min,
1year store) .
Your algebra is fine .
If you'd like to halve that ; you'd have to go to some of the denser/even
plating technologies , 'm just starting to unravel (validate) the potentials
.
check http://www.pulseplating.com ,
Moti should be able to help you
paul
ps
if you'd keep it JIT (or close),
with short storage the lowered Ni & Au deposits would become less critical .
Than, in conjunction with denser plate, 1umNi & .3umAu should hold you
safely,
with up to 1/2 year in good store prior assembly, in my estimate .
Once assembled , you should have no worries .
Would be interested in Andy's opinion on new plating rigs myself,
will forward you one of his copper dendrites notes.
-----Original Message-----
From: Glenn Pelkey [mailto:[log in to unmask]]
Sent: Friday, 26 May 2000 10:35
To: [log in to unmask]
Subject: [TN] Nickel Thickness on Flex
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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