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Subject:
From:
Steven Creswick <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Steven Creswick <[log in to unmask]>
Date:
Mon, 5 Sep 2011 08:06:49 -0400
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Cantagallo,

Hope this helps.

A nominal thickness of 4µm provides enough thickness to prevent leaching, in
most cases.  The ±2µm provides the plating operation with a readily
achievable process window, thereby keeping your/their costs down.  Even at 2
µm one should have good leach resistance and durability.

Three possible issues come to mind.

1 - Even though the rate of dissolution of Ni in the solder is quite slow
[function of temp and alloy], at 0.5µm of Ni you may run into Ni leaching
issues.  Some thick film Cu pastes are fritted, meaning that they bind to
the Al2O3 substrate by mechanical [glass] means.  Some of these pastes
can/do have an excess of frit [glass] at the surface, which makes them
difficult to solder to.  Plating over this surface provides a uniform
surface to solder to.  If your plated surface is in poor condition and you
expose the underlying Cu, the solderability of the Cu may not be all that
good.  There are a lot of "it depends" - on the exact Cu used, Cu firing
conditions, plating control, solder alloy, and solder reflow conditions.

2 - At 0.5µm, the Ni layer may not totally/uniformly cover the underlying
Cu.  If the substrate is subjected to elevated temperatures, the Ni may
diffuse through the thin Ni layer and into the Au layer.  If the substrate
is then allowed to 'sit around' in this condition for prolonged periods of
time, the exposed Cu may oxidize and render the surface only partially
solderable.

3 - Even though you did not ask, if the Ni layer is thin [by accident?], it
is possible that the Au layer is also very thin [plating process not in
control] - making item 2 even worse. This can also result in oxidized Ni,
which is also hard to solder to.


If you are thinking about reduced Ni thickness as a cost savings - I would
not do it.  The Ni plating is cheap.  Likely cost you more as a 'special
process'.

If you are asking about reduced Ni thickness because a shipment came in that
way - I would send it back and request they ship what you asked for.

Best wishes,

Steve Creswick
Sr Associate - Balanced Enterprise Solutions
http://www.linkedin.com/in/stevencreswick
                616 834 1883





-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of
[log in to unmask]
Sent: Monday, September 05, 2011 5:52 AM
To: [log in to unmask]
Subject: [TN] Fw: Electroless Ni plating thickness

Hello Technetters.

We use a ceramic substrate covered with Cu layer. This Cu layer is plated 
with ENIG process. 
We solder SMD's on it with SnPb process (vapor phase and iron).
The ASTM specifications give a thickness of Ni 4 ± 2 µm.
Where comes from this value ?
What could be an issue with thinner Ni layer like 0.5 µm ?
Thanks to answer.

Best regards,

CANTAGALLO Luigi

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