Hi Siegmund,

I think that the intermetallic you see isn't Sn/Ni but Sn/(Ni+Cu) an I'd bet that either the component leads are made of Cu (or have exposed Cu in the toe), or you Cu is coming from under the ENIG layer. 

Thickness of the layer you see could be. A bit higher then one would like to see, but it's difficult to "judge" without seeing it. Can you ask Steve to post the images or you can send them directly  to me. The trhickness of a "regular" intermetallic layer at an ENIG interface (considering that there is no source of Cu present) is up to 1 micron.

Regards,

Vladimir
Sent from my Blackberry Wireless 
Vladimir Igoshev, 519-888-7465 ext.5283


-----Original Message-----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Tue Feb 01 09:11:34 2005
Subject: [TN] ENIG - Failures

Hello all

We see the following issue on an ENIG coated PCB (soldered with SnPb):
After reflow solder joint is ok but cross section shows a quite irregular
IMC phase (about 3 mikrometer thick, not homogenous, looks more like stones
on a plane)
After the following wave process (component is on the top side) solder joint
is very fragile and in the cross section some fractures are seen.
Has somebody any picture how a perfect IMC on ENIG should look like? I would
expect a homogeous layer just a few nm thick.

Any ideas?

Siggi

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