Many ways to cause an obstacle, we had an annoying event years ago with black nickel, any treatment was useless, scratching, etching, swearing, so we tried to find out what it was. The answer at that time was not expected: the underlying copper had diffused just right through the nickel barrier and started oxidizing and intermetalizing. We found beneath a nickel barrier that was not a barrier, it was cracky like clay in the sun, and even did not cover the foot of the copper conductors. After saying hello friends to our supplier, the normal quality returned. I agree, it's sometimes frustrating to see green gold, black nickel, yellow copper, blue tin and so on. Lucky enough there are tons of experienced guys in the game.
Ingemar
-----Original Message-----
From: Ryan Grant [mailto:[log in to unmask]]
Sent: den 1 juni 2000 16:30
To: [log in to unmask]
Subject: Re: [TN] Black nickel barrier problem w/immersion Ni/Ag
George,
What are the other reasons ENIG has solderability issues?
I have an ENIG board that will initially wet (with an iron), then
dewets after a pass through the reflow oven. The dewetting only occurs on a
handful of BGA pads. The dewetted pads do appear black. Not that it is
"black pad", rather, the surface topology is rough and doesn't reflect
light.
I am very familiar with the papers Jarmo mentioned, but I am not a
board fab guy, so I don't know all the issues. Any ideas?
Thanks
Ryan Grant
Advanced Technology Engineer
MCMS
(208) 898-1145
[log in to unmask]
> -----Original Message-----
> From: George Milad [SMTP:[log in to unmask]]
> Sent: Wednesday, May 31, 2000 1:24 PM
> To: [log in to unmask]
> Subject: Re: [TN] Black nickel barrier problem w/immersion Ni/Ag
>
> The Black Nickel issue is a very low level defect (ppm), with big
> ramifications when it is encountered. In absence of a good understanding
> of
> how this occurs, it has become a "Catch all" for any solderability issues
> associated with ENIG. Many defects that may have other explanations go un
> investigated once they are labeled "Black Nickel".
>
> The immersion gold step is a controlled corrosion reaction. Occasionally
> this could go out of control and may create a "Black Ni" pad, under the
> immergent Au. This gold will have a tendency to peel if tape tested,
> depending on the degree of severity of the corrosion. The underlying Ni
> is
> compromised and may not wet.
>
> Some of the ways that this can occur are:
> Uneven Ni deposit:
> An uneven Cu surface (pitted, corroded etc)
> Solder mask residues on the incoming Cu surface
> Cu/tin intermetallics as above
> Uneven catalyzation. Catalyst bath operated out of control.
> Ni bath chemistry out of the specified operating range
>
> Gold bath too aggressive:
> Excessive dwell time in the Au bath
> High Temperature (outside the control limits)
> Au bath chemistry out of specified range.
>
> Most board shops today are fully aware of this condition and are making
> sure
> that their ENIG processes are running within the specified vendor
> recommendations.
> George Milad
> Shipley
>
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