sum of many's efforts, our labs, Xilinx's lab, IVF's in Sweden, Lea Ronal's own lab, Atotech's lab etc
cooperation, my friend!
Ingemar
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]
Sent: den 18 april 2005 15:19
To: [log in to unmask]
Subject: Re: [TN] ENIG - no more problems?
Inge,
we had a realy nasty experience with ENIG and I think it was this brittle fracture. Now, the boards have been sent to a lab and P was found, so we managed to convince our customer that the problem belonged to the PCB fab and not to our process. But the analysis did not go as far as yours, metastable NiSn3, etc. What I want to know is how did you managed to go this far with the analysis, was it your lab that did not stop until finding the culprit, or it was you knowing what to ask? See what I mean, I think you used your internal lab, am I right? But if you weren't, how to make sure one would get a valid and exhaustive answer?
Thanks,
Ioan
> -----Original Message-----
> From: TechNet [SMTP:[log in to unmask]] On Behalf Of Ingemar Hernefjord (KC/EMW)
> Sent: Monday, April 18, 2005 6:10 AM
> To: [log in to unmask]
> Subject: Re: [TN] ENIG - no more problems?
>
> Missed who started the question.
>
> Anyway, we had our bad expensive experience and also made our expensive countermeasure job some years ago. And we found, that there was no simple answer, nor simple remedy, but fully controllable with some efforts. A lot of TNs helped me and we summed it all in a 180 page report. No ENIG problems sinse then. What was really interesting at that time was, that we found one central reason for brittle solder joints, in terms of too much Phosphorous between the nickel grains. This phenomenon was limited to just the uppermost fraction of a micrometer of the nickel plating. The solder wetted good enough, and a normal intermetallic layer was formed, but, somewhere within the joint, an abnormal layer was created, a brittle and unreliable one, we called it the dark mystic line, because of the less than one micrometer thickness. The typical nickel with cracked intergraneolous and P-richness can be seen on a couple of pics, which I send to Stephanos Gregorius.
>
> We also learned that the normal Ni3Sn4 was not the bad guy, but a metastable NiSn3, that is normally growing only in pure Tin (edge connectors can be hit). That layer haunted us for a long time, escaped all observation and cheated us until Xilinx told us about it. That was the end of the 'mystic' thin line.
>
> I also add, that you can make several faults in the analysis, go lost in the chemical labyrinth and walk in circles. Thanks to a lot at TN and whole Ericsson specialist ensemble, we cracked the nut(s). The remedy list containted nearly 30 paragraphs!
>
> I think Jack Crawford got a shorted version of my report for the IPC archive. It's not a techy salvation report, but filled with arguments and opinions and facts and numerous references and names on knowing people in the ENIG game.
>
> Nowadays, no ENIG problems (crossed fingers)
>
> Good Luck, whoever the questioner was
>
> Ingemar Hernefjord
> Ericsson Microwave Systems
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]
> Sent: den 14 april 2005 17:54
> To: [log in to unmask]
> Subject: [TN] ENIG - no more problems?
>
>
> Just listened to a Lead Free presentation by one of our assembly materials
> suppliers. They tested different pastes on different board finishes using a
> variety of different patterns, spacings, aperture sizes, etc,...
> By far and away, ENIG was the best finish for performance, for wetting,
> defects, voiding, ...
> The guy making the presentation said that he felt a lot of the initial
> concerns re ENIG - black pad being the biggest - have been resolved, and
> that they are no longer a concern, that they have determined what the cause
> of it is and eliminated it. Anyone want to comment on that? I'm not sure
> if he is correct, or just out of the loop.
> It was interesting as well: ImmAg got a very bad rating from them in
> performance, even though many on this forum really praise that finish. It
> exhibited dewetting (they printed solderpaste pads on an area with no>
> soldermask, and the solder did not stay and spread where it was printed, it
> crept together with other pads into a big blob, like you might see a water
> drop do) and the amount of voiding was impressive!!
> About 4 years ago I joined this forum, and one of the reasons was because I
> was looking for info on ENIG. We had done a prototype run of a couple of
> boards and they failed miserably. They were never analyzed in depth, so it
> wasn't figured out what exactly caused the failure. It was the excuse we
> needed to not choose this finish and some of the extra costs associated with
> it.
> However, with the Pbfree push now, I don't know if we should re-examine
> whether to use the finish. For products where we needed a flat finish, we
> have gone to ImmSn, but we still use HASL wherever possible.
>
> Genny
>
> "Genius may have its limitations, but stupidity is not thus handicapped"
> Elbert Hubbard
>
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