Hi Ervin,
I'm sure you will get some good ideas from the real experts on the forum but
I thought I would give you my opinion. I have had the pleasure of
performing failure analysis on a number of assemblies in the last 2 years
that failed because of "Black Pad" and one thing that I have seen on all of
them (and in all of the published reports that I have seen) is the presence
of the hyper-corrosive gold plating cracks in the nickel layer. On several
of these failures we were able to obtain bare boards from the same date code
and sure enough these exhibited the same cracks. The problem is that these
cracks are very small and the microsections have to be prepared really
well, and these microsections need to be evaluated using a SEM. Some of
the more severe cracks can be seen using a good metallurgical microscope,
but to get a good look at them a SEM is needed.
So my opinion is that your vendor should supply a number of microsections
through random BGA pads or the smallest pitch SMT pads on your board, and
evaluate these microsections at sufficient magnification (2000-5000x) to
determine if these cracks are present.
On a side note, we are working on a possible non-destructive screening
method for the "Black Pad" defect here where I work using our SEM, which is
a low-vacuum type with a large chamber (we can fit a board up to 12-14
inches square) in the chamber. It's still in the very early stages but I
would be glad to talk with you off line if you are interested.
Good luck!
Wade McFaddin
Nextek Inc.
email: [log in to unmask]
256-772-1995 ext. 1064
> -----Original Message-----
> From: Ervin Weisz [SMTP:[log in to unmask]]
> Sent: Thursday, February 06, 2003 4:43 PM
> To: [log in to unmask]
> Subject: [TN] Evaluating ENIG finish
>
> Hello Everyone,
> I wish to present you with an issue that has troubled me for quite a
> while.
>
> We have been ordering more and more PCBs with ENIG finish and are
> generally pleased - it's flat, it solders nicely and the products seem to
> be O.K.
> However, on the other hand - we are very well aware of problems associated
> with ENIG, i.e - the "black pad" phenomena - solder joints cracking,
> components actually "popping off" and other "goodies".
>
> I am looking for good means to evaluate my ENIG finished boards, before I
> waste a considerate amount of money while trying to assemble them. Luckily
> for us, our manufacturer seems to understand our dilemma and is very
> willing to cooperate with us on performing any in-process or final test
> that we specify.
>
> So, here's the catch: what do I specify ?
>
> Assume that you could ask for anything (within reason, of course) - what
> tests would you ask your manufacturer to perform to assure you that he
> will give you high quality ENIG finish, good solderability, durable, long
> life solder joints, etc.?
>
> Thank you in advance,
>
> Yehuda E. Weisz
> +(972)-3-6342045
> +(972)-53-556897
>
>
>
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>
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