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January 2001

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From:
"Ingemar Hernefjord (EMW)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 24 Jan 2001 12:55:55 +0100
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Thanks Hans Shin and ya'll hou'wanna help (to use Steve's language),
I'm concentrating on reducing my list on 25 matters that can cause BGA lift trouble.

Did this: provoked a soldered 560BGA by installing a separating force in one end and gradually increase the force until getting a rupture. At first nothing happened but suddenly there was 'frrritch' and whole row began to get apart. But several hundreds left with GRADUAL impact, last in row didn't get any force at all. This way I had the possibility to study exactly how the rupture occurs. Now a surprise. The classical elongated rupture structure occurred only on the periphery of the board's solder pad, and on some, just small strikes here and there. The rest (90%) of the solder pads were just shiny Nickel. That RING of genuin solder is so strong that you could hang a 200 pound Texas  guy (visit at Mac Donald included)  in the 560BGA package without rupture! I can now omit bad joints caused by a bleeding solder mask, instead the best adhesion was all around the solder mask interface. I will be another person after this, sigh. Double sigh.

My intricate question: when you guys have real strong BGA solder joints, do you know how they look like on inside? Do you have 100% adhesion all over the solder pad? Do you at all have a requirement in your spec on this? Don't you just rely on tempchange, ageing and other verification. Perhaps you don't even need verifying.

Thanks again for all support, will let you know the end...if there is such a one.

Ingemar

-----Original Message-----
From: Hans Shin [mailto:[log in to unmask]]
Sent: den 23 januari 2001 17:20
To: [log in to unmask]
Subject: Re: [TN] Increased Phosphorus in Electroless Ni


I thought Mark was referring to Mike Walsh's article in Circuitree (January 2001).  In either case, Mike Walsh is not "discounting the previous work or theories," but "offer here a new and novel description of the black pad problem and its possible elimination."  And, they strongly believe that their "work shows that the problem of black pad and many of the other plagues of ENIG are traceable to the nickel bath."

Ingemar, I think any of those instruments would be fine, although I don't expect that layer to be organic, so you may want to exclude FTIR.  XPS will probably help, because it also gives you the binding energies of the elements detected.

Hans Shin
Pacific Testing Laboratories, Inc.
http://www.pacifictesting.com/

-----Original Message-----
From:   Ingemar Hernefjord (EMW) [SMTP:[log in to unmask]]
Sent:   Tuesday, January 23, 2001 3:51 AM
To:     [log in to unmask]
Subject:        Re: [TN] Increased Phosphorus in Electroless Ni

Guys, I begin to feel schizo,
one says this and another that, and me being slow thinker, not easy. Mark you said this: "The cause of the black pad phenomenon has been found and fixed,
 and it has nothing to do with phosphorous!" And you refer to CircuiTree's article by George M. But he pointed that phosphorous was one of mayor concerns, didn't he?: " Major factor Effects on black pad formation are The Structure of Nickel deposit, The Phosphorous Content of the Nickel deposit, The Uniformity of the Nickel and Gold Coatings and finally The Corrosion Rate of the Immersion Gold."

Another one, not Mark, but all of you: Lucent's people have led us back to the central issue, the dark, thin, brittle and elusive shadow, I mean the extremly thin layer between ordinary Ni3Sn4 and the Nickel on the lands. I have asked a lot of people about their experience of compund findings, but no respons yet. What tool do you recommend for examination the layer? EDS? FTIR? XPS? SIMS? or what? Cross sectioning with polishing seems to smear and mislead. Suppose that the BGA falls of,
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