Thanks for all the discussion. We are still digging into it here. I will
keep you posted.
I am trying to figure out if there was a reliability study which varied
phosphorous content.
I have found some other references on the subject and have ordered the
articles but not yet read them:
> Some References:
>
> 1. Electroless Ni/Au Plating Capability Study of BGA Packages,
> Franz Cordes and Ron Huemoeller, Amkor Technology
> Future Circuits International, Issue 4
>
> 2. A Root Cause Failure Mechanism for Solder Joint Integrity of
> Electronic Ni/Au Surface Finishes
> Nicholas Biunno, HADCO Corp
> Future Circuits International, Issue 5
>
> 3. Gold Plating Factors that Affect Solderbility of Electroless
> Ni/Au Surfaces
> Don Gudeczauskas, Shigeo Hashimoto and Masayuki Kiso
> PC Fab, July 1999
>
> 4. The Effect of Electroless Ni/Au Plating Parameters on PBGA Solder
> Joint Attachment Reliability
> Z. Mei, P. Johnson, A. Eslambolchi, M. Kaufmann, Hewlett Packard
>
> Presentation
>
I have also found some recent Au-Sn intermetallic formation and reliability
information at:
http://www.binghamton.edu/physics/cottsfm.html
"Effect of Au-Intermetallic Compounds on Mechanical Reliability of
Sn-Pb/Au-Ni-Cu Joints," Zribi, A., Chromik, R.R., Presthus, R.,Clum,J.,
Zavalig, L., Cotts, E.J., EEP, Advances in Electronic Packaging, vol. 26-2,
no.2, pp. 1573-1577 (1999)
Steph
Stephan Meschter [log in to unmask]
Lockheed Martin Control Systems Phone :(607)770-2332
600 Main Street, MD R52F FAX :(607)770-2056
Johnson City, NY 13790-1888 MARCALL: 8 * 255-2332
> ----------
> From: Ingemar Hernefjord
> (EMW)[SMTP:[log in to unmask]]
> Reply To: TechNet E-Mail Forum.;Ingemar Hernefjord (EMW)
> Sent: Friday, September 08, 2000 5:56 AM
> To: [log in to unmask]
> Subject: Re: [TN] Increased Phosphorus in Electroless Ni
>
> Hope I can send two cents back to you when you need help, Ryan, I have
> imported the Biunni file and we will start SEM/EDAX/FIB and TOFSIMS
> immediately, guess we may really have hyperactive IG as you suggest, of
> many root causes this issue seems radical and logical. Should it be so I
> will let you know, maybe a trophy to hang on the wall. So, wait and
> see....thx anyway
>
> Ingemar
>
> -----Original Message-----
> From: Ryan Grant [mailto:[log in to unmask]]
> Sent: den 7 september 2000 16:33
> To: 'TechNet E-Mail Forum.'; 'Ingemar Hernefjord (EMW)'
> Subject: RE: [TN] Increased Phosphorus in Electroless Ni
>
>
> Ingemar,
> Have you read Nicholas Biunno's paper titled "A Root Cause Failure
> Mechanism for Solder Joint Integrity of Electroless Nickel/Immersion Gold
> Surface Finishes"? It has been a major breakthrough in understanding your
> problem. Your problem is not unique. I have seen exactly the same, as
> have
> many others in the industry. ITRI has formed a task force working on this
> for quite some time. Nicholas' paper can be found from several sources
> including SMTA 1999 proceedings, Future Circuits volume 5, as well as some
> of the trade magazines. If you don't have any of these sources, let me
> know.
>
> Thanks
>
> Ryan Grant
> Advanced Technology Engineer
> MCMS
> (208) 898-1145
> [log in to unmask]
>
>
> > -----Original Message-----
> > From: Ingemar Hernefjord (EMW) [SMTP:[log in to unmask]]
> > Sent: Thursday, September 07, 2000 7:50 AM
> > To: [log in to unmask]
> > Subject: Re: [TN] Increased Phosphorus in Electroless Ni
> >
> > Thanks, Robert, more than two cents for me, rather two bucks.
> > Extreme case: we lift off a suspected 600I/O superBGA, and find that the
> > board pads look extremly gray and funny, SEM=no SnPb left, nearly
> nothing,
> > optical=looks like molding something with a wax form, you see the
> contours
> > of BGA solidified balls footprint, yes like a mirror of them. TOFSIMS on
> > pads tell about lots of Ni and P and also Cu. Foot on BGA balls all have
> 2
> > micron thick Ni3Sn4 (think it was that one)which is normal. So,
> something
> > happened between the "wanted" intermetallic and the bulk board pad
> nickel.
> > You didn't solve our problem, but added essential knowhow and
> inspiration
> > to go on searching, thx.
> >
> > Ingemar Hernefjord
> > Ericsson Microwave Systems
> >
> > -----Original Message-----
> > From: Furrow, Robert Gordon (Bob) [mailto:[log in to unmask]]
> > Sent: den 6 september 2000 22:22
> > To: 'TechNet E-Mail Forum.'; 'Ingemar Hernefjord (EMW)'
> > Subject: RE: [TN] Increased Phosphorus in Electroless Ni
> >
> >
> > I have heard rumblings on several occasions regarding high P% causing
> > brittle intermetalic failures at the nickel / solder interface. I guess
> I
> > just wanted to ask this as a sanity check to see if I am comprehending
> the
> > immersion process correctly. If the nickel layer is codeposited in an
> > electroless process with say 6% to 9% of phosphorus, wouldn't the nickel
> > layer nearest the solder joint show a higher concentration of P relative
> > to
> > nickel? I say this based on the immersion gold process, where one atom
> of
> > nickel goes into solution as one atom of gold replaces it. Wouldn't this
> > mean at the gold / nickel interface that there are just a many atoms of
> P
> > still present whereas a substantial amount of nickel has been replaced
> by
> > gold. When soldering is accomplished, the gold dissolves into the bulk
> > solder joint and the reduced amount of nickel is left around the
> original
> > number of P atoms. If analyzed, the thin interfacial layer of nickel
> (less
> > than 10 microinches) would have a high P content relative to the
> > underlying
> > nickel. Isn't this a natural consequence of the immersion gold process
> and
> > to be expected? If so, isn't it more correct to say all soldered
> > connections
> > near the nickel / solder interface are expected to have an elevated P
> > content relative to the bulk nickel rather than a thin high P% layer
> > caused
> > a "black pad" brittle fracture,.
> >
> > Thanks,
> > Robert Furrow
> > SMT Process Engineer
> > Lucent Technologies
> > 978-960-3224 [log in to unmask]
> >
> > > -----Original Message-----
> > > From: Ingemar Hernefjord (EMW)
> [SMTP:[log in to unmask]]
> > > Sent: Tuesday, September 05, 2000 11:28 AM
> > > To: [log in to unmask]
> > > Subject: Re: [TN] Increased Phosphorus in Electroless Ni
> > >
> > > Have little time to read TN nowadays, sorry for that, have to erase
> most
> > > before reading, but this one gripped me, because our process engineers
> > > have just got nervous attacks caused by BGA-soldering problems (double
> > > sided with 100-600 I/O PBGAs)on FR4 boards, electrical and mechanical
> > > disorder that is under investigation just now. Small project,
> > fortunately,
> > > not the large numbers like in our telecom fabs, anyway, one issue that
> > > came up was the high P% of the electroless Ni, from 7 up to 12%.
> During
> > > the up/down ramp for normal soldering intermetallics will be created,
> > > which is normal, but you may also get a strange interface layer
> between
> > > this tin-nickel and the nickel barrier itself, superthin, strange,
> > > unpredictable layer, hardly visible even in high magnification, can
> > cause
> > > severe disrupture from CTE-mismatch or other impact. Some of our
> > > metalurgist say this is connected with too high a P% in Nickel. When
> > other
> > > baths were used, with much lower P, the problems disappeared. T!
> > > hat is why I'm interested in what other experiences may come up.
> > >
> > > Ingemar Hernefjord
> > > Ericsson Microwave Systems
> > >
> > > -----Original Message-----
> > > From: Meschter, Stephan J [mailto:[log in to unmask]]
> > > Sent: den 5 september 2000 15:02
> > > To: [log in to unmask]
> > > Subject: [TN] Increased Phosphorus in Electroless Ni
> > >
> > >
> > > Hi:
> > > We are presently using electroless Ni/Immersion gold
> > metallization
> > > on our SMT PWBs. Our present requirements are:
> > > > A. FINAL FINISH TO BE IMMERSION GOLD PLATING, 10 MICRO
> > > INCHES
> > > > THICK
> > > > MAXIMUM, OVER 6-9% PHOSPHORUS CONTAINING
> ELECTROLESS
> > > > NICKEL PLATED
> > > > BASE 0.0003 TO 0.0007 INCHES THICK OVER ELECTRO
> > > > DEPOSITED COPPER.
> > > >
> > > One of our PWB suppliers intends to change their Electroless Nickel
> > bath.
> > > The current
> > > phosphorous content of plated nickel is between 6% and 9%. The new
> bath
> > > will
> > > produce phosphorous content between 9% and 12%.
> > >
> > > Reason: The higher phosphorous content prevents occurrences of
> > > "black pad nickel" and also better resist excessive attack on the
> nickel
> > > by
> > > Immersion Gold. So we expect to reduce, or even eliminate, rejections
> of
> > > product due to excessive gold or for black nickel under gold.
> > >
> > > Does the increased phosphorous content eliminate black pad nickel?
> > > Is there going to be an effect on solderability or long term solder
> > joint
> > > life?
> > > Will the PTH barrel become stronger and result in increased stress in
> > the
> > > connections between the inner plane and the PTH?
> > >
> > > We are concerned that we may be trading one set of problems for
> another.
> > >
> > > Thanks in advance for any help you can offer.
> > >
> > >
> > >
> > >
> > > Steph
> > >
> > > Stephan Meschter [log in to unmask]
> > > Lockheed Martin Control Systems Phone :(607)770-2332
> > > 600 Main Street, MD R52F FAX :(607)770-2056
> > > Johnson City, NY 13790-1888 MARCALL: 8 * 255-2332
> > >
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