Ingemar,
For item c below -
Klein - Wassink references a patent (US 4,603,805) that removes the
phosphorous from the electroless nickel surface and in turn improving the
solderability of the surface. It uses a high temperature exposure (350 degC)
in an oxidizing atmosphere of the Ni-P to oxidize the phosphorous which is
followed by lower temperature exposure (300 degC) in a reducing atmosphere
to remove the phosphorous oxides. Unfortunately, the temperatures are too
hot to be useful for PWB applications.
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]]
> Sent: Monday, September 11, 2000 10:42 AM
> To: 'TechNet E-Mail Forum.'; 'Meschter, Stephan J'
> Subject: RE: [TN] Increased Phosphorus in Electroless Ni
>
>
> Gerry, Rudy, Stephan,
> According to Biunni, I saw something very similar to intergrain
> concentrations of P in the EN. Studied solderpads before and after
> KCN-etch with backscatter, then started etching of Nickel. As far as I
> understand I saw exactly same strange intergrain P-rich Nickel (Biunni's
> report Fig 19c,d). Continous etching showed that the P continued deeper
> into the Nickel, following the grain boundaries (with grains I mean 1-2
> micron 'agglomerations, what is normally seen in a metalurgical
> microscope). So, it seems to me as the Phosporous is enriched from
> starting of smallest Nickel clusters during plating, is pushed because of
> lower energy in front of the enlarging clusters, until a certain level is
> reached when finally the P is locked between the now large grains. Is this
> the mechanism that gives the EN a little better 'ductility': a soft
> P-compound or cement that accepts more mechanical stress than 'clean'
> grain-to-grain structure? When I see the concentrations of P in between
> the Nickel grains, I'm not astonished about a 'black mysterious layer'
> between the normal Ni3Sn4 and the bulk Nickel or Copper. The black (by
> backscatter) regions between the Nickel grains holds some 12-15% P while
> the the rest of the Nickel domes holds much less P. If the gap between the
> Nickel grains can be called 'corrosion' like in Biunni's article, I don't
> know. According to the definition of the word, corrosion means that
> something is broken up, so...it may be what Biunni call hyperactive IG
> that causes intergrain cracking and brittle Phosporous/xxxx-layers.
>
> Biunni's report reveals the blackish and superthin layer as a Phosporous
> compound, but not what it is, and he concluded the report with saying that
> this layer is fragile and that it's riscy to solder on such EN. Moreover,
> Biunni's article says that the blackish P enrichment between Nickel grains
> is caused by the following Immersion Gold, could then be interesting to
> prove this by looking on a board BEFORE immersion gold. Have not done that
> myself.
>
> Now my questions:
>
> a) as so many use P in the EN-bath, why don't much more people have
> trouble with bad BGA or FlipChip soldering (and other components too)? Is
> the superthin 'black layer' only developed under certain circumstances
> during solder?
>
> b) If you already have such boards, then what do you do? Can one ever rely
> on such ENIG? Can the soldering be done in such a way that only normal
> NiSn intermetallics grow and not the 'black layer'?
>
> c) how can I specify that I want no black layers in my soldering and no
> enrichment of Phosporous between Nickel grains in the.
>
> Sorry for asking again, but I have not the same brain capacity as now
> deserted Paul Klasek. I can send a few photos to you, Gerry,R and S, so
> you can stop me if I'm on the wrong track.
>
> Ingemar Hernefjord
> Ericsson Microwave Systems
>
> PS. Hear sometimes that american and english companies can't make good
> PWBs for BGA and FlipChip soldering, at least not when you talk about very
> dense doublesided boards, the japs are said to be superiour that way. Is
> there any substance in that or just the ordinary amateur gossips?
> Hmmm...guess there will be few answers...
>
>
>
> -----Original Message-----
> From: Meschter, Stephan J [mailto:[log in to unmask]]
> Sent: den 8 september 2000 21:26
> To: [log in to unmask]
> Subject: Re: [TN] Increased Phosphorus in Electroless Ni
>
>
> 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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