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 Ni!
ckel 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
> > >
> > > ##############################################################
> > > TechNet Mail List provided as a free service by IPC using LISTSERV
> 1.8d
> > > ##############################################################
> > > To subscribe/unsubscribe, send a message to [log in to unmask] with
> > > following text in
> > > the body:
> > > To subscribe: SUBSCRIBE TECHNET <your full name>
> > > To unsubscribe: SIGNOFF TECHNET
> > > ##############################################################
> > > Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
> > > additional
> > > information.
> > > If you need assistance - contact Keach Sasamori at [log in to unmask] or
> > > 847-509-9700 ext.5315
> > > ##############################################################
> > >
> > > ##############################################################
> > > TechNet Mail List provided as a free service by IPC using LISTSERV
> 1.8d
> > > ##############################################################
> > > To subscribe/unsubscribe, send a message to [log in to unmask] with
> > > following text in
> > > the body:
> > > To subscribe: SUBSCRIBE TECHNET <your full name>
> > > To unsubscribe: SIGNOFF TECHNET
> > > ##############################################################
> > > Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
> > > additional
> > > information.
> > > If you need assistance - contact Keach Sasamori at [log in to unmask] or
> > > 847-509-9700 ext.5315
> > > ##############################################################
> >
> > ##############################################################
> > TechNet Mail List provided as a free service by IPC using LISTSERV 1.8d
> > ##############################################################
> > To subscribe/unsubscribe, send a message to [log in to unmask] with
> > following text in
> > the body:
> > To subscribe: SUBSCRIBE TECHNET <your full name>
> > To unsubscribe: SIGNOFF TECHNET
> > ##############################################################
> > Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
> > additional
> > information.
> > If you need assistance - contact Keach Sasamori at [log in to unmask] or
> > 847-509-9700 ext.5315
> > ##############################################################
>
> ##############################################################
> TechNet Mail List provided as a free service by IPC using LISTSERV 1.8d
> ##############################################################
> To subscribe/unsubscribe, send a message to [log in to unmask] with
> following text in
> the body:
> To subscribe: SUBSCRIBE TECHNET <your full name>
> To unsubscribe: SIGNOFF TECHNET
> ##############################################################
> Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
> additional
> information.
> If you need assistance - contact Keach Sasamori at [log in to unmask] or
> 847-509-9700 ext.5315
> ##############################################################
>
##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8d
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe: SUBSCRIBE TECHNET <your full name>
To unsubscribe: SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Keach Sasamori at [log in to unmask] or
847-509-9700 ext.5315
##############################################################
##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8d
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe: SUBSCRIBE TECHNET <your full name>
To unsubscribe: SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Keach Sasamori at [log in to unmask] or
847-509-9700 ext.5315
##############################################################
|
