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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