Hi team - the "incompatibility" of Pd and SnPb solder is an old wives tale.
There was one published paper that concluded there was a problem but a
dozen papers since that one was published showing no issues. Rockwell
Collins has been using ENEPIG with SnPb for over 10 years with no issues.
Just like gold, palladium can form a brittle IMC phase (PdSn4) in the
solder joint microstructure that can degrade its integrity but the same
reaction can happen with SAC solder as well. Just need to do a good job of
creating an adequate solder reflow profile to avoid the IMC phase.
Dave
On Thu, Sep 6, 2018 at 4:17 PM, Guy Ramsey <[log in to unmask]> wrote:
> Thanks for the heads-up. This is a SAC 305 solder application. We would
> have pushed back hard if the solder were SnPb.
>
> On Thu, Sep 6, 2018 at 5:09 PM Yuan-chia Joyce Koo <[log in to unmask]>
> wrote:
>
> > +1. watch out Pd formation of IMC with Pb/Sn solder...
> > jk
> > On Sep 6, 2018, at 1:44 PM, George Wenger wrote:
> >
> > > Guy,
> > >
> > >
> > >
> > > Don’t get mad at me for saying it but the third finish on my least
> > > favorite finish is ENEPIG.
> > >
> > >
> > >
> > > George
> > >
> > >
> > >
> > > From: Guy Ramsey [mailto:[log in to unmask]]
> > > Sent: Thursday, September 06, 2018 10:32 AM
> > > To: TechNet E-Mail Forum <[log in to unmask]>; George Wenger
> > > <[log in to unmask]>
> > > Subject: Re: [TN] R: [TN] Ni intermetallic thickness target
> > >
> > >
> > >
> > > The surface finish is ENEPIG
> > >
> > >
> > >
> > > On Thu, Sep 6, 2018 at 10:21 AM George Wenger
> > > <[log in to unmask] <mailto:[log in to unmask]> > wrote:
> > >
> > > I agree Richard. The difference sounds like a solder wetting
> > > variation do to the pad and not the reflow process.
> > >
> > > RIGHT ON RICHARD OSP over bare copper is just below Immersion Tin
> > > which is at the top of my list of least favorite finishes.
> > >
> > > -----Original Message-----
> > > From: TechNet [mailto:[log in to unmask] <mailto:[log in to unmask]> ] On
> > > Behalf Of Stadem, Richard D
> > > Sent: Thursday, September 06, 2018 9:56 AM
> > > To: [log in to unmask] <mailto:[log in to unmask]>
> > > Subject: Re: [TN] R: [TN] Ni intermetallic thickness target
> > >
> > > Dave's Rant and what you have posted below are all too true. But
> > > one thing I know for sure; OSP over bare copper is next to
> > > immersion tin on the bottom of my list of favorite finishes. I was
> > > wondering if the variation in IMF could be caused by some pads
> > > having thicker OSP coverage, and thus blocking or interfering with
> > > the wetting of the solder onto the pad during reflow? Is there a
> > > way you could mechanically or chemically remove the OSP on a scrap
> > > PWB on only some of the pads for the DDR3 part, then print the
> > > paste as you normally would and reflow the board using your
> > > existing reflow profile, then have them microsection that and see
> > > if you get different/better results? This would eliminate the part
> > > plating as a causal factor, and possibly prove the OSP is at least
> > > a major contributor to the issue, and possibly exonerate your
> > > reflow profile, thus eliminating several factors as the issue. My
> > > suspicion stems from the fact that if OSP is not properly applied
> > > immediately some of the copper pads may have oxidized, leading to
> > > the variation in IMF amongst pads. The simple fact that pads right
> > > next to each other have major variation pretty much rules out the
> > > reflow parameters unless there is a correlation between pads with
> > > heavy copper connections or some other cause.
> > >
> > > -----Original Message-----
> > > From: TechNet [mailto:[log in to unmask] <mailto:[log in to unmask]> ] On
> > > Behalf Of Guy Ramsey
> > > Sent: Thursday, September 06, 2018 7:10 AM
> > > To: [log in to unmask] <mailto:[log in to unmask]>
> > > Subject: Re: [TN] R: [TN] Ni intermetallic thickness target
> > >
> > > We infer that an IMC has formed by visual evidence, wetting and
> > > spreading.
> > > In the case of bottom only terminations we seek evidence by other
> > > means. We can't see the contact angle or determine what forces
> > > created the spreading.
> > > In this case a lab cross sectioned a DDR3 memory device. The lab
> > > observed continuous intermetalic on the individual pads but
> > > characterized the IMC layer as too thin and inconsistent from pad
> > > to pad. Where one pad exhibited 70uin of IMC the neighboring pad
> > > measured less than 10uin. I found very little discussion of this
> > > in white papers. But, I did find a nicely done DOE, Effects of
> > > reflow profile and thermal conditioning on intermetallic compound
> > > thickness for SnAgCu soldered joints. This paper contained data
> > > about the thickness of IMC formed at different temperatures and
> > > dwell times. To some extent irrelevant because the base was OSP
> > > copper.
> > > However, the standard deviations in measured data on this
> > > experiment were much lower than the deviations the lab found at the
> > > DDR memory pads. Is a large variation a cause for concern. How thin
> > > is too thin? My first impressions of the report fell in line with
> > > Dave's Rant, that trying to establish a reflow profile to achieve
> > > some standard IMC thickness was a fool's errand. But, on
> > > reflection, variation from assignable causes is always the enemy.
> > >
> > > On Wed, Sep 5, 2018 at 6:01 PM Bob Landman
> > > <[log in to unmask] <mailto:[log in to unmask]> >
> > > wrote:
> > >
> > >> Hi Rich,
> > >>
> > >> You mean K100LD, right?
> > >>
> > >>
> > >> https://www.kester.com/products/product/k100ld-lead-free-silver-
> > >> free-a
> > >> lloy-bar-solder
> > >>
> > >> Bob
> > >>
> > >> -----Original Message-----
> > >> From: TechNet <[log in to unmask] <mailto:[log in to unmask]> > On
> > >> Behalf Of Stadem, Richard D
> > >> Sent: Wednesday, September 05, 2018 3:26 PM
> > >> To: [log in to unmask] <mailto:[log in to unmask]>
> > >> Subject: Re: [TN] R: [TN] Ni intermetallic thickness target
> > >>
> > >> That is also true, but there is really good information out there
> > >> regarding the fact that too thick of an IMC is worse than too thin.
> > >> That is because of the brittle nature of the alloy you end up with;
> > >> nickel, gold, palladium, tin, and with SAC305 you add silver and
> > >> copper.
> > >> Although the gold, palladium, and silver are very low percentages,
> > >> the
> > >> combination of these and a significant percentage of nickel with no
> > >> lead can make for a very brittle IMF, especially if it is at the 100
> > >> uinch or thicker levels. So in that case, perhaps 20 to 70 uinches
> > >> may
> > >> be quite ideal. I am trying to find the reports I saved in my
> > >> bottomless stack of "important stuff".
> > >> Also, the IMF formation is self-limiting, but it depends on the
> > >> factors of time above solidus, temperature, component plating,
> > >> solder alloy type, etc.
> > >> These were all listed as having significant impact on the thickness
> > >> along with even very small amounts of germanium and other dopants.
> > >> So,
> > >> for example, Kester KL100D has very different properties from SAC305,
> > >> yet it is almost 100% tin. KL100D is very similar to Sn63.
> > >> If there was a concern, then I would rather rely on actual
> > >> reliability
> > >> tests taken over time, rather than the average thickness variation of
> > >> a bunch of microsections. It's very difficult to guess at exactly
> > >> what
> > >> thickness might be ideal, but reliability results prove that,
> > >> assuming
> > >> you know for sure what thickness you have with your samples. And
> > >> remember, the IMF grows over time; it is never the same 3 months
> > >> or two years later.
> > >>
> > >> -----Original Message-----
> > >> From: TechNet [mailto:[log in to unmask] <mailto:[log in to unmask]> ]
> > >> On Behalf Of SALA GABRIELE
> > >> Sent: Wednesday, September 05, 2018 1:39 PM
> > >> To: [log in to unmask] <mailto:[log in to unmask]>
> > >> Subject: [TN] R: [TN] Ni intermetallic thickness target
> > >>
> > >> Keep in mind also the terminal finishing.....
> > >> One reflow or two reflow ? etc
> > >>
> > >> Too early to fix a reliable IMC thickness ..... too many variables
> > >> playing !!!
> > >>
> > >> GS
> > >>
> > >>
> > >> -----Messaggio originale-----
> > >> Da: TechNet [mailto:[log in to unmask] <mailto:[log in to unmask]> ] Per
> > >> conto di Guy Ramsey
> > >> Inviato: mercoledì 5 settembre 2018 19:34
> > >> A: [log in to unmask] <mailto:[log in to unmask]>
> > >> Oggetto: Re: [TN] Ni intermetallic thickness target
> > >>
> > >> ENEPIG
> > >>
> > >> On Wed, Sep 5, 2018 at 1:17 PM Stadem, Richard D
> > >> <[log in to unmask] <mailto:[log in to unmask]>
> > >>>
> > >> wrote:
> > >>
> > >>> What is the finish plating?
> > >>>
> > >>> -----Original Message-----
> > >>> From: TechNet [mailto:[log in to unmask] <mailto:[log in to unmask]> ]
> > >>> On Behalf Of Guy Ramsey
> > >>> Sent: Wednesday, September 05, 2018 11:59 AM
> > >>> To: [log in to unmask] <mailto:[log in to unmask]>
> > >>> Subject: [TN] Ni intermetallic thickness target
> > >>>
> > >>> Recently, I was reviewing a lab report. It concluded that the
> > >>> manufacturer should increase the IMC thickness as a part of process
> > >> changes . . .
> > >>> It stated that, while there are no industry specifications for IMC
> > >>> thickness it s generally accepted that for Pb-free assemblies the
> > >>> IMC thickness should be in the 20 to 120 uin range. It seems to be
> > >>> critical of a process that produces IMC between 10 and 70 uin on
> > >>> pads across a single device.
> > >>> Does anybody have reference papers or texts that would support this
> > >>> target and process critique?
> > >>>
> > >>
> >
>
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