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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