The surface finish is ENEPIG On Thu, Sep 6, 2018 at 10:21 AM George Wenger <[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]] On Behalf Of Stadem, Richard D > Sent: Thursday, September 06, 2018 9:56 AM > To: [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]] On Behalf Of Guy Ramsey > Sent: Thursday, September 06, 2018 7:10 AM > To: [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]> > 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]> On Behalf Of Stadem, Richard D > > Sent: Wednesday, September 05, 2018 3:26 PM > > To: [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]] On Behalf Of SALA GABRIELE > > Sent: Wednesday, September 05, 2018 1:39 PM > > To: [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]] Per conto di Guy Ramsey > > Inviato: mercoledì 5 settembre 2018 19:34 > > A: [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] > > > > > wrote: > > > > > What is the finish plating? > > > > > > -----Original Message----- > > > From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey > > > Sent: Wednesday, September 05, 2018 11:59 AM > > > To: [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? > > > > > >