+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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