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September 2018

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From:
"Stadem, Richard D" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D
Date:
Wed, 5 Sep 2018 19:26:29 +0000
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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?

>


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