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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:
Thu, 6 Sep 2018 17:32:58 +0000
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Very good point. Even if there was criteria, how do we inspect for that?



-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of David Hillman

Sent: Thursday, September 06, 2018 10:50 AM

To: [log in to unmask]

Subject: Re: [TN] R: [TN] Ni intermetallic thickness target



Hi Guy - I guess I am confused as how the IMC could be unacceptable if

there are not industry defined standards and there is no linkage to a

failure mode. Seems very very subjective.



Dave



On Thu, Sep 6, 2018 at 9:15 AM, Guy Ramsey <[log in to unmask]> wrote:



> Not linked to a root cause, but observed as unacceptable,  too thin and

> inconsistent.

> soak time (150 to 200) = 150 sec

> reflow time (above 217) = 75 sec

> peak temp = 250

> Seven thermal couples placed at various places on and in the board all

> within 3 degrees delta.  The board is heavy, Megtron 6 with 34 copper

> layers. Most of the thermal load is the board. There would be very little

> difference from pad to pad on any given component.  Solder mask defined

> pads conform to MFG recommendations.  We learned that the DDR packages are

> several years old. Maybe the solder spheres are hosed?

>

> On Thu, Sep 6, 2018 at 9:38 AM Wayne Showers <[log in to unmask]

> >

> wrote:

>

> > IMC has been the bane of my existence more than once.  So here is my take

> > from experience backed up with some lab evidence.

> > I have had failures attributable to insufficient IMC.  Almost all of

> these

> > were corrected by either ramp-to-peak or increased time above liquidus /

> > intimate contact time / temperature.

> > For SAC, the intimate contact temperature I have been able to dial in on

> > is time above 208C after liquidus is achieved.

> > For SnPb, the intimate contact temperature I have been able to dial in on

> > is time above 177C after liquidus is achieved.

> > I have found that if I can back end a little more time above these

> > temperatures on the profile, I have more consistent joints.  I have not

> > devoted a whole lot of 'science' on these numbers just 20+ years of trial

> > and error coupled with white papers, IPC BOK, and other research.

> >

> > I have yet to have a problem or a return tied to excessive IMC.  I am

> sure

> > that at some point excessive IMC may cause or have caused a failure

> mode, I

> > just have not seen it.  The few times where it may have been a

> contributing

> > cause, I also cooked the parts making cross-sectioning of the IMC moot.

> >

>


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