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July 2011

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Subject:
From:
Chris Mahanna <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Chris Mahanna <[log in to unmask]>
Date:
Fri, 1 Jul 2011 09:12:13 -0400
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Julie,
From what Steve posted, I don't think anyone can tell for sure.  But, it sure looks to me like the component ball attach (maybe reworked) produced a very small soldered area allowing it to hang-on.  I see this in the center on the bottom right picture.  During your reflows, I don't think anything changed, because if it didn't solder the first time, it isn't going to.   Of course, if you feel that you've proven good joints as received and after first reflow, then this is off-base.

I'm betting the component manufacturer did have trouble with his Ni, and the effects were random, which is throwing off your conclusions.
BTW, high resolution optical pictures might be more telling in this case.

Part of my reasoning is the exceptional rarity of ball drop/ dewet.  I don't have an exact number, but we are surely in the 100,000s of balls sectioned and I've never seen it.
Were as bad as-received component side joints are rare, but seen regularly.

Good luck and happy 4th.

Chris

Chris Mahanna
Robisan Lab



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Julie Silk
Sent: Thursday, June 30, 2011 8:57 PM
To: [log in to unmask]
Subject: Re: [TN] BGA ball dewet from substrate

I agree it's very strange.  I don't have cross-sections after the first reflow yet.  The raw parts show very nice joints between ball and substrate.  The faulty balls are mostly at the interior rows (empty center, no balls there).  It is one part, one supplier -- but nothing fishy on the raw part.  Looks like electrolytic Ni/Au on the substrate.  Steve Gregory is posting a picture.  Could the upside-down part sag so much in the middle during reflow that it pulls away??

--------------------------------
Julie Silk
Environmental Compliance Technical Program Manager Agilent Technologies
707-577-4296
[log in to unmask]


-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Thursday, June 30, 2011 3:49 PM
To: TechNet E-Mail Forum; SILK,JULIE (A-Sonoma,ex1)
Subject: RE: [TN] BGA ball dewet from substrate

Is this random with respect to location?  Is it particular to one part/supplier?

It seems very strange that a properly reflowed BGA solderball connection would "dewet" itself during a subsequent reflow operation.

A cross section after the first reflow will probably explain what happened.




-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Julie Silk
Sent: Thursday, June 30, 2011 3:29 PM
To: [log in to unmask]
Subject: Re: [TN] BGA ball dewet from substrate

The substrate pad shows an intermetallic layer, demonstrating that there had been a metallurgical bond.  Also, the surface of both pad and ball are smooth -- not a fracture, but as if reflowed.  I have a good picture from the FA report to share once I figure out how.  I believe that if you were to analyze the very first layer on the BGA substrate pad, it would have a layer of solder.

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