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November 2012

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From:
"Thayer, Wayne - IS" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Thayer, Wayne - IS
Date:
Fri, 9 Nov 2012 19:23:04 +0000
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Hi Julie-

I'm sure you are correct about the flux being a symptom rather than the cause.  The BGA had been reballed and they must have overheated it which somehow caused an evil phase of intermetallic to form.  As to whether fluxing and reheating will fix a BGA, I agree that's what it looks like was attempted here, and I agree it was inappropriate for this condition, but I can't agree that there aren't SOME cases where re-fluxing and re-flowing won't fix!

Thanks,

Wayne

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Julie Silk
Sent: Friday, November 09, 2012 12:02 PM
To: [log in to unmask]
Subject: Re: [TN] Limits on flux residue

I'd say "cottage" fix up.  {shudder}

__________
Julie Silk
Environmental Compliance Technical Program Manager EMG Customer Experience and Quality Agilent Technologies, Inc [log in to unmask]
707-577-4296 (TN 577-4296)


-----Original Message-----
From: Joyce Koo [mailto:[log in to unmask]]
Sent: Friday, November 09, 2012 8:11 AM
To: 'TechNet E-Mail Forum'; SILK,JULIE (A-Sonoma,ex1)
Subject: RE: [TN] Limits on flux residue

"the practice of injecting flux and reheating to hope that the bad joints melt together." Is it industry approved method (I mean with published reliability data to compare with non-repaired part)?  Or just "cottage" fix up method (anything goes, as long as make it work for the moment, like wet towel wrap of a heat up unit for example)?

Joyce Koo
Materials Researcher - Materials Interconnect Lab Research In Motion Limited
Office: (519) 888-7465 79945
Mobile: (226) 220-4760

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Julie Silk
Sent: Friday, November 09, 2012 10:59 AM
To: [log in to unmask]
Subject: Re: [TN] Limits on flux residue

Are the open joints caused by the excessive flux?  Or are both the excessive flux and the open joints caused by rework?  I would bet on the latter.  I can't visualize a scenario where the flux would cause good joints to open.  Ugly, sure, but very common with reworked BGAs.  Reworking BGAs does not always successfully make good joints on all balls, and neither does the practice of injecting flux and reheating to hope that the bad joints melt together.  It's possible and even likely that they make a contact joint vs metallurgical that fails later.  The flux is a symptom, not a cause.

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