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January 2017

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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:
Mon, 23 Jan 2017 18:13:09 +0000
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I have never heard of using nitrogen to mitigate warpage, only oxidation.

I do not see how it would affect warpage, but I could be very wrong.

However, nitrogen could help the solder joints flow out a little better by reducing oxidation, and as an indirect benefit, help reduce issues caused by warpage.

But because solder wetting is improved in a nitrogen atmosphere, it could likewise exacerbate solder shorting. 

But the presence of the nitrogen (or lack thereof) would not directly affect the amount of warpage. Warpage is related to the heat exposure, more precisely, the ramp rate and the effect is has on the various parts of the TI Omap component itself. If the topside surface is expanding faster than the bottom, the chip will curl down in the corners. If the bottom is expanding faster, the chip will curl upwards in the corners. This may be caused not only by a difference in the CTE between the top and bottom of the part, but also by the core (heatspreaders, etc.)



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

From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Wettermann

Sent: Monday, January 23, 2017 11:29 AM

To: [log in to unmask]

Subject: [TN] Nitrogen Reflow and Warpage Issues on POPs



Dear Technetters:







We have a Class 3 customer with very complex, high density placements (think cell phone for the military). This board is laden w/0201s, 0.4mm pitch BGAs, shields, mirrored BGAs and the TI Omap POP (0.4/0.5mm pitch).





The problems in this board assembly for some time have been isolated to this OMAP part.  We have lots of shorts and opens (randomly-spaced) as confirmed by electrical testing, dye and pry and cross sectioning. The Omap has been shown to warp 5-7 mils depending on the reflow profile.( It is a no clean SAC305 process). We have profiled the reflow process by embedding TCs in the corners of the balls of the device (ball interface with the board where all of the problems are) , the die,  neighboring components etc. We dialed in the profile as low of a temp as possible.





We are running several DOEs to come up with a placement/rework process.



As part of the investigation the client is fixated on nitrogen reflow being part of the solution to these warped BGAs. Nitrogen reflow IMHO is the solution for joint aesthetics, wetting issues and enhanced reliability of the interconnection.





? Does anyone have experience with hot air reflow using nitrogen where its addition helped to mitigate warpage issues?





Thanks!





--

Bob Wettermann

BEST Inc


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