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