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