Robert: Howya doin' bud?
You say "BGA Shorting!!!" I say "Too Much Solder!!!" So, earlier comments about aperture design are appropriate, make good points, and I think we both agree that improvements could be made in your stencil design, but I'm not inclined to steer you in that direction, because your bridging occurs both with: � Solder paste (including flux). � Flux only.
OK. Let�s try it again: You say "BGA Shorting!!!" I say "Vias!!!"
Just drifting-off (sorry, Nancy), but if that view that you posted is the flux only, there seems to be a pant load of paste there (I know, I know, that�s what�s causing the shorting, Dave), but most connections seem fine. It�s that the shorted areas seem to be getting extra material from someplace. Where the blank is the excess paste on the shorted leads coming from? What�s different about those pads?
OK, I�m back, I wonder if we can narrow our focus to either BGA or board design by: 1 Reflowing the component, bug-down only with flux on a ceramic or oven-proof glass plate. 2 Similarly, reflowing the board only with flux only and balls. I reckon you wouldn't need to "ball" all the pads, just those that are bridging.
Continuing to be contrary, but taking a different angle(s): � Moisture entrapment in array devices causes solder shorts 80% of the time. Cracks in array devices from moisture entrapment occur the bottom side of components. Use an acoustic microscope to find cracks. � From the looks of things, I�d guess that you�re using Liquid Photo Imageable (LPI), but do you have "solder-dams" between the pads and vias?
Good luck Dave F