Done thousands of these perimiter/super BGA's and found one solution using
SRT 1000 and up machines. After tremendous frustration, raised the "pro"
nozzle 80 to 100 mils off board surface, using paste flux, and eliminated
problem forever. Sure! Talk to "Big Ernie" and brother about what we did at
HP a couple of years ago.

Had to thermally insulate close proximity devices using ceramic in some
cases and Kapton tape in lesser affected areas.

This worked so well, provided other problems as dogbones at right angles and
exposed dogbone traces, several places at which I worked gave me a big hug,
uhg!

Another thing, for us at Cray, etc. - we had the luxury/need to remove heat
sinks and go from there. Also used micro stencils taped to board surface
using microscope when applying solder paste though hardly ever did after
achieving success with paste flux unless using hard balls.

So much more. Wish I could remember.

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