Hi Technetters,

        My buddy and I have a disagreement on using Resistivity of Solvent Extract (ROSE) for measuring cleanliness on a Flip Chip board.  So, we're throwing it to league of experts on this forum for feedback

        Here's the story:  The board and assembly are very simple.  One flip chip die at about 0.002 square inches and one board about 0.490 square inches.  Flux is applied only to the flip chip die, reflowed, and DI inline washed.

        Here's the disagreement:  I say use 2X the surface area of the die for the calculation.  My good friend says use 2X the board surface.  Of course, you can see one number is much higher than the other in ug/sq inch NaCl equiv.  My logic for using only the die area is to understand the process cleanliness at that location only, but I recognize the entire board surface could be cross contaminated in some manner.  We also loaded the machine with 32 of these units to get something measurable.  When we only put 4 in, nothing showed up, but the smallest entry for surface area is 0.1 square inches.

Thanks for your input!

Glenn