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May 2003

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From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 23 May 2003 19:05:38 +0300
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Glenn

I agree that using the die area would give a larger value, but are you
sure that you can discount the PCB area. Have you measured the PCB, by
itself, before attaching the die, and, with no die/flux but after
cleaning? Remember the fact that putting the flux only on the die is
meaningless because it will spread over the PCB well beyond the condines
of the die area during reflow.

Brian

Glenn Pelkey wrote:
> 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
>
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