Glenn, if you are performing this with an Omegameter or other "static"
methods, the tests would be a waste of time regardless of area used. You
need to use a Dynamic system with a minimum solution resistivity of 450 meg
ohms. The solution volume should be 1 gallon or less, and have a
temperature of 38C minimum. Control your IPA percentage in the range of 75
to 78%. Use the same number of samples when testing, hence the same area.
In fact, you may wish to use an area of 1 and record the number of microgram
equivalents in absolute.
Now that you have a system to measure, you will be able to study,
differentiate, and validate cleaning processes. You will also be able to
see when changes have been introduced. Best Regards
Greg Miller
Principle Process Engineer
L-3 Communications Display Systems
Alpharetta, GA
770-346-8154
----Original Message-----
From: Glenn Pelkey [mailto:[log in to unmask]]
Sent: Friday, May 23, 2003 9:59 AM
To: [log in to unmask]
Subject: [TN] ROSE for Flip Chip
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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