Thanks for all your informative replies. I do know that Motorola is using a No Clean Eutectic Solder for their BGA's. We are in Aerospace and is using a Water Soluble Paste Flux.
a) Can anyone explain to me about the effect of their mixture.
b) What enhancement does my BGA will have when using a WS paste flux with regards to corrosion, 25 years life cycle of the solder joint.
c) What's the benefit in using a WS paste flux on a BGA with No Clean solder joint process?
d) Why can't I use a No Clean Flun only for that BGA which has a no clean process from the supplier?
e) Is the reason that I have to use a WS is that because it's Class 3 and is an Aerospace Standard.
f) Are all aerospace electronics products using Water Soluble for both flux and paste?
The reason is that I'm planning to apply a No Clean instead of Water Soluble just on the BGA pads for soldering to get rid of the flux residue issue that we can't remove from our BGA. And will just switch back to WS paste once we got the proper cleaning system.