Since Whites are my favorite MX switches but I have them only on a switch tester, I was messing around, taking different switches apart, switching parts around and trying to "hack" Blues or Greens into Whites.
Redditor /u/ripster55 did some great work on this:
http://imgur.com/a/wuToY but in the end the "Soft Click" still seems to be a bit of a mystery.
he comes to the conclusion that it might be different plastics on the slider parts which seemed the most plausible to me as well.
While messing around I had some temporary success. I made a Blue into a White by switching the springs around. I think I put in a stronger spring and is was actually even better than. a White. Felt the same but was even quieter.
However, that didn't stick. Its back to normal now, no matter what spring I use. I have taken my Whites apart so many times now that I have apparently killed the "Soft Click". They now feel and sound pretty much like a Blue (not as loud and snappy as a Green, though).
That leads me to believe that the "Soft Click" might indeed come from the lube (that is now gone on my Whites from taking them apart so often) and that apart from the slightly stronger springs, Whites are built identical to Blues.
I will try relubing them with different lubes, but that doesn't seem like a very exact process to me to reliably convert 100 Blues into Whites...