De-gassing a flux changes its properties so much that we can’t sell it as the same flux anymore! Beyond eliminating air bubbles, the main things that happen when you airlessly package a flux are: 1) Viscosity drops, 2) Tackiness usually drops a little – but remains similar (which influences visc./tack ratio), and 3) The flux becomes more uniform with a smoother consistency. 4) Workable life tends to increase.
The real advantages to this are the visc./tack ratio and smooth consistency. A flux with low viscosity and relatively high tack allows a chip to transfer maximum flux on each sphere after dipping. It also holds the chip in place better – with lower initial placement force. The smooth consistency resists separation and promotes uniform chemical balance from bump to bump across the chip. The increase working life allows a material to work over a longer time without a noticeable change in transfer efficiency.
Airless packaging is a huge advancement in flux manufacture, and it allows dipping applications to be possible where only spray applications could work before.