Fred,
I did not mean to mislead. My article was more broad based and did not focus on fluxes. It looked
at the overall process, its management (of lack thereof), and how difficult it is to overcome
certain issues as oxide and intermetallic formations preventing good solder wetting at fab,
solderability during assembly, and long term reliability. My main thoughts were presented as no
flux type or amount can overcome the excessive oxidation often present just before board
introduction to the HASL process.
I also was concerned about process managers attempting to overcome non-wetting by slowing down the
cycle and/or cranking up the heat. Both contribute to excessive intermetallic formations. Again,
part of this is due to the inability of any flux, or amount of it, to remove excessive oxidation
often present on panels coming out of the last rinse, micro-etch, or drying cycle.
My concern, as above, always has been the inability of many to attempt control of an often
uncontrollable process. Flux only is a part of the equation just as it is in any soldering form. As
you know, HASL is analogous to wave soldering, but for the wave soldering process (or any other
form) to be successful, it must have solderable surfaces. It's just that at fab, the definition of
a solderable surface is not always known.
I too would like more information about fluxes used in HASL, but mainly concerning operator
knowledge and use. However, my experience has been simply focused on board shops not always paying
proper attention to flux chemistry as density/specific gravity, and/or proper maintenance. Today's
bigger concern is focused on composition, and the rest as above. This too prompts my curiosity as
we all are headed toward no-clean, VOC free, and lead free soldering.
Enjoy,
Earl Moon
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