Vectronics VEC-1500K - Manual (Page 11)

6
No. 66
Regular
3.3%
No. 56
Medium
2.2%
No. 50
Small
1.1%
For general bench work and field repairs, "regular-core " (3.3%) solder delivers
the most flux, providing the fastest chemical action and best preparation of metal
surfaces. For hand assembly operations where metals are highly solderable and
surfaces pre-cleaned, 2.2% or even 1.1% solder will do the job--and leave less
residue behind for clean-up.
It's always important to check core size when you select a roll of solder. Solder
wires with low flux delivery may perform poorly on unprepared surfaces, and
may also cause your iron to "de-wet". De-wetting (or loss of tinning) is a
condition where solder no longer adheres to the tip because there isn't enough
flux available to keep it free of oxides. If forced use solder with a medium or
small core for general bench work, apply supplemental flux to each connection
before heating. This will protect your iron and to ensure adequate joint
preparation.
LESSON 2
Kinds of Flux
Flux is essential for successful hand-soldering. However, not all fluxes have the
same chemical composition or working characteristics. Different formulations
do the job in slightly different ways. In this section, we'll take a closer look at
what flux does, and cover the various types of flux in common use for hand
soldering.
How Flux Works: When exposed to air, most "raw" solderable metals quickly
attract oxygen molecules and form a layer of oxide. Once oxide forms, the
surface is rendered chemically "passive". This means no molecular bonding
sites are available for combining with other metals! If you apply solder to a
passive oxidized surface, it will bead up into a ball and pull away--much like
water on a freshly waxed automobile (Figure-A). This process is called
retraction
. Solder retracts because there are no bonding sites on the surface
where it can take hold and hang on. Instead, a ball forms because internal
cohesion attracts the solder molecules toward each other.