All fluxes are active to some degree - obviously some more than others.
Fluxes are composed of organics as rosins, resins, and other neat stuff and
some are highly active - even enough to affect stainless steel, as an
example. Others are mildly activated as those found in no clean types. The
following are some types and considerations:

Flux
Flux is defined as a chemically and physically active compound that when
heated to specified temperatures it promotes base metal surface wetting by
molten solder. It does this by removing minor surface oxidation, surface
films, or other contamination. It then protects the surfaces from
re-oxidation during the soldering process. Various flux types (see H-P Hand
Soldering and Final Assembly Course) include:

Rosin
Rosin flux primarily is composed of natural resin extracted from oleoresin
of pine trees and refined. Typically, these fluxes are made up of 60%
solvent and 40% solids.

Rosin flux (Type R) is an organic material distilled from pine tree sap. The
active ingredients in this flux type primarily consist of abietic and
pimaric acids. After rosin is extracted from pine trees, it is superficially
processed to remove undesirable impurities while neutralizing the acid
residues remaining from the extraction process. The purified material is
called water-white rosin. It is used to manufacture rosin based flux.

Some manufacturers hoping to overcome difficulties associated with obtaining
and processing natural rosin, chemically synthesize substitute materials.
These materials are called "resins."

Pure rosin is a solid at room temperature and is chemically inactive while
being insulative. Rosin melts at about 72 degrees C. (160 degrees F.) and
the organic acids become active at around 108 degrees C. (225 degrees F.).
This flux type's peak capability is effected around 262 degrees C. (500
degrees F.). This is the temperature rosin begins decomposing into reducing
gases. At temperatures above 346 degrees C. (650 degrees F.), the flux
becomes inactive and polymerizes. This causes residue removal difficulties
from board and solder joint surfaces.

When solder surfaces require a more active flux, chemical compounds called
activators are added to the rosin. The most commonly known rosin flux
containing activators is called rosin, mildly activated or RMA.

Activators are thermally reactive compounds (such as amine hydrochlorides)
that break down at elevated temperatures. At these temperatures,
hydrochloric acid is released to dissolve the surface oxides, tarnishes, and
other contaminates. Mildly activated rosin flux (RMA) may contain a variety
of activators in amounts less than 1%. Limits are placed on their electrical
and chemical properties before and after soldering

Rosin activated flux (RA) typically contains 1% - 5% activators. RA flux is
used in applications when RMA is not strong enough. For military purposes,
their use usually is limited to component tinning of sealed devices and
solid wire. When warm, these fluxes can conduct electricity and can leave
residues that can cause corrosion or shorting path formation between
conductors.

Organic Acid Flux
Organic acid (OA) fluxes are types having active ingredients such as organic
acids, organic hydrohalides, amines, and amides. These fluxes are water
soluble since they contain no rosin. Good cleaning is critical with these
flux types since the salt residues left by them are corrosive and
conductive.

OA fluxes also are referred to as water soluble fluxes (WSF's). These fluxes
are more aggressive. They generally are classified in J-STD-004 as types M
or H. OA fluxes have active ingredients such as organic acids, organic
hydrohalides, amines, and amides. All are corrosive activator materials.
These fluxes are water soluble or water washable since they contain no
rosin, or any low rosin or resin levels. Good cleaning is critical with
these flux types as their residues are corrosive and electrically
conductive.

Resin
Resin flux primarily is composed of natural resins other than rosin types
and/or synthetic resins.

Organic
Organic elements are based on carbon atom structures. All life forms are
organic. Organic fluxes are primarily composed of organic materials other
than rosin or resin.

Inorganic
Inorganic elements are based on other than carbon atom structures. Inorganic
fluxes are solutions composed of inorganic acids and/or salts.

LR, or No-Clean Fluxes
Low residue (LR) fluxes usually have lower solids content (less than 5%)
than traditional high-solids rosin fluxes. LR fluxes also are referred to as
no-clean or "leave on" fluxes. Their residues are not intended for removal
from assemblies so cleaning is not required. Their primary activator
materials are weak organic acids (adipic or succinic acid). These materials
are benign on a board surface and act as electrical insulators. LR fluxes
may be higher solvent borne (isopropanol) or water borne in the case of
volatile organic compound (VOC) free no clean fluxes.

Low residue fluxes are not no-residue fluxes. Although benign, visible
residues do remain on the assembly. For this reason, customers may require
them to be cleaned. This often is requested for cosmetic rather than
functionality reasons. If the flux residues have a significant thickness,
they could interfere with electrical testing as "bed of nails" types.
However, a different probe point, greater spring strength, or rotating
probes often solve this problem. Low residue fluxes also might build up on
test pins over time. This requires preventive maintenance as regular
cleaning.

Halides
Halides are organic salts added to flux as activators. Halides are
corrosive.

Fluxing Activities And Classes
A liquid flows freely over a surface only if in doing so the total free
energy of the system is reduced. In soldering, the free energy of a clean
surface is higher than a dirty one. Therefore, it is more likely to promote
solder flow. With respect to this, fluxing activities are:

1) Chemical
Chemical fluxing activity reduces the oxides from the surface to be soldered
and protects this surface from oxidation by covering it.

2) Thermal
Thermal fluxing activity assists transferring heat from the heat source to
the material being soldered.

3) Physical
Physical activities allow the transportation of oxides and other reaction
products away from the material surfaces being soldered. In consideration of
these three fluxing activities, the following should be noted:

There are two basic ways fluxes eliminate oxidation. They dissolve it into
"solution" or they reduce it back to metal. If reduced, it clearly
"disappears" and should not be re-deposited as an oxide (to be determined
through supplier qualification). Some old flux types "dissolved" oxides by
reacting as a fatty acid (rosin) with the metal in the oxide. Then, it was
"pushed aside" by solder flow and wetting action. In which mode a flux
works, clearly depends on which flux is used. Some fluxes use both modes.

ANSI/J-STD-004 differentiates flux activities into three classes. They are
Low (type L), Medium (type M), and High (type H). ANSI/J-STD-004 further
classifies fluxes as to whether or not they contain halides. For example, a
type L0 flux is a low activity, halide free flux. An L1 flux is a low
activity flux containing some halide amount.

Numbers of industry and consortia studies have been conducted concerning low
residue flux reliability. Type L fluxes have been shown relatively benign
concerning corrosion and electrolytic failure mechanisms. For this reason,
Section 4.2 allows the manufacturer to use a type L flux (L0 or L1) without
going through the testing outlined in Appendix D. If the manufacturer
chooses to use a more aggressive flux (types M and/or H), the potential
exists for corrosive flux residues. If so, the manufacturer must go through
the Appendix D testing to demonstrate adequate removal of potentially
harmful flux residues.

It is highly recommended that the manufacturer not use a type H flux on
printed wiring assemblies in any way at any time. It is recommended that, if
used at all, a type H flux be limited to component lead tinning. Even then,
this may be done only when it can be demonstrated that the highly aggressive
flux residues may be thoroughly removed.

----- Original Message -----
From: Nicholas LAI <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, September 13, 1999 5:53 PM
Subject: [TN] Active/non-active flux.


> Hello morning,
>
> What is active flux anf non-active flux?
> What is the different?
> How to applicable?
>
>
> Best Regard,
> Nicholas lai
> 9/14/99
>
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