Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02230331 1998-04-27
"Organic Acids Activated Low Residue No Clean Solder Flux Composition"
Background of the Invention
I . Field of the Invention
s The present invention is directed to a liquid solder flux, and, more
particularly, to an
organic acid activated liquid solder flux specifically formulated for cleaning
electronic circuit
assemblies, such .as printed circuit boards, during the fabrication thereof.
Adipic acid, acetic acid,
and formic acid :in a solvent, such as isopropanol and ethyl acetate, are used
to remove solder
flux, oils, waxes and greasy substances, as well as adhesive and other
residues from various
to substrates.
2. Description of the Prior Art
Soldering with a soft solder, such as tin-lead based alloy melting at between
200°C to
260°C, is widely employed in the electrical and electronics industries.
In order to produce a
satisfactory soldered joint, it is necessary to use a flux with the soft
solder in order to remove any
residual surface oxide films and hence provide a clean surface and in order to
reduce the surface
tension of the molten solder and hence promote good wetting of the surface by
the solder. It is
important that tire molten solder fully wea the surfaces to be joined during
the tinning step, as
unwet portions result in voids at the surfaces after soldering is complete,
and the voids can cause
2e> later failure of the bond.
Therefore, the surface to be fluxed must be cleaned of a portion of the oxide
and
contaminant coating prior to fluxing. Equally important, the soldered array
must be carefully
CA 02230331 1998-04-27
cleaned after soldering is complete, in a postcleaning process, to remove any
unreacted flux and
reaction products of the flux treatment. Any remaining flux or reaction
products can continue
reacting with the bonded pieces and corrode them during service. Such
corrosion caused by
fluxes is a major concern for many types of solder bonding, as the bonded
pieces are sometimes
used in environments having conditions such as high humidity and high
temperature that
accelerate corrosion reactions that might otherwise proceed slowly. Tiny
amounts of unreacted
flux or reaction products that remain on the surface following soldering and
postcleaning can
therefore have disastrous consequences. Because of the consequences of solder
failures and the
significance of solder joints, the soldering process has been studied
extensively.
Fluxes now in use include mixturca of inorganic acids in inorganic vehicles or
solvents
such as water, inorganic acids in petrolatum pastes, salts in water,
petrolatum paste or organic
solvent, organic acids in water, organic halogens in water, amines and amides
in water, and
natural or modified rosins. All of these fluxes require postcleaning of the
soldered joint. Fluxing
can also be carried out in a reducing environment, as by accomplishing the
soldering process in a
hydrogen gas atmosphere. Postcleaning is not required, but maintenance and use
of a pure
hydrogen atmosphere in large scale production operations is di~cult, and can
lead to related
hydrogen embrittlement. In sum, there is known no effective, generally
applicable approach to
fluxing which avoids the need for postcleaning of the soldered parts.
There exists a need for an improved approach to soldering, and particularly to
the fluxing
20 operation, which increases the reliability of the joining process by
promoting effective wetting of
the solder to the piece during the tinning step, and also reduces the
incidence of post-soldering
failures due to corrosion or related causes. Work continues in an efFort to
develop suitable fluxes
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CA 02230331 1998-04-27
that permit making a solder joint faster and better, in a manner that is both
environmentally
acceptable and also does not require special precautions to protect the health
and productivity of
production line workers.
Summary of the lnvention
T'he present invention provides a solder flux, and related method for fluxing
a surface and for
joining two pieces together using the flux. The flux promotes even, smooth,
regular wetting of
the surface of the piece by solder, with a virtual absence of unwetted
portions. Use of the flux
does not require cleaning of the surface prior to fluxing or postcleaning of
the bonded portions of
nr the pieces after soldering is complete. The ingredients of an organic acids
activated solder flux
increase the reaction to metal oxides and make wetting by the solder easier
and faster. Any
residue of the activated agent boils off with the heat of soldering. The flux
evaporates entirely
during the fluxing process, leaving no residue or reaction products to
interfere with the use of the
bonded components, or cause corrosion or other harmful post-bonding effects.
At ambient
temperature, the flux is a liquid having a viscosity comparable with that of
water, and can be
readily provided in open containers at the point of use. The vapors from many
embodiments of
the flux are not odorous and offensive to persons who use the flux, and
contact of the flux to the
body does not cause injury. The flux can l.herefore be used in assembly
operations involving hand
labor without special precautions such as required with some other fluxes.
2c~ In accordance with the invention, organic acids activated liquid solder
flux comprising a
flux base and the organic acids dissolved in sufficient solvent to form a
liquid solder flux is
provided. The organic acids consist essentially of carboxylic acid derivatives
of a short to
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CA 02230331 1998-04-27
medium-chain hydrocarbons. The amount of the organic acid derivatives range
from an amount
ef~'ective to provide improved fluxing action to an amount sufficient to form
a saturated solution.
The flux of the invention is applied to the surface to be fluxed by briefly
immersing the
surface into the flux, spraying the flux onto the surface, or by other
convenient means. The
s surface is then tinned by dipping the surface into liquid solder, brushing
the liquid solder onto the
surface, or other convenient means.
When the flux of the invention is used, the surface to be fluxed and bonded
need not be
specially cleaned prior to application of the flux. The surface should not
have grease, thick dirt,
or other impenetrable barrier that prevents contact of the liquid flux to the
surface. In the other
~ o aspect of the invention, the organic acids are mixed with an evaporative
organic solvent to form a
flux. The organic acids must be present in an ef~'ective amount, which is
typically in the range of
from about 1 part of acid mixture to 99 parts of solvent. Full fluxing
effectiveness is normally
reached with about 1 part of the acid mixture for 95 parts of the solvent.
Acceptable evaporative
organic solvent would be isopropanol and ethyl acetate. Acceptable organic
acids are those that
t 5 sublime fully at t:he fluxing temperature when mixed with the solvent.
Adipic acid is especially
preferred in this embodiment. Significant amount of evaporative organic acid,
such as formic acid
and acetic acid, would improve the surfaces to be joined during the tinning
step.
A wide variety of types of pieces can be fluxed and joined by the processes of
the
invention. Conventional electronic components such as resistors, diodes,
capacitors, transistors,
2.o integrated circuita, and the like are included. Subassemblies can be
formed or joined. Wires,
connectors, printed wiring boards, and the like can be joined together or with
active components.
7'he processes are also operable in conjunction with non-electronic soldering
operations, such as
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CA 02230331 1998-04-27
general metal joining, fabrication, and the like. There are no known
limitations on such uses of
the flux.
It will be appreciated that the present invention presents an important
advance in the art of
soldering and fluxes. The flux of the invention is highly effective in
promoting wetting of the
a portions of components to be joined by solder, producing an evenly tinned
surface. The flux and
its reaction products evaporate completely by the conclusion of the fluxing
operation, so that
postcleaning is not required. The flux is easy to use in fluxing the surfaces
and in bonding
components. It is not dangerous to contact to the skin, and does not have an
objectionable odor,
so that the flux can be used in mass production soldering operations.
nr Further, the purpose of the foregoing Abstract is to enable the Canadian
Intellectual
Property Office (CIPO) and the public generally, and especially the
scientists, engineers and
practitioners in the art who are not familiar with patent or legal terms of
phraseology, to
determine quickly from a cursory inspection the nature and essence of the
technical disclosure of
the application. Accordingly, the Abstract is neither intended to define the
invention or the
iapplication, which only is measured by the claims, nor is it intended to be
limiting as to the scope
of the invention in any way.
It is therefore an object of the present invention to provide a new and
improved
composition for cleaning the surface of various soldered articles and which
has all of the
advantages of the prior art and none of the disadvantages.
?o It is another object of the present invention to provide a new and improved
composition
for cleaning the surface of various soldered articles which may be efficiently
manufactured and
marketed.
CA 02230331 1998-04-27
An even further object of the present invention is to provide a new and
improved
composition for cleaning the surface of various soldered articles which is
susceptible of a low cost
of manufacture with regard to both materials and labor, and which accordingly
is then susceptible
of low prices of sale to the consuming public, thereby making such composition
available to the
buying public.
Still yet a further object of the present invention is to provide a new and
improved
composition for cleaning the surface of various soldered articles and which is
adapted to be
topically applied to such articles in a colourless thin liquid, easily
sprayable form.
These together with still other objects of the invention, along with the
various features of
~ c7 novelty which characterize the invention, are pointed out with
particularity in the claims forming a
part of this disclosure. For a better understanding of the invention, its
operating advantages and
the specific objects attained by its uses, reference should be made to the
following detailed
description of the preferred embodiments of the invention.
Description of the preferred Embodiment
The present invention is embodied in a flux used in conjunction with
soldering. The flux
preferably is a mixture of adipic acid, acetic acid, formic acid and the
evaporative organic solvent
system including isopropanol and ethyl acetate, with the ratio of acid and
solvent being from
about 2 part of acid mixture for each 50 parts of evaporative organic solvent
system. While
2r> greater proportions of acid are operable, completely effective results are
obtained with less than
about 1.5 parts of acid mixture. Preferably, the solvent system is isopropanol
and ethyl acetate.
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Both the acid nuxture and solvent system should be without impurities that
would not evaporate
during fluxing.
A flux having reagent grade adipic acid, reagent grade acetic acid, reagent
grade formic
acid, reagent grade isopropanol and ethyl acetate, mixed in the ratio of 1
part by volume of adipic
acid to 2 parts by volume of acetic acid to 2 parts by volume of formic acid
to 85 parts by volume
of isopropanol to 10 parts by volume of ethyl acetate, is the presently most
preferred embodiment
of the invention. This flux mixture is prepared by adding the required volume
of adipic acid,
acetic acid, formic acid slowly to the isopropanol and ethyl acetate, taking
care not to splatter the
acid or overheat the solution. Consequently, the preparation of the flux
mixture should be
~ o accomplished by a person skilled in making acid mixtures, using good
ventilation and appropriate
safety equipment including at least goggles, a rubber apron, and rubber
gloves.
The flux mixture can be contacted to the skin without burns or injury,
although it is
recommended that any flux touching the skin be washed away as soon as
possible. Nevertheless,
the flux mixture is much safer than many other commercial liquid fluxes, which
quickly burn the
skin. The dominant odor of the flux is that of the solvent, in the preferred
case the isopropanol
and ethyl acetate. While prolonged exposure to this odor is not recommended,
exposure to a
weak odor or for brief periods is not immediately harmful. Thus, the flux is
safe to handle in
ordinary conditions of good ventilation and a reasonably safe working
environment. It is seen that
the flux and approach of the present invention yield important advantages in
soldering. Good
2o tinning and soldering are achieved, without the need for cleaning and
postcleaning. The flux is
nontoxic, and can be used in production operations where hand wiring is done.
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While the present invention has been fully described above with particularity
and detail in
connection with what is of ordinary skill in the art that many modifications
thereof may be made
without departing from the principles and concepts set forth herein. Hence,
the proper scope of
the present invention should be determined only by the broadest interpretation
of the appended
claims so as to encompass all such modifications.
IS
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