Method of removing organic flux using peroxide composition

A composition for removing organic contaminants, such a flux residues, from a solid substrate comprises: (a) hydrogen peroxide in the amount of about 3 to 5 percent by weight of the composition; (b) an alkaline compound in sufficient amount to provide a pH of at least 10.5 in the composition; (c) about 0.1 to 0.3 percent by weight of a chosen wetting agent which is unreactive with the hydrogen peroxide and the alkaline compound; and (d) purified water as the balance of the composition. Optionally, the composition may further comprise about 0.5 to 2.0 percent by weight of a chosen metal protective agent. The solid substrate having organic contaminants thereon is exposed to the above noted composition whereby the organic contaminants are removed from the substrate and are converted into non toxic and non-hazardous products. Thus, negative environmental impact is avoided by the present process. In an alternative embodiment, the organic contaminant removal is further enhanced by exposing the composition and the organic contaminants on the substrate to ultraviolet radiation.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to a composition and method for 
removing organic contaminants from solid substrates. More particularly, 
the present invention relates to a hydrogen peroxide composition for 
removing organic contaminants such as solder flux; and to a method of 
using this composition. 
2. Description of the Background Art 
In the fabrication of printed circuit boards, integrated circuits, and 
various electronic components and devices, solder is used to join various 
component metal parts together. The solder itself comprises an alloy, such 
as of zinc and copper or of tin and lead. Prior to application of the 
solder to the metal surface, the surface is treated with a fluxing agent 
to remove oxides and other contaminants which might interfere with the 
metal bonding, and to prevent reformation thereof during the solder 
process. These fluxing agents are typically organic materials such as 
natural rosin extracted from pine tree sap, organic acids such as 
carboxylic acid, hydrazines, amines and amides, or inorganic materials 
such as inorganic acids or salts. The most commonly used fluxing agent is 
acid rosin flux. The term "rosin flux" is used herein to mean a flux 
material which comprises rosin, i.e., the resin after distilling 
turpentine from the exudation of species of pine, and containing abietic 
acid and its anhydride. Typically, a small amount of another acid is added 
to rosin flux to activate it and such compositions are referred to as 
"acid rosin flux" or "activated rosin flux." After the solder operation 
has been completed, excess flux as well as flux residues remain on the 
soldered surface, and these residues are resinous, waxy and conductive. 
These flux residues and excess flux must be removed prior to subsequent 
processing steps in order to prevent reaction thereof with the bonded 
part, leading to corrosion and resultant electrical insulation losses. 
Defluxing solvents which are widely used at present are halogenated 
hydrocarbons such as 1,1,1-trichloroethane and Freon (a tradename of E. I. 
DuPont for polyhalogenated hydrocarbons including chlorine and fluorine). 
While these organic materials are effective defluxing solvents, they have 
the serious disadvantage that they have a negative impact on the 
environment due to air pollution and ozone depletion. In fact, recent 
environmental legislation mandates that these materials be banned or their 
production severely restricted in the next few years. When these materials 
are used, even in small quantities, expensive management systems for 
transport, storage, use, and disposal and environmental protection 
equipment must be used to prevent air and water discharges. In addition, 
waste solvents require energy intensive regeneration operations for these 
materials. 
While numerous aqueous cleaners are available which are viable degreasing 
solvents, none of these has been found to be effective as an electronic 
component defluxing solvent. In addition, the resulting organic laden 
aqueous solvents require further processing before disposal. 
Thus, an urgent need exists in the electronics industry for a solvent which 
effectively removes organic flux residues while at the same time avoiding 
any negative environmental impact. Such a solvent would also be desirable 
for removing other organic materials from other substrates. 
SUMMARY OF THE INVENTION 
The general purpose of the present invention is to provide a new and 
improved composition and method for removing organic contaminants from a 
chosen solid substrate while avoiding negative environmental impact. This 
composition and method possess the advantages of the above prior art 
processes while overcoming their significant disadvantages. 
The above general purpose of this invention is accomplished by first 
providing a composition comprising: (a) hydrogen peroxide in the amount of 
about 3 to 5 percent by weight of said composition; (b) an alkaline 
compound in sufficient amount to provide a pH of at least 10.5 in said 
composition; (c) a chosen wetting agent in the amount of about 0.1 to 0.3 
percent by weight of said composition, said wetting agent being unreactive 
with said hydrogen peroxide and said alkaline compound; and (d) purified 
water as the balance of said composition. 
Optionally, the composition may further comprise a chosen metal protective 
agent in the amount of about 0.5 to 2.0 percent by weight of said 
composition, said metal protective agent being unreactive with said 
hydrogen peroxide and said alkaline compound. 
The solid substrate having organic contaminants thereon is exposed to the 
above noted composition whereby the organic contaminants are removed from 
the substrate and are converted into non-toxic and non hazardous products. 
Thus, negative environmental impact is avoided by the present process. In 
an alternative embodiment of the present invention, the organic 
contaminant removal is further enhanced by exposing the composition and 
the organic contaminants on the substrate to ultraviolet radiation. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The composition of the present invention is effective for removing organic 
contaminants from a solid substrate while at the same time avoiding 
undesirable impact on the environment. The composition of the present 
invention is especially useful for removing flux residues which 
contaminate surfaces after a soldering operation. These flux residues 
typically comprise resinous, waxy contaminants which are the breakdown 
products from the soldering operation. The substrates which are soldered 
comprise, for example, printed wiring boards, integrated circuits, 
electronic components, electronic devices, electronic connectors, or 
electronic cables. In accordance with the present invention, the 
by-products, such as carbon dioxide, nitrogen, and water, which are formed 
are non-hazardous and can be removed without having a negative 
environmental impact. 
The composition in accordance with the present invention comprises: (a) 
hydrogen peroxide (H.sub.2 O.sub.2) in the amount of about 3 to 5 percent 
by weight; (b) an alkaline compound in a sufficient amount to provide a pH 
of 10.5 or higher in the composition; (c) a chosen wetting agent which is 
unreactive with hydrogen peroxide and the alkaline compound and which is 
present in the amount of about 0.1 to 0.3 percent by weight of the 
composition; and (d) purified water as the balance of the composition. 
Optionally, if the substrate comprises metal, a metal-protective agent is 
added to protect the metal surface from attack by the peroxide and alkali. 
The metal protective agent is unreactive with the hydrogen peroxide and 
the alkaline compound and is present in the amount of about 0.5 to 2.0 
percent by weight of the composition. 
The hydrogen peroxide acts as a solvent, emulsifier, and oxidant. While not 
limiting the present invention to a particular theory of operation, it is 
believed that the hydrogen peroxide has the following effect. After being 
immersed in the present composition, a flux-contaminated substrate invokes 
selective adsorption of hydrogen peroxide into the flux film and rapid 
decomposition of the inorganic peroxide. The selective adsorption of 
hydrogen peroxide by the rosin based contaminant films is due to the ether 
like solubility chemistry of hydrogen peroxide. Following adsorption, 
hydrogen peroxide rapidly decomposes into water and oxygen gas. The oxygen 
emulsifies the resinous contaminant, increasing surface area and solvency. 
This adsorption and emulsification process is observed as spontaneous 
foaming on the contaminated surface. The scrubbing foam enhances the 
cleaning activity of the solvent, dramatically improving penetration of 
solvent into low-tolerance spacings. After the organic flux contaminants 
have been removed from the substrate, they are oxidized by the action of 
nascent or atomic oxygen which is formed by the spontaneous decomposition 
of hydrogen peroxide, and are decomposed into carbon dioxide, nitrogen, 
and water. This effect is evidenced by a change in color in the 
composition from amber when it contains dissolved flux, to clear. The 
contaminants may be dissolved or suspended material. 
The effectiveness of the composition of the present invention is believed 
to be due to a synergistic relationship between pH, peroxide chemistry and 
the wetting agent. It was found that peroxide based formulations with pH's 
of 2 (acidic) and 7 (neutral) did not effectively remove contaminants. In 
these cases, the flux contaminants tended to gel and discolor on the 
substrate surfaces. Alkaline formulations having a pH of greater than 10.5 
were considerably more effective at solubilizing the flux residues than 
acid or neutral solutions. (This is probably due to ionization of flux 
acids by basic solutions, forming primative soaps.) Thus, the alkaline 
compound is added to the present composition to provide a pH of at least 
10.5, preferably within the range of 10.5 to 11.5. The alkaline compound 
may be, for example, sodium hydroxide or potassium hydroxide, with sodium 
hydroxide being most preferred. If sodium hydroxide is used, it is present 
in the amount of about 0.2 to 0.5 percent by weight of the composition. 
The wetting agent must be chosen to be compatible with the other components 
in the present composition. Conventional wetting agents such as sodium 
alkylaryl sulfonate and other organic synthetic detergents decompose 
rapidly in the presence of strong alkaline oxidizing/ bleaching solutions 
such as the composition of the present invention. This results in rapid 
decomposition of the hydrogen peroxide solvent and excessive foaming in 
the solution. A preferred wetting agent for use in the present composition 
comprises sodium 2-ethylhexyl sulfate (obtained from Niacet Co., Niagara 
Falls, N.Y.). It has good solubility, stability, and penetrating action in 
near-boiling alkaline and acid solutions, and is one of the few anionic 
surfactants stable in concentrated bleaching solutions. Other suitable 
wetting agents for practising the present invention may comprise sodium 
metasilicate or short chain branched surfactants. The wetting agent is 
used in the present invention in the amount of about 0.1 to 0.3 percent by 
weight of the composition. If the substrate comprises a metal, such as in 
a printed wiring board, the metal surfaces must be protected from attack 
by the peroxide and alkali in the present composition. The particular 
metal protective agent used depends on the specific metal being protected. 
For example, calcium and phosphorous compounds are used as protective 
agents for copper. The selection of the particular protective agent for a 
particular metal is known in the art and will not be detailed here. 
Suitable metal protective agents for practising the present invention 
include sodium carbonate or sodium metasilicate. The metal protective 
agent is present in the amount of about 0.5 to 2.0 percent by weight of 
the composition. 
The optimum operating temperature of the present composition to provide 
effective contaminant removal within a short period of time is within the 
range of 51.7 to 71.1.degree. C. (125.degree. to 160.degree. F.). Within 
this range, flux contaminants may be removed in 1 to 3 minutes. A 
preferred temperature for use of the present composition is about 
60.degree. C. (140.degree. F.). The increased temperature promotes the 
reaction, improves penetration of the composition by softening gummy 
contaminants, and keeps particulates in suspension so that they do not 
deposit on the cleaned substrates. In addition, the elevated temperature 
optimizes the effectiveness of the ultraviolet radiation for cleaving 
bonds in organic materials, as described below. 
The contaminants which can be removed in accordance with the present 
invention comprise organic materials which include, but are not limited to 
the residues left by commonly used flux materials. These flux residues 
comprise oils, resins, and other organic materials. Since the present 
composition and method are effective for cleaving carbon to-carbon bonds, 
they may be used for the removal of other organic compounds as well. Such 
materials include, but are not limited to, oil, grease, lubricants, 
photoresist, adhesive residues, plasticizers, or dyes. 
The solid substrate from which contaminants can be removed in accordance 
with the present invention may comprise any material which is not 
adversely affected by the peroxide or alkaline components of the present 
composition. Such materials include, but are not limited to, 
polyimide/polyamide laminates and epoxy/glass laminates which are used in 
printed wiring boards, silicon which is used in electronic devices, and 
anodized aluminum or polyimide which are used in cables and connectors. 
The solid substrate may have a simple or complex configuration and may 
include interstitial spaces which are difficult to clean by known methods. 
The substrate may be in the form of a continuous layer or in the form of 
discrete particles. 
In accordance with an alternative embodiment of the present invention, 
ultraviolet radiation is used to enhance the cleaning process. When 
hydrogen peroxide is exposed to ultraviolet radiation having a wavelength 
within the range of 184 to 300 nanometers (nm), preferably about 253 nm, 
such as from a xenon flash lamp, the hydrogen peroxide is dissociated to 
form a hydroxyl radical (OH.sup.-) which is very reactive. This hydroxyl 
radical then cleaves the carbon-to-carbon bonds in the organic contaminant 
material, forming carbon dioxide and water. In addition, the ultraviolet 
radiation itself also cleaves the carbon-to-carbon bonds in the organic 
contaminant materials, adding even further effectiveness to the cleaning 
process. The source of ultraviolet radiation, such as a xenon flash lamp 
or a mercury vapor lamp, is located external to the chamber containing the 
substrate to be cleaned and the present composition, and the radiation is 
directed into the cleaning chamber. For this purpose, a quartz window is 
provided on one surface of the cleaning chamber to permit transmission of 
the ultraviolet radiation. Optionally, a focusing barrel may be provided 
between the quartz window and the radiation source to improve the 
efficiency of the ultraviolet radiation transmission. Such methods for 
introducing radiation into reaction chambers are well known. 
The composition of the present invention may be used in essentially the 
same manner as known defluxing agents are used, namely in a spray or soak 
operation. If used in a soak operation, it is desirable to keep the 
present composition agitated, by air or mechanical or ultrasonic means. As 
an added feature in the present method, after the substrate has been 
treated with the present composition, residual alkaline materials (alkali 
or alkali salts) remaining on the substrate are neutralized. A preferred 
neutralization agent comprises hot carbonated water, which is applied at 
51.7.degree. to 71.1.degree. C. (125.degree. to 160.degree. F.). The 
carbonated water may be formed by bubbling carbon dioxide into deionized 
water. The use of the carbonated water rinse keeps the rinse water below a 
pH of 9.5, which is the regulated limit for disposal in a sewer. After the 
neutralization step, the substrate is rinsed in hot water at 51.7.degree. 
to 71.1.degree. C. (125.degree. to 160.degree. F.), preferably with air 
agitation, and then dried, preferably with hot air. In an exemplary batch 
processing technique, in which contaminated substrates are loaded into a 
chamber and treated, in turn, with the present composition, neutralizing 
agent, water, and hot air, the following approximate processing times may 
typically be used: 
______________________________________ 
Step Time 
______________________________________ 
a. Exposure of contaminated substrate 
3 minutes 
to present composition 
b. Neutralization 3 minutes 
c. Hot water rinse 4 minutes 
d. Hot air drying 5 minutes 
______________________________________ 
Thus, the present process can be completed within 15 minutes. 
Alternatively, the present process may be practised as an "in line" 
process. The contaminated substrates are loaded into a rack and the rack 
is lowered in sequence into a series of chambers containing, respectively, 
the present composition, the neutralizing agent, and deionized water 
sprayers. As yet another alternative, this in line processing may be 
accomplished by a conveyorized system. 
After the substrate has been treated with the present composition, the 
substrate is removed from the chamber containing the composition. The 
starting composition is then re established by the addition of hydrogen 
peroxide and, if necessary, the other components of the composition. Thus, 
the bulk cleaning solvent remains in place and does not require disposal. 
Rather, the composition is regenerated in situ by the addition of 
component materials as required. 
As an added feature of the present invention, the present composition 
removes metallic oxides from the substrate and thus serves also as a 
solder brightener. This eliminates the need for a secondary process, such 
as treatment with fluoroboric acid.

Examples of practise of the present invention are as follows. 
EXAMPLE 1 
This example illustrates the use of the composition and method of the 
present invention to remove solder flux from printed wiring boards. 
It should be noted that while the present composition is non toxic, general 
safety precautions, such as the use of goggles and protective clothing, 
are necessary. 
The test samples comprised polyimide/polyamide laminate printed wiring 
boards containing copper metallization and having been exposed to Alpha 
611, a solder flux obtained from Alpha Metals Company of Alpharetta, Ga., 
and comprising a mildly activated rosin flux. The composition of the 
present invention comprised: approximately 3.0 percent by weight hydrogen 
peroxide; approximately 0.2 percent by weight sodium hydroxide; 
approximately 0.1 percent by weight sodium 2-ethylhexyl sulfate as the 
wetting agent; approximately 0.5 percent by weight sodium metasilicate as 
the metal protective agent; and the balance being purified water. The 
temperature of the composition was maintained at 60.degree. C. 
(140.degree. F.). The samples were treated in a batch process as 
previously described herein using the previously described processing 
steps and times. The present composition was nearly transparent prior to 
introduction of flux-contaminated materials, with only trace amounts of 
gas liberation visible. When the contaminated material was introduced, 
vigorous gas formation on the flux residue was observed. This action 
continued as the flux was emulsified and dissolved into solution. 
Continued gas formation was visible as the dissolved flux residues 
continued to be oxidized. Completion of the decomposition was indicated by 
slow gas evolution and change in fluid color. Surface foaming was minimal. 
Complete removal of the flux residues was accomplished in an average of 
less than two minutes. The soldered joints were clean and free of oxides, 
i.e., bright in appearance. 
By contrast, it was found that alkaline solutions alone did not effectively 
separate the bulk of the flux residues from the substrate. In addition, 
alkaline solutions with wetting agents, but without hydrogen peroxide, 
required in excess of 10 minutes to separate flux residues from the 
substrate. Even after separation, the flux residues did not disperse well. 
EXAMPLE 2 
This example illustrates the use of the composition and method of the 
present invention to remove solder flux from cable connectors. 
A soft anodized aluminum connector was treated with the composition of the 
present invention as described in Example I except using a temperature of 
160.degree. F. (71.degree. C.) and 60-second rinse times for both the 
neutralization and final rinse steps. There was no visually detectable 
degradation of the anodized aluminum by exposure to the present 
composition. 
In another experiment, a cable made of Kapton (a trademark of E.I. du Pont 
de Nemours for a polyimide) was contaminated with Kester 197, a mildly 
activated rosin based flux obtained from Litton-Kester Company of Chicago, 
Ill. The Kapton cable was treated in accordance with the present invention 
as described above. Complete removal of the flux was accomplished as 
determined by visual inspection under 25X magnification. 
EXAMPLE 3 
This example illustrates the use of the embodiment of the method of the 
present invention in which ultraviolet radiation is used to enhance the 
contaminant removal. 
The composition and method described in Example 1 are used except that the 
composition and the substrate containing contaminants are exposed to 
radiation from a xenon flash lamp as previously described herein. The 
cleaning process proceeds generally as described in Example 1, except that 
complete flux removal is accomplished more rapidly. 
As previously discussed, the organic contaminants are oxidized by the 
present composition to form carbon dioxide, nitrogen, and water. The 
carbon dioxide and nitrogen are non-hazardous and may be exhausted into 
the atmosphere. The water by-product contains no noxious material and may 
be disposed of in a sewer without further treatment or may be re used. The 
hydrogen peroxide in the present composition is decomposed during the 
cleaning operation into atomic oxygen or hydroxyl radicals and water and 
the former react with the contaminants to form the above-noted products. 
Insoluble precipitates, such as cellulose gums, may also be formed as by 
products of the bond cleaving of the present composition, and may be 
readily removed by filtration. Thus, no toxic or hazardous materials are 
formed as a result of the present method. Consequently, the present 
process obviates the need for the expensive solvent emission control and 
waste management procedures required when using prior art halogenated 
solvents. In addition, environmental pollution and exposure of workers to 
hazardous materials are also avoided by the present composition and 
method. 
While the previous discussion has focused on the use of the present 
composition and method to remove flux residues from solid substrates, it 
is not intended to limit the present invention to this particular 
contaminant. Rather, it is intended to include within the scope of the 
present invention the removal of any organic material from a given solid 
substrate. 
Having thus described exemplary embodiments of the present invention, it 
should be noted by those skilled in the art that the within disclosures 
are exemplary only and that various other alternatives, adaptations and 
modifications may be made within the scope of the present invention. 
Accordingly, the present invention is not limited to the specific 
embodiments as illustrated herein, but is only limited by the following 
claims.