WO1993016160A1

WO1993016160A1 - Defluxing composition and use thereof

Info

Publication number: WO1993016160A1
Application number: PCT/US1993/001028
Authority: WO
Inventors: Frank Fusiak; Edward W. Lamm; Victor T. Roberts
Original assignee: Isp Investments Inc.
Priority date: 1992-02-10
Filing date: 1993-02-05
Publication date: 1993-08-19

Abstract

This invention relates to a composition suitable for the removal of an acid or rosin modified flux residue from a printed circuit board, which composition consists essentially of (a) between about 30 and about 80 weight % of a flux solubilizing agent selected from the group of an N- C1 to C6 alkyl pyrrolidone, an N- C1 to C4 alkyl caprolactam, tetramethylurea, dimethylimidiazolidinone and mixtures thereof and (b) between about 20 and about 70 weight % of a non-toxic, water-soluble, corrosion controlling agent which is not the same as (a) and which has a boiling point within about 25 °C of said flux solubilizing agent and is selected from the group of C2 to C3 alkylene glycol, tetra-lower alkyl urea, 2 to 4 poly(propylene glycol lower alkyl ether) and 2 to 4 poly(propylene glycol lower alkyl ether acetate). The invention also relates to the process for using said composition in a semi-aqueous defluxing process.

Description

DEFLUXING COMPOSITION AND USE THEREOF

In one aspect the invention relates to a non-flammable, biodegradable defluxing composition in which the active defluxing solvent is readily reclaimable after use for recycling. In another aspect, the invention relates to a semi-aqueous process for removing an acid or rosin modified flux from the surface of a printed circuit board or an equivalent component on which elements are soldered or joined by brazing.

BACKGROUND OF THE INVENTION

Several processes are known for soldering circuit components onto a suitable substrate. For example, prior to a soldering operation for attachment of components, an acid or rosin modified soldering flux is conventionally applied to insure an adherent bond of solder. The printed circuit board may be protected with a solder mask or stencil which covers all areas of the substrate except those areas where solder is intended to contact and adhere to a conductive surface portion. Application of flux and solder can be done by hand, wave or reflow methods. In wave soldering, the substrate is mechanically conveyed over, and contacted first with flux and then with molten solder. The solder adheres to all conductive surfaces on the substrate except where masked. In the reflow soldering process, a paste containing both flux and solder is applied only to the points where solder bonds are to be made, the circuitry components are set in the paste and the entire circuit board assembly is heated to melt the solder and to bond the circuitry component to the substrate. The flux material which remains on the board assembly after soldering must be completely removed since even traces can cause permanent failure of the circuitry through corrosion, absorption of water and other effects. In the past chlorofluorocarbons have been used to effectively remove substantially all of the flux; however, with current evidence that these halogenated hydrocarbons cause depletion of the ozone layer and consequent damage to the environment, other defluxing solvents for use in semi-aqueous systems have been sought. The semi-aqueous cleaning process involves washing the surface of a contaminated substrate with a solvent which is capable of dissolving the flux residue and removing the resulting solution from the printed circuit board which is then rinsed with water and dried.

Among the proposed cleaning solvents, U.S. patents 4,640,719; 4,983,224 and 4,867,800 are directed to the use of terpene mixtures; however, terpenes are odorous, relatively insoluble in water, and have low flash points; thus they are not easily removed from the substrate surface by simple washing techniques. Additionally, the terpene alpha-limonene, has been found to induce tumors and therefore presents a potential health hazard. Although U.S. 4,983,224 seeks to improve the water solubility by adding a surfactant to the terpene mixture, this measure does not alter other objectionable properties of these mixtures. U.S. patent 4,276,186 advocates the use of N-methylpyrrolidone and alkanolamine mixtures optionally in admixture with halogenated hydrocarbons. However, these mixtures are difficult to recover due to the low volatility of the alkanolamines. Furthermore, alkanolamines are corrosive and some have been found to be carcinogenic. Tetrahydro- furfuryl alcohol (Canadian Patent 2,026,335 and U.S. Patent 4,664,721) and hydroxymethyl pyrans are also among the alternative defluxing agents which have been recommended. However, these agents are not sufficiently active and require formulation with activators to produce desired defluxing results. In addition, tetrahydro- furfuryl alcohol is known to cause damage to mucous membranes and to the cardiovascular system.

Compositions for the removal of circuit board fluxes require certain properties which are not found in paint and varnish removers, many of which contain butyrolactone as in the paint or ink removers employed in U.S. patents 5,098,592; 5,024,780; 4,812,255; 4,836,950 and British Patent 2,191,501. In the present flux removing compositions, butyrolactone reacts to cause objectionable spotting of the circuit board. Also, poly(ethylene glycol alkyl ether acetates or poly(ethylene glycol alkyl ethers) as employed in U.S. patent 4,428,871; 4,401,748; 4,401,747 and 4,744,834 for the removal of naphthoquinone sulfonic ester and other photoresists and amide photosensitizers, are to be avoided due to the toxicity of residual ethylene glycol and ethylene oxide. Finally, the corrosive acid compositions used in U.S. patents 5,035,829, 4,812,255 for paint removal are not effective for defluxing abietic acid modified fluxes commonly used on circuit boards. Because of the obvious chemical differences between acid or rosin modified flux compositions and inks, such as pigment suspensions, or paints which are classified as urethane, acrylic latex, acrylic enamel, alkyl enamel or nitrocellulose lacquer, distinctly different properties are needed in compositions for their removal.

Accordingly, it is an object of this invention to provide a superior defluxing composition which is non-flammable, non-carcinogenic, biodegradable and which possesses a high flash point. - A -

Another object is to provide a defluxing composition which is effective in the complete removal of flux deposits from a surface having solubilizing properties at least equal to the chlorofluorocarbons and terpenes while being non-corrosive, non-carcinogenic, and non-ozone depleting.

Yet another object is to provide a defluxing composition which avoids spotting of a circuit board.

Another object of this invention is to provide a semi-aqueous process for the removal of flux deposits from a printed circuit board in which the solvent and rinse water are reclaimable.

These and other objects of the invention will become apparent from the following description and disclosure.

THE INVENTION

In accordance with this invention there is provided a defluxing replacement for the use of chlorofluorocarbon (CFC) solvents which are widely used to clean printed circuit boards. The present defluxing composition is biodegradable and minimizes harm to humans and the environment. Instant composition has a high flash point above 150°F. and is comprised of non-flammable, water soluble components having individual boiling points which differ by not more than about 25°C. The present invention resides in a defluxing composition containing an active, water soluble agent for solubilizing the flux material and a corrosion controlling component which interacts to regulate the activity of the defluxing agent with respect to a given substrate, which is most often composed of epoxy glass, glass, ceramic or metal; although other substrate materials such as acetals, polyether i ides, polyimides, polypropylene oxides, polytetrafluoroethylene etc. are also suitably employed as substrates.

Suitable defluxing solubilizing agents employed herein include a tetra lower alkyl urea, e.g. tetramethylurea, dimethylimidiazolidinone, an N- C to C₅ alkyl lactam optionally substituted on a ring carbon atoms with lower C to C₆) alkyl, e.g. an N- C to C₆ alkyl pyrrolidone, an N- C to C₄ alkyl caprolactam and mixtures of these agents. The lactams such as for example, N-methyl-2-pyrrolidone, N-ethy1-2-pyrrolidone, N-methyl-methylpyrrolidone, N-methyl caprolactam, N-ethyl-methylcaprolactam, N-cyclohexylpyrrolidone and any mixture of the above non-toxic compounds which solubilize flux resulting from a soldering or brazing operation, are preferred. The active defluxing agent comprises between 30 and about 80 weight % of the composition; the remaining 20 to 70 weight % being represented by a dissimilar, corrosion controlling component. Representative of suitable corrosion controlling agents are monomeric C₂ to C₃ alkylene glycols, tetra- lower alkyl ureas, 2-4 poly(propylene glycol lower alkyl ethers) and the corresponding 2-4 poly(propylene glycol alkyl ether acetates) . Suitable examples of such corrosion controlling agents include dipropylene glycol methyl ether, dipropylene glycol mono methyl ether acetate, tripropylene glycol ethyl ether, tetrapropylene glycol methyl ether, dipropylene glycol isopropyl ether and the like, and mixtures thereof, all of which act as diluents and regulate the activity of the defluxing solubilizing agent so as to avoid damage to the substrate and/or circuitry components while permitting complete separation and dissolution of residual or excess flux after soldering or brazing. A particularly preferred defluxing composition comprises between about 40 and about 60 weight % of N-methy1-2-pyrrolidone and between about 60 and about 40 weight % of dipropylene glycol lower alkyl ether, most preferably dipropylene glycol methyl ether, which is applied as a liquid to the substrate surface contaminated with residual or excess flux which, for example, can result from soldering a masked or unmasked printed circuit or other wiring board surface or from through hole assemblies and reflowed surface mount assemblies.

The amount of defluxing composition employed for cleaning can vary between about 0.1:1 and about 1:2 volumes of flux/volume of defluxing composition, preferably between about 0.2:1 and about 3:5 volumes of flux/volume of defluxing composition.

Because of their high flash points, i.e. above 150°F. , the present non-volatile compositions are safely handled by operators in the cleaning process. The present process also realizes low material consumption and significant reduction in load to waste disposal.

The water soluble compositions of this invention can be employed in batch or in-line cleaning of soldered or brazed products. The in-line cleaning process is one in which the circuit board or equivalent component is fed to a conveyor belt which carries the soldered substrate through various treating zones including a defluxing zone and a subsequent water wash and/or steam jet washing zones.

One method of preparing a printed metal circuit board involves applying an acid based or rosin based flux, most commomly an abietic acid flux, over the entire board surface so as to clean the board and to remove any oxidized layer from the surface of the metals to be joined. Thus, when soldering is effected, a nascent metal to metal bond is achieved and the soldered component is held firmly in place. A typical solder paste or flux used in printed circuit boards contains from about 8 to about 20 weight % of an acid such as abietic, levopimaric, d-pimaric, neoabietic, or Cll acid and between about 75 and about 95 weight % metals such as lead-tin alloy and alloys of mercury-indium, bismuth-indium and silver which may also contain minor amounts of antimony, copper, iron, zinc and aluminum. In addition to the above rosin acids, the flux may also comprise zinc and ammonium chlorides, hydrogen chloride or hydrogen fluoride. Organic halogen containing compounds have also been used. However, the acid component of the soldering paste is usually a cycloaliphatic rosin acid containing at least 14 carbon atoms which provides wetting and penetration of the metal soldering component. Rosins such as tree gum, gum rosin or wood rosin, can be used in place of acid in the flux.

In the process of affixing an element to a substrate, the heat required for the soldering operation causes the paste to melt and an acid based flux to form over the substrate surface. Heavy metals also appear in the flux resulting from the soldering operation. Brazing compositions normally have a sodium or potassium borate base which also include boric acid, an alkali metal fluoride, bifluorides or other halide components as well as silver-copper, copper-zinc, copper-phosphorous and/or aluminum-silicon alloys. These brazing compositions also produce unwanted flux during the brazing operation which can be easily removed by the present process. It has been found that the defluxing composition of the present invention requires no surfactant material since it is water soluble and is easily removed by subsequent water washing or steam jet treating operations. Indeed the presence of a surfactant is detrimental since, because of its low volatility, it is not easily reclaimed and recycling operations, as employed in continuous cleaning processes, are unfeasible. The compositions of this invention do not form emulsions or azeotropes with water so that reclaiming the cleaning liquids for reuse is commercially achievable. Also the boiling points of the present composition ranging from about 170°C. to about 400°C. or more contributes to the easy and complete removal of flux contamination by simple vacuum distillation. Further, the reclamation of substantially purified water for recycle after the washing step reduces the volume of disposable material, thus providing a process which is ecologically attractive.

In a preferred method of defluxing a printed circuit board, the board containing residual flux material is treated with the present composition under agitation achieved by spraying, by immersion with ultrasonic vibration or by other mechanical means. After a period of between about 30 seconds and about 30 minutes, preferably between about 1 and about 5 minutes, during which loosening or dispersal and dissolving of the flux material in the cleaning composition takes place, the board is subjected to forced air blow-off which removes the defluxing composition containing the unwanted flux material. The contaminated, high boiling defluxing composition can be easily regenerated by distillation and the reclaimed composition recycled to the initial treating step. The printed circuit board is then subjected to a water rinse at an elevated temperature, for example, at between about 120° and about 175°F. under a pressure from about 20 to about 100 psig. for a period of from about 1 to about 10 minutes. Most preferred water washing is carried out at a temperature between about 135° and about 150°F. under a pressure of from about 35 to about 80 psig. for a period of from about 1 to about 5 minutes. The rinse water recovered from this step, containing remaining portions of the contaminated defluxing composition, can be purified by distillation and recycled to the washing zone, if desired. The resulting still bottoms can be combined with the contaminated defluxing composition in the composition distillation zone to minimize the volume of non-volatile residue released to waste disposal. The water washed circuit board is then submitted to forced air drying to complete the defluxing operation. As an alternative or as a subsequent addition to the water washing step, the printed circuit board can be subjected to steam jet washing as described in U.S. patent 5,051,136, with attendant advantages. For example, when a steam jet is applied at such a pressure and temperature as to eliminate substantially all moisture from the circuit board, the drying operation can be significantly shortened or in some cases eliminated since at a sufficiently high temperature all moisture is vaporized. The steam jet can also be applied after water washing to dry up any water droplets entrained in the soldered components and in narrow spaces between soldering sites.

In the present invention, the percent of components in the composition, consisting of a defluxing, solubilizing agent and a corrosion controlling agent, are extremely critical since below 30 weight % of the defluxing component, inadequate cleaning occurs; whereas above 80%, attack on the substrate surface is evidenced. Further, it will be understood that within the percentages of the composition, mixtures of defluxing agents and/or corrosion controlling agents can be employed if desired. For example, the 30-80% of defluxing component can consist of a mixture in any proportion of, N-methyl-2-pyrrolidone and dimethylimidiazolidinone combined with dipropylene glycol methyl ether alone or in admixture with tetramethylurea. Other mixture combinations are also apparent from the foregoing disclosure and these also fall within the scope of this invention. However, it is equally important to select compositions wherein the boiling points of the components vary by not more than about 25°C. Observation of this limitation is needed for contributory defluxing action and achieves one of the economic advantages of the present process since the ease of recovery and recycle of a regenerated defluxing composition is an important consideration from a commercial standpoint.

Having thus described the present invention reference is now had to the accompanying examples which more particularly point out specific features and preferred embodiments but which are not to be construed as limiting to the scope of the invention as more broadly defined above and in the appended claims.

EXAMPLE 1

Circuit Board Preparation I

The circuit boards used for the cleaning evaluations were Detrex, non-functional, surface mount board assemblies. The board material was FR-4 epoxy-glass as designed and manufactured for Detrex Chemical Industries Inc. by Xetel. Each unmasked, printed circuit board was approximately 6-3/4" long by 4-1/2" wide and 1/16" thick. Each single sided board assembly was populated with thirty-two surface mount components shown below together with quantities, pitch centers (distance between leads) , and stand-off distance (distance from top board surface to bottom of component) . - 11 -

MOUNT COMPONENTS

Pitch Stand-Off

Centers Distance

50 mils 25 mils

50 mils 8 mils

4-7 mils

6 mils

5 mils

Prior to placement of surface mount components, approximately 2.5 grams of solder paste, i.e. Alpha Metals 63 Sn/37 Pb rosin modified acid flux (RMA) 376 EH 88-2-25 (Metal content = 88 wt. %, Flux content = 12% mildly activated) were hand screened onto each test board using a 8 mil thick copper stencil in direct contact with the board surface. A Celmac Model SMT-85 Robotic Surface-Mount Placement System was used to place the surface mount components on each test board after screen application of solder paste. A Grieve Corporation Model FCF-270 electric heated convection oven at 185°F. was used to pre-bake each test board assembly for 20 minutes; after which an Open Top Vapor Phase Reflow System was employed to reflow each test board assembly. The reflow unit was then charged with FC-70 Fluorinert™* (manufactured by Minnesota Mining and Mfg. Co.) to reflow the solder paste on the circuit board assembly. Freon® TF** was introduced into the unit to form a vapor blanket above the FC-70 Fluorinert™. During the reflow process, each board assembly was subjected to 30 seconds of vapor dwell time in the FC-70 followed by 15 seconds in Freon® TF. Each board assembly was then cleaned within 10 minutes after vapor phase reflow.

EXAMPLE 2

ULTRASONIC DEFLUXING OF CIRCUIT BOARDS

The following cleaning solutions were prepared by simple mixing of the components at ambient conditions.

* a perfluorocarbon mixture boiling at 419°F. ** Trichlorotrifluoroethane

CLEANING SOLUTIONS

Weight %

Components B D E G* H*

N-methyl-2- pyrrolidone (NMP) 100 85 70 55 30 15 10 50

Dipropylene glycol monomethyl ether

I-¹ (DPM) -— 15 30 45 70 85 100

Gamma-butyro- lactone (BLO) 90 50

* comparative for corrosion control

A Detrex Model HS-1-7A portable stainless steel tank assembly units complete with one 25.5 kHz ultrasonic transducer and companion CTR-750A generator were used in conducting the cleaning evaluations of this example. Each unit was filled with approximately three gallons of the selected solution (A-I) . In order to provide a solvent spray cleaning cycle, the tank was retrofitted with a 1-1/2 high pressure (HP) stainless steel centrifugal spray pump complete with stainless steel braided hose and a hand held spray wand with Veejet type spray nozzle operating at 30 psig. The rinse tank was a Detrex Model HS-1-7A portable stainless steel tank assembly complete with a 25.5 kHz ultrasonic transducer, a companion CTR-750A generator, a 1/15 HP spray pump and wand with a spray operating at 10 psig. , was employed as a rinse assembly. The tank was filled with approximately three gallons of tap water.

The cleaning cycle of a circuit board was carried out by spraying the circuit board with the solution under 30 psig at 130°F. for 30 seconds and then immersing the board in the solvent at 130°F. with agitation provided by an ultrasonic transducer for about 1.5 minutes. The board was then spray rinsed with tap water at 90°F. and 10 psig for about 45 seconds, after which the board was immersed in water at 90°F. and agitated with a 25.5 kHz ultrasonic transducer for about 1.5 minutes and then dried with a hot air gun for about 1.5 minutes, after which the board was examined for flux residue using an Aus Jena Stereozoom Microscope at 25x magnification. Ionic contamination tests were conducted on each board using a Kenco Model 600 Omegameter containing 5000 ml of 75% isopropanol/25% water test cell solution with a 15 minute test duration; however, in cases where significant flux was still apparent, ionic contamination was not determined. After cleaning, circuit boards are required to have an ionic contamination below of 15 ^ιg NaCl/in² in order to meet existing military specifications for cleanliness.

The cleaning results for the above solutions were as follows:

Formula Visual (25X1

A No visible flux residues apparent; however, microscopic ruptures of the substrate are present.

B No visible flux residue apparent; however, slight microscopic ruptures of the substrate are present, but less than with solution A.

C No visible flux residue, no ruptures, no board spotting.

D No visible flux residue, no ruptures, no board spotting.

E No visible flux residue, no ruptures, no board spotting.

F Slight flux residue apparent.

G No visible flux residue; however, whitish haze and spots on board surface are present.

H No visible flux residue, no ruptures, however, whitish spotting of the board appeared.

I Flux residue apparent throughout. Formula Ionic Contamination (υq NaCl/in² of board area)

A 0 B 1 C 5 D 11

E 11 F 87 H 5.5

EXAMPLE 3

Spray Under Immersion Circuit Board Defluxing

The solvents blends A, D-F, J and I were prepared as before by simple mixing at ambient conditions.

SOLVENTS

Components D E

NMP 100 55 30 15 5 DPM 45 70 85 95 100

The circuit board preparation was identical to the procedure in Example 1 except the components were hand mounted and tests were conducted at ambient temperature without ultrasonics. The circuit board was sprayed at 25 psig with the solution for 30 seconds and then immersed in the solvent for 60 seconds with agitation provided by a spray wand. The board was removed from the immersion tank and sprayed at 25 psig for an additional 30 seconds followed by a water spray at 10 psig for 30 seconds. The board was then immersed in a water rinse tank for 30 seconds with agitation supplied by a water spray wand and then removed from the tank and sprayed with water at 10 psig for an additional 30 seconds. The board was blown with hot air and then with a heat gun to dry.

The results of these experiments are reported as follows:

Solution Visual (25X) Ionic Contamination

Excellent flux removal, with ruptures 8.7 jig NaCl/in^

D Excellent flux removal, no ruptures 4.3 jαg NaCl/in² Excellent flux removal, no ruptures 5.4 g NaCl/in² Slight visible flux, no ruptures 4.0 μq NaCl/in²

J Visible flux residues

I Visible flux residues

EXAMPLE 4

Circuit Board Preparation II

The circuit boards used in this example were FR-4 epoxy-glass as designed and manufactured for the Institute for Interconnecting and Packaging Electronic Circuits by Northern TeleCom. Each unmasked, printed circuit board was approximately 4-1/2" long by 4" wide and 0.059" thick. Each single sided board assembly was populated with two 68 I/O leadless chip carrier. Prior to placement of surface mount components, approximately 0.38 grams of solder paste, i.e. Alpha Metals 63 Sn/37 Pb RMA 376 EH 80-2-45 (metal content ^*-^*** 90 wt. %, flux content ^*= 10% mildly activated rosin flux) was screened onto each test using a copper stencil in direct contact with the board surface. The equipment and procedures used for component placement, pre-baking and reflowing were similar to those in Example 1, except that pre-baking was performed for 45 minutes at 70°C. An FC-5311 Fluorinert™ solvent (b.p. 419°F.) was used during reflowing, and each board was wave soldered on a Hollis wave solder, 16" conveyor finger type machine.

Prior to wave soldering, each board was spray coated with an RA type flux (Alpha 1585) . With the wave solder unit operating at 4.5 ft/min. , the boards were passed through two pre-heat zones operating at 178°C. and 235°C. , respectively. After exiting the pre-heat zones, the boards passed through the solder wave which had a solder pot temperature of 262°C. This method is typically used to secure through hole devices, however, in this case its purpose was to close-off the via holes under the mounted SMT devices, trapping any remaining flux. Each board was removed from the machine and inspected prior to cleaning.

EXAMPLE 5

In-Line Circuit Board Defluxing

A Detrex Model SA-20 in-line semi-aqueous cleaning system equipped with a conveyor belt and compressed air knife drying chamber was used to clean the circuit boards prepared in Example 4. The unit was filled with approximately 110 gallons of about 55% N-methyl-2-pyrrolidone and about 45% dipropylene glycol monomethyl ether. In order to effect a spray under immersion cleaning cycle, the unit was fitted with a 15 HP stainless steel centrifugal pump having steel spray bars equipped with Veejet spray nozzles operating under a spray pressure of 75 psig. The rinse system comprised three tanks, each equipped with 7-1/2 HP pumps in order to maintain approximately 60 psig water spray rinse.

The cleaning cycle was carried out by spraying under immersion the solvent composition onto the mounted circuit board at 95°C. and 60 psig. for 2 minutes. The board was then removed from the cleaning tank via the conveyor belt and the solvent was removed by air blow-off. The board was then spray rinsed with tap water at 60/25 psig (top/bottom nozzles) and 140°F. for 60 seconds followed by air knife drying. The board was then tested for ionic contamination and residual flux, as described above. This experiment was repeated 4 times and the averaged results are reported in the following tabulation.

For co parsion, a circuit board prepared as in Example 4 was subjected to benchmark vapor batch defluxing using commercial trichlorotrifluoroethane (CFC-113) , methanol, nitromethane azeotropic blend in a vapor degreaser. The board was lowered at a rate of approximately 10 ft/min into a boil sump and agitated with the chlorofluorocarbon blend for 3 minutes, after which it was removed and allowed to drain for 30 seconds before immersing it in a rinse sump for 1 minute. The board was then allowed to equilibrate for 30 seconds in the vapor zone above the rinse tank before completely withdrawing it from the rinse sump. The board was then tested for ionic contamination and residual flux. Solvent System Ionic Contamination* Residual Flux*

NMP/DPM blend 3.2 μg NaCl/in² 2763 μg/ iπ CFC-113 azeotrope 10.7 μg NaCl/in² 3945 ig/in^**

* Average of 4 circuit boards.

EXAMPLE 6

Abietic Acid Loading

The following compositions were tested for their ability to solubilize abietic acid (normally considered the criterion for circuit board defluxing) by admixing 5-30 g. of abietic acid to 25 g. of solvent. Each of the resulting mixtures was shaken vigorously for 2 minutes at ambient temperature and then placed on a rotating wheel overnight. The results are listed below:

Wt. % Abietic Acid Solvent Dissolved

Deionized Water 1

Propylene glycol 4 50% aqueous Tetrahydrofurfuryl Alcohol with 5% Ethanolamine 4.5

Trichlorotrifluoroethane (CFC-113) 5

Propylene Carbonate 8

Isopar*- M (mix of C₉ to C₁₃ isoparaffins) 10

Gamma-Butyrolactone 22

Dipropylene Glycol 33

Tripropylene Glycol 33

Dipropylene Glycol Monomethyl Ether (DPM) 45

Tripropylene Glycol Monomethyl Ether (TPM) 43

1,1,1-Trichloroethane 50

Dichloromethane 60

Tetramethylurea 55

N-methy1-2-pyrrolidone (NMP) 60

N-cyclohexy1-2-pyrrolidone 42

N-ethyl-2-pyrrolidone 44 d-Limonene 40

Dimethylimidiazolidinone 43 55% N-methy1-2-pyrrolidone and 45%

Dipropylene Glycol Monomethyl Ether 52 50% Tetramethylurea and 50%

Dipropylene Glycol Monomethyl Ether 56 50% Dimethylimidiazolidinone and 50%

Tripropylene Glycol Monomethyl Ether 50 50% N-ethy1-2-pyrrolidone and 50%

Propylene Glycol 48

As shown above, the present compositions possess acid solubilizing properties at least as effective as chloro- or chlorofluoro- and terpene mixtures. EXAMPLE 7 Spent Solvent Recovery

To a 250 ml round bottom 3-neck flask, 198.8 g of spent solvent (NMP/DPM - 55/45) contaminated with 0.5 weight % non-volatile flux residue and 1% water was flash distilled in a one-plate distillation set up at 100 mm Hg. The main fraction (177.5 g) collected at a pot temperature of 136°C. and head temperature of 135°C. was found to contain 1.2% water and 98.8% solvent on analysis.

EXAMPLE 8 Contaminated Water Recovery

One hundred grams of water contaminated with approximately 10% by weight of the NMP/DPM Blend (55/45) was charged to a 250 ml 3 neck round bottom flask and flash distilled in a one plate distillation set up at atmospheric pressure and 100°C. The main fraction (89.8 g) was found to contain 99.3% water on analysis. The still bottoms were found to contain 99.8% solvent.

Examples 7 and 8 indicate that the present degreasing, defluxing operation can be carried out in a continuous manner with only occasional partial replacement of solvent and/or acid rinse water. Unlike the amino activated blends of the prior art, the use of the present comparatively lower boiling compositions, are economically recoverable after the defluxing operation, thus greatly reducing the cost of the overall operation.

It will be understood that any of the other compositions in the foregoing disclosure can be substituted for those solutions C-E used in Example 2 to provide a similarly efficient defluxing operation.

Claims

WHAT IS CLAIMED IS:

1. A defluxing composition for removing an acid or rosin modified flux composition in the manufacture of circuit board assemblies which consists essentially of (a) an effective flux solubilizing, board non-degrading amount of a water soluble compound selected from the group of tetra lower alkyl urea, dimethylimidazolidinone, an N- C to C₆ alkyl, 5 or 7 membered ring lactam which is optionally substituted on a carbon of the ring with C_λ to C₄ alkyl and mixtures thereof and (b) a corrosion controlling amount of a water soluble compound which is not the same as (a) having a boiling point varying by not more than 25° from (a) and which is selected from the group of C₂ to C₃ alkylene glycol, tetra-lower alkyl urea, 2 to 4 poly(propylene glycol lower alkyl ethers) , 2 to 4 poly(propylene glycol lower alkyl ether acetates) and mixtures thereof.

2. The composition of claim 1 wherein (a) is between about 30 and about 80 wt. % of the composition.

3. The composition of claim 1 wherein (a) is between 40 and 60 wt. % and the flux solubilizing compound is a lactam.

4. The composition of claim 3 wherein said lactam is N-methy1-2-pyrrolidone.

5. The composition of claim 3 wherein (b) is between 60 and 40 wt. % and the corrosion controlling compound is a propylene glycol C_λ to C₄ ether or propylene glycol C₂ to C₄ alkyl ether acetate.

6. The composition of claim 5 wherein (b) is dipropylene glycol methyl ether.

7. The composition of claim 1 having a flash point above 150°F.

8. The process of applying the composition of one of claims 1, 2, 3, 5 and 6 over the surface of a circuit board which is contaminated with an acid or rosin based flux, agitating said composition on the contaminated board at a temperature of from about 135° to about 150°F. under a pressure of from about 35 to about 80 psig for a period of from about 1 to about 5 minutes and then rinsing said board with water and/or steam to remove residuals and to provide a defluxed circuit board.

9. The process of claim 8 wherein the volume ratio of said flux to said composition is between about 0.1:1 and about 1:2.

10. The process of claim 9 wherein the volume ratio of said flux to said composition is between about 0.2:1 and about 3:5.