METHOD AND COMPOSITION FOR CLEANING ARTICLES

Abstract: In a method for cleaning articles, especially for removing flux after soldering, an article is contacted with a hydrocarbon-containing fluid containing one or more hydrocarbons selected from C8 to C15 paraffinic and naphthenic hydrocarbons and with an alcohol-containing fluid containing one or more alcohols selected from C5 to C15 straight-chain or branched-chain, saturated aliphatic alcohols. The hydrogen-containing fluid and alcohol-containing fluid are preferably in the form of a liquid mixture. Efficient cleaning of articles, for example of electronic components after soldering, is possible without the use of halogen-containing solvents.

Description: METHOD AND COMPOSITION FOR CLEANING ARTICLES The present invention relates to a method of cleaning articles, and to a cleaning composition for use in the method. In the manufacture of printed circuit boards (PCBs), it is usual for soldering flux to be applied to the boards to promote strong bonding of the solder to the board. The flux and solder may be applied, for example, by the wave soldering method or the reflow soldering method. After soldering, flux remains on the boards. That residual flux must be removed in order to reduce the possibility of early circuit failure. The fluxes used in the manufacture of electronic components, for example, PCBs, using a soldering technique are generally rosin-containing fluxes or synthetic water-soluble fluxes. Rosin-containing fluxes include rosin mildly activated (RMA) and rosin activated (RA) fluxes, which are obtained by activation of a rosin- containing flux using, for example, organic acids, amines, amides or halogen-containing compounds. Many of the activating materials decompose on soldering thus giving rise to inorganic substances that can damage the electronic components. The residue to be removed thus comprises a combination of rosin molecules and inorganic substances. In many previously used methods for defluxing articles after soldering, the residual flux has been removed using halogenated hydrocarbon solvents. It has become recognised in recent years, however, that these solvents have a particularly harmful effect on the environment. Further, because of their physical properties, special requirements are required in their storage, handling and disposal. It is therefore desirable to avoid the use of halogenated hydrocarbon solvents, "if possible. European Patent Specification No. 416,763 discloses compositions for cleaning dirty articles, for example, PCBs, comprising terpene hydrocarbons or other non- halogenated solvents. After the cleaning step, remaining traces of solvent are said to be removed azeotropically, by forming an azeotrope between the solvent and an aqueous medium, the azeotropic mixture being evaporated from the surface of the article. Optionally, a low boiling organic solvent, for example a ketone, amine, ether or alcohol may be included in the cleaning composition to promote formation of an azeotrope. The low boiling organic solvent, if present, is preferred to be a C3 to C4 alcohol. Japanese Patent Specification No. 3-6300 discloses the use of an oleophilic detergent comprising a terpene hydrocarbon selected from IOC monoterpenes to 15C sesqui- terpenes, with turpentine oil and a surfactant. The composition may further contain an alcohol (the only example given being a C3 alcohol) , ether, ketone, ester, aromatic compound or water. US Patent Speci ication No. 4,983,224 discloses a cleaning composition comprising a terpene or terpenol, a surfactant and an aprotic solvent, for example, DMF or DMSO. European Patent Specification No. 120,319 discloses a cleaning composition for removing wax from electronic components, the composition containing halogenated or non-halogenated hydrocarbon, a fluorinated alcohol having at least two fluorine atoms and, optionally, a further, polar, organic solvent. The hydrocarbon may be, inter alia, petroleum ether. The further polar organic solvent may be, for example, an alcohol. As alcohols there are proposed aliphatic, cyclic and aromatic alcohols that in each case have seven or fewer carbon atoms. British Patent Specification No. 2,175,004 discloses a cleaning composition for removing dirt and grease from metal and plastic surfaces, the composition containing from 85 to 97 parts by weight of a non-aromatic hydrocarbon including aliphatic and/or cyclo-aliphatic compounds, from 3 to 15 parts by weight of alkylated aromatic substances containing at least one C8 to C18 alkyl group and, in a preferred form, from 0.1 to 1 part by weight of an additive which renders the composition more incompatible with water, so facilitating separation from water after the cleaning step. The additive may be selected from aliphatic alcohols having from 8 to 20 carbon atoms, ether derivatives of alkylene glycols and hydroxycarboxylic acids having more than 8 carbon atoms. British Patent Specification No. 1,524,448 discloses a cold cleaner for removing oily and fatty contaminations from surfaces. The composition may contain a mineral oil fraction, which is preferred to be a mostly paraffinic or naphthenic fraction, and saturated or unsaturated aliphatic alcohols or alicyclic alcohols with from 6 to 20 carbon atoms and/or fatty acids, and a sulphosuccinic acid diester. As alcohols, unsaturated alcohols are said to be preferred- International Patent Specification No. WO 87/00209 discloses a method of cleaning rosin flux or adhesive tape residue from printed circuit and/or wiring boards, in which boards are contacted with a composition containing a terpene, optionally in combination with a surfactant that is capable of emulsifying the terpene. European Patent Specification No. 412,475 discloses a cleaning composition for cleaning PCBs, the composition containing, a dibasic ester and a hydrocarbon solvent other than a terpene. As hydrocarbon solvents are proposed petroleum derived solvents, for example, mineral spirits, naphthas and aromatics. The composition may contain a further component, for example a non-ionic surfactant, for improving the miscibility of the dibasic ester and hydrocarbon solvent. European Patent Specification No. 104,633 discloses a method of cleaning PCBs in which the boards are immersed in an azeotropic liquid solvent. The azeotropic liquid may contain a low molecular weight alcohol, for example, a C3 or C4 alcohol, together with a hydrocarbon of relatively low molecular weight, for example, cyclohexane or heptane. European Patent Specification No. 302,313 discloses a method of cleaning objects in which the objects are treated in a closed container with an azeotropic mixture of water and a further solvent, for example, methylene chloride, trichloroethylene or tetrachloroethane. The present invention provides a process for cleaning an article comprising contacting the article with: (i) a hydrocarbon-containing fluid comprising one or more hydrocarbons selected from C8 to C15 paraffinic and naphthenic hydrocarbons and having an aromatics content of not more than 8% by weight, based on the combined aromatics and hydrocarbon content of the fluid, (ii) an alcohol-containing fluid comprising one or more alcohols selected from C5 to C15 straight-chain or branched-chain, saturated aliphatic alcohols, the fluids being substantially free of any halogen- containing organic compound and component (ii) representing at least 5% by volume, based on the total hydrocarbon and alcohol content, when the process comprises contacting the article with a liquid mixture comprising components (i) and (ii). Advantageously, the fluid or fluids contain not more than 5 pp of halogen. The article may be contacted sequentially with a hydrocarbon-containing fluid and an alcohol-containing fluid- Preferably, however, the article is contacted with a liquid mixture of the said fluids the said mixture comprising from 75 to 95 parts by volume of one or more hydrocarbons selected from C8 to C15 paraffinic and naphthenic hydrocarbons, and from 5 to 25 parts, preferably from 8 to 15 parts, by volume of one or more alcohols selected from C5 to C15 straight-chain or branched-chain, saturated aliphatic alcohols. It will be appreciated- that the aromatics content of the liquid mixture will be not more than 8% by weight based on the combined aromatics and hydrocarbon content of the mixture. Advantageously, the hydrocarbon-containing fluid is a distillation fraction obtained in the distillation of petroleum. The hydrocarbon-containyig fluid preferably contains from 0.5 to 2 parts by volume of normal and iso- paraffins per part by volume of naphthenes. Preferably, the amount of aromatics, if present, does not exceed 2%, and more preferably does not exceed 1%, by weight, based on the total weight of hydrocarbons and aromatics. For example, the hydrocarbon-containing fluid may contain approximately 55 parts by volume of normal and iso- paraffins, and approximately 45 parts by volume of naphthenes, with less than 1% by weight, based on the total weight of the fluid, of aromatics. The distillation boiling range of the hydrocarbon- containing fluid is preferably within the range of from 150°C to 260°C at atmospheric pressure. The alcohol-containing fluid, which may advantageously contain alcohols selected from C6 to C8 alcohols, preferably comprises a mixture of aliphatic primary alcohols which may be linear or branched. The distillation boiling range of the alcohol-containing fluid is preferably within the range of from 150°C to 310°C at atmospheric pressure. In the cleaning process, the article may be contacted with the hydrocarbon and alcohol components by immersion in the liquid components or a liquid mixture thereof, either without or, more preferably, with ultrasonic agitation, by spraying, by contacting the article with vapour under conditions such that condensation occurs, or by a combination of the said methods. If the article is contacted sequentially with the hydrocarbon-containing fluid and the alcohol- containing fluid, the article may be contacted first with either of the fluids. The fluids or mixture with which the article is contacted may be at a temperature of from ambient temperature to 90°C, more preferably at a temperature of 40 ° to 50°C. The cleaned article may then be dried in air, preferably in hot air. Optionally, the article may be contacted with a detergent solution and rinsed with water to remove the detergent solution before drying. The detergent solution may comprise an alkylbenzene sulphonate and an alkylphenol alkoxylat , for example, an alkylphenol ethoxylate. The alkyl groups of the alkyl¬ benzene sulphonate and the alkyl phenol alkoxylate may in each case advantageously be an aliphatic, cyclic or alicyclic alkyl group having from 8 to 14 carbon atoms. The detergent solution may, for example, be a mixture of a dodecylbenzene sulphonate and a dodecylphenol ethoxylate. After the article has been contacted with detergent solution, residual detergent may expediently be removed by rinsing with water, preferably with deionised water. The application of detergent solution and subsequent rinsing assist the removal of the potentially harmful inorganic substances that may be present in the residual flux. The article is preferably an electronic component, more especially a PCB. While the method of the invention may be used with particular advantage in the cleaning of articles that have been soldered with the use of a rosin-containing flux, the method may also be used in the cleaning of articles that have been soldered with the assistance of synthetic water-soluble fluxes. The invention further provides a composition for cleaning articles, comprising: (i) from 75 to 95 parts by volume of a distillation fraction obtained by distillation of petroleum, the said fraction containing not less than 92%, prefer¬ ably not less than 99%, by weight, based on the total weight of the fraction, of hydrocarbons selected from C8 to C15 paraffinic and naphthenic hydrocarbons; and (ii) from 5 to 25 parts by volume of one or more alcohols selected from C5 to C15 straight-chain or branched- chain, saturated alcohols, the composition being substantially free of any halogen- containing organic compound. The process of the invention is particularly advantageous in the removal of flux residue after soldering. The use of a hydrocarbon-containing fluid and an alcohol-containing fluid enables excellent removal of flux residue to be attained without the use of any halogenated solvent. It is thought that the advantageous cleaning effect is obtained because, as a result of using a combination of a polar solvent and a non-polar solvent, both polar and non-polar components of the flux residue are readily dissolved. By selecting hydrocarbon components and alcohol components within the respective carbon number ranges specified, the dissolution of rosin molecules is enhanced. The use of mixtures of hydrocarbons and/or mixtures of alcohols also promotes dissolution of the rosin molecules. The solvents and solvent mixture used in accordance with the invention enable the use of halogen-substituted organic compounds, which are known to have ozone depleting properties, to be avoided, while excellent cleaning is obtainable. Further, the mixture has low toxicity and a high flash point so that it is relatively safe to use and complicated handling procedures are unnecessary. Moreover, it is non-corrosive to materials generally used in the manufacture of PCBs. The following Examples illustrate the invention: Example 1 Defence Standard 59-47 combs and circuit boards were soldered by one of the following three methods: (a) Liquid Fluxes The board or comb was wave soldered at 250°C using 63/37 (tin/lead) alloy, at a conveyor speed of 1.5 meter per min. The upper side of the board or comb was preheated to about 90°C prior to soldering. The flux was applied using a brush. In each case either a RMA, RA, a water soluble synthetic or a no clean liquid lux was used. ("No clean" fluxes are fluxes that can, at least in the case of lower grade electronic parts, be used without any need for subsequent cleaning. ) (b) Solder Creams The cream used was of AAS powder at 86% metal, with a 62% tin content. The cream was applied to the board or comb by manual screen printing and reflowed by heating in a BTU infrared oven. In each case either an RMA cream flux or a "no clean" synthetic water-soluble cream flux was used. (c) Flux Cored Wire The board or comb was hand soldered with 60/40 (tin/lead), melting point 362°C, 16 SWG 5-core, solder containing a RA flux, at a bit temperature of 360"c. Eight soldered printed circuit boards and eight soldered combs were cleaned with a cleaning composition containing 10 parts by volume of isomeric C6, C7 and C8 alcohols and 90 parts by volume of a hydrocarbon fluid consisting of Cll to C13 paraffinics and naphthenics. Certain properties of the mixture were determined and were as follows:- IBP and FBP represent the respective temperatures at which boiling commences and finishes. PMCC means Pensky- Martens closed cup. Each soldered board or comb was individually cleaned in 500 ml of the cleaning composition under ultrasonic agitation at 45°C. The soldered board or comb was then rinsed by immer ¬ sion in a detergent solution containing 10% by volume of a mixture of dodecylbenzene sulphonate and dodecylphenol ethoxylate in deionised water. The board or comb was then rinsed in deionised water and dried in hot air. Examination for residual ionic contamination was performed on the cleaned board or comb individually in a Kenco Omegameter for 15 minutes using a set volume of test solvent composed of 75/25 v/v isopropanol/deionized water. A series of unsoldered boards and combs were also tested to provide a baseline for the purpose of com ¬ parison. The results are shown in Table I, in which the ionic contamination level is the amount of ionic material relative to a baseline determined by measuring the average contamination of a number of unsoldered combs and boards. Table I The surface insulation resistance (SIR) of the boards and combs was also determined. For the SIR test, the initial insulation resistance of each board or comb was measured using a voltage of 500 V DC for 1 minute prior to placing each board or comb in a humidity chamber at 40°C, 90% relative humidity (RH) for 96 hours. The SIR was then measured again under the humid conditions (90% relative humidity at 40°C) using 500 V DC. The results of the SIR test are given in Table II. The results demonstrate that effective cleaning of residual soldering fluxes is achieved, with ionic contamination levels well below the MIL P-28809A 2 requirement of 14μg NaCl/sq. inch (2.2 μg/cm ) equivalent. The results also indicate that, after the cleaning step, the resistivity of the boards and combs is approximately the same as, or lower than, the resistivity of the uncleaned boards. Thus, the cleaning step has no detrimental effect on insulation resistance. In many cases, SIR is improved after cleaning. The cleaned boards also perform satisfactorily in the SIR test after being subjected to an atmosphere of RH 90% at 40°C for 96 hours. Table II Example 2 A cleaning mixture containing 5 parts by volume of isomeric C6 and C7 alcohols and 95 parts by volume of CIO to C13 paraffins and naphthenes was prepared. Physical data relating to the mixture were deter¬ mined as follows: To evaluate the efficiency of rosin removal from the circuit boards, six PCBs coated with activated fluxes were cleansed, each PCB being cleansed individually in 100 ml of cleaning mixture at 45°C, with ultrasonic agitation, for five minutes. After cleaning, the specimen was removed, dried and the residual rosin remaining on the board extracted by 100 ml of isopropyl alcohol (IPA). The rosin content of the IPA was determined by spectrophotometry at wavelength 242 nm. For comparison purpose, a halogenated cleaning fluid containing 93 parts by volume of CFC-113 and 7 parts by volume of methanol was prepared and six PCBs coated with activated fluxes were cleansed individually by the condensing vapour (b.p. 48 ° C) of the halogenated fluid for five minutes in a closed container. Upon cleansing, the specimens were treated as in the case of the hydrocarbons/alcohols cleaning. The results are given in Table III, which indicates that an average cleaning efficiency (that is, % rosin removal) of 87% is obtained using the hydrocarbon/alcohol mixture, compared with only 61% using the halocarbon solvent system. Table III

Claims: CLAIMS 1. A process for cleaning an article comprising contacting the article with: (i) a fluid comprising one or more hydrocarbons selected from C8 to C15. paraffinic and naphthenic hydrocarbons and having an aromatics content of not more than 8% by weight, based on the combined aromatics and hydrocarbon content of the fluid, (ii) a fluid comprising one or more alcohols selected from C5 to C15 straight-chain or branched-chain, saturated aliphatic alcohols, the fluids being substantially free of any halogen- containing organic compound and component (ii) representing at least 5% by volume, based on the total hydrocarbon and alcohol content, when the process comprises contacting the article with a liquid mixture * comprising components (i) and (ii). 2. A process as claimed in claim 1, in which the fluids are in the form of a liquid mixture comprising: (i) from 75 to 95 parts by volume of one or more hydrocarbons selected from C8 to C15 paraffinic and naphthenic hydrocarbons, and (ii) from 5 to 25 parts by volume of one or more alcohols selected from C5 to C15 straight-chain or branched- chain, saturated aliphatic alcohols. 3. A process as claimed in claim 2, in which the mixture contains from 8 to 15 parts by volume of alcohol component. A . A process as claimed in any of claims 1 to 3, in which the alcohols are selected from C6 to C8 alcohols. 5. A process as claimed in any of claims 1 to 4, in which there is used as the hydrocarbon-containing fluid a distillation fraction obtained in the distillation of petroleum, the distillation fraction containing not more than 8% by weight of aromatic material, based on the total weight of the distillation fraction. 6. A process as claimed in any of claims 1 to 5, in which the hydrocarbon-containing fluid contains not exceeding 2%, and preferably not exceeding 1%, by weight of aromatics, based on the combined aromatics and hydrocarbon content. 7. A process as claimed in any of claims 1 to 6, in which the article is immersed in the fluids or mixture and is subjected to ultrasonic agitation. 8. A process as claimed in any of claims 1 to 7, in which, after contact with the said fluids or mixture, the article is contacted with a detergent solution. 9. A process as claimed in claim 8, in which the detergent solution comprises an alkylbenzene sulphonate and an alkylphenol alkoxylate. 10. A process as claimed in any of claims 1 to 9, in which the article is a PCB. 11. A composition for cleaning articles comprising: (i) from 75 to 90 parts by volume of a distillation fraction obtained by distillation of petroleum, the said fraction containing not less than 92% by weight, based on the total weight of the fraction, of hydrocarbons selected from C8 to C15 paraffinic and naphthenic hydrocarbons; and (ii) from 5 to 25 parts by volume of one or more alcohols selected from C5 to C15 straight-chain or branched- chain, saturated aliphatic alcohols, the mixture being substantially free of any halogen- containing organic compound. 12. The use in the cleaning of an article of a mixture comprising: (i) from 75 to 95 parts by volume of one or more hydrocarbons selected from C8 to C15 paraffinic and naphthenic hydrocarbons, and (ii) from 5 to 25 parts by volume of one or more alcohols selected from C5 to C15 straight-chain or branched- chain, saturated aliphatic alcohols, the mixture having an aromatics content of not more than 8% by weight, based on the combined hydrocarbon and aromatics content, and being substantially free of any halogen-containing compound.

Inventors: LEE THOMAS WEE SUN, LEE, THOMAS, WEE, SUN
Applicants: EXXON CHEMICAL LTD, EXXON CHEMICAL PATENTS INC, EXXON CHEMICAL LIMITED, EXXON CHEMICAL PATENTS INC.
Application year: 1992
Main classification: C23G5
IPC codes: C11D1, C11D7, C23G5, H01L21, H01L23, H05K3