GB2120964A - Processes of applying solder - Google Patents

Abstract

Processes for soldering printed circuit boards with molten solder are disclosed, including fluxing the boards with a heated flux composition maintained at a flux temperature which is sufficient to heat at least a portion of the board to an elevated temperature at or above about 65.5 DEG C, but below the temperature of the molten solder, and then contacting the heated and fluxed board with the molten solder while it is still at an elevated temperature of at least about 65.5 DEG C. In addition, flux compositions for use in these processes are also disclosed, comprising specified flux activators and organic fluxing vehicles having boiling points above about 199 DEG C, and which compositions use liquids at room temperature.

Description

SPECIFICATION Processes for applying solder The present invention is directed to processes for soldering printed circuit boards and the like. More particularly, the present invention is directed to improvements in processes for soldering printed circuit boards, integrated circuits, electronic components, etc., employing molten solder baths, such as wave soldering apparatus, and to flux compositions for use in processes for soldering printed circuit boards.

The mass soldering of printed circuit boards and other electronic components using molten solder baths, such as by means of wave soldering and/or drag soldering apparatus, has become extremely widespread and quite important from a commercial standpoint. As the use of printed circuit boards increases, the need to streamline these processes and at the same time improve their efficiency and speed has also increased.

The procedures employed in connection with such commercial soldering processes generally include a system for carrying the printed circuit board through a multi-stage process, such as by mounting the boards on a belt or chain-drive mechanism to be carried through the various soldering stages. In the past, these stages have included an initial fluxing stage where solder flux is applied to at least one side of the printed circuit board, usually the side opposite the one on which the components are mounted. Conventionally, these solder fluxes are applied by foaming, wave, or spray applications.Further, the fluxes employed generally include an activator for removing oxidation from the metallic surfaces for preseritation of a clean oxide-free surface to the solder stage, "blanketing" materials which maintain the hot, clean, metallic surface free from reoxidation by preventing contact with oxygen in the air, and volatile solvent systems, which serve as vehicles to apply the activators and blanketing components to the printed circuit boards.

In these commercial soldering systems it has generally been necessary to heat the printed circuit boards to specific elevated temperatures prior to application of the molten solder thereto. This has been accomplished by transporting the board from the fluxing stage to various types of heating equipment designed to moderately heat the printed circuit boards prior to soldering. These have generally comprised various types of radiant and/or convection heaters. This is done for a number of important reasons, including minimization of the thermal shock which would be experienced by these circuit boards on contacting the molten solder, initiation of the activators contained in the solder flux, removal of the volatile solvent vehicle from the flux so as to prevent spattering of the flux upon contact with the hot solder, acceleration of solder wetting, etc.It is therefore clear that these intermediate heating steps have been of critical significance in these prior processes.

These fluxed and pre-heated circuit boards are then contacted with hot molten solder, which can be in the form of a wave, or by skimming the circuit board over the molten solder surface, i.e., by drag soldering, etc.

The printed circuit boards are then removed from contact with the solder, and the board surface spontaneously cools, with quick solidification of the solder coating thereon.

An example of such a prior process is that shown in U.S. Patent No. 3,482,755, which employs a series of heated banks 27 intended to dry the flux and to bring the board temperature up to about 121 C in order to minimize thermal shock. These heated banks can include hot air devices, hot plates, etc. As another example, in patents such as U.S. Patent No.3,439,854, heater rods 18 are employed. Similar devices are disclosed in U.S. Patent Nos. 3,778,883 and 3,122,117. Such pre-heating of the printed circuit boards, and foam fluxing itself, is also shown in U.S. Patent No. 4,009,816, which is assigned to the assignee of this application.

In patents such as U.S. Patent No. 3,112,723, automatic soldering processes are discussed, as is the desirability of eliminating the intermediate heating step. This patent reads "a very active fluxing resin is used diluted three to one with alcohol, and the amount applied is critical. With good quantity control, uniform flux distribution, and the proper pre-selected time interval between fluxing and solder application, no intermediate heating is required to get soundly soldered connections by this process." This patent, however, does not discuss or suggest the use of heated flux solutions which do not include volatile solvents such as the alcohols employed therein. In addition, in U.S. Patent No. 3,585,708 the patentee discloses using cascades of flux and solder in adjacent stations, in which crude corn oil is employed as the fluxing agent.

There are othertypes of soldering processes which are known in the art as "condensation" type processes, i.e. in which hot saturated vapors generated by continuously boiling heat-transfer liquids are employed to contact the circuit boards in the soldering environment. These include U.S. Patent No. Re.

30,399. Also, in IBM technical disclosure bulletin No. 5, Volume 23, October 1980, wave soldering under a heated flux is disclosed. In this disclosure wave soldering is conducted while the entire printed circuit board is immersed in a heated flux, which has a solder wave immersed in it, and the flux in such a case is not confined to the surface of the board which is to be soldered. The flux obviously must therefore be maintained at a temperature substantially the same as that of the molten solder itself, e.g., about 260 C.

However, with most electronic components exposure to such high temperatures is not possible.

Substantial efforts have continued to find improvements in these automated fluxing systems, particularly so that these intermediate heating steps can be avoided without experiencing any deleterious effects therefrom.

According to the present invention, there is provided a process for applying solder from a supply of molten solder to a surface which is to be soldered, said supply of molten solder being maintained at a predetermined solder temperature, said process comprising the steps of fluxing said surface by contacting said surface which is to be soldered with a heated flux composition maintained at a flux temperature sufficient to heat at least a portion of said surface to an elevated temperature of at least about 65.5 C, but below said predetermined solder temperature, and contacting said heated and fluxed surface with said supply of molten solder while it is still at an elevated temperature of at least about 65.5do. In the preferred embodiment, the step of contacting said surface with said supply of molten solder is carried out directly from said fluxing step without any intermediate heating of said surface therebetween.

According to the present invention, there is also provided a solder flux composition for use in fluxing surfaces which are to be contacted with a supply of molten solder, wherein said solder flux composition comprises a flux activator selected from the group consisting of amine hydrohalides, quaternary ammonium halides, carboxylic acids, sulfonic acids, phosphonic acids, esters of sulfuric and phosphoric acids, inorganic acids, inorganic salts and mixtures thereof, and an organic fluxing vehicle, both said organic fluxing vehicle and said flux composition having a boiling point of above about 199 C, and said flux composition being a liquid at room temperature.

The flux compositions of the present invention must satisfy certain strict criteria in order to be useful in the processes hereof. In particular, and as compared to prior conventional fluxes which have been applied by foam, wave, or spray techniques, the flux compositions of the present invention do not include a volatile solvent system serving as a vehicle therefor. In this manner, a flux which is stable or of low volatility at the pre-heating temperatures of this invention, is obtained. Because the flux compositions of the present invention are to be utilized at elevated temperatures, generally between about 77 and 190.5 C, flux materials can now be utilized which would otherwise be unacceptable in conventional flux compositions.These include materials which would be solids, semi-solids, or highly viscous liquids at ordinary room temperatures, so long as the overall flux compositions hereof remains liquid at room temperature.

These compositions must therefore not only demonstrate the necessary desirable fluxing characteristics, i.e., removal of oxidation and preventing re-oxidation of metallic surfaces, but they now must also demonstrate stable perforance at the elevated temperatures at which they are to be utilized. Materials should therefore be selected whose vapor pressures, at the elevated temperatures at which the fluxes are to be applied, are sufficiently low so as to provide reasonable flux stabilities. In particular, vapor pressures at the temperatures of operation of below about 50 torr, and preferably below about 20 torr, are employed. The temperatures of operation, i.e., at which these fluxing agents are to be maintained, will generally be somewhat above those temperatures to which it is intended that these printed circuit boards be heated before they come into contact with the molten solder.In most cases it is desired that at least a portion of the printed circuit boards be heated to temperatures in the range of between about 65.5 and 1 070C before they come into contact with the molten solder. It will therefore generally be necessary to maintain the flux compositions hereof at temperatures significantly in excess of these temperatures. The degree of this excess will vary depending upon the particular environment in which any individual process is being conducted, but it is necessary to do so to insure that particular portions of these circuit boards will reach and maintain these desired temperatures to the point in the process where soldering is to be carried out.In this respect, it should be understood that where only a portion of the printed circuit board actually contacts the heated flux compositions hereof, a temperature gradient will be created across the board. With a thin, single sided board this does not create much of a problem. However, as multi-sided and muiti-layer boards become more and more common, the potential problems created by larger temperature differences also increase. For example, in such cases, if only the underside of the board contacts the heated flux composition, the top of the board will be at a considerably lower temperature than the bottom.With a two-sided board (i.e., with circuitry on both sides), or where it is multi-layered, it may be necessary for the top of the board to also reach a desired elevated temperature, so that it can be insured that when the soldering operation is carried out, the solder will be drawn through holes in the board to all of its desired locations, etc. In such environments it is preferred that the top of the board also reach a minimum temperature, generally of at least about 52 C, at the point in the process when the board is no longer in contact with the heated flux compositions hereof.

It should also be noted that it is within the scope of this invention to employ some other form of heating in connection with this process, but principally for the purpose of heating the top surface of the board, for example. That is, even in that case, this invention still requires that at least a portion of the board (e.g., the lower surface) will be heated to a temperature of at least 65.5 C, exclusively by means of contact with the heated flux compositions thereof.

In any event, the degree of such excess heating required of the flux compositions hereof (i.e., over and above the required minimum temperature to which at least a portion of the board is to be heated) depends upon such factors as the contact time between the printed circuit boards and the heated flux composition, the length of time and/or distance between the fluxing and soldering steps, the speed with which the components are moving through the process, the thickness of the board, the number of board layers, the presence of heat sinks on the board, such as components, other massive items or ground planes, etc. It may therefore be necessary to utilize flux compositions which can be operated at temperatures of up to about 65.5 C or more in excess of the desired temperatures (i.e., to which at least a portion of the board is to be heated), and generally the flux compositions will be maintained at temperatures of between about 10 and 65.5 C in excess of these temperatures at which the printed circuit boards are to be maintained when they come into contact with the molten solder.Thus, in a situation where at least a portion of the printed circuit boards are to be at a temperature of between about 65.5 and 107 C before they come into contact with the molten solder, it will generally be necessary to maintain the flux compositions hereof at temperatures between about 93 and 190.5 C, depending on the speed with which the circuit board is moving through the process and the distance between contact of the circuit board with the flux and with the molten solder.

The flux compositions of the present invention therefore desirably boil at a temperature of above about 199 C, preferably above about 210 C, and most preferably above about 227 C. The organic fluxing vehicles hereof must likewise have a boiling point of greater than about 199 C, preferably greater than about 210 C, and most preferably greater than about 227 C. The organic fluxing vehicles having these properties are generally selected from among a number of types of compounds which have been known to be useful as fluxing agents, albeit under different conditions.These include the glycols, glycol ethers, polyols, polyglycols, polyglycol ethers, such as the aliphatic and aromatic ethoyxlated branched or straight-chain alcohols, the waxes, fats, oils, rosins, modified rosins, rosin derivatives, alkalene carbonates, and mixtures of these compounds, again as long as they also possess these required characteristics.

Among the glycols having these properties are included compounds such as diethylene glycol, triethylene glycol, tetraethylene glycol, 1,5 pentanediol, dipropylene glycol, 2-ethyl,1 3 hexanediol, tripropylene glycol, 1,4 butanediol.

Among the glycol ethers having these properties are included compounds such as methoxy triglycol, ethoxy triglycol, 1 butoxyethoxy-2 propanol, butoxy triglycol, tripropylene glycolmethyl ether, ethylene glycol phenyl ether, propylene glycol phenyl ether, diethylene glycol ethyl ether, diethylene glycol n-butyl ether, diethylene glycol dibutyl ether, diethylene glycol n-hexyl ether, ethylene glycol monohexyl ether, etc.

Additional compounds having these properties are also included within the scope of this invention. These include polyols, such as glycerine, 1,2,6-hexanetriol, pentaerythritol, mannitol, and sorbitol; polyglycols, such as polyethylene glycols (e.g. Union Carbide Carbowax compositions), polypropylene glycols, polyethylene glycol-polypropylene glycol copolymers, polyalkylene glycols (such as Jefferson Chemical Co.'s Jeffox WL series functional fluids, or Union Carbide Ucon-H or HB series, etc.); the polyglycol ethers, such as nonyl phenol polyethylene glycol ethers, such as Rohm & Haas TRITON-N series, and the octylphenol polyethylene glycol ethers, such as Rohm & Haas TRITON-X series, and other polyglycol surfactants derived from various phenols, the ethoxyiated aliphatic alcohols and their derivatives, such as Union Carbide TERGITOL 25-L series, TMN series, 15-S series and X series, BASF Wyandotte Corp.L, P, and F series PLURONIC polyols; the crystalline and non-crystalline waxes having melting points below those of the heated flux compositions; animal, vegetable and mineral fats; oils, such as mineral oils; waxes; gum rosin, wood rosin, or tall oil rosin, or modified rosins and rosin derivatives, i.e., derivatives of rosin which have been modified by polymerization, hydrogenation, disproportionation, isomerization, esterification or ethoxylation, such as modified rosin products of the Hercules Co., including Dymerex, Polypale Resin, Staybelite Resin, Staybelite Ester 10, Hercolyn D, and Pentalyn C; and the alkalene carbonates such as propylene and ethylene carbonate.In general, as long as these compounds meet the above noted physical requirements and do not react chemically with the other materials of the flux at its intended functioning temperature over the useful functional life of the flux to an extent so that it impedes the performance of the flux, they can be employed in the processes hereof. That is, compounds within the classes of compounds set forth above and others can be employed, as long as the overall composition remains a liquid at room temperature, and exhibits sufficient chemical stability and low evaporation rates to provide a stable flux composition when used at the required temperatures hereof.

The other essential component in such flux compositions is the flux activator, which is intended to actually effect the removal of oxidation from the metallic surfaces of the printed circuit board, so that clean, oxide-free surfaces are present during the actual soldering thereof. In addition to such fluxing ability, these compositions must also demonstrate the same type of thermal stability and low evaporation rates as do the fluxing vehicles set forth above. In addition, these flux activators should demonstrate solubility in these fluxing vehicles, and should not react chemically therewith in the same manner as is set forth above with respect to the fluxing vehicles themselves.Preferably, these flux activators will also have a boiling point of at least about 143 C, depending on the amount to be used, and again so long as the overall flux remains below the required temperature of about 1990C set forth above.

In particular, the amine hydrohalides are particularly useful as flux activators. These include compounds such as monoethylamine hydrochloride, diethanolamine hydrochloride, glutamic acid hydrochloride, diethyl amine hydrobromide, dimethylamine hydrochloride, betaine hydrochloride, triocytylamine hydrochloride, or any of a large number of such amine salts previously employed for such purposes. Quaternary ammonium halides, such as tetramethyl ammonium bromide, tetrabutyl ammonium chloride, and cetyl trimethyl ammonium bromide can also be utilized. Also, certain inorganic salts, such as ammonium and zinc halides, can be used. It has also been found that certain non-halide bearing compounds can also be employed as the flux activators hereof. Thus, certain organic acids meeting the above physical requirements may be employed as the flux activators hereof. These can include carboxylic acids such as sebacic, adipic, succinic, citric, tartaric, malic, benzoic, glycolic, lactinic, levulinic, myristic, salicylic, and phthalic acids, and the like. In addition, sulfonic acids, such as p-dodecylbenzene sulfonic acid and p-toluene sulfonic acid can be used, as can comparable phosphonic acids.

Also, esters of sulfuric and phosphoric acids can be utilized, such as isooctyl acid phosphate, and certain inorganic acids such as phosphoric acid, can be used. Thus, by employing these non-halide bearing flux activators, problems of corrosion and the like which can result from the use of certain of the halide bearing activators can be avoided. It is noted in this regard, that in that case these more highly polar flux activators may then require the use of more highly polar organic fluxing vehicles, so as to maintain the overall solubility of the flux compositions hereof. In that case, polyols such as glycerine can be highly effective for such purposes.

In addition to now making it possible to entirely eliminate the pre-heating step, if that is desired, the flux compositions of this invention can also permit conventional processes to operate at increased speeds. That is, the printed circuit boards will now be able to be moved through the process at increased speeds. The principal reason for this is that since the pre-heating of these printed circuit boards is being effected at the same time that they are in direct contact with the heated flux compositions, as opposed to being done entirely by the more conventional but less direct pre-heating methods previously utilized (e.g., via radiant or convection heating), the temperature of the circuit boards is raised much more rapidly by the direct thermal contact hereof.Furthermore, since the flux compositions of this invention do not include any of the volatile solvents employed in prior flux compositions, the need to evaporate these volatile solvents during such pre-heating is now eliminated, and therefore the overall heating requirements of the past are concomitantly reduced. This provides yet another factor which permits these circuit boards to be moved more rapidly through the system, i.e. it eliminates the necessity to reduce the speed of the conveyor belt or similar apparatus normally utilized, as has been previously required in order to ensure complete solvent evaporation prior to soldering. The solvent evaporation itself has resulted in a severe limiting of the speed at which the printed circuit boards can travel between the fluxing and soldering steps.One reason for this is that in the past evaporative cooling of the solvent has occurred as the solvent absorbed the necessary heat of vaporization to vaporize same. It was thus necessary to increase the time between fluxing and soldering, such as by utilizing lower speeds of movement of the circuit boards, in order to permit sufficient thermal energy to be applied to the circuit board to fully evaporate the solvent from the board and to heat the board to the required pre-heating temperatures. This is unnecessary in accordance with the present invention since the flux compositions hereof incorporate materials having little or no evaporation during pre-heating, thus contributing little if any evaporative heat loss to the boards.

There are a number of other significant advantages which can be realized by utilizing the flux compositions of the present invention in the process hereof. Among these is the fact that since there are no volatile solvents present in these flux compositions, no such solvents can be present on the printed circuit boards when they are being soldered. This, in turn, eliminates the possibility of solder spattering upon contact with the molten solder itself, which has been a serious problem in the past. That is, the presence of any such volatile solvents on the boards during their contact with the molten solder has resulted in explosive boiling and expansion of the solvent vapors generated by the rapid temperature changes to which the flux is subjected.This can be particularly significant in connection with the soldering of chip components to the bottom side of such printed circuit boards, since such explosive vehicle evaporation in that case can result in damage to the chips, removal from the board itself, etc. Such spattering can also result in the percolation of liquid solder through the component lead holes in the circuit board, resulting in the production of balls of metallic solder on the opposite or component side of the circuit board. This can result in the generation of electrical short circuits between the component leads and functional electrical failures in the circuits.

Another advantage of this invention is that it is no longer necessary, as in the past, to continuously add thinners or volatile solvents to the supply of flux composition. This has been necessary with the use of these volatile solvents, which are constantly being evaporated during use. With the elimination of these volatile solvent components, it is no longer necessary to periodically replenish same in order to maintain the composition of the flux relatively constant.

Another important advantage associated with this invention is the fact that by using the heated flux compositions hereof it can be insured that moisture in the air will not be absorbed by the flux material, with its associated problems. In the past, where fluxing operations are carried out at or near room temperature, many of the materials utilized are hygroscopic, and a substantial problem of moisture absorbtion from the air is encountered.

Furthermore, overheating of the circuit boards can now also be prevented. In the past, the use of radiant heaters and the like raised the possibility of such overheating. However, with the use of the compositions of the present invention, the temperature of the circuit board prior to solder contact cannot exceed the controlled temperature of the flux composition itself.

In addition, the fire hazards which are inherent in the prior use of volatile vapors during fluxing are greatly reduced, if not eliminated, by the removal of these volatile solvents. Further, the energy requirements for pre-heating can now be significantly decreased with elimination, or at least reduction, in the use of conventional radiant heaters, hot air convection systems, and the like. Finally, the overall heating of the board will now be far more uniform than was the case in the past.

In addition to all of the above requirements, the fluxing agents of the present invention must also include only compounds which do not give rise to rapid chemical changes, such as polymerization, pyrolysis, oxidation, or other reactions which could adversely affect the flux properties therein. Thus, the flux composition of this invention can also include conventional inhibitors to prevent decomposition, anti-oxidants and thermal stabilizers, wetting agents, surfactants, coloring agents, etc., all of which will be appreciated by those of ordinary skill in this art, again so long as these compounds serve their normal functions without interfering with the above-required physical characteristics of the flux compositions hereof.

In accordance with the process of the present invention, the printed circuit boards will generally be carried through the fluxing and soldering operation on a conveyor belt or chain-drive mechanism or the like, which is preferably maintained to operate substantially continuously. The assembled circuit boards, including the components which are to be soldered to the board, are initially mounted with respect to the conveyor belt or chain-drive mechanism by conventional means prior to moving through the system. The boards are then initially transported to a location where the solder flux compositions of this invention are to be applied to at least the underside thereof, i.e., opposite to the side on which the components are usually mounted.As noted above, the fluxing agents hereof can be applied in various forms, such as a flux foam, wave, or spray, or by being dragged across the flux. When the flux is to be applied in the form of a flux foam, the foam is produced by entraining the fluxing agents in a heated gas stream, i.e. in order to prevent the cooling of the flux which could occur if a gas stream were employed at a temperature lower than that of the flux itself. A typical such foam fluxing operation is shown in U.S. Patent No. 4,009,816, which is incorporated herein by reference thereto. Another typical foam fluxing operation is described in "Guidelines For Selecting Wave Soldering Systems" by Kenneth G. Boynton of Hollis Engineering, Inc., in which a porous ceramic cylinder or "stone" is employed to create a flux foam, and this disclosure is also incorporated herein by reference thereto.On the other hand, the use of spray fluxing techniques are discussed in "Automatic Monitoring And Control System For Wave Soldering Systems", Westinghouse Defense and Electronic Systems Center, Systems Development Inc., Baltimore, Md., U.S.A., Pgs. 11-14, 1980. This document discusses the use of a paint sprayer using high pressure compressed air to apply a fine aerosol flux mist, and all of such disclosure is incorporated herein by reference thereto. Finally, equipment is also commercially available for the application of flux in the form of a wave. This includes the Hollis Console Model Wave Fluxer, Model WF-1, sold by Hollis Engineering, Inc. of Nashua, New Hampshire, U.S.A.

After fluxing, the printed circuit boards continue travelling on a conveyor belt or the like to the soldering location. While it is still within the scope of the present invention to employ some conventional radiant or convection pre-heating of the boards, this can now be included merely to augment the heating effected by the fluxing operation itself, and/or to permit the soldering line itself to run at considerably higher speeds than was possible in the past, where such pre-heaters alone were employed for such purposes. Also, it is possible to employ a heated air knife to impel a stream of heated air onto the surface of the printed circuit boards prior to their soldering for removing a portion or excess of the flux therefrom.The significant point is that the flux compositions of the present invention, and the processes for their use, allow for elimination of any such additional pre-heating devices.

As for the soldering step itself, the surface of the printed circuit boards contacts the hot molten solder, which is preferably presented in the form of a solder wave, which is generated by pumping the liquid solder up through a chimney-like structure. Several commercial wave soldering machines are available, and typical examples of same are shown in U.S. Patent Nos. 3,921,888 and 4,208,002, the disclosures of which are also incorporated herein by reference thereto. Additional disclosures of wave soldering and dip soldering processes are contained in articles entitled "Mass-Soldering Equipment For The Electronics Industry", in Tin And Its Uses, Nos. 127 and 128, 1981, all of which is incorporated herein by reference thereto.

Finally, after leaving the solder bath the thus-treated circuit boards can then contact a cleaner to remove excess flux from the entire assembly, after the solder has solidified. This completes the electrical and mechanical connection of the component leads to the board circuitry.

In connection with each of these soldering processes, the temperature of the molten solder is generally at least about 232 C, and generally between about 238 and 315.5 C, depending upon the alloys being used.

Thus, as indicated above, the fluxing vehicles of the present invention must at least be stable and maintainable at the operating temperatures of the flux, generally between about 93 and 190.5 C. Preferably, the temperature of flux composition of the present invention will thus be maintained at between about 93 and 190.5 C, most preferably between about 107 and 163 C. In this manner, at least a portion of the fluxed and pre-heated circuit boards will be raised to a temperature of between about 65.5 and 1070C when they come into contact with the molten solder, which as noted will generally be between about 232 and 315.5 C, and more typically between about 246 and 274 C.

Typical examples of flux compositions which can be employed in accordance with the present invention include the following: Example! Percent weight Polyethylene Glycol-polypropylene Glycol Copolymers such as 78 Jeffox WL-1 400* Diethylene Glycol 20 Dimethylamine Hydrochloride 2 100 *Jefferson Chemical Co., Inc. Subsidiary of Texaco, Inc.

Example Il Percent by weight Triethylene Glycol 98 Tetramethyl ammonium bromide 2 100 Example 111 Percent by weight Triethylene Glycol 76 TRITON-X-100 (Union Carbide) 20 Citric Acid 4 100 Example IV Percent by weight 1,5 Pentanediol 84 TERGITOL TMN-6 (Union Carbide) 10 Adipic Acid 2 Monoethylamine Hydrochloride 4 100 Example V Percentby weight Diethylene Glycol 94 Diethanolamine Hydrochloride 4 Tartaric Acid 2 100 Example VI Percent by weight Ethylene Carbonate 96 Citric Acid 2 Dimethylamine Hydrobromide 2 100 Example VII Percent by weight Mineral Oil (Protol-Witco Chemical Co.) 75 Myristic Acid 15 Isooctyl Acid Phosphate 10 100 Example VIII Percent by weight Mineral Oil (Protol-Witco Chemical Co.) 85 p-Dodecylbenzene Sulfonic Acid 15 100 Example IX Percent by weight Mineral Oil (Protol-Witco Chemical Co.) 85 Trioctyl Amine Hydrochloride 15 100 Example X Percent by weight Butyl Carbitol (Union Carbide) 55 Gum Rosin 42 Dimethyl Amine Hydrochloride 3 100 Example Xl Percent by weight Butyl Carbitol (Union Carbide) 55 Staybelite Resin (Hercules) 42 Dimethylamine Hydrochloride 3 100 Exampe XII Percent by weight Butyl Carbitol (Union Carbide) 55 Pentalyn C (Hercules) 42 Dimethylamine Hydrochloride 3 100 Example XIII Percent by weight Butyl Carbitol (Union Carbide) 55 Ethoxylated Rosin Amine Derivative (Polyrad 1110 Hercules) 42 Diethylamine Hydrochloride 3 100 Example XIV Percent by weight Glycerine 97 p-tolune Sulfonic Acid 3 100 It will be understood that a person skilled in the art may make many variations and modifications without departing from the spirit and scope of the invention. All such modifications and variations are intended to be included within the scope of the invention as defined in the appended claims.

Claims (19)

1. A process for applying solder from a supply of molten solder to a surface which is to be soldered, said supply of molten solder being maintained at a predetermined solder temperature, said process comprising the steps of fluxing said surface by contacting said surface which is to be soldered with a heated flux composition maintained at a flux temperature sufficient to heat at least a portion of said surface to an elevated temperature of at least about 65.5 C, but below said predetermined solder temperature, and contacting said heated and fluxed surface with said supply of molten solder while it is still at an elevated temperature of at least 65.5 C.

2. The process of Claim 1, wherein said contacting of said surface with said supply of molten solder is carried out directly from said fluxing step without any intermediate heating of said surface therebetween.

3. The process of Claim 1 or 2, comprising the step of contacting said surface with a stream of heated air prior to said contacting with said supply of molten solder.

4. The process of Claim 1, 2, or 3, further comprising the step of mounting said surface to be soldered on carrier means for transporting said surface through said fluxing and solder contacting steps.

5. The process of Claim 4, wherein said carrier means is adapted to transport said surface through said fluxing and contacting steps along a substantially continuous path.

6. The process of any one of the preceding claims, wherein said heated flux composition is maintained at a flux temperature sufficient to heat at least a portion of said surface to a temperature of between about 65.5 and 107 C, and wherein said predetermined solder temperature is at least about 232 C.

7. The process of any one of the preceding claims, wherein said heated flux composition is substantially free of volatile components, whereby said heated flux composition has a boiling point above about 1 99 C.

8. The process of Claim 7, wherein said heated flux composition has a vapor pressure of less than about 50 torr at said flux temperature at which said heated flux composition is maintained.

9. The process of any one of the preceding claims, wherein said heated flux composition is maintained at a temperature of greater than about 77 C.

10. The process of Claim 9, wherein said heated flux composition is maintained at a temperature of between about 93 and 1 90.5 C.

11. The process of any one of the preceding claims, wherein said surface is a surface of a printed circuit board.

12. A solder flux composition for use in fluxing surfaces which are to be contacted with a supply of molten solder, wherein said solder flux composition comprises a flux activator selected from the group consisting of amine hydrohalides, quaternary ammonium halides, carboxylic acids, sulfonic acids, phosphonic acids, esters of sulfuric and phophoric acids, inorganic acids, inorganic salts and mixtures thereof, and an organic fluxing vehicle, both said organic fluxing vehicle and said flux composition having a boiling point above about 199"C, and said flux composition being a liquid at room temperature.

13. The solder flux composition of Claim 12, wherein said organic fluxing vehicle and said flux composition have boiling poirJts above about 210 C.

14. The solder flux composition of Claim 12, wherein said organic fluxing vehicle and said flux composition have a boiling point above about 227 C.

15. The solder flux composition of Claim 12, 13, or 14, wherein said organic fluxing vehicle comprises a compound selected from a group consisting of glycols, glycol ethers, polyglycols, polyols, polyglycol ethers, waxes, fats, oils, rosins, modified rosins, rosin derivatives, alkalene carbonates, and mixtures thereof.

16. The solder flux composition of Claim 12, 13, 14, or 15, wherein said flux activator is selected from the group consisting of carboxylic acids, sulfonic acids, phosphonic acids, esters of sulfuric and phosphoric acids, non-halogenated inorganic acids and salts, and mixtures thereof, and wherein said organic fluxing vehicle comprises a highly polar organic fluxing vehicle.

17. The solder flux composition of any of Claims 12-16, wherein the surface to be contacted is the surface of a printed circuit board.

18. A process for applying solder from a supply of molten solder to a surface which is to be soldered, substantially as described.

19. A solder flux composition for use in fluxing surfaces which are to be contacted with a supply of molten solder, substantially as described.