MXPA99000760A - Funding medium for soldeo that does not require cleaning, without - Google Patents

Abstract

The present invention relates to a flux formulation without a surface-active agent for use in the assembly of electronic circuit boards as a formulation that does not require cleaning. The formulation contains a flux solution having a fluxing agent consisting essentially of one or more weak organic acids and a solvent consisting essentially of water. The fluxing solution is used to transport the fluxing agent before the deposition of the same on a welding site for the improvement of the reliability that is generated by the absence of hygroscopic residues and to avoid the environmental degradation that is generated, by the absence of the VOCs The method consists of the step of: heating the flux solution and dispersing it as a dew fi

Description

FUNDING MEDIUM FOR SOLDEO THAT DOES NOT REQUIRE CLEANING, WITHOUT VOC Reference to the related application This patent application relates to United States patent application Serial No. 327, 938, filed on October 24, 1994 (now Patent United States No. 5, 447, 577, which was published on September 5, 1995); and with the request of the States United Series No. 327, 941, filed on October 24, 1994 (now United States Patent No. 5, 443, 660, which was published on August 22, 1995).

Technical Field This invention relates to a fluxing medium for welding operations without volatile organic substances, which does not require cleaning.

BACKGROUND OF THE INVENTION There are two types of flux technology widely used in the electronics industry: liquid spraying and liquid foaming. In both techniques, to achieve uniform deposition, the solvent in the flux must moisten the electronic board that is to be released to form a continuous film. Traditionally, the volume of solvent needed to moisten: a board is relatively large. But for a welding operation that does not have cleaning steps after welding, the flux residue after welding should be benign and minimal in quantity. Therefore, most fluxes that do not require cleaning usually have very high solvent content (95 to 99%) and low solids content (usually 1% to 5%). There are basically two types of solvents in current use: volatile organic compounds (VOCs) that evaporate easily during the welding process, and water. Fluxes with low solids content that use alcohol or other organic compounds as solvents easily moisten the board. However, they emit large amounts of VOCs during the welding process and, in this way, create environmental problems. Water based fluxes with low solids content, on the other hand, need a surfactant to help wetting, since water has a very high surface tension when it is distributed over the electronic board and metals that are going to link. The surfactants leave a hygroscopic residue after the welding operation and thus have to be cleaned or the final product has to be protected with a coating or a shaping encapsulant. The question of better ways to "clean precision electronic components without solvents that destroy ozone" has led to the development of cleaning processes that reduce the need for solvents. Now techniques have emerged to use supercritical carbon dioxide instead of environmentally hazardous CFC-based solvents to remove particulates and organic contaminants introduced during the manufacture of circuit boards. However, the use of a supercritical carbide dioxide [sic] may tend to adversely attack the board itself or a plastic housing that can accommodate the board. Therefore, for these, among other reasons, supercritical carbon dioxide can be a suboptimal approach to clean electronic circuit boards. U.S. Patent No. 5,447,577 (issued to the assignee of the present application) discloses that by heating a water solution of adipic acid the solubility of the adipic acid in water is drastically increased (column 4, line 26). As a result, it is possible to achieve a uniform deposition of the flux using only a small fraction of the solvent that is used in the fluxes with low solid content, conventional (column 4, line 12). The minimum amount of solvent can eliminate the need for a surfactant that leaves highly hygroscopic residues. In this way, cleaning after welding or the need for a conformal coating or encapsulant (column 4, line 23) is avoided. In this manner, the description of the patent? 577 focused on the use of supercritical carbon dioxide (claims 1-14) as a solvent and carrier for the flux. Claims 15-18 describe the use of carbon dioxide in a low pressure state as a stream separated from the flux.

SUMMARY OF THE INVENTION The invention relates to a flux formulation for use in the assembly of electronic circuit boards. The formulation consists of a flux solution having a fluxing agent consisting essentially of one or more weak organic acids and a solvent consisting essentially of water. The flux solution serves to transport the flux agent before the deposition of the same on a welding site for the improvement of the reliability that is generated by the absence of hygroscopic waste and to avoid the environmental degradation that is generated, by the absence of the VOCs The invention also consists of a method for delivering a flux formulation without a surfactant agent for use in the assembly of electronic circuit boards as a formulation that does not require cleaning. The method consists in the preparation of the previous flux solution. The flux solution is heated to create a heated flux solution and to increase the solubility of one or more of the organic acids in the solvent, thereby decreasing the proportion of the solvent needed in the fluxed flux solution and decreasing the hygroscopic residue. that remains after welding. The fluxed solution of the flux is applied by spraying so that the flux solution disperses as fine particles.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a flow diagram of the process illustrating the main steps of the method of the present invention.

BEST MODE (S) FOR CARRYING OUT THE INVENTION In a broad sense, the invention relates to a flux formulation for use in the assembly of electronic circuit boards. The formulation includes one or more weak organic acids and a solvent consisting essentially of water. The solution of the flux transports the flux agent through a means of deposition of the same in a welding site for the improvement of the reliability that is generated by the absence of hygroscopic residues and to avoid the environmental degradation that is generated, by the absence of VOCs. The method of the present invention requires the supply of the flux formulation in an electronic circuit board with components that are to be soldered together. The method (Figure 1) includes the following steps: preparing a flux solution having a fluxing agent consisting essentially of one or more weak organic acids and a solvent consisting essentially of water; heating the flux solution to create a heated flux solution and to increase the solubility of the one or more organic acids in the solvent, thereby decreasing the proportion of the solvent needed in the flux solution and decreasing the remaining hygroscopic residue after welding; and applying the fluxed solution of the flux through a dispersion medium so that the flux solution is dispersed as fine particles. Figure 1 illustrates a flow chart of the process, of the steps for the method that is used in the practice of the present invention. The preferred flux is a water solution of a weak organic acid, such as adipic acid with very high solids content (up to 62.5%) contained in a closed container, heated to near the boiling point of water (ie, 100 ° C). Heating the water-based flux drastically increases the solubility of the weak organic acid, such as adipic acid in water. At 25 ° C, 100 ml of water dissolves 1.44 g of adipic acid, while at 100 ° C, 100 ml of water dissolves 160 g. Low-solids, water-based fluxes, formulated to be spray applied or conformed to current-use flux technology, typically contain less than 5% solids. Through heating, a flux containing as much as 62.5% activator can be achieved. Usually, concentrations of 2-5% of adipic acid in water are used. The use of the flux flux solution to disperse the flux provides different advantages over the flux technologies currently used in the electronics industry because this flux has a high solids content, and still provides a uniform deposition. As a result, this method requires only a small fraction of the solvent that is used in the current low solids fluxes to achieve uniform deposition. This overcomes some of the problems associated with the use of a solvent in the additional fluxes. The method of this invention disperses the flux into very fine particles. In this way, it is not necessary for the solvent to wet the board completely to achieve uniform deposition of the flux. Therefore, for fluxes that use a VOC as a solvent, the volume of VOC emitted during welding operations can be greatly reduced. For a water-based flux it is possible to eliminate the need for a surfactant that leaves hygroscopic residues and, thus, eliminates post-solder cleaning or the need for a conformal coating or encapsulant. To minimize the ionic contamination of the board, the diluting water must be deionized or distilled. The addition of a biocide is not necessary because the temperature of the flux during the operation is too high to remove most of the bacteria. For use with the present invention, the purity of the water can be carefully controlled. Other co-solvents such as alcohols, amines and the like can be used if their concentration is limited to less than 5% by volume, subject to environmental regulations for the use of VOCs. The fluxing agent that is described consists essentially of one or more weak organic acids. These acids include adipic acid, glutaric acid, succinic acid and mannolic acid [sic]. If desired, the acids can be mixed. The step of applying the fluxed solution of the flux by means of dispersion effectively distributes the fluxed solution of the flux at a flow rate between 5-50 ml / min as fine particles. The dispersion of the flux can be achieved by means of dispersion, as it can be by providing a low volume flow of the flux dosed in an atomizing nozzle. This may consist of a gas-operated spray nozzle using air, nitrogen, carbon dioxide or gas suitable for dispersion of the flux, or an ultrasonic spray nozzle that uses a piezoelectric impeller for the atomization of the flux. It is also possible to use other suitable spray nozzles such as bell and rotary atomizers. In general, the diameter of the dew drop is approximately 10-400 microns. The results of the test have shown that the product is reliably improved by removing the surfactants commonly used in water-based fluxes. The test procedure measures the leakage current that passes between two sets of fingers in an interdigitated pattern under a certain voltage bias in two different environmental conditions: ?? C "- 85 ° C, 85% relative humidity,, D "- 2 ° C, 100% relative humidity. (Continued) Fo__rra__Lation of the Current Type of R ga Riga flow flux "C" (amperes)? D "(arthpere) Alpha NB300A2 Flux (1.114-0.32) E-6 (2.494-1.72) E-5 available in the Senju ZR-80 Eundente ccmercio (3.934-0.19) E-5 (4.194-0.04) E-5 available in the ccpercio Preferably, at lower leakage current better, because this reflects less pollutants, such as hygroscopic waste (ie, cleaning is unnecessary). The Alpha NR300A2 compound is available from Alpha Metals, New Jersey. Senju ZR-80 is available from Mitsui Comtek located in Saratoga, California. The previous test illustrates that the leakage current (the means used to assess the reliability of the flux residues) measured in the heated flux is comparable to the VOC flux that is currently used as a reference, and is often lower than fluxes without VOCs that contain a surfactant. The reduction in leakage current shows great improvement in the reliability of the product after the teachings of the present invention.

The criterion for reliability is that the leakage current that is measured in both environments must be equal to or less than that of PS-1. This is the flux, which does not require cleaning, which is currently used in production, with a content of 99% alcohol, or VOC, as the solvent. The result of the adipic acid solutions heated without surfactants and dispersed by an ultrasonic spray nozzle are mentioned in the foregoing. Both series of data meet the reliability criterion. Of the solutions described, preferably a solution of 3-4% adipic acid in water is used. Thus, the present invention describes a method of heating a flux for water-based welding, which does not require cleaning to increase the solubility of one or more weak organic acids in the solvent. The reliability of the product is improved by eliminating the surfactant agent that is commonly present in conventional water-based fluxes. The high content of solids that is achieved through heating allows the reduction in the volume of the spray, which in turn eliminates the need for a surfactant, thus avoiding a high hygroscopic residue after welding, which causes a deterioration in the reliability of the product. The greatly increased solubility of the adipic acid can be used without the need for carbon dioxide for the dispersion of the flux, which can be achieved more effectively using a low volume ultrasonic spray system. The mist that is deposited on the board is insufficient to aggregate and form a large drop. In this way, a surfactant agent is not required. The method described is not limited only to the spray flux. Other techniques, such as the addition of the flux by immersion, the addition of the flux by waves and the addition of the flux by foaming can use the invention described herein.

Claims (16)

1. A flux formulation without a surfactant agent for use in the assembly of electronic circuit boards as a formulation that does not require cleaning, the formulation consists of: a flux solution having a fluxing agent consisting essentially of: one or more organic acids weak; and a solvent consisting essentially of water; The fluxing solution is used to transport the fluxing agent before it is deposited in a welding site for the improvement of the reliability that is generated by the absence of hygroscopic waste and to avoid the environmental degradation that is generated, due to the absence of the VOCs

2. The flux formulation of claim 1, wherein the one or more weak organic acids is selected from the group consisting of adipic acid, glutaric acid, sulfinic acid, malonic acid and mixtures thereof.

3. The flux formulation of claim 1, wherein the solvent consists essentially of deionized water.

4. The flux formulation of claim 1, wherein the solvent consists essentially of distilled water.

5. The flux formulation of claim 1, wherein the one or more weak organic acids consists of adipic acid having a solids content of up to 62.5% dissolved in water heated to about 100 ° C.

6. The flux formulation of Claim 1, wherein the fluxing agent consists of adipic acid with a concentration of up to 160 grams of adipic acid per 100 ml of water at about 100 ° C. The flux formulation of claim 1, wherein the flux solution It consists of 2-5% adipic acid in water. 8. A method for delivering a flux formulation without a surface active agent for use in the assembly of electronic circuit boards as a formulation that does not require cleaning, consists of: preparing a flux solution having a fluxing agent consisting essentially of: one or more weak organic acids; and a solvent consisting essentially of water; The fluxing solution serves to transport the fluxing agent before the deposition of the same in a welding site for the improvement of the reliability that is generated by the absence of hygroscopic residues and to avoid 3 environmental degradation that is generated by the absence of VOCs; heating the flux solution to create a heated flux solution and to increase the solubility of the one or more organic acids in the solvent, thereby decreasing the proportion of the solvent needed to transport an effective amount of the fluxing agent and thereby decreasing the hygroscopic residue that remains after welding; and applying the solution of the heated flux through a dispersion medium so that the flux solution disperses as fine particles. The method of claim 8, wherein the one or more weak organic acids are selected from the group consisting of adipic acid, glutaric acid, succinic acid, mannolic acid [sic] and mixtures thereof. The method of claim 8, wherein the solvent consists essentially of deionized water. The method of claim 8, wherein the solvent consists essentially of distilled water. The method of claim 8, wherein the one or more weak organic acids consists of adipic acid having a solids content of up to 62.5% dissolved in water heated to about 100 ° C. The method of claim 8, wherein the fluxing agent consists of adipic acid with a concentration of up to 160 grams of adipic acid per 100 ml of water at about 100 ° C. The method of claim 8, wherein the flux solution consists of 2-5% adipic acid in water. 15. The method of claim 8, wherein the step of applying the fluxed solution of the flux through a dispersion medium consists in distributing the fluxed solution of the flux at a flow rate between 5-50 ml / min. 16. The method of claim 15, wherein the step of applying the fluxed solution of the flux consists in dispersing the spray having a droplet size between about 10-400 microns in diameter.