DK151234B - APPLICATION OF A SOLVENT MIXTURE FOR CLEANING OF CONNECTED ELECTRONIC ARTICLES - Google Patents

Description

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The present invention relates to the use of a solvent mixture for the purification of soldered electronic articles, such as printed circuits, for solder fits and other impurities. A printed circuit consists of a 5 panel or a card on which an electrical circuit is applied by means of printing or etching. Then various electronic components are mounted on the panel, which components are soldered to the circuit by means of soldering. Such electronic components can e.g.

10 being transistors and capacitors. Often, such soldering is done by the circuit panels in a soldering machine. First, the panels are passed by means intended to apply flux to the panels. The flux is used to remove oxides from the surface to be soldered. The flu-15 agent often consists of wood rosin. It is preferably applied in liquid form, e.g. by spraying.

After the flux is applied, the panel of the printed circuit is brought into contact with a bath of molten solder. After the soldering operation is completed, the panel should normally be cleaned to remove the flux and other impurities. This is necessary for a variety of reasons. In operation, electronic components generate heat that can increase their temperatures to above 60 ° C. The flux may be electrically conductive at these elevated temperatures, which may result in undesirable creep currents.

In those cases where the flux contains halogens, these creep flows may occur at room temperature. Another reason why it is necessary to clean the panel is that it is usually desirable to apply a plastic film to the panel with the printed circuit. Even in small quantities, the presence of the flux may impede or make it impossible to apply such plastic films to the printed circuit board because the flux prevents adhesion of the plastic film to the panel surface.

Another reason is that insufficiently cleaned electronic components become sticky and therefore difficult to remove.

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just to deal with and their appearance deteriorates.

It is known that printed circuit panels can be purified with various solvents such as a mixture of ethanol and methyl chloroform or a mixture of isopropanol and trichlorotrifluoroethane. The use of such agents has caused certain disadvantages, such as poor cleaning activity, a detrimental effect on the electronic components or the risk of fire because the agents are flammable.

10 From Danish Patent Application No. 2072/69 (Danish Patent Specification No. 132,588) it is known as a cleaning agent to use mixtures containing tetrachlorodifluoroethane. This compound has a melting point of + 24 ° C, and even mixtures with an aliphatic alcohol have a rather high melting point, cf. table 5 in the said Danish patent application. These mixtures must therefore be difficult to handle as they solidify slightly at lower temperature. On the other hand, in the mixtures in question, there is no risk of solidification.

Another advantage of the present invention is that the mixtures used are non-flammable, whereas most of the compounds used in the aforementioned Danish Application No. 20.72 / 69 have a flash point, which is extremely inappropriate from a fire-proof type. from a standpoint of view.

A further advantage of the present compositions is that the chlorinated compounds used are inexpensive and readily available, while tetrachlorodifluoroethane is not a commercially available product and is expensive to prepare.

According to the present invention, it has been found that excellent results are obtained by using a solvent mixture which is characterized in that it consists of 3-50% by weight of at least one alcohol having 35-6 carbon atoms and 50-97% by weight of at least one chlorinated hydrocarbon of the group consisting of perchlorethylene, 151234

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3 trichlorethylene and methyl chloroform, for cleaning soldered solder paste and other impurities.

The alcohol may be aliphatic or cyclic. For this purpose, it has been found that pentanol is a particularly useful alcohol, especially when used in combination with perchlorethylene. It is preferred to use a solvent consisting of from 10 to 20% by weight pentanol and from 80 to 90% by weight perchlorethylene. This solvent is not flammable, it has a low vapor pressure, resulting in a slight loss of solvent by evaporation, and it can be easily recovered by azeotrop distillation. Among the pentanol isomers, the use of 1-pentanol is preferred.

The use of solvents containing perchlorethylene is preferred because it has been found to have the least detrimental effect on electronic components. Such components are usually coated with a plastic wrap and they are usually marked with paint of different colors. Solvents containing perchlorethylene combine a low attack on such plastic films and labels with a high cleaning efficiency on fluxes and other impurities. In perchlorethylene-based solvents, it is preferred to use alcohols having a boiling point of 115-150 ° C, whereby the percent content of the alcohol 25 falls within that of FIG. 1 in the accompanying drawing. Preferred alcohols that can be used in combination with perchlorethylene are 3-pentanol (bp 116 ° C), 1-butanol (bp 118 ° C), 2-pentanol (bp 119 ° C), 3-methyl-1- pentyn-3-ol (b.p. 121 ° C), 3-methyl-3-pentanol (b.p. 122 ° C), 2-methyl-1-butanol (b.p. 128 ° C), 3-methyl-1- -butanol (b.p. 130 ° C), 4-methyl-2-pentanol (b.p. 133 ° C), 1-hexen-3-ol (b.p. 134 ° C), mixed isomers of primary amyl alcohol (b.p. 127-139 ° C), 1-pentanol (b.p. 138 ° C), 3-ethyl-1-pentyn-3-ol (b.p. 138 ° C), cyclopentanol (b.p. 141 ° C), 2-35 -ethyl-1-butanol (b.p. 146 ° C) and 2-methyl-1-pentanol (b.p.

148 ° C). Other Applicable Alcohols Usable in 4 151234

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combination with perchlorethylene, is 2-methyl-3-buten-2-ol (bp 99 ° C), 2-butanol (bp 99 ° C), 2-methyl-2-butanol (bp 102 ° C) , 2-methyl-3-butyn-2-ol (b.p. 104 ° C), 2-methyl-1-propanol (b.p. 108 ° C), 2,2-dimethyl-1-propanol (b.p.

5 114 ° C), 3-hexen-1-ol (b.p. 156 ° C), 1-hexanol (b.p. 158 ° C) and cyclohexanol (b.p. 161UC).

In solvents based on trichlorethylene, it is preferred to use alcohols having a boiling point of 90--115 ° C /, whereby the percentage content of the alcohol falls within that of that of FIG. 3 in the accompanying drawing. Preferred alcohols that can be used in combination with trichloroethylene are 2-methyl-3-buten-2-ol (bp 99 ° C), 2-butanol (bp 99 ° C), 2-methyl-2-butanol ( b.p. 102 ° C), 2-methyl-3-butyn-2-ol (b.p. 104 ° C), 2-methyl-1-propanol (b.p.

(108 ° C), 2,2-dimethyl-1-propanol (bp 114 ° C) and 3-pentanol (bp 116 ° C). Other useful alcohols that can be used in combination with trichlorethylene are 1-butanol (bp 118 ° C), 2-pentanol (bp 119 ° C), 3-methyl-1-pentyn-3-ol (bp 121 And 3-methyl-3-pentanol (b.p. 122 ° C).

In methyl chloroform-based solvents, it is preferred to use alcohols having a boiling point of 82-105 ° C, whereby the percentage content of the alcohol falls within that of FIG. 2 in the accompanying drawing. Preferred alcohols that can be used in combination with methyl chloroform are 2-methyl-2-propanol (bp 83 ° C), 2-methyl-3-buten-2-ol (bp 99 ° C), 2-butanol (b.p. 99 ° C), 2-methyl-2-butanol (b.p. 102 ° C) and 2-methyl-3-butyn-2-ol (b.p. 104 ° C). Other useful alcohols that can be used in combination with methyl chloroform are 2-methyl-1-propanol (bp 108 ° C), 2,2-dimethyl-1-propanol (bp 114 ° C), 3- pentanol (bp 116 ° C) and 1-butanol (bp 118 ° C).

The following examples illustrate some particularly useful solvents. Parts are parts by weight unless otherwise stated.

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5 (1) 13.5% 1-pentanol 86.5% perchlorethylene (2) 10.0% mixed isomers of primary amyl alcohol 90.0% perchlorethylene 5 (3) 8.0% 4-methyl-2-pentanol 92, 0% perchlorethylene (4) 7.0% 2-ethyl-1-butanol 93.0% perchlorethylene (5) 12.0% 2-butanol 88.0% trichlorethylene (6) 7.0% 2-methyl-2 -butanol 93.0% trichloroethylene (7) 6.0% 2-methyl-2-propanol 94.0% methyl chloroform (8) 5.0% 2-butanol 95.0% methyl chloroform.

The solvent used in accordance with the present invention can in some cases produce a perfect cleaning effect on printed circuit panels without requiring any mechanical treatment of the panel. For example, if the printed circuit board. has been soldered using the flux "Zeva Flux Lubricant" type C 2 p, the flux can be removed by simply immersing the panel at room temperature in a solvent consisting of 13.5% by weight 1-pentanol and 86.5% by weight perchlorethylene. IN

in other cases, it may be desirable to improve the cleaning effect by treating the panel at a higher temperature or by simultaneously exposing the panel to a mechanical treatment such as brushing. A brush operation removes and then insoluble impurities. It is therefore preferred to treat printed circuit panels in a machine where the panels are exposed to the simultaneous action of a solvent and brushes. The temperature of the solvent is preferably 20-50 ° C.

Preferably, the solvent is passed through the machine countercurrent to the panels. The solvent used, 6

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Preferably, leaving the apparatus is recovered by distillation and the thus-purified solvent is re-introduced into the machine. The purification provided by distillation is facilitated if the solvent has a composition approximately equal to the azeotropic mixture formed by the distillation process. A mixture of 1-pentanol and perchlorethylene has e.g. an azeotropic composition of about 15% by weight of 1-pentanol and 85% by weight of perchlorethylene and boiling at approx. 119 ° C. However, it should be noted that due to evaporation, a loss of the solvent occurs in the purifier. The component with the lowest boiling point evaporates most easily. In a mixture of 15% 1-pentanol and 85% perchlorethylene, the evaporation ratios of the two components are so different from the azeotropic ratio that the solvent in the machine will be deprived of perchlorethylene. Therefore, it is required that the new solvent supplied to the machine to offset the loss caused by evaporation must have an increased percentage of perchlorethylene. For example, if

If a solvent of 85% perchlorethylene is desired in the machine, the new solvent must, for example, contain e.g. 90 or 95% perchlorethylene.

After taking into account the loss due to evaporation 25 and the desired azeotropic distillation, it is preferred to give the solvent a percentage of alcohol which depends on the boiling point of the alcohol as shown in the drawing. 1 relates to a mixture of an alcohol and perchlorethylene; 2 shows a mixture of an alcohol and methyl chloroform; and FIG. 3 a mixture of an alcohol and the trichloroethyl.

35 In each figure, the abscissa represents the boiling point of the alcohol (° C) and the ordinate the percentage of alcohol.

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7 The hole in the solvent. The preferred solvent is within the range shown in the figures. It can be seen from FIG. 1 e.g. it is clearly seen that the preferred percentage of 1-pentanol (b.p. 138 ° C) when mixed with per-chloroethylene is from 5 to 20% by weight. The preferred percentage of cyclopentanol (bp 141 ° C) is from 5 to 18% by weight. The preferred percentage of 4-methyl-2-pentanol (bp 133 ° C) is from 7 to 24% by weight. The preferred percentage of 2-ethyl-1-butanol (bp 146 ° C) is from 10 to 13% by weight. It is a particular advantage of the present invention that most of the solvent mixtures of the invention have a high flash point so as to reduce the risk of fire. The alcohols having a high boiling point produce azeotropic mixtures which have no flash point. Eg. For example, the azeotropic mixture of 1-pentanol and perchlorethylene has no flash point at a temperature below its boiling point of 119 ° C.

Claims (4)

Use of a solvent mixture consisting of 3-50% by weight of at least one alcohol of 4-6 carbon atoms and 50-97% by weight of at least one chlorinated 5 hydrocarbon of the group consisting of perchlorethylene, trichlorethylene and methyl chloroform for the purification of soldered electronic articles for solder paste and other impurities. Use according to claim 1, wherein the solvent mixture consists of perchlorethylene and an alcohol having a boiling point of 115-150 ° C, wherein the percentage content of the alcohol falls within that of FIG. 1. Use according to claim 1 / wherein the solvent mixture consists of trichlorethylene and an alcohol having a boiling point of 90-115 ° C, whereby the percentage content of the alcohol falls within that of FIG. 3. Use according to claim 1, wherein the solvent mixture consists of methyl chloroform and an alcohol having a boiling point of 82-105 ° C, whereby the percentage content of the alcohol falls within that of FIG. 2.