JPS6349364A - Method for checking flame retardance of flame retardant flux - Google Patents

Abstract

PURPOSE:To prevent the danger of inflammation and explosion for a long period of time by adding a specific ratio of a halogenated hydrocarbon solvent to a solvent of flux and checking the compsn. change thereof by measurement of the specific gravity, thereby checking the flame retardance. CONSTITUTION:The halogenated hydrocarbon solvent is incorporated at >=20wt% into the solvent of the flux and the compsn. change thereof is checked by meas uring the specific gravity, by which the flame retardance is checked. The content of the halogenated hydrocarbon solvent is controlled in accordance with the result thereof. The danger of inflammation or explosion thereof is thereby prevented even if said solvent is used by being sprayed with a spray fluxer for an automatic soldering device or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for checking flame retardancy of flame retardant flux, and in particular to a spray type fluxer used in automatic soldering equipment for soldering electronic components to printed circuit boards. This invention relates to a method for checking the flame retardancy of flame retardant flux used in

2. Description of the Related Art General electronic devices in which electronic components are mounted on printed circuit boards are widely used. This printed circuit board is made by covering the surface of a laminate with copper foil and etching the copper foil to form a circuit.In order to attach electronic components to such a printed circuit board, the printed circuit board is continuously transported. Automatic soldering is used to automatically load electronic components onto a board and solder their terminals to the circuit portion of the printed circuit board. In order to carry out such soldering, for example, squirted molten solder is brought into contact with the parts that need to be soldered, but flux is usually applied in a pre-process. This is to prevent direct contact of high-temperature solder, such as 230 to 250°C, to the circuit part of the printed circuit board, as the copper foil on the circuit part will be oxidized, impairing solder wettability and adhesion. - This is to reduce the previously oxidized copper foil portion and make it a fully curved copper surface for better solder adhesion.

For this reason, conventional fluxes are based on, for example, rosin or rosin-modified resin, to which a small amount of an activator such as amine hydrochloride and various other additives are added depending on the purpose, and then alcohol is added. Generally, it is dissolved in a solvent as the main component. When electronic elements are automatically soldered to a printed circuit board using this flux, the flux is stored in a fluxer in an automatic soldering device and applied by a foaming type, jet type, or spray type application method.

Among these, the spray-type applicator applies atomized flux to the soldering part, so it can be applied uniformly, and compared to the one that immerses the soldering part in the flux liquid, the spray-type applicator applies the atomized flux to the soldering part. There is no flux build-up, the preheating efficiency is increased, and since the flux is not reused, dust and reaction products with the printed circuit board do not mix with the flux when the flux comes into contact with the printed circuit board, so fresh flux is always available. For reasons such as availability, soldering is especially used for high-density mounting printed circuit boards.

As this spray type coating device, for example,
As described in Japanese Patent No. 87262, a rotating roll having a large number of through holes is immersed in flux, and the fluff held in each through hole is blown off with air blown out from a nozzle inside the roll to atomize and solder. Examples include those that are supplied to the department. Since such a spray coating device atomizes flammable flux, there is a high risk of fire. Therefore, an exhaust duct is provided to prevent the concentration of the solvent from increasing around the flux.

Problems to be Solved by the Invention However, in the case of a flux made of a solvent, mainly alcohol, the flash point of the flux is near room temperature, and if there is a source of flame near the fluxer, there is a risk of fire. Particularly in automatic soldering equipment, the flux solvent may ignite due to sparks generated when the switch of the electrical control mechanism is opened or closed, or from static electricity, which is particularly likely to occur in low humidity.

Additionally, since flux is preheated after being applied, if a sheathed heater or panel heater with a surface temperature of 300 to 600°C is installed right next to the fluxer, the surface temperature of this heater will be higher than the ignition temperature of the flux solvent. As printed circuit boards that are tall and coated with flux pass over the heater, the flux drips down and ignites, or it carbonizes without burning out, which becomes a ignition source that can ignite the flux solvent. Also, depending on the concentration of the solvent in the air, it may cause an explosion.

For example, in the case of rosin-based flux using isopropyl alcohol as a solvent, the flash point is 14°C, the ignition point is 400°C,
The explosion range is 2 to 12 vol%, and there is a risk of fire and explosion.

To prevent such risks, we proposed using a flame-retardant flux containing a halogenated hydrocarbon solvent in the flux solvent composition, but since the flux is used for a long time in automatic soldering equipment, It is unavoidable that the solvent composition changes during use. As a result of this change in solvent composition, if the amount of halogenated hydrocarbon solvent decreases, the above-mentioned danger of fire and explosion will occur, so countermeasures have been desired.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a solution to the solvent composition associated with the use of a flame-retardant flux containing 20% by weight or more of a halogenated hydrocarbon solvent in the solvent composition of the flux. The present invention provides a method for checking the flame retardancy of a flame retardant flux, which is characterized in that the change in N is checked by measuring the specific gravity to check the flame retardancy.

Since the specific gravity of the halogenated hydrocarbon solvent is greater than that of other flux components, the range of its content can be determined by measuring the specific gravity, and thereby the N(ffl) property of the flux can be determined.

Next, the present invention is R?　I[fl.

The flux of the present invention can be used in any of the jet type, foaming type, and spray type fluxers. As shown in the drawing, a rotating cylinder 1 having a large number of through holes on its circumferential surface is partially immersed in flux stored in a flux tank 2, and the flux retained by this immersion is placed in the air, and the interior of the rotating cylinder is heated. An example is a type in which air is atomized by blowing it out from a large number of nozzles formed in a tube 3 disposed in a tube 3, and the atomized air is supplied to a printed circuit board a. Note that 4 is a supply tank for fresh flux and solvent.

The flux used in the present invention is made by using rosin or its modified resin as a resin component, adding an activator as necessary, and various additives depending on the purpose, and adding a solvent to the flux.

Examples of the rosin or its modified resin include rosin modified resins manufactured by Arayo Kagaku Kogyo, such as Ester Gum, Super Ester, Malquid, and Tamanol.

Examples of the activator include amines, ta-acids, organic acid salts of amines, and inorganic acid salts of amines.

Furthermore, examples of the flux solvent used in the present invention include alcohols, esters, ketones, aromatic solvents, and the like. Specifically, examples of alcohol-based solvents include methyl alcohol (flash point: 10°C, hereinafter the flash point is shown in parentheses), ethyl alcohol (12°C), isopropyl alcohol (12°C), n-propyl alcohol (
(15℃), normal butanol (29℃), isobutanol (27℃), and benzyl alcohol (96℃). Examples of alcohol ether solvents include ethyl cellosolve (45℃) and butyl calpitol (78℃).
, butyl cellosolve (61'C), ethyl carpitol (94°C), butyl carpitol acetate (116
°C), butyl cellosolve acetate (88 °C), benzyl acetate (96 °C), methyl isobutyl ketone (15.6 °C), cyclohexanone (63.9 °C), isophorone (80 °C), α-terpineol as other solvents. (69℃), turpentine (35℃), toluene (
4,4°C), O-xylene (17°C), II+-xylene (25°C), p-xylene (end °C), tetralin (7°C),
1°C), decalin (57°C), and the like. The above flash point is based on the Solvent Pocket Book (for the Society of Organic Synthetic Chemistry, Ohmsha Co., Ltd., first edition published on November 25, 1962).

In addition, as the halogenated hydrocarbon solvent, trichlorotrifluoroethane (CC1zFCCI F Engineering), 1°1
．． Examples include 2-1-lichloroethane, 1.1.1-)lychloroethane, trichlorethylene, perchlorethylene, and the like. These halogenated hydrocarbon solvents are preferably contained in an amount of 20% by weight or more in the solvent composition of the flux.

The ratio of the above resin component and solvent is 3 to 50% by weight of the resin component.
, the solvent is used in a range of 50 to 97%, and when an activator is used in this, the activator is used in an amount of 0.1 to 10% by weight. In any case, when an activator is used, it is particularly preferable that the amount of alcohol solvent in the flux solvent be at least 3% by weight or more from the viewpoint of solubility of the flux component. When the resin component is 3 to 50% by weight, it can cover the copper foil part of the printed circuit board better than when it is less than this, and when it is more than this, the contact of molten solder is caused by an excessively applied flux coating. This may prevent solder from wetting the printed circuit board's copper foil AIS.

The mixing ratio of the halogenated hydrocarbon solvent and other solvents in the flux solvent is preferably determined based on the following criteria.

■By mixing a flammable solvent with a halogenated hydrocarbon solvent, it becomes flammable, non-flammable, or non-combustible, thereby preventing the risk of fire in practical terms.

Generally, the mixing ratio of the halogenated hydrocarbon solvent in the solvent is most preferably 50% (weight ratio) or more, taking into account flammability and ignitability, but preferably 20% or more. At this time, it is also necessary not to impair the drying properties of the flux coating film.

For this purpose, the flash point of these mixed solvents is set to a temperature higher than room temperature. For example, the flash point of a mixed solvent based on the mixing ratio of perchlorethylene and toluene (flash point 4.4°C) is perchlorethylene/toluene, 75/3.
5.50150.25/75 is 35℃ and 18
℃ and 11℃, so mix equal amounts of both.

O-xylene (flash point 29℃) instead of this toluene
If 0-xylene is used, the flash point will be 34° C. when it is 75% by market weight, and if the amount of 0-xylene is greater than this, the flash point will disappear. Also, instead of toluene, methyl isobutyl ketone (flash point 15.6°C) was used at a weight ratio of 75/25.5015.
0.25/75, the respective flash points are 38"C1
Since the temperature will be 24℃ and 18℃, add 25℃ of perchlorethylene.
Use at least % by weight. Furthermore, when the flash point is high, such as cyclohexanone (flash point 63.9° C.), there is no flash point even if it is made 75% by market weight, and the risk of ignition can be reduced accordingly. However, in this case, if a solvent with too high a boiling point is used, the drying properties of the flux will be delayed, so the solvent should be adjusted appropriately. At this time, since the rate of volatilization differs depending on the type of solvent, the solvent composition changes while the flux is actually used, and it is necessary to adjust it, but this can also be done by controlling the specific gravity of the flux. . For example, when isopropyl alcohol and trichlorotrifluoroethane are mixed, the volatilization rate of the latter is much faster than the former, so the specific gravity may be measured and only the latter may be used as the diluting solvent.

In the case of spray application, the volatility of the solvent is not a problem as with other methods; in fact, if the rate of volatilization is too slow,
It is desirable not to slow down the rate of volatilization because the drying of the flux will be slow and the applied flux will flow through the leads from the lead insertion hole and go around the back, as is the case when mounting leaded electronic device parts on a printed circuit board. .

In particular, when using a high boiling point solvent, it is desirable to keep this in mind and reduce the proportion of the solvent used.

■Do not impair the solubility of resin components, hydrohalides, and activators such as organic acids.

To this end, the proportion of halogenated hydrocarbon solvents in which these activators have good solubility, such as alcohol, is increased and the proportion of halogenated hydrocarbon solvents in which these activators have poor solubility is decreased.

■Soldering after using flux does not harm performance, does not corrode the copper foil of printed circuit boards, and does not leave any residue after soldering that harms electrical insulation.

For this purpose, it is preferable to use a solvent that is volatile to the extent that it sometimes evaporates at least during soldering.

■Low toxicity.

In addition to the above, antifoaming agents and thixotropic agents can also be used in the flux of the present invention, and these include fluorine, silicone,
Examples include using 0.1 to 10% by weight of an alcohol defoaming agent and 1 to 10% by weight of a thixotropic agent such as kaolin, Aeroseal (1 bottle manufactured by Aerosil), organic bentonite, and hydrogenated castor oil. .

A flame-retardant flux is created in this way, but when this flame-retardant flux is used with the above-mentioned spray type fluxer, even if the solvent evaporates during the process, the halogenated hydrocarbon solvent and other components, such as resin, Since the specific gravity is different from that of the activator and the like, by measuring this, it is possible to trace the range of the content of the halogenated hydrocarbon solvent.

For example, the specific gravity of the above halogenated hydrocarbon solvent is trichlorotrifluoroethane (CCj!z FCCI F2
) 1.572.1, 1.2- ) Lichloroethane 1.4
41.1.1.1-trichloroethane 1.338,
) Lichlorethylene 1.464, perchlorethylene 1.623, which is greater than 1. In comparison, the specific gravity of the above-mentioned solvents used for flux is 1
In addition, the resin is also less than 1, and the activator °ζ is used in a small amount, so its specific gravity in the entire flux is small and can be ignored, so it accounts for more than 20% of the total solvent composition. The content of the halogenated hydrocarbon solvent has a large effect on the measured specific gravity of the entire flux, and by measuring this, the content range of the halogenated hydrocarbon solvent can be estimated.

Once the content of the halogenated hydrocarbon solvent is known in this way, the halogenated hydrocarbon solvent can be added to maintain the flammability of the flux.

In addition, in the case of a spray type fluxer as shown in the figure, the amount of applied flux can be controlled by changing the rotational speed of the rotating cylinder 1, so if the flux concentration becomes high, it is necessary to perform operations such as lowering the speed. This has the advantage of allowing a wide range of flux concentration control, and there is often no problem in practice even if the solvent composition slightly deviates.

Example Next, the present invention will be explained in detail.

a, phenol-modified rosin 10 gb, benzoic acid 1gC, dimethylamine hydrochloride 0.3 gd, isopropyl alcohol
35 ge, l-lichlorotrifluoroethane 6
5 g This example uses a solvent consisting of isopropyl alcohol mixed with trichlorotrifluoroethane.

The results of measuring the flash point using the following measurement method based on the mixing ratio of isopropyl alcohol and trichlorotrifluoroethane are as follows. Since the solvent in this example will not ignite if the trichlorotrifluoroethane concentration is 55% by weight or more, it will boil. There is no ignition until then.

Here, the flash point is measured using a tag open cup (tag open type).

The material of this example was coated with the spray type fluxer shown in the figure, and soldered using the automatic soldering method R. At this time, J! of trichlorotrifluoroethane compared to isopropyl alcohol! I! Since the flux is highly volatile, the concentration of trichlorotrifluoroethane in the solvent decreases as the flux is used, so this was tracked by specific gravity control and trichlorotrifluoroethane was added to keep the solvent composition constant. The specific progress of this specific gravity management is as follows.

After soldering, the results showed that there was no defective soldering, no corrosion of the copper foil on the printed circuit board, and no deterioration of the insulation properties of the insulating film.The water solubility of the solvent of the flux in Yuko's example was 9.1% by weight. (24°C), there is no deterioration in the properties of the flux even if some water is mixed into the flux. Therefore, there is no need to use the flux in a sealed state, and the flux can be stored and used in a spray fluxer with an open flux surface.

As described in detail, according to the present invention, a halogenated hydrocarbon solvent is added to the flux solvent, and changes in the composition are checked by measuring specific gravity, so that N flammability can be checked. If the content of halogenated hydrocarbon solvents is controlled based on the above, automatic soldering will be possible even if the flux is sprayed in the form of a mist in equipment such as a spray fluxer, and there will be no risk of ignition or explosion over a long period of time. Can prevent danger.

[Brief explanation of the drawing]

The figure is a sectional view of the spray type fluxer in use. In the figure, 1 is a rotating cylinder, 2 is a flux tank, and 3 is a tube having a nozzle. August 13, 1985 Patent applicant Gin Ishii Yoshihiro Yamiyano

Claims (1)

[Claims] (1) Check the flame retardancy by measuring the specific gravity to check the change in the solvent component due to the use of a flame retardant flux containing 20% by weight or more of a halogenated hydrocarbon solvent in the solvent composition of the flux. A flame-retardant tick method for flame-retardant flux characterized by: