JPS5922632B2 - Water-soluble flux for soldering printed wiring boards - Google Patents

Description

Detailed Description of the Invention The present invention relates to a water-soluble flux used when soldering components to a printed wiring board or when coating a printed wiring board with solder. This relates to a water-soluble flux that does not deteriorate the insulation resistance of glass epoxy resin.

There is a strong thermal shock when soldering printed wiring boards, and hydrogen chloride gas and other corrosive gases from the decomposition of activators and other organic and inorganic substances in the flux can damage the base of printed wiring boards. The material is often damaged, causing so-called measling in some areas, where salt and other impurities can adhere and cause insulation failure.

When soldering printed wiring boards, the above must be taken into consideration when selecting a flux, but conventional fluxes lack consideration of these points, making it difficult to select a satisfactory flux. There were significant restrictions.

As printed wiring boards are used in all fields due to the development of electronics, poor insulation of printed circuit boards has become a serious problem, and it is hoped that a water-soluble flux with excellent insulation properties will emerge. . Conventionally used water-soluble fluxes for soldering are based on water-soluble carriers such as glycerin, ethylene glycol, and polyalkylene glycol, to which are added hydrochlorides of amines, amino acids, etc., and then mixed with water or alcohol. The viscosity has been adjusted to an appropriate level.

Such water-soluble fluxes do not have sufficiently satisfactory performance in terms of maintaining insulation resistance. The present inventor prepared water-soluble fluxes using various combinations of the above-mentioned carrier and activator, and investigated the effects of these fluxes on the insulation resistance of glass epoxy resin, which is the base material of printed wiring boards, and found that the results were satisfactory. In all cases, a decrease in insulation resistance of about 103 or more was observed.

When we investigated the factors that have a large effect on such deterioration of insulation resistance, we found that low-molecular acids and aldehydes, which are decomposition products of polyalkylene glycol, etc., poison the epoxy resin and cause so-called measling. Therefore, the present inventor investigated the effects of combining various polyalkylene glycols and activators with various antioxidants that act to prevent oxidation, such as polyalkylene glycols, at high temperatures. The present invention was completed by discovering a combination that has excellent retention effects.

That is, the present invention comprises a polyalkylene glycol having a ratio of oxyethylene group EO to oxypropylene group Po of 25:75 to 85:15 and a molecular weight of 500 or more, and an antioxidant that prevents oxidation of the polyalkylene glycol at high temperatures. The present invention provides a water-soluble flux for soldering printed wiring boards, optionally containing a conventional activator.

Regarding the polyalkylene glycol that is the base material of the water-soluble flux of the present invention, low molecular weight ones such as glycerin and ethylene glycol are not effective in maintaining the insulation properties of printed wiring boards, and have a molecular weight of 500 or more. Must be the one above.

Generally commercially available polyalkylene glycol is a polyalkylene ether glycol with a functional group (-0H group) at the end, which is a copolymer of oxyethylene and oxypropylene. Regarding the ratio of oxyethylene EO to oxypropylene PO, the insulation is better as the amount of PO increases. The higher the amount, the worse the water solubility; that is, the ratio of EO/PO in the range of 25:75 to 85:15 was effective in maintaining insulation properties. As an antioxidant for preventing oxidation of polyalkylene glycol, which is the base material of the water-soluble flux of the present invention, during soldering work, it is effective in preventing oxidation of the base material at a temperature of 180 to 270°C. Yes, for example dilaurylthiopropionate,
Examples include mercaptobenzothiazole, diphenyl paraphenyl diamine, hydroquinone dimethyl ether, dibenzothiazine, zinc alkyl thiophyl ester, alkyl phenyl diamine, hydroquinone dimethyl ether, and diphenylol propane, which are 0. Used in amounts of 0.05-1%.

In addition, activators used as necessary to make the soldering action of the water-soluble flux of the present invention effective include methylamine, ethylamine, diethylamine, triethylamine, n-propylamine, n-butylamine, monoethanolamine, Examples include triethanolamine, ethylenediamine, hydroxylamine, β-phenylethylamine, diphenylamine, hydrazine, glutamic acid and their hydrochlorides. The invention will be explained in more detail by the following examples.

Examples 1 to 4 Printed circuit board R-1701 (JISG
E-4) was etched to make a comb-shaped electrode, the flux was applied to it by dipping, and solder coating was performed using a Tulder coater (HSC-224-D) manufactured by Dainippon Screen Mfg. Co., Ltd., to form a comb-shaped electrode. was washed with water, dried, and the insulation resistance immediately after and after 96 hours of humidification were measured.

A blank test without flux was also conducted at the same time. Insulation resistance measuring device: TOASUPERMEGO
HMMETERMODELSM-5E500VDC0 humidification tank: TABAIHUMIDI'RYcABINETL
H-110 50°C 95% RH 96 hours.

The solder leveler conditions are as follows.

Flux: 5 seconds immersion Solder: 240°C, 6 seconds immersion Hot air: 180°C, 1 second Flux of each example is polyalkylene glycol 80
%, activator 2%, antioxidant 0.5%, and remaining water. A sample without the antioxidant was also produced as a comparative example.

The compositions of the fluxes of Examples and Comparative Examples are shown in Table 1.

The results of insulation resistance measurements of the water-soluble fluxes of Examples and Comparative Examples immediately after leveling and after 96 hours of humidification are shown in Table 2.

From the results in Table 2, the insulation resistance of the water-soluble flux according to the present invention after 96 hours of humidification is 10 to 100 times larger than that of the comparative example that does not contain an antioxidant. This proves the excellent effects of antioxidants.

Claims (1)

[Claims] 1. Polyalkylene glycol with a molecular weight of 500 or more and a ratio of oxyethylene groups to oxypropylene groups of 25:75 to 85:15, and an antioxidant that exhibits an antioxidant effect on the polyalkylene glycol at a temperature of 180 to 270°C. A water-soluble flux for soldering.