RU1825700C - Preservative flux for soldering of printed circuit boards - Google Patents

Abstract

Use1 soldering and tinning of printed circuit boards with hinged elements and blocks of electronic equipment. The inventive preserving flux contains the following components, wt.%: Pine rosin 10-30; orthophosphoric acid 1.3-1.5; dimethylformamide 11-15; ethyl alcohol the rest is 4 tablets.

Description

The invention relates to soldering, in particular to fluxes, which are used mainly in the process of soldering and tinning with fusible solders, for example, printed circuit boards with attachments and blocks of electronic equipment.

To achieve this goal, the preservation flux for soldering printing units additionally contains dimethylformamide in the following ratio, wt.%.

Rosin pine 10-30

Dimethylformamide 11-15

Orthophosphorne

acid 1.3-1.5

Ethyl alcohol

The addition of orthophosphoric acid to the flux facilitates the removal of the oxide film from the soldered compound and further increases the corrosion resistance of this compound after soldering. Residues of the fluorine with phosphoric acid can therefore not be removed, and the printing units can be immediately varnished for sealing or left unvarnished depending on the operating conditions of the product.

To prove the beneficial effect of phosphoric acid, Table 1 is provided.

The data on the surface insulation resistance of the substrate are presented in Table 2.

It can be seen from Table 2 that a change in the concentration of orthophosphoric acid in the range of 0.2-2.0 wt.% Practically does not affect the surface insulation resistance of the substrate.

The addition of dimethylformamide to the flux improves its preservative properties by giving the flux plasticity and protecting it from mold. This substance belongs to the group of aldehydes and is a derivative of dimethylamine and formic acid.

In the preparation of orthophosphoric flux, the acid partially forms an ether with ethanol to liberate water.

With

with

00

go eat VJ oh oh

+ ЗС2Н5ОН - Ethyl alcohol

In the presence of water released according to this reaction, dimethylformamide decomposes into formic acid and dimethylamine

(CHCH - N - C f

H20

ABOUT

// - (СНз) 2 - NH С - Н

HE

Dimethylamine

In turn, dimethylamine interacts with phosphoric acid to form a complex aminophosphide, which is a good insecticide.

OH OH R - OH

4 he

/he

about P -

+ HN

/

CH3

SNZ

N

/

SNZ

f H20

.

 OH CH3 Dimethylaminophosphide

Thus, the pressure in the flux of dimethylformamide provides a solution to the problem, making the flux more elastic and resistant to bactericidal contamination and mold, improving its bactericidal properties.

To prove the beneficial effect of the addition of dimethylformamide, a flux was prepared, wt.%:

Pine Rosin29, 6

Ethyl

alcohol69.1

Orthophosphorna

acid1.3

The flux was divided into 10 parts and a certain amount of dimethylformamide was added to each part (samples 2-10). Sample 1 - without dimethylformamide.

A layer of prepared fluxes was deposited on a transparent glass, dried at 60-70 ° C for 1 h. Samples were placed in a thermostat with p - const 98%. A piece of ple

0

5

0

5

0

5

0

5

0

0-С2Н5 0 Р О-СаНб + ЗНаО

O-C2H5 Ethyl Phosphate

canopy, and the thermostat was placed in a thermostat at 30-40 ° C. After 10 days in humid conditions, the mold dried out of all samples with dimethylformamide. On the sample without dimethylformamide, mold remained.

Further, these samples were placed in a cold chamber and tested at -60 ° C for 2 hours with a gradual decrease and increase in temperature. Then the samples were examined using a BM-4 microscope. The results are summarized in Gab.Z.

It can be seen from Table 3 that dimethylformamide is sufficient from 11 to 15% by weight of the weight of the flux to impart a preservative and elastic properties to the flux. A smaller amount of dimethylformamide does not provide a dense crack-free coating when tested for cold resistance. A larger amount does not provide a dense coating.

The inventive flux is prepared as follows.

A portion of ground pine rosin is dissolved in ethanol, then photophosphoric acid and dimethylformamide are added according to the formulation.

Table 4 shows examples of specific performance of the flux composition and test results for the limit, average and transcendent values of the ingredients, as well as the characteristics of the prototype flux.

As can be seen from Table 4, the inventive flux provides a high coefficient of solder flowability, a low deoxidation rate, thereby ensuring high-quality soldering, as evidenced by a significant reduction in the amount of gap in printed circuit boards. Moreover, the more phosphoric acid is added, the better the soldering. However, to ensure the reliability of the device where the inventive flux without washing was used in the test, it should be limited to a limit of 1.4 wt.% Phosphoric acid by weight of the flux, since a greater amount of acid contributes to the darkening of the solder sites, which is associated with the absorption of water, which, in turn, helps to reduce the insulation resistance of the printed circuit board. Less than 1.1 mes.% Orthophosphoric acid is impractical to enter, because soldering is obtained with icicles, indicating a weak flux activity.

The flux according to the invention has no unpleasant odor irritating the mucous membrane of the eyes and respiratory tract, and is suitable for both manual and group soldering of printing units.

Claims (1)

SUMMARY OF THE INVENTION Preservative flux for soldering printing units containing pine rosin, phosphoric acid, ethyl alcohol, characterized in that, in order to increase the preserving properties of the flux while maintaining the electrical insulation properties of the product, it additionally contains dimethylformamide in the following ratio of components, wt.%: Pine rosin 10-30 Orthophosphoric acid1.3-1.5 Dimethylformamide 11-15 Ethyl alcohol G a 6 l i c a 1 table 2 Table 3 Table