RU2463144C2 - Flux for low-temperature soldering - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: proposed flux may be used wiring radioelectric components and IC on p.c.b. operated in harsh environment. Flux comprises activator consisting of the mix of carboxylic acids 3-10 wt %, organic solvent made up of the mix of alcohols - 30 wt % and esters - 60-70 wt %. All components are ecologically safe and based on natural biodegradable stock. Solder does not contain amines, surfactants and water.

EFFECT: high surface electrical resistance.

4 tbl, 1 ex

Description

The present invention relates to radio electronics and can be used for mounting electronic components and integrated circuits on printed circuit boards and the formation of reliable and high-quality soldered joints designed to operate in harsh operating conditions.

The well-known industry standard OST 4G 0.033.200 - 1986, “Solders and fluxes for soldering” - [1], which applies to solders and solder fluxes (filler materials), approved for use in the production of special electronic equipment (REA) and household electronic equipment equipment (ARB) for tinning and soldering of mounting joints and structural units. However, industry standard [1] does not specify specific flux compositions for low temperature brazing.

Also known are Technical Specifications TU 1718-001-07518266-2009 Low Activated Fluxes (Avangard OJSC) - [2], which apply to weakly activated solder fluxes for automated or mechanized installation, designed to remove oxide film from the surface of soldered materials and solder, protection metal surfaces and solder from oxidation during the soldering process and lowering the surface tension of the molten solder at the metal-solder-flux interface. The weakly activated soldering fluxes according to [2] are used to ensure the assembly of electronic modules and the installation of an electronic component base (ECB), including functional electronics products for harsh operating conditions. They are compatible with the following coatings: hot tinning tin-lead, immersion tin, immersion gold, immersion silver. Assembled printing units using weakly activated fluxes are used in household and special electronic equipment: for manual and mechanized processes of soldering and tinning of mounting elements, preliminary tinning of the conclusions of the radioelements of the conductors of printed circuit boards and the conclusions of the circuits of the microcircuits before installation in the case in the products of electronic equipment, subject to the complete removal of residues flux.

However, the source [2] does not indicate specific flux compositions for low-temperature brazing based on organic acids.

The classification of non-corrosive weakly activated fluxes, solder pastes, washing fluids that are approved for use in the manufacture of special radio electronic equipment (REA) in the process of automated surface mounting of electronic modules for harsh operating conditions, as well as their composition, properties and applications of these technological materials are given in the well-known American National Standard ANSI / J-STD-004, January, 1995 "Joint industry standard. Requirements for Soldering Fluxes ”- [3]. The standard [3] defines the requirements for weakly activated fluxes depending on the chemical basis of the non-volatile component and in accordance with their corrosive effect and the properties of the electrical conductivity of the flux or its residues. However, certain components and their percentage ratios are not introduced in the standard [3], that is, in other words, specific flux compositions for low temperature brazing are not indicated.

So, according to the standard [3] for soldered compounds using fluxes based on organic acids (Organic (OR)), the classification presented in Table 1 is introduced.

Table 1 Flux base Flux activity level (% halogen content) Flux type Organic (OR) Organic Acids Low (0%) OR0 Low (<0.5%) ORL1 Medium (0%) ORM0 Medium (0.5-2.0%) ORM1 High (0%) ORH0 High (> 2.0%) ORH1

Soldered joints of high reliability, including those using weakly activated flux, are necessary in devices for medicine, transport equipment (railway, aviation, marine), in military and space technology. For such soldered compounds of high reliability based on organic acids, according to the standard [3], the ORL0 classification was determined, according to which the level of activity of weakly activated flux and the percentage of halogens in it are minimal, that is, practically absent. That is, from table 1 it follows that for soldering the most critical compounds, weakly activated fluxes based on organic acids (Organic (OR)) corresponding to the ORL0 type should be used.

So, for soldering REA of highly responsible units of medical, space and military equipment, it is necessary to match weakly activated fluxes to the most stringent requirements for the quality of soldered joints for their durability and reliability in the most adverse operating conditions.

Manufacturing techniques and components of weakly activated fluxes are known according to the author’s book Ning-Cheng Lee “Reflow soldering technology, troubleshooting and troubleshooting: surface mounting, BGA, CSP and flip-chip technology”. - M .: Publishing house "Technologies", 2006, - 392 p., Ill., Table. - [4], pp. 63-88.

However, the known material [4] does not indicate specific compositions of weakly activated fluxes that would satisfy the conditions of the standard [4] according to the ORL0 classification for mounting critical joints.

Known flux bundle of solder paste for the installation of electrical and radioelements according to the patent of the Russian Federation: RU 2337800, publ. November 10, 2008, IPC B23K 35/36, B23K 35/363 - [5], in the following ratio of components, wt.%, Including: tin-lead solder powder 83.125-91.875, pine oil 2.565-2.835, ethyl cellosolve 1.368-1.512 ethyl cellulose 0.1197-0.1323, rosin 4.4973-4.9707, acetic acid 0.8645-0.9555, technical triethylamine 2.4605-2.7195.

A disadvantage of the known flux binder from [5] is that the compound of technical acetic acid and technical triethylamine forms a salt, triethyl ammonium acetate, which is an ionic compound. Subsequently, if moisture gets in, this ionic compound will conduct an electric current, which significantly reduces the reliability of the circuit board.

Known flux for soft soldering according to Japan patent: JP 3499904 B2 7116889 A, publ. 10/22/1999, IPC B23K 35/363 - [6], containing an activator, which is used as a carboxylic acid having a carboxyl group, which creates an activating effect at the temperature of the solder and reacts with the oxides on the brazed surfaces, cleaning these surfaces. Carboxylic acid having a monocyclic structure, a heterocyclic structure or a structure with ether bonds allows multiple carboxylation to be performed. The flux practically does not dissolve in the presence of moisture, providing increased electrical insulation and preventing current leakage. The flux is not bleached and does not require washing after soldering.

Known flux bundle from a binder solder paste according to the patent of the Russian Federation: RU 703996, publ. 08/20/1997, IPC B23K 35/24 - [7], in the following ratio of components, wt.%, Including: an organic solvent selected from the group: benzene, xylene, toluene, acetone, butyl acetate 15-20; polymerized methacrylic acid ester 0.1-5, lanolin 0.1-2, water - the rest.

Also known flux bundle from the composition of the binder solder paste with a reduced amount of solids after soldering according to the patent of the Russian Federation: RU No. 886388, publ. 08/20/1997, IPC B23K 35/24 - [8], in the following ratio of components, wt.%, Including: acrylic polymer 8-15, organic solvent - the rest, and polybutyl methacrylate or butyl methacrylate copolymer can be used as an acrylic polymer with butyl acrylate: butyl methacrylate 75-95, butyl acrylate 5-25, and the acrylic copolymer additionally contains methyl methacrylate in an amount of 5-25.

The disadvantage of flux bundles according to [6], [7] and [8] is that they are practically not laundered, and this is unacceptable for printed circuit boards of responsible use, in which, to ensure high-quality application of a moisture-proof coating, the remains of the binder solder paste must be completely washed .

So, for soldering REA of highly responsible units of medical, space and military equipment, it is necessary to comply with fluxes and flux bundles based on them to the most stringent requirements for the quality of soldered joints, their durability and reliability in the most adverse operating conditions.

Known binder for solder paste according to the application of WIPO: WO 2098601, publ. 03/19/2001, IPC B23K 35/363 - [9] containing at least one lubricating additive, for example, branched chain fatty alcohol or fatty acid containing 8-50 carbon atoms, including at least 4 carbon atoms per an alkyl chain, or a fatty acid ester.

The disadvantage of the analogue [9] is that the substance: tirendibromide contains halogen, which is part of its flux-bundle, and this is not allowed for use according to the ORL0 standard [3] for critical compounds.

Known flux bundle of solder paste according to Japan patent: JP 3155778, publ. 04/16/2001, IPC B23K 35/363 - [10], containing low-temperature solder powder, as well as components selected from the group consisting of rosin, resin, activator, thixotropic additive, organic diluent and additive that suppresses flux thickening with dissociation constant ≤2.5. As an additive to suppress flux thickening, carboxylic acid is used in an amount of 0.5-5 wt.%, Or derivatives of this acid, preferably chloride or carboxylic bromide.

The disadvantages of the analogue [10] is that the chlorides or bromides of carboxylic acid used in it are an active substance containing halogens, which is not allowed for use according to the ORL0 standard [3] for critical compounds.

Known flux for low temperature brazing according to the patent of the Russian Federation: RU No. 2096152, publ. November 20, 1997, IPC B23K 35/363 - [11], which does not require washing after soldering and contains, wt.%: A mixture of mono- and dibasic organic acids insoluble in water, containing from 4 to 10 carbon atoms - 3, 5-6.0; natural or synthetic resin - up to 5.0; benzotriazole - 0.1-0.5; monohydroxy alcohol or its mixture in ethyl acetate or triacetin - the rest. The flux may additionally contain polyoxyethylated esters of lauric, oleic acid with an average molecular weight of 596 and 503, respectively, or polyoxyethylated fatty alcohols of fraction C ₁₀ -C ₁₈ with a molecular weight of 1000 in an amount of up to 0.25 wt.%.

The disadvantages of the analogue [11] is that, firstly, the flux is poorly washed, and this is unacceptable for printed circuit boards of critical use, in which, to ensure high-quality application of a moisture-proof coating, the remains of the binder solder paste must be completely washed; secondly, flux residues on the printed circuit board during operation will absorb moisture, which will inevitably lead to a decrease in electrical resistance; thirdly, the presence in the flux of polyoxyethylated esters of lauric, oleic acid greatly reduces the electrical resistance of the flux, which is unacceptable for critical compounds.

Known flux for low temperature brazing according to the patent of the Russian Federation: RU No. 2022747, publ. November 15, 1994, IPC B23K 35/363 - [12], which contains the following components, parts by weight: oleic acid 24-26; ethanol 56-61; surfactant (surfactant) 14, dibutyl phthalate 2-4.

As a disadvantage of the analogue [12], it can be noted that the oleic acid entering it has a very low activity, it is resins during heating and subsequently poorly washed after soldering. In addition, the use of surfactants in the flux is not acceptable for soldering critical compounds.

A known method of tinning the findings of the radioelements of the patent of the Russian Federation: RU 2386521, publ. 04/20/2010, IPC B23K 1/20, H01C 17/00 - [13], according to which the surface treatment of the leads is carried out with an active hydrazine-containing flux containing, wt.%: Hydrazine dihydrochloride 2.0-4.0, dihydric alcohol 57 0-42.0, surfactant 8.0-4.0, glycerol 33.0-50.0. Then, the leads are immersed in the molten solder in a group way at a temperature of molten solder of 320-400 ° C.

Known flux for low temperature brazing according to the patent of the Russian Federation: RU 2347656, publ. 02/27/2009, IPC B23K 35/363 - [14], according to which the flux contains components in the following ratio, wt.%: Technical glycerin 30.5-32.1, triethanolamine 20.2-22.2, urea 12 , 2-13.3, ammonium citrate 11.5-12.2, alcohol - the rest.

The disadvantage of using fluxes [13] and [14] is the presence of glycerin in them, which can penetrate the ends of the board or into the capillary mounting gaps, after which there are difficulties with washing it. Glycerin not washed in the capillary gaps of the printed circuit board will absorb moisture during operation and thereby reduce the insulation resistance. In addition, the presence of halogens in the analogue [13] is not permissible for use according to the ORL0 standard [3] for critical compounds; the use of ammonium citrate in the analogue [14] will lead to the formation of citric acid salts, which ultimately leads to corrosion, as well as to the presence of ions.

Known flux for soldering printed circuit boards according to Japanese patent: JP 3221707 B2 05185284 A, publ. 12/03/1991, IPC B23K 35/363 - [15], according to which the flux contains volatile aliphatic carboxylic acid and a volatile organic diluent. The melting point of the acid is 35 ° C, and its boiling point is in the range of 150-300 ° C. Carboxylic acid, which evaporates during soldering, is an activator and does not leave any traces after soldering. Due to this, rinsing of soldered joints with water is not required and the eclectic reliability of soldered joints of printed circuit boards is increased. Flux can significantly increase the productivity of the process of soldering printed circuit boards.

However, the use of volatile aliphatic carboxylic acid creates additional inconveniences, namely, volatile aliphatic carboxylic acid evaporated from flux according to [15] strongly pollutes nearby equipment and ventilation system, and this in turn leads to unjustified expenses for cleaning the equipment and ventilation system.

The known method and flux for low-temperature soldering of electro-radio elements on printed circuit boards according to Japan patent: JP 3132745 B2 7323390 A, publ. 05/26/1995, IPC B23K 35/363 - [16], according to which the flux contains pimelic acid; a first diluent, for example pimelic acid dissolving isopropyl alcohol, and a second propylene glycol monoethyl ether type diluent, the temperature of which is higher than the boiling point of the first diluent. After soldering, this flux does not leave an ionic residue on the surface of the soldered printed circuit board. This flux prevents corrosion and short circuiting of PCB conductors.

The disadvantage of the prototype according to [16] is the use of pimelic acid in it, which has a smell, and the use of such a flux causes inconvenience to personnel, and also requires the installation of additional ventilation for the soldering site with such a flux.

The prototype of the invention are a method and a flux for forming a dense grid of ball leads on the contact pads of crystals of integrated circuits (ICs) according to US patent US 6550667 BB, publ. 11/29/2000, IPC B23K 35/362 - [17], according to which a single-phase flux contains dicarboxylic acid, the amount of which is sufficient for the reaction with the oxidized surface of IC contact pads located with a high density; a first organic solvent, as well as a second organic solvent, the evaporation temperature of which is higher than that of the first solvent. Preferably, the flux contains 8-10% dicarboxylic acid; 25-75% of the first organic solvent and 10-35% of the second solvent. The preferred ratio of the first and second solvent is 1: 3.

The disadvantage of the prototype [17] is the relatively low flux wettability of the elements of the semiconductor soldering components. To increase the wettability of the flux, for example, when soldering with a solder made of a eutectic gold / lead alloy, the temperature and the exposure time (the time the temperature affects the semiconductor components) are increased and they exceed standard values. This in turn brings the temperature to the semiconductor components of the solder, which can cause the failure of these components.

The above-mentioned disadvantages of analogues and prototype set the task of creating a flux for low-temperature soldering for mounting components and products of critical electronics, suitable for wave soldering or selective soldering, corresponding to the ORL0 type of the standard [3].

That is, flux for low temperature brazing:

- having good wettability, under standard conditions of soldering in temperature and endurance;

- all substances which are part of which are environmentally friendly to the environment are based on natural, natural biodegradable raw materials that are not harmful to the environment;

- the composition of which does not contain amines, surfactants, synthetic polymers (resins) and water;

- after soldering which (and subsequent washing) there are no ions (salt residues) in the soldered joint, which ensures a high surface electrical insulation resistance for a long time;

- flux residues after soldering which do not conduct electric current.

This problem is solved in that the flux for low-temperature brazing consists of the following ratio of components, wt.%:

carboxylic acid activator 3-10% a mixture of organic solvents in the form of alcohols and thirty% esters 60-70%

High reliability of soldered joints (including those using lead in tin solders) is necessary in devices for medicine, transport equipment, and military and space technology.

The activator of the proposed flux is a mixture of organic acids based on carboxylic acid.

The designation of fluxes for low-temperature brazing based on organic acids according to [2] is as follows: ФО-5А, where Ф - flux, О - organic (based on organic acids), 5 - serial number of the flux composition, A - development company (Avangard OJSC ").

According to the assortment, fluxes are divided into fluxes with water-washable residues and fluxes with semi-water-washable residues. ФО-5А is with water-soluble residues and with semi-water-washed residues.

During tests, the flux grade ФО-5А (ORL0) during soldering of the DIP component showed excellent results; during tests on all samples, the flux rises in the output of the component through mounting holes, an even soldered connection with high-quality wetting of the component leads and contact pads.

For washing flux FC-7A (ORL0), OZh-21A Lira and OZh-27A Vega washing fluids developed at Avangard OJSC were used.

After soldering, the flux must be washed using aqueous, semi-aqueous washing liquids and in deionized water.

After soldering, all residual fluxes ФО-5А (ORL0) are completely removed in the jet-washing unit and in an ultrasonic (UZV) bath with washing liquids ОЖ-27А "Vega" with a concentration of 25% and ОЖ-21А "Lira" with a concentration of 100%.

Flux residues after washing with aqueous or semi-aqueous detergents are resistant to high humidity and temperature effects. The operating temperature range of the inventive flux for low-temperature soldering is from plus 179 to plus 225 ° C and it can be used to solder components on printed circuit boards 1-4 of the operating hardness group according to GOST 23752.

Flux residues after washing with aqueous or semi-aqueous detergents are compatible with epoxy, epoxy ester, urethane, silicone and acrylic moisture-proof coatings and compounds, as well as compatible with solder masks.

For the preparation of flux substances of qualification are used: technical, pure or higher qualifications.

The main properties of the flux FO-5A are shown in table 2.

table 2 No. p / p Parameter Name Parameter value one Appearance clear amber to brown amber liquid 2 Density, g / cm ³ 0.823-0.827 3 The spreadability coefficient of the molten solder POS-61 under the action of flux > 1.1 four The effect of flux residues on the surface insulation resistance, Ohm > 10 ⁹ 5 Halogen content,% 0 6 Flux Copper Mirror Corrosion acc.

The test results of the flux by the value of the surface insulation resistance in normal climatic conditions (NKU) are shown in table 3.

Gumboil ФО-5А (ORL0) complies with the requirements of GOST 23752-79 regarding the effect on the surface insulation resistance both in NKU and when exposed to high humidity and temperature.

According to the results of the tests, we can conclude that the proposed flux for low-temperature soldering based on natural rosin shows high-quality results on wetting the output surfaces and mounting holes during selective soldering, fully meets the requirements of TU 1718-001-07518266-2009 on the effect on surface insulation resistance , does not contain halogens and is recommended for use for soldering products of responsible use.

The manufacturer plans to supply the flux in a ready-to-use form. In this case, flux marking is carried out by self-adhesive labels directly on the technological packaging. The content of the marking includes the full name of the material in accordance with this Technical Specification, net weight, production date and batch number. The flux itself is contained in a sealed plastic container of various shapes and sizes. As a shipping container, standard cardboard boxes are used.

If the technology changes during the production of flux or the composition of materials from another batch is applied, the manufacturer carries out additional type tests. The composition of such tests is determined by the degree of possible influence of the proposed changes and factors on the quality of the flux. The assessment of the acceptability of the proposed changes is carried out according to the results of testing the flux for compliance with the requirements of TU [2] and by comparing these results with the results of tests of serial production (table 4).

Moreover, each batch of flux has a quality certificate, which indicates: the name of the manufacturer and the country of origin; grade of flux for low-temperature soldering; batch number; production date; designation of normative and technical documentation. To the first batch of flux received by the consumer, a registered copy of technical specifications can be attached [2].

We give one of the possible examples of the implementation of flux for low-temperature brazing in the composition of the ingredients in the following unit ratio, wt.%:

activator in the form of a mixture of carboxylic acids:

adipic acid 2% oxalic acid 2% succinic acid 2%

a mixture of organic solvents in the form of alcohols:

isopropyl alcohol fifteen% isobutyl alcohol fifteen%

and esters:

di-butyl phthalate 34% di-ethyl phthalate thirty%

In this case, the materiality of the features of the claims is necessary to say the following.

An increase in the activator in the form of a mixture of carboxylic acids of more than 10% leads to a decrease in insulation resistance, and a decrease in it of less than 3% leads to deterioration of soldering, that is, to a decrease in the wettability of the solder of the leads of the REA electronic equipment.

An increase in the composition of organic solvents in the form of alcohols of more than 30% leads to deterioration of soldering due to a decrease in the amount of activator, and a decrease in the amount of alcohols less than 30% leads to an unjustified increase in the proportion of activator in the form of a mixture of carboxylic acids, which will lead to an increase in flux residues after soldering and to reduce insulation resistance.

The presence of a large number of high-boiling esters allows longer exposure to the oxides (oxides) of the brazed surfaces and thereby increases the wettability of the solder leads of the components, and improves the quality of REA soldering. The more solvent (high-boiling ester) is held in the flux, the longer the activator's activity, which allows longer exposure to soldered surfaces.

However, an increase in the composition of organic solvents in the form of esters of more than 70% leads to the fact that the esters in the flux during soldering do not evaporate to the desired value, and this leads to increased stickiness of the flux residues and, consequently, to additional impurities, and their reduction less than 60% leads to faster evaporation of esters from the flux, which leads to its dryness and a significant decrease in the quality of REA soldering, which leads to an increase in the amount of scrap (non-solder).

The last three paragraphs of this answer show the importance of using more esters in relation to alcohols than in the prototype [17].

The mutual overall composition according to the value of the above ingredients is multivariate. It is selected empirically, and subsequently repeatedly passes field tests to clarify the composition.

When you change the percentage of components of the claimed flux for low-temperature brazing, more or less than indicated in the claims, its quality and effectiveness are significantly impaired.

We believe that the proposed flux for low-temperature brazing has all the criteria of the invention, since:

- the inventive flux is new to well-known technical solutions related to the substance, and therefore meets the criterion of "novelty";

- the totality of the features of the claims of the inventive flux is unknown at this level of technology and does not follow the well-known rules for the creation of fluxes for low-temperature soldering, which proves compliance with the criterion of "inventive step";

- the implementation of the inventive flux does not present any structural, technical and technological difficulties, which implies compliance with the criterion of "industrial applicability".

Literature

1. The industry standard OST 4G 0.033.200 - 1986, "Solders and fluxes for soldering."

2. Specifications TU 1718-001-07518266-2009. Low activated fluxes (Avangard OJSC).

3. American National Standard ANSI / J-STD-004, Januaru, 1995 "Joint industry standard. Requirements for Solderinq Fluxes. "

4. Ning-Cheng Li "Reflow soldering technology, troubleshooting and troubleshooting: surface mounting, BGA, CSP and flip-chip technology." - M .: Publishing house "Technologies", 2006, - 392 p., Ill. Tab., Pp. 63-88.

5. Patent RU 2337800, publ. November 10, 2008, IPC B23K 35/36, B23K 35/363, “Solder paste for the installation of electrical and radio elements using screen printing”.

6. Patent JP 3499904 B2 7116889 A, publ. 10/22/1999, IPC B23K 35/363, “Flux for soft soldering”.

7. Patent RU 703996, publ. 08/20/1997, IPC B23K 35/24, “Solder Paste Binder”.

8. Patent RU 886388, publ. 08/20/1997, IPC B23K 35/24, "Solder paste binder with a reduced amount of solids."

9. WIPO Application: WO 2098601, publ. 03/19/2001, IPC B23K 35/363, “Binder for solder paste”.

10. Patent JP 3155778, publ. 04/16/2001, IPC B23K 35/363, “Solder Paste”.

11. Patent RU No. 2096152, publ. November 20, 1997, IPC B23K 35/363, “Flux for low-temperature soldering”.

12. Patent RU No. 2022747, publ. November 15, 1994, IPC B23K 35/363, "Flux for low-temperature soldering."

13. Patent RU 2386521, publ. 04/20/2010, IPC B23K 1/20, H01C 17/00, “Method for tinning the findings of radioelements”.

14. Patent RU 2347656, publ. 02/27/2009, IPC B23K 35/363, “Flux for low-temperature soldering”.

15. Patent JP 3221707 B2 05185284 A, publ. 12/03/1991, IPC B23K 35/363, "Flux for soldering printed circuit boards."

16. Patent JP 3132745 B2 7323390 A, publ. 05/26/1995, IPC B23K 35/363, “Method and flux for the low-temperature soldering of electronic components on printed circuit boards”.

17. Patent US 6550667 BB, publ. November 29, 2000, IPC B23K 35/362, “Method and flux for forming a dense grid of ball leads on the contact pads of crystals of integrated circuits (IC)” - prototype.

Claims (1)

Flux for low-temperature brazing, characterized in that it consists of an activator in the form of a mixture of carboxylic acids and an organic solvent in the form of a mixture of alcohols and a mixture of esters, in the following ratio, wt.%:
carboxylic acids 3-10 alcohols thirty esters 60-70