RU2463145C2 - 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. Proposed flux contains the following components, in wt %: modified high-hydrated rosin ester-base synthetic resin - 10-20, activator consisting of carboxylic acid - 2-10, organic solvent representing mix of alcohols (30-50) and glycols (40). 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 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, and protect the surface metals and solder from oxidation during soldering 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 natural rosin.

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 joints using fluxes based on natural rosin (Rosin (RO)), the classification presented in Table 1 is introduced.

Table 1 Flux base Flux activity level (% halogen content) Flux type Rosin (RO)
Rosin Low (0%) Rool0 Low (<0.5%) Ro1 Medium (0%) ROM0 Medium (0.5-2.0%) ROM1 High (0%) Roh0 High (> 2.0%) Roh1

Highly reliable soldered joints, including those using weakly activated flux, are necessary in devices for medicine, transport equipment (railway, aviation, marine), and in military and space technology. For such soldered joints of high reliability based on natural rosin according to the standard [3], the classification “ROL0” was determined, according to which the level of activity of weakly activated flux and the percentage of halogens in it is minimal, that is, practically absent. That is, from table 1 it follows that for soldering the most critical compounds, weakly activated fluxes based on natural rosin (Rosin (RO)) corresponding to the ROL0 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 technologies”, - M .: Technologies Publishing House, 2006 ., - 392 p., Ill., Tab. - [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 ROL0 classification for mounting critical joints.

Known flux bundle from "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-linker from [5] is that the compound of acetic acid and technical triethylamine forms a salt, triethyl ammonium acetate, which is an ionic compound. Subsequently, in the event of moisture, this ionic compound will conduct an electric current, which significantly reduces the reliability of the circuit board.

Known "Flux for 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 soldering temperature and reacts with oxides located 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 the "Solder Paste Binder" 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 a 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 a copolymer of butyl methacrylate with butyl acrylate can be used as an acrylic polymer : 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" on 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 in the alkyl chains, or esters of fatty acids.

The disadvantage of the analogue [9] is that the substance: tirendibromide contained in its flux-bundle contains halogen, and this is not allowed for use according to the ROL0 standard [3] for critical compounds.

The well-known "Liquid flux for soldering jewelry from gold alloys" according to the patent of the Russian Federation: RU 2354519 C2, publ. 12.12.2008, IPC B23K 35/363, B23K 103/08, B23K 101/30 - [10], containing components in the following ratio, wt.%: Pine rosin 10-20; medical vaseline 2.5-25; anhydrous lanolin 5-12.5; ethyl alcohol - the rest.

Liquid flux according to [10] has a reduced boundary friction between adjacent parts of the parts during processing due to the lubricating properties of the flux, but its disadvantage is insufficient wettability, which leads to loss of water in the holes, and poor fillets, that is, leads to soldering defects. In addition, liquid flux [10] does not have an activator in its composition, which leads to its low activity.

Known "Flux for soldering" according to the patent of the Russian Federation: RU 2400340 C1, publ. September 27, 2010, IPC B23K 35/363 - [11], which contains components in the following proportions, wt.%: Technical glycerin 30.0-32.0; triethanolamine 2.5-3.0; rosin 8.0-9.35; carbamide 6.0-9.0; sodium hydroxide 1.1-1.5; alcohol - the rest. The selected quantitative ratio of components allows you to activate the process of removal of oxide films and to ensure high quality soldered joints, to increase their corrosion resistance and reliability.

Also known "Flux for soldering" according to the copyright certificate of the USSR: SU 725849, publ. 04/05/1980, IPC B23K 35/362 - [12], which contains urea, rosin and ethyl alcohol, glycerin, in the following ratio, wt.%: Urea 5-10, rosin 15-25, glycerol 0.1- 10, ethyl alcohol - the rest.

The disadvantage of using fluxes [11] and [12] is the presence of glycerin in it, which can penetrate the ends of the board or into the capillary mounting gaps, after which there are difficulties with washing it. Glycerin that is not washed in the capillary gaps of the printed circuit board will absorb moisture during operation and thereby reduce the insulation resistance.

The well-known "Flux for soldering electronic products" according to the copyright certificate of the USSR: SU 1792554 A3, publ. 10.27.1995, IPC B23K 35/363 - [13] containing rosin, ethyl cellulose, a solvent in the form of terpineol and surfactants, which are used catamine and tributyl phosphate in the following ratios, wt.: Rosin 31.8- 34.4, terpineol 51.5-53.0, ethyl cellulose 6.0-6.4, catamine 7.7-8.5, tributyl phosphate 0.3-0.4.

The disadvantage of flux [13] is that it contains in its composition a lot, up to 42% of solids, and this causes difficulties when washing the soldered joint.

The well-known "Flux for brazing solder from an alloy based on tin, lead-free" "according to US patent US 6630036 BB, publ. 10/07/2003, IPC B23K 35/34 - [14], which is added to rosin and used for soldering using lead-free solders, such as Sn-Ag or Sn-Ag-Bi solders, and containing abietic acid as the main component and a solid acid compound in which there are no halide ions. The flux has an increased activity, does not destroy the soldered material, withstands high temperatures and is well washed after soldering.

The disadvantage of the analogue [14] is the weak activity of abietic acid, which can lead to non-soldering, that is, to defects in soldering. Inorganic acids contained in the flux can lead to corrosion of soldered parts. In addition, being an imported flux for low-temperature brazing, it is relatively expensive and does not meet the required quality for critical applications. The flux is designed for soldering household appliances, the service life of which is relatively short (for example, cell phones, radio equipment, etc.).

The prototype of the invention is a flux bundle from "solder paste" according to Japan patent: JP 3155778, publ. 04/16/2001, IPC B23K 35/363 - [15], containing low-temperature solder powder, as well as components selected from the group consisting of rosin, resin, activator, thixotropic additive, an organic diluent and an additive that suppresses flux condensation with a constant dissociation ≤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 disadvantage of the prototype [15] 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 ROL0 standard [3] for critical compounds.

The above disadvantages of analogues and prototype set the task of creating a flux for low-temperature soldering based on natural rosin for mounting components and products of critical electronics, suitable for wave soldering or selective soldering, corresponding to the type "ROL0" standard [3].

That is, soldering flux:

- 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, surface-active substances (surfactants) of synthetic polymers (resins), 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 soldering flux consists of the following ratio of components, wt.%:

modified highly hydrogenated rosin 10-20% activator, in the form of a mixture of carboxylic acids 2-10% a mixture of organic solvents, in the form of alcohols 30-50% and glycols 40%

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

In ordinary rosin (natural raw materials), depending on the place and conditions of its origin, the melting temperature lies in the range 60 ÷ 85 ° C, and the acid number is 140 ÷ 190, which allows us to talk about its unstable properties, and therefore, this leads to unpredictable soldering results.

The rosin based on natural components used in the proposed technical solution is a modified highly hydrogenated rosin, the melting point of which is stable and lies in a narrow range of 80 ÷ 82 ° C, and the acid number is 175 ÷ 180. The use of such a modified highly hydrogenated rosin based on natural components can significantly stabilize the properties of the proposed flux and thereby improve the quality of soldering and the reliability of soldered joints.

The activator of the proposed flux is a mixture of organic acids based on carboxylic acid. Good rheological properties of the flux are provided by its base - modified highly hydrogenated rosin.

The designation of flux for low-temperature brazing based on natural rosin is as follows: FK-7A, where F is flux, K is rosin (based on natural rosin), 7 is the serial number of the flux composition, A is the development company (Avangard OJSC),

According to the assortment, fluxes are divided into fluxes with water-washable residues and fluxes with semi-water-washable residues. FC-7A is a flux with water-based residues and semi-water-washed residues.

During testing, the flux FC-7A (ROL0) during soldering of the DIP component showed good results - on all samples there is a rise in the flux along the output of the component through the mounting holes, an even soldered connection.

For washing the flux FC-7A (ROL0), OZh-21A Lira and OZh-27A Vega washing fluids developed at Avangard were used.

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

All solids of the flux FC-7A (ROL0) after soldering are completely removed in the installation of jet washing with liquid ОЖ-27А "Vega" with a concentration of 25%.

After washing the flux FC-7A (ROL0) in deionized water, a bluish “halo” is observed around the contact areas, most likely due to the hydrolysis of the rosin included in the flux. The presence of a bluish “halo” does not reduce the insulation resistance. When blasting with liquid ОЖ-27А "Vega" with a concentration of 30%, a bluish "halo" does not form.

Also, all residual flux FK-7A (ROL0) after soldering is completely removed in the ultrasonic treatment unit with liquid ОЖ-21А "Lira" with a concentration of 100%.

Flux residues after washing with aqueous or semi-aqueous washing liquids 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 FC-7A 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 0.818-0.822 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 ¹⁰ 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 FK-7A (ROL0) meets the requirements of GOST 23752-79 regarding the effect on the surface insulation resistance both in low-voltage switchgear and when exposed to high humidity and temperature.

Based on the test results, 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 complies with 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).

Table 4 The name of the types of tests and their sequence Acceptance
tests Qualification
tests Periodic tests TU item number Technical requirements table 1 Control methods Appearance + + + one 7.1 Density + + + 2 7.2 The spreadability coefficient of the molten solder POS-61 under the action of flux + + + 3 7.3 The effect of flux residues on the surface insulation resistance + + four 7.4 Halogen content + + 5 7.5 Flux Copper Mirror Corrosion + + 6 7.6

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 performance of the soldering flux in the composition of the ingredients in the following unit ratio, wt.%:

modified highly hydrogenated rosin fifteen% activator, in the form of a mixture of carboxylic acids: adipic acid 2.5% phthalic acid 2.5% organic solvent mixture: isopropyl alcohol 40% isobutyl alcohol 5% glycol-butyl cellosolve thirty% glycol ethyl cellosolve 10%

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

An increase in rosin by more than 20% leads to an increase in flux residues after soldering, which will lead to a decrease in insulation resistance, and a decrease in it by less than 10% leads to a deterioration in soldering, i.e., a decrease in the wettability of solder leads of components of electronic equipment (CEA).

An increase in the activator in the form of a mixture of carboxylic acids by more than 10% leads to a decrease in insulation resistance, and a decrease of it by less than 2% leads to a deterioration of soldering, that is, to a decrease in wettability by solder of the CEA leads.

An increase in the composition of organic solvents in the form of alcohols (monohydric alcohols) by more than 50% leads to deterioration of soldering due to a decrease in the proportion of rosin and activator, and a decrease in the amount of alcohols by less than 30% leads to an unjustified increase in rosin and activator in the form of a mixture of carbon acids, which will lead to an increase in flux residues after soldering and to a decrease in insulation resistance.

An increase in the composition of organic solvents, in the form of glycols (dihydric alcohols), by more than 40% leads to the fact that the glycol in the flux does not evaporate during soldering to the required value, and this leads to increased stickiness of the flux residues, and therefore to additional pollution, and their decrease by less than 40% leads to faster evaporation of glycol from the flux, which leads to its dryness and a significant decrease in the quality of soldering.

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 soldering to 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 based on natural rosin 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 set of 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 represent 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 Fluxes weakly activated (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. RF 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. Japan patent: JP 3499904 B2 7116889 A, publ. 10/22/1999, IPC B23K 35/363, “Flux for soft soldering”.

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

8. RF patent: RU 886388, publ. 08/20/1997, IPC B23K 35/24, "Solder paste binder with a reduced amount of solid residues."

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

10. RF patent: RU 2354519 C2, publ. 12.12.2008, IPC B23K 35/363, B23K 103/08, B23K 101/30, “Liquid flux for soldering jewelry made of gold alloys”.

11. RF patent: RU 2400340 C1, publ. 09/27/2010, IPC B23K 35/363, "Flux for low-temperature soldering."

12. USSR copyright certificate: SU 725849, publ. 04/05/1980, IPC B23K 35/362, "Flux for soldering."

13. USSR copyright certificate: SU 1792554 A3, publ. 10.27.1995, IPC B23K 35/363, "Flux for soldering electronic products."

14. US Patent: US 6630036 BB, publ. 10/07/2003, IPC B23K 35/34, “Flux for brazing solder from an alloy based on tin, lead-free”.

15. Japan Patent: JP 3155778, publ. 04/16/2001, IPC B23K 35/363, "Solder paste" - prototype.

Claims (1)

Low temperature soldering flux, characterized in that it consists of a modified highly hydrogenated rosin, an activator in the form of a mixture of carboxylic acids and an organic solvent in the form of a mixture of alcohols and glycols, in the following ratio, wt.%:
modified highly hydrogenated rosin 10-20 carboxylic acids 2-10 alcohols 30-50 glycols 40