WO2000054928A1

WO2000054928A1 - Soldering flux composition

Info

Publication number: WO2000054928A1
Application number: PCT/KR2000/000158
Authority: WO
Inventors: Kwan-Young Chang; In Duk Park; Seung-Ho Won
Original assignee: Morning Chemical Co. Ltd.
Priority date: 1999-03-05
Filing date: 2000-03-02
Publication date: 2000-09-21
Also published as: AU3197000A; KR20010089333A; KR20000062088A; KR100440234B1

Abstract

The present invention relates to a flux composition, especially a soldering flux composition comprising 20-60% by weight of phosphate compound containing 50-60% by concentration of phosphoric acid, 10-30% by weight of organic acid, 1-20% by weight of VIII transition element and 5-30% by weight of viscosity modifier. The composition according to the present invention can be broadly applied in our daily lives and industrial fields where welding flames can not be employed, including electricity and electronics, thin tube processing and foil welding fields.

Description

Title of the Invention

Soldering flux composition

Field of the Invention

This invention relates to a soldering flux composition. More particularly, this invention relates to a soldering flux composition making it easy to solder materials, which are conventionally hard to connect by soldering, such as stainless steels, coppers, zincs, tins and thick iron plates. Thus, the composition in accordance with the present invention can be widely applied in our daily lives and industrial fields where welding flames cannot be employed, as well as the fields of electricity and electronics, thin tube processing and thin plate welding.

Background of the Invention

In general, a stainless steel is widely used in our daily lives and industrial fields. Due to its advantages of high strength, non-corrosiveness and ever-lasting shine, it is broadly employed as from domestic and architectural materials to industrial materials. In case of welding between stainless steel materials, usually argon welding or welding using oxygen and acetylene torch, and arc welding in some cases, is employed in order to obtain clean welded zones . For mechanical products containing heat exchangers, the interior thereof is typically made up of copper tubes having good heat conduction and the exterior thereof of stainless steel plates. In this case, argon welding is employed, but silver-lead welding can be also applied in order to improve the degree of sealing in welded zones .

Although argon welding results in relatively satisfactory welded zones, it damages considerably human's eyes and skins during a welding operation and costs a lot due to the continuing consumption of argon except for welding rods. In addition, since it is a high temperature fusion welding which is conducted over 1,500°C, especially when welding stainless steels, it also has detrimental defects of corrosiveness in the welded zones and losses of anti-corrosiveness and shine which all result from the generation of stress and the change of constituents of stainless steels during the welding operation.

In case of silver-lead welding, although it is not seriously harmful to welding operators, the price of welding rods is too high since the content of silver in the welding rods reaches 40- 95%. In addition, although it is conducted at a much lower temperature than argon welding, since it uses high temperature flames of over 800°C, it can affect base metals, and, especially when welding stainless steels, causes corrosiveness in welded zones, whereas, when welding copper products, no serious loss of anti-corrosiveness is made.

In order to overcome these problems, a great number of trials have been continuously made to weld between stainless steel and stainless steel, stainless steel and tin, stainless steel and copper, stainless steel and iron, stainless steel-zinc-copper, zinc and iron, copper and copper, tin and tin, iron and tin, and copper and tin by using welding agents for low temperature- and low price welding such as Pb-Sn or Ag-Sn and a low temperature welding machine, i.e. an electrical soldering iron. However, appropriate welding flux compositions for the above purposes have not been developed.

The composition for a low temperature welding flux depends on the type of welding agents and welding temperature (electrical soldering or brazing). However, the most common flux composition and the function of the ingredients for the typically used Pb-Sn or Ag-Sn welding agents are as follows:

Rosin : 30-70% by weight Solvent : 20-50% by weight Viscosity modifier : 1-10% by weight

Activator : 0.01-1% by weight

Acid : 0.1-1% by weight

Rosin : At a high temperature, the active ingredient of rosin, i.e. abietic acid removes the oxides in junction zone, increases the degree of spreading and viscosity of a flux composition against a base metal, and helps block contacting with oxygen in the air. Examples of such rosin include gum rosin, tallrosin, woodrosin, hydrogen-added rosin, esdelgum.

Solvent : This uniformly dissolves solid phase rosin and the rest liquid & solid phase ingredients, and then evaporates out during a welding operation. Examples of such solvent include butylcellosolve, 1, 3-butadiol, butyl calbytol, hexan calbytol.

Viscosity modifier : This provides adequate flow resistance and stickiness to improve a welding efficiency. Examples of such viscosity modifier include castor wax, high fatty acid amid, hard castor oil.

Activator : This promotes adhesion and fusion between welding agents and base metals with the action of halogen elements dissolved and produced at a high temperature. This usually exists as hydrochloride or bromide of aliphatic amine. Examples of such activator include ethylamine hydrochloride and dimethylamine bromide.

Acid : This helps the function of abietic acid of rosin. Examples of such acid include fumaric acid, tin acid and phthalic acid.

Typical fluxes, which are usually employed for welding between iron plates or zinc-coated steel plates, leave brown residues during a welding operation, and, in case of insufficient preheating, result in a quite low welding strength and welding quality.

In particular, there have been recently more inventions regarding cream-type soldering fluxes for electronic circuit board, which fluxes contain a lower temperature welding agents than common welding fluxes. In brief, the prior arts in this area are as follows.

UK Patent Publication No. 2 278 370 discloses a flux composition comprising a non-oxidative acid such as SnCl₂ and HC1 and a viscosity modifier such as glycerol, polyethyleneglycol and sorbitol, but not including 2nCl₂. European Patent Publication No. 0 619 162 discloses a flux composition comprising a bis(2- oxazoline) compound, a dichiol compound, an organic carboxylic acid compounds and an activator. US Patent No. 5,281,281 discloses a no-clean, low-residue, rosin-free soldering flux comprising a solvent consisting essentially of demineralized water present in an amount of at least about 95% by weight based on total weight of the soldering flux, and a fluxing agent selected from the group consisting of a C₂ -C₁₀ dicarboxylic acid, a onocarboxylic acid and a hydroxy acid. Further, US Patent Nc. 5,296,046 discloses a flux composition comprising a carrier solvent, an oxide removing agent such as 2-amino-isophthalic acid and 5-amino-isophthalic acid, and a compound that deliberates nitrogen upon heating. Furthermore, Japan Patent Publication No. 5-337686 discloses a soldering flux comprising 0.5-3% by weight of silicone compound, and Japan Patent Publication No. 5-318176 discloses a rosin based cream-type solder such as maleic acid and benzoic acid. Still, Japan Patent Publication No. 6-15483 discloses a flux composition which does not leave residues and presents non-corrosiveness in the soldered parts for a long time, comprising benzimidazole, imidazolthiol compound and triazole compound. Still further, Japan Patent Publication No. 6-155078 discloses a rosin-type flux in which alkyl amine or allophatic amine complex salt of boron trifluoride is added as an activator. In the meantime, Korea Patent Publication No. 81-49 discloses a flux composition comprising a neutral estel derived from polyhedric alcohol instead of the essential ingredient i.e. rosin, an organic monocarboxylic acid and an activator.

Besides, although a number of patents have been disclosed, no flux composition has been yet described or available to meet the multifunction of the flux composition according to the present invention.

Detailed description of the Invention

The object of the present invention lies in providing a multifunctional flux composition which makes soldering the metals as described above easier by using a simple electrical soldering iron and low temperature soldering agents such as Pb- Sn or Ag-Sn alloy. In order to accomplish this object, the soldering flux composition in accordance with the present invention comprises 20-60% by weight of phosphate compound containing 50-60% by concentration of phosphoric acid, 10-30% by weight of organic acid, 1-20% by weight of VIII transition element, and 5-30% by weight of viscosity modifier.

The present invention provides an increased productivity and a new method of manufacturing thanks to an unnecessary preheating base metals and an easiness of soldering between thick plates, thick and thin plates, or plates different in type and nature. Thus, the conventional manufacturing methods using argon, arc or high temperature flame welding may be replaced by the composition according to the present invention, leading to an economically efficient production and, eventually, the generalization of high quality-products. Especially, the composition according to the present invention may be applied broadly in our daily lives and industrial fields where welding flames cannot be employed, as well as in the fields of electricity & electronics, thin tube processing and thin plate welding. Even in the case where using lead is prohibited due to its toxicity to human beings, silver-tin (5-70: 95-30) can be employed as a welding agent. That is, since the multifunctional flux according to the present invention has an ability to lower the melting point of welding agents, silver-Sn welding agent, of which melting point is higher than that of Pb- Sn welding agent, can be employed at a low temperature

Examples

Without other mentions, "%" means "% by weight" in the following examples .

Example 1

A flux composition was prepared by uniformly mixing at about 50 °C 50% of potassium phosphate containing 50% by concentration of phosphoric acid, 10% of nickel carbonate, 20% of octyl acid and 20% of acetic acid.

Example 2

A flux composition was prepared by the same method as described in Example 1, except that 60% of potassium phosphate containing 60% by concentration of phosphoric acid, 10% of nickel chloride, 20% of malonic acid and 10% of isopropyl alcohol were used.

Example 3

A flux composition was prepared by the same method as described in Example 1, except that 40% of sodium phosphate containing 50% by concentration of phosphoric acid, 20% of palladium chloride, 20% of acetic acid and 20% of paraffin oil were used.

Example 4 A flux composition was prepared by the same method as described in Example 1, except that 20% of calcium phosphate containing 60% by concentration of phosphoric acid, 20% of palladium acetate, 30% of formic acid and 30% of castor wax were used.

Example 5

A flux composition was prepared by the same method as described in Example 1, except that 50% of ammonium phosphate containing 60% by concentration of phosphoric acid, 20% of nickel hydroxide, 10% of octyl acid and 20% of high fatty acid were used.

Example 6

A flux composition was prepared by the same method as described in Example 1, except that 50% of calcium phosphate containing 50 % by concentration of phosphoric acid, 10% of palladium acetate, 10% of malonic acid and 30% of oxidized titanium were used.

The flux compositions according to Examples 1-3 are liquid type compositions, whereas the compositions according to Examples 4- 6 are cream- or paste type compositions .

Soldering by using the flux composition in accordance with the Examples generates no residues and smokes , provides an excellent soldering quality even in the wet condition and complete adhesion of the soldered parts, and prevents corrosion at the time of the soldering in manufacturing print circuit assembly and needs no further processing after soldering. In addition, the flux composition according to the present invention may be broadly applicable and presents superior features to other flux compositions. In particular, the cream- and paste- type flux compositions in accordance with the present invention produce clear waste matters during a soldering process to make the test for the soldered parts easy, and improve the vibration resistance of the soldered parts. Also, such flexible clean waste matters provide a resistance against high temperature and oxidation.

Industrial applicability

The following paragraphs describe the present invention more specifically.

Since soldering agents made up of alloys having a low melting point, such as Sn-Pb alloy(70-20: 30-80) or Sn-Ag alloy(95-30: 5-70), cause a relatively low cost and are used in a soldering operation using an electrical soldering iron, they have been readily employed as soldering means. However, the use of such soldering agents is limited to, for example, very thin and small galvanized iron plates, iron plates or copper plates soldering applications, and thus such soldering agents cannot be employed for soldering, for example, stainless steel plates, thick iron plates or zinc plates .

In comparison with the conventional flux compositions comprising rosin or esters of polyhydric alcohol, the present invention provides a new type of flux composition which makes it possible soldering at a low temperature between the same or different types of stainless steels, copper alloys, iron alloys and tin alloys .

This is possible because soldering by using the flux composition in accordance with the present invention is not one operating by simply melting lead to connect, but one by generating a fusion alloy with very strong soldered parts due to the flux between base metals and soldering agents. For example, when soldering stainless steel plates on thick iron plates having a thickness of layer than 2cm, it is possible by using the multifunctional flux composition according to the present invention without pre-heating to complete the soldering operation in an instant without generating stress in base metals and heat loss.

As described above, the flux composition according to the present invention comprises 20-60% by weight of phosphate compound containing 50-60% by concentration of phosphoric acid, 10-30% by weight of organic acid, 1-20% by weight of VIII transition element and 5-30% by weight of viscosity modifier.

Preferred phosphate compound as a major ingredient in the composition according to the present invention includes ammonium phosphate, potassium phosphate, sodium phosphate and calcium phosphate, but is not limited to said compounds. Preferably, the phosphate compound in the flux contains 50-60% by concentration of phosphoric acid. This amount is defined on the basis that when mixed with other ingredients in the flux, the phosphoric acid is highly active upon heating, removes impurities and oxides existing on the surface of base metals and creates reaction conditions, whereas it does not exert high oxidation power at the ambient temperature. Meanwhile, a preferred amount of the phosphate compound is 20-60% by weight. If the amount is less than 20% by weight, the phosphate compound shows a decrease in its oxidation power and activity, whereas if the amount is more than 60% by weight, it shows an excess in its oxidation power and activity, probably leading to fragility in the soldered parts.

The organic acid as used in the present invention has a strong tendency to make coordinate covalent bonds with iron, copper or stainless steel in the mixed state with other ingredients of the flux when heating, leading to activate the surface of such metals . Such organic acid is at least one member selected from the group consisting of malonic acid, octyl acid, acetic acid and formic acid. The amount of the organic acid is preferably 10-30% by weight. If the amount is less than 10% by weight or more than 30% by weight, soldering agents get tangled or fused in a circular form during a soldering operation to inhibit a soldering adhesion.

Preferred VIII transition element includes nickel compounds (for example, nickel carbonate, nickel chloride or nickel oxide) or palladium compounds (for example, palladium chloride or palladium acetate), and the amount of such element in the flux composition is preferably 1-20% by weight. The VIII transition element plays an important role as a catalyst or a intermediate layer to enhance a bond strength between metals which are hard to connect each other. Thus, if the amount gets out of the range of the preferred one, it results in a poor connection between the soldered metals or a tangle due to an excessive soldering adhesion.

The viscosity modifier is used in an amount of 5-30% by weight. It provides the desired degree of viscosity and adhesion of the flux composition according to the present invention, and may be prepared in liquid-, cream- or paste- type by changing its mixing ratio in the flux. The viscosity modifier is, for example, paraffin oil, castor wax, polyvinylalcohol(PVA) resin, high fatty acid amid, oxidized manganese, oxidized titanium, acetone, and/or isopropyl alcohol. If the viscosity modifier is employed in out of the said amount, the flow condition of the flux composition is poor, soldered parts may have residues or be weak, and durability of such soldered parts may decrease.

Claims

1. A soldering flux composition comprising 20-60% by weight of phosphate compound containing 50-60% by concentration of phosphoric acid, 10-30% by weight of organic acid, 1-20% by weight of VIII transition element, and 5-30% by weight of viscosity modifier.

2. The composition according to claim 1 , wherein said phosphate compound is ammonium phosphate, potassium phosphate, sodium phosphate or calcium phosphate.

3. The composition according to claim 1, wherein said organic acid is at least one member selected from the group consisting of malonic acid, octyl acid, acetic acid and formic acid.

4. The composition according to claim 1, wherein said VIII transition element is nickel compound or palladium compound.

5. The composition according to claim 1, wherein said viscosity modifier is at least one member selected from the group consisting of paraffin oil, castor wax, poly-vinylalcohol(PVA) resin, high fatty acid amid, oxidized manganese, oxidized titanium, acetone and iso-propylalcohol .