JP2000052088A - Flux, solder paste using flux, and soldering method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent migration of flux used in a non-cleaning condition, and use the flux residue as an insulating film by containing rosin or/and modified rosin and activator, and also a specific melt flow rate ethylene-vinyl acetate copolymer at a specific melt flow rate. SOLUTION: Ethylene-vinyl acetate copolymer with the melt flow rate of 500 g/10 min or more is contained at 1-50 wt.%. The flux contains 5-30 wt.% fatty acid amid or/and fatty acid bis amid, and the solder paste is obtained by mixing a solvent diluent of the flux and the powder solder. Additionally, soldering is carried out using the flux, and the flux residue after soldering is remained as an insulating film. Furthermore, soldering is carried out using the solder paste, and it is preferable that the flux residue after soldering is remained as an insulating film. Thereby, elements can be built on a circuit substrate at excellent workability and safety, without cleaning/removing the flux residue.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flux and a method for soldering using the flux, and more particularly to a method for soldering an electronic component to a circuit board without cleaning the flux residue.

[0002]

2. Description of the Related Art Flux is indispensable in soldering. An oxide film on a base material surface is removed and cleaned, and an air barrier film is formed on a base material surface and a solder surface to prevent oxidation.
It has the effect of reducing the interfacial tension of the solder and increasing the wettability.

[0003] Rosin is used as the main component of this flux, but rosin alone has a weak activity and is difficult to achieve the above-mentioned effects sufficiently, so that a hydrohalide of an organic amine, an organic acid, Activators such as salts of organic acids and organic amines are added.

However, under the addition of an activator, erosion of the conductor due to the reaction of forming a complex between the flux residue and the base material after soldering is unavoidable. Therefore, in the past, the flux residue was washed and removed with a CFC-based cleaning solution. Was.

[0005] Recently, the destruction of the global environment due to destruction of the ozone layer of CFC compounds has been regarded as a problem on a global scale, and alcohol (mainly isopropyl alcohol) and water ( The use of a water-soluble flux or the addition of a saponifying agent is required), a semi-aqueous cleaning solution, an alternative fluorocarbon containing a hydrogen atom in a molecule (for example, HCFC-22)
Although the use of 5) and the like is under consideration, alcohols have a low flash point and are dangerous, and water or semi-aqueous systems require cumbersome drainage treatment, and drying of fine parts is not easy. In addition, a high-cost special cleaning device (for example, an ultrasonic cleaning device) is required, and alternative fluorocarbons are required to have an ozone depletion potential and a global warming potential of 0 to small, and are expensive. is there.

[0006] Practical use of non-cleaning flux is being studied, and a proposal for a corrosion-resistant flux capable of preventing corrosion of a base material (conductor) due to a flux residue (Japanese Unexamined Patent Publication No. Hei 3-
238195, Japanese Patent Publication No. 4-33557, etc.),
Proposals have been made for a low solidification flux for avoiding probe pin contact failure of an in-circuit tester.

[0007]

SUMMARY OF THE INVENTION However, the present inventors have found that a problem that must be solved in order to commercialize a non-cleaning flux is that a flux residue crack due to a heat cycle during use of a circuit board is used. I learned that there is migration caused by this.

That is, heat stress cracks occur in the flux residue due to the heat cycle during use of the circuit board,
In the cracks, an electrolyte solution is generated due to moisture absorbed and ions eluted from the flux residue (eg, halogen ions), and a weak current flows through the electrolyte solution under the application of a voltage to a circuit board. Is eluted by the electrolysis reaction, and the eluted conductor material ions are discharged and precipitated in the cathode-side conductor, and the conductor material atoms grow in a dendritic shape toward the anode side, eventually causing a short circuit between both conductors. There is actually a normal reflow flux between silver electrodes formed by a thick film method with an interval of 0.5 mm (Comparative Example 2 described later).
Was applied and dried, a crack was formed between the electrodes, and a DC voltage of 100 volts was applied for 1000 hours at a temperature of 40 ° C. and a relative humidity of 92%. Observation revealed that migration had occurred.

Therefore, the present inventors have intensively studied means for preventing the generation of cracks in the heat cycle of the flux residue, and as a result, the melt flow
It has been found that it is effective to include an ethylene / vinyl acetate copolymer having a rate of 500 g / 10 min or more in the flux.

Hitherto, it has been known that an ethylene / vinyl acetate copolymer having a low melt flow rate and a high molecular weight is used as one component of a flux. For example, Japanese Patent Application Laid-Open
Japanese Patent Application Laid-Open No. 777791 discloses that "a flux composition is applied to a support film, the applied flux is transferred onto a circuit board by heat and pressure, and the electronic component is temporarily fixed to the wiring board using the transferred flux as a fixing agent. And then flow
Addition of an ethylene-vinyl acetate copolymer to a flux in a method of soldering electronic components by a method ".

Japanese Patent Application Laid-Open Nos. 55-54298 and 56-6798 disclose "in order to prevent explosion and scatter due to thermal expansion of the flux of a fluxed solder (linear solder with a built-in flux)". Addition of an ethylene / vinyl acetate copolymer to a flux in a flux-coated linear solder in which a flux layer is coated on the solder surface. "

However, the former (JP-A-58-777)
No. 91), in order to increase the cohesive force of the flux at the time of transfer and to surely transfer the flux to the circuit board side, an ethylene / vinyl acetate copolymer having a relatively high molecular weight must be used. Not melt flow
Ultra low molecular weight ethylene with a rate of 500 g / 10 min or more
Vinyl acetate copolymers are unsuitable. In the latter case (JP-A-55-54298 and JP-A-56-6798), it is necessary to impart a certain degree of contact wear resistance to the flux-coated linear solder, and the melt flow rate is 500 g / m2. Ultra-low molecular weight low-strength ethylene
A vinyl acetate copolymer is unsuitable because of poor mechanical strength.

However, the present inventors have found that if an ethylene / vinyl acetate copolymer having a melt flow rate of 500 g / 10 min or more is added to a normal flux, the occurrence of cracks due to the heat cycle of the flux residue will be prevented. It has been found that migration can be sufficiently prevented, migration can be eliminated, and the flux residue can be used as an effective insulating film by maintaining its insulating property stably.

The object of the present invention is based on this finding,
It is an object of the present invention to provide a flux which can sufficiently prevent migration in a flux used without washing, and which can effectively utilize a flux residue as an insulating film, and a soldering method using the flux.

[0015]

The flux according to the present invention contains at least rosin and / or modified rosin and an activator, and has a melt flow rate of 500 g / 10 m2.
The composition is characterized by containing 1 to 50% by weight of an ethylene / vinyl acetate copolymer of in or more, and 5 to 30% by weight of a fatty acid amide and / or a fatty acid bisamide.

The soldering method according to the present invention is characterized in that soldering is performed using the above-mentioned flux, and the flux residue after soldering is left as an insulating film.

The above melt flow rate is JIS K72.
It is measured based on 10-1976 and has an inner diameter of φ9.50 ±.
It has a through-hole of 03mm and an inner diameter of φ2.0
Using a test apparatus in which a sample is filled into a hole of a heater cylinder equipped with a die of 95 ± 0.005 mm and a lower end of a piston having a weight attached to an upper end is inserted into the hole, Weight of 325 gf {3.185 N} and the test temperature of 125 ° C., the amount of extrusion X in 10 minutes
(G) is measured and determined from Xg / 10 minutes.

The above-mentioned fatty acid amide / fatty acid bisamide suppresses the adhesiveness of the flux, and particularly when used as a flux of solder paste, to prevent separation, and when used as a flux for a solder paste. Is used to prevent the flux from running out. For example, one or more of stearic acid amide / stearic acid bisamide, palmitic acid amide and the like can be used.

The rosin and / or modified rosin includes natural rosin, polymerized rosin, phenol-modified rosin,
Maleated rosin, hydrogenated rosin and the like can be used.

As the activator, a hydrohalide of an organic amine, an organic acid, a salt of an organic acid and an organic amine, and the like can be used. For example, diethylamine hydrochloride, cyclohexylamine hydrochloride, dioctylamine hydrochloride, propylamine hydrochloride, diethylamine hydrobromide, cyclohexylamine hydrobromide, dioctylamine hydrobromide, propylamine hydrobromide Salts, glutaric acid, adipic acid, sebacic acid, methyl maleic acid, cyclohexylamine adipate and the like can be used.

In the flux according to the present invention, a corrosion inhibitor (for example, phthalic acid, benzotriazole compound, gallic acid ester such as n-propyl gallate, etc.) for suppressing conductor corrosion due to the flux residue is added. Can also.

The mixing ratio of the flux according to the present invention is usually 98 to 49% by weight of rosin and / or modified rosin.
Preferably 93-65% by weight, active agent 1-10% by weight
Preferably 2 to 5% by weight, 500 g of melt flow rate
1 to 5 minutes of ethylene / vinyl acetate copolymer
0% by weight, preferably 5 to 30% by weight.

The flux according to the present invention is diluted with a solvent and used at a predetermined viscosity according to the application. For example, when used as a paste-like flux of a solder paste (mixture of paste-like flux and powdered solder) used in the reflow method, hexylene glycol, octylene glycol, butyl carbitol may be used. Solvents such as xylene, toluene and the like having a relatively low boiling point, such as xylene and toluene, are used as the solvent for the liquid flux used in the flux bath in the flow method. Solvent used

According to the soldering method according to the present invention, the electronic component is soldered to the circuit board by the reflow method using the flux according to the present invention, and the flux residue is left without being removed by washing and used as an insulating film. can do. That is, a solder paste obtained by mixing the paste flux and the powder solder according to the present invention is applied to a circuit board with a predetermined printing pattern by a mesh screen, and the applied solder paste is applied. The electronic components are temporarily fixed using the paste as an adhesive, and further passed through a heating furnace.
The strike is melted and solidified, and the flux residue is left as an insulating film without being washed.

Further, the soldering method according to the present invention can be carried out by a flow method. That is, the lead wire of the electronic component is inserted and supported in the hole of the circuit board, and the liquid flux according to the present invention is blown out of a porous tube such as a porous ceramic tube or a sintered metal tube in a tank. And applying the flux by passing the circuit board over the foaming liquid surface while foaming, and then preheating the circuit board and immersing the circuit board in a jet solder bath or a static solder bath to remove the electronic components. The solder wire is soldered to the conductor of the circuit board, and the flux residue is left as an insulating film without being washed.

Further, the hollow solder rod is filled with the flux (solid) according to the present invention, drawn into a predetermined diameter to form a fluted solder wire, and soldered with the solder wire using a trowel. Can also be implemented.

The ethylene / vinyl acetate copolymer having a melt flow rate of 500 g / 10 min or more added to the flux according to the present invention has extremely low mechanical strength because of its extremely low molecular weight. Therefore, it has a function of absorbing the stress by exhibiting rubber elasticity, so that the molecular chain is hardly broken by the stress and the generation of cracks due to repeated heating can be prevented well even though the mechanical strength is extremely low. Therefore, even when exposed to a heat cycle, the occurrence of thermal stress cracks in the flux residue can be sufficiently prevented, and migration can be eliminated well.

The vinyl acetate content of the ethylene / vinyl acetate copolymer used in the present invention is preferably 20 to 40%. (If it is less than 20%, the rubbery properties are insufficient and the rubber is not suitable for preventing cracking. % Or more, the tackiness increases and dust easily adheres to the flux residue).

In the flux according to the present invention, a flowable ethylene / vinyl acetate copolymer having a melt flow rate of 500 g / 10 min or more is used despite the addition of the ethylene / vinyl acetate copolymer. Because I use
The wettability of the solder can be promoted well, and the wettability required for soldering can be sufficiently ensured. The preferred range of the melt flow rate of the ethylene / vinyl acetate copolymer used in the present invention is 800 to 2,000 g / 10 min or less (when the 2,000 g / 10 min or more, dust easily adheres to the flux residue).

In the present invention, the addition amount of the ethylene / vinyl acetate copolymer is from 1 to 50% by weight, preferably from 5 to 30% by weight, as described above. 50% by weight
When the value exceeds the above, dust easily adheres to the flux residue, and the moisture absorption of the attached dust causes a problem that the surface resistance of the flux residue decreases.

The residue of the flux according to the present invention contains an ethylene / vinyl acetate copolymer which is more excellent in insulation resistance than rosin or the like. As a result, the soldered portion can be stably held without occurrence of electrolytic corrosion or the like. Therefore, according to the present invention, not only can the cleaning solution not be used for cleaning the flux residue be used to contribute to environmental protection, but also the flux residue can be effectively used as an insulating film to improve the reliability of soldering.

[0032]

EXAMPLES Example 1 A paste-like flux was used.
Its composition is 20% by weight of polymerized rosin, 29% by weight of hydrogenated rosin, 5% by weight of stearic acid bisamide, 5% by weight of caster wax, 10% by weight of ethylene / vinyl acetate copolymer of melt flow rate 1000g / 10min, 1% by weight of cyclohexylamine hydrobromide (activator), 20% by weight of hexylene glycol, and 20% by weight of butyl carbitol acetate.

Comparative Example 1 The procedure of Example 1 was repeated except that an ethylene / vinyl acetate copolymer having a melt flow rate of 400 g / 10 min was used.

Comparative Example 2 The procedure of Example 1 was repeated except that the blended amount of the polymerized rosin was 25% by weight, the blended amount of the hydrogenated rosin was 34% by weight, and the ethylene / vinyl acetate copolymer was not blended. Same as Example 1.

With respect to each of the paste-like fluxes of these Examples and Comparative Examples, 90% by weight of powdered solder (63% by weight of Sn—remainder Pb, particle size of 45 μm or less) and 10% by weight of paste-like flux were used. Prepare paste,
JIS Z 3197-1986 Resin-based flux test method for soldering 6.10 The spread rate was measured based on the spread test, and the result was 91% for Example 1, 92% for Comparative Example 2, and 85% for Comparative Example 1. In Example 1, the melt flow rate was set to 500 g / 10 min or more even though the ethylene / vinyl acetate copolymer was added to the flux, so that the normal flux (Comparative Example 2) was used. The same excellent wettability can be guaranteed.

Further, the solder paste is applied to a circuit board using a metal mask, and reflowed in an infrared heating furnace.
Thereafter, when a heat cycle test was performed 1,000 times (30 samples for 30 minutes at -30 ° C. and 30 minutes for 30 minutes at + 60 ° C.) (the number of each sample was 20), Example 1 and Comparative Example 1 were obtained.
No crack generation was observed at all in the flux residue in the sample of Comparative Example 2, whereas a large number of cracks were observed in the sample of Comparative Example 2.

For each of the fluxes of the above Examples and Comparative Examples, the surface insulation resistance value after leaving the flux residue at a temperature of 40 ° C. × relative humidity 92% × 2000 hours was measured. In the case of Comparative Example 1, the initial surface insulation resistance value was reduced by only one digit or less, whereas in the case of Comparative Example 2, the initial surface insulation resistance value was reduced by three digits or more.

Example 2 A flux for a cored solder having a composition of 24% by weight of natural rosin, 23% by weight of hydrogenated rosin, 30% by weight of stearamide and 1000 g / 10 min of melt flow rate. 20% by weight of ethylene / vinyl acetate copolymer, 2% by weight of cyclohexylamine hydrobromide (activator), 1% by weight of dibromopropanol
And

Comparative Example 3 The procedure of Example 2 was repeated except that an ethylene / vinyl acetate copolymer having a melt flow rate of 400 g / 10 min was used.

Comparative Example 4 The procedure of Example 2 was repeated except that the blending amount of natural rosin was 34% by weight, the blending amount of hydrogenated rosin was 33% by weight, and the ethylene / vinyl acetate copolymer was not blended. Same as Example 2.

For each of the fluxes of these examples and comparative examples, a flux cored solder (Sn 63% by weight-balance Pb) with a built-in flux amount of 2% by weight was manufactured, and JIS Z
3197-1986 Test method for soldering resin flux 6.10 The spread rate was measured based on the spread test. The result was 92% for Example product 2, 93% for Comparative example 4, and 87% for Comparative example 3, and In Example 2, although the ethylene / vinyl acetate copolymer was added to the flux, the melt flow rate was set to 500 g / 10 min or more, which was almost the same as that in the case of using a normal flux (Comparative Example 4). Excellent wettability could be guaranteed.

The above-mentioned flared solder is used for 350 times.
Solder on the copper land of the circuit board with a solder iron at ℃
Further, when a heat cycle test was performed 1,000 times (30 samples for 30 minutes at -30 ° C. and 30 minutes for 30 minutes at + 60 ° C.) (each sample was 20 samples), Example 2 and Comparative Example 3 were performed.
No crack generation was observed at all in the flux residue in the sample of Comparative Example 4, whereas a large number of cracks were generated in the sample of Comparative Example 4.

For each of the fluxes of Example 2 and Comparative Examples 3 and 4, the surface insulation resistance of the flux residue was measured in the same manner as described above. Although the insulation resistance was reduced by only one digit or less, that of Comparative Example 4 was reduced by three digits or more.

[0044]

According to the present invention, good solderability can be obtained without poor wetting due to excellent flux wettability, and even if the flux residue after soldering is exposed to a heat cycle, Since migration can be prevented by preventing the generation of cracks in the residue, and the insulation of the flux residue can be sufficiently maintained and can be effectively used as an insulating protective film, excellent work without cleaning and removing the flux residue. It is possible to mount circuit elements on a circuit board with reliability and safety.

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[Procedure amendment]

[Submission date] November 15, 1999 (1999.11.
15)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Name of invention

[Correction method] Change

[Correction contents]

Patent application title: Flux and its use
Solder paste and soldering method

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0001

[Correction method] Change

[Correction contents]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flux and its flux.
The present invention relates to a solder paste using a flux and a method for soldering using a flux thereof, and is particularly useful for soldering an electronic component to a circuit board without cleaning a flux residue.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction contents]

The object of the present invention is based on this finding,
A flux and a flux that can sufficiently prevent migration in a flux used without washing and that can effectively utilize a flux residue as an insulating film.
It is an object of the present invention to provide a solder paste used and a soldering method using the flux thereof .

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction contents]

In the soldering method according to the present invention, soldering is performed using the above-mentioned flux or a solder paste using the flux, and a flux residue after soldering is left as an insulating film. It is a configuration characterized by the following.

Claims (3)

[Claims] 1. A flux comprising rosin and / or modified rosin and an activator, and 1 to 50% by weight of an ethylene / vinyl acetate copolymer having a melt flow rate of 500 g / 10 min or more. . 2. The flux according to claim 1, which contains 5 to 30% by weight of a fatty acid amide and / or a fatty acid bisamide. 3. A soldering method comprising: performing soldering using the flux according to claim 1; and leaving a flux residue after the soldering as an insulating film.