KR20060016056A - Flux for soldering, soldering method, and printed curcuit board - Google Patents

Abstract

Provided are soldering fluxes having improved flux stability, soldering methods and printed circuit boards using the same. A flux containing a resin having an ability to form a film, an activator, and a solvent, and used for soldering to a substrate electroless nickel plated, containing from 0.1 to 20% by weight of an organic acid metal salt based on the total amount of the flux, The activator is an organic acid having the same organic acid or lower acidity than the organic acid constituting the organic organic acid metal salt. As a result, the stability of the organic acid metal salt can be improved, and high bonding strength can be maintained for a long time.

Soldering, Flux, Soldering Methods, Printed Boards

Description

Soldering Flux, Soldering Method and Printed Board {FLUX FOR SOLDERING, SOLDERING METHOD, AND PRINTED CURCUIT BOARD}

BACKGROUND OF THE INVENTION Field of the Invention [0001] The present invention relates to a soldering flux used for soldering various electronic components onto a printed circuit board. The present invention relates to a flux and soldering used for soldering a solder paste onto a copper land of a printed circuit board which is electroless nickel plated. It relates to a method and a printed circuit board.

Conventionally, when soldering an electronic component onto a printed board, soldering was carried out in a copper land formed on the printed board using tin-lead alloy soldering or lead-free soldering. Electroless plating of nickel is often performed on the surface of an electric land in order to prevent copper oxidation.

However, when electroless nickel plating is performed on an electric land, hypophosphite is used as a reducing agent, so that a small amount of phosphorus compound remains in the nickel plating layer.

For this reason, when soldering using a braze alloy on the surface of electroless nickel plating, nickel in nickel plating diffuses into the molten braze alloy, and local phosphorus segregates at the boundary between the nickel plating layer and the braze alloy, and the extreme Condensation occurred, the joining strength decreased, and the solder was peeled off.

 Therefore, the present inventors first proposed to contain 0.1 to 20% by weight of a metal salt in the flux used when soldering to a substrate electroless nickel plated (Japanese Patent Laid-Open No. 2003-236695). That is, by including the metal salt in the flux, the metal in the metal salt is replaced with nickel and precipitated, whereby reaction between the nickel and the metal in the braze alloy is suppressed, and diffusion of nickel on the land surface into the braze alloy is suppressed. For this reason, phosphorus concentration is prevented at the boundary between land and solder, and the joining strength of solder can be improved.

However, when the flux containing a predetermined amount of metal salt is stored for a long time as described above, problems such as a large decrease in the bonding strength of the solder and the insulation resistance between the lands, as compared with the flux immediately after manufacture, occur. When the insulation resistance between the lands is lowered, for example, shorts are likely to occur between the lands, thereby deteriorating the reliability of the solder and the printed circuit board. For this reason, it is desired to raise the storage stability of the flux containing a metal salt.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a soldering flux having a high storage stability of the flux, a soldering method using the same, and a printed circuit board.

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining in order to solve the said subject which the flux containing a metal salt has, as a result, when the flux is preserve | saved for a long time, compared with the flux immediately after manufacture, the joining strength of solder and insulation resistance between lands fall. It was found that the organic acid metal salt in the flux was decomposed by the inorganic acid (hydrochloric acid usually added in the form of amine hydrochloride) added as an activator. The lowering of the insulation resistance, for example, occurs in a soldering method in which the flux is printed on the front surface of the substrate having lands, and then the solder balls are placed on the electrical lands to be reflowed to join the solder balls to the lands. easy. This is presumably because metal is precipitated by decomposition of the metal salt to form a thin metal film between the lands, and the metal film is not removed by washing. In addition, it is considered that the decomposition strength of the metal salt is deteriorated, so that the effect of modifying the bonding strength due to the addition of the metal salt is insufficient.

The present invention has been completed by such a fact, that is, the soldering flux of the present invention contains a resin having an ability to form a film, an activator and a solvent, and is used when soldering to a substrate electroless nickel plated. It is characterized by containing an organic acid metal salt of 0.1 to 20% by weight based on the total amount of the flux, and wherein the activator is an organic acid having the same or lower acidity as the organic acid constituting the electric organic acid metal salt.

As described above, according to the present invention, since the activator added in the flux is an organic acid having the same or lower acidity as the organic acid constituting the organic acid metal salt, the organic acid metal salt can be prevented from being decomposed even when the flux is stored for a long time. Improves the stability.                         

It is preferable that the soldering flux of this invention has one of the following structures (1)-(6) again.

(1) The electric organic acid metal salt is preferably a metal salt selected from gold, silver, copper, lead, zinc, bismuth, indium, antimony and nickel, and particularly preferably copper salt of organic acid.

(2) The organic organic acid metal salt is preferably a metal salt of a saturated fatty acid having 7 to 21 carbon atoms of a hydrocarbon group excluding a carboxyl group, and particularly preferably a copper salt of saturated fatty acid.

(3) The resin having the ability to form an electric film is particularly a rosin or an acrylic resin.

(4) The electroactive agent is rosin.

(5) A resin having an electric film-forming ability is a rosin, and the rosin also serves as an electroactive agent.

(6) It does not contain a halogen compound.

In the first soldering method according to the present invention, the soldering flux is printed on a substrate having copper lands on which a surface is electroless nickel plated, and then the solder balls are placed on an electric land and heated to ripple the solder balls. And solder ball to land. It is preferable that the solder ball used is free of lead from the viewpoint of environmental impact.

In the second soldering method according to the present invention, a paste in which the solder flux and the solder powder are mixed is printed on a substrate having a copper land on which a surface is electroless nickel plated, and then heated to reflow the paste to land. Forming a braze alloy on the surface is characterized.

The present invention provides a printed circuit board on which solder is bonded by these soldering methods.

Moreover, after electroless nickel plating is performed on the board | substrate, the board | substrate which carried out other metal plating, such as gold, in consideration of the improvement of solder wettability on it is also used generally. In the present invention, the term "substrate subjected to electroless nickel plating" is a concept including a substrate which is further subjected to other metal plating such as gold on nickel plating.

The soldering flux of the present invention contains a resin, an active agent, an organic acid metal salt, and a solvent having a film forming ability. As resin which has a film formation capability, rosin or a thermoplastic acrylic resin is mentioned, for example.

As acrylic resin, molecular weight is 10000 or less, Preferably it is 3000-8000. When molecular weight exceeds 10000, there exists a possibility that crack resistance and peeling resistance may fall. In addition, in order to promote the active action, it is preferable to use an acid value of 50 or more, and it is preferable that the softening point is 230 ° C. or lower since it is necessary to soften during soldering.

For this reason, acrylic resin has a monomer which has a polymerizable unsaturated group, for example (meth) acrylic acid, its ester (for example, methyl (meth) acrylate, etc.), crotonic acid, itaconic acid, (anhydrous) maleic acid, and its ester Radicals such as bulk polymerization, liquid phase polymerization, suspension polymerization, emulsion polymerization, and the like using (meth) acrylonitrile, (meth) acrylamide, vinyl chloride, vinyl acetate, and a catalyst such as peroxide. It is preferable to use what was polymerized by polymerization.

As the rosin, rosin and derivatives thereof that have been conventionally used for fluxes can be used. As the rosin and its derivatives, conventional rubber, earthenware, wood rosin can be used, and as the derivatives thereof, heat-treated resin, polymerized rosin, hydrogenated rosin, formylated rosin, rosin ester, rosin-modified maleic acid resin, rosin-modified phenolic resin, Rosin-modified alkali resins.

The content of the resin having a film forming ability is 20 to 80% by weight, preferably 30 to 65% by weight based on the total amount of the flux. When content becomes less than 20 weight%, there exists a possibility that wettability may deteriorate. On the other hand, when content exceeds 80 weight%, a viscosity adjustment may not be performed and workability may deteriorate.

Examples of the metal component of the organic acid metal salt added to the flux of the present invention include gold, silver, copper, lead, zinc, bismuth, indium, antimony and nickel, and copper is particularly preferable. Moreover, various fatty acids, resin acids, etc. are mentioned as an organic acid component. Specifically, saturated fatty acids having a carbon number of about 7 to 21 carbon atoms in the alkyl moiety such as stearic acid, octylic acid, naphthenic acid, and rosin acid (including ditelfenic acid such as abietin acid and pimaric acid) Jisan etc. can be mentioned.

Specific examples of the organic acid metal salt include copper stearate, octyl acid bismuth, and copper naphthenate.                     

The content of the organic acid metal salt is 0.1 to 20% by weight based on the total amount of the flux. When the content is less than 0.1% by weight, it is difficult to suppress the diffusion of nickel on the land surface into the braze alloy, so that the bonding strength of the braze cannot be improved. On the other hand, when content exceeds 20 weight%, there exists a possibility that insulation resistance may fall.

The active agent in the present invention is an organic acid having the same or lower acidity as the organic acid constituting the organic acid metal salt. The acidity can usually be evaluated by the acidity constant (ka) of the solution (p ion) or the pKa value (-log Ka). In general, since the acidity tends to decrease as the carbon number of the organic acid increases, an organic acid having a low acidity means an organic acid having more carbon atoms than the organic acid constituting the organic acid metal salt. For example, for copper octylate, an organic acid such as stearic acid having a larger carbon number may be used as an activator. In addition, the rosin including the rosin acid described above can be suitably used as an organic acid having a low acidity.

It is not preferable to use an organic acid having an acidity higher than that of the organic acid constituting the organic acid metal salt as the activator, since the acid may decompose the organic acid metal salt. Illustrative combinations of organic acid metal salts and activators (organic acids) include, for example, copper stearic acid and stearic acid, copper stearic acid and rosin.

The content of the activator is preferably 0.1 to 30% by weight based on the total amount of the flux. When the content is less than 0.1% by weight, the function of the activator, that is, the active force for removing and purifying the metal oxide on the metal surface is insufficient, and there is a fear that the solderability is lowered. On the other hand, when content exceeds 30 weight%, since the film formability of a flux falls and hydrophilicity becomes high, there exists a possibility that corrosion property and insulation may fall. In addition, when rosin is used in a form of use which functions both as a resin and an active agent, the content of rosin and its derivatives should be such that their functions are not impaired.

Examples of the solvent include, for example, alcohol solvents such as ethyl alcohol, isopropyl alcohol, ethyl cersorbate, butyl carbitol and hexyl calbitol (diethylene glycol monohexyl ether), ester solvents such as ethyl acetate and butyl acetate; And hydrocarbon solvents such as toluene and teleffin oil.

It is preferable to add a solvent in the range of 5-70 weight% with respect to the flux total amount. When the organic solvent is less than 5% by weight, the viscosity of the flux is increased, and the applicability of the flux may deteriorate. On the other hand, when the organic solvent exceeds 70% by weight, the proportion of the active ingredient (resin, etc.) as the flux decreases, which may lower the solderability.

The flux of the present invention is produced by mixing and heating the components described above. The flux of this invention may contain other components, such as a thixotropic agent, in addition to the above-mentioned component. Examples of the thixotropic agent include hydrogenated castor oil (cured castor oil), beeswax, carnauba wax, stearic acid amide, hydroxystearic acid ethylene bisamide, and the like. The content of the thixotropic agent is preferably 1.0 to 25% by weight based on the total amount of the flux.

In addition, the flux of the present invention may be used in combination with known resins such as polyester resins, phenoxy resins, and terpene resins, which are conventionally used as base resins for fluxes, and additives such as antioxidants, flavoring agents and deglossants are added. You may.                     

The flux of the present invention is used for the case where electroless nickel plating is applied to the land of the substrate. The metal of the land to be subjected to the electroless nickel plating is not limited, but the metal is preferably copper.

Moreover, the kind of braze alloy at the time of soldering is not limited, either ordinary tin-lead alloy brazing can be used, and the so-called which mixes metals, such as silver, zinc, bismuth, indium, antimony, etc. based on tin. It is also possible to use lead-free soldering.

According to the soldering method of the present invention, the above solder flux is printed by screen printing or the like on a substrate having a copper land on which a surface is electroless nickel plated, and then the solder balls are placed on an electric land, heated to solder. Reflow the ball and join the solder ball to the land. As the solder ball, it is preferable in the environment to be formed by the aforementioned lead-free solder. Reflow of a solder ball is performed by printing at 150-200 degreeC after printing, or by heating at the temperature of 170-250 degreeC directly, without printing. Printing and reflow may be performed in the atmosphere or inert gas such as nitrogen, alcohol, helium or the like.

In the present invention, a paste in which the solder flux and the solder powder are mixed is printed on a substrate having a copper land electroless nickel plated on the surface, and then heated to reflow the paste to form a solder alloy on the land. It may be.

Next, the soldering flux of the present invention will be described in detail with reference to Examples, but the present invention is not limited only to the following Examples.

Examples 1-8 and Comparative Examples 1-7

[Selection of Copper Salt and Active Agent]

The following materials were selected as metal salts.

A: (C ₇ H ₃₅ COO) ₂ Cu

B: (C ₇ H ₁₅ COO) ₂ Cu

C: (C ₂₁ H ₄₃ COO) ₂ Cu

D: (C ₇ H ₃₅ COO) ₂ Pb

The following materials were selected as activators.

E: C ₇ H ₁₅ COOH

F: C ₇ H ₃₅ COOH

G: C ₂₁ H ₄₃ COOH

_{H: (CH 3) 2 CHNH} 2 · HCl

Here, the strength of the acidity is in the order of H> E> F> G.

[Preparation of Rosin Flux]

WW grade mound rosin 70 parts by weight

Hexyl Calbitol 25 parts by weight

5 parts by weight of hydrogenated castor oil

Each material was mixed and melted at 120 degreeC according to the said prescription, and it cooled to room temperature, and prepared the viscous flux.                     

[Preparation of Acrylic Flux]

50 parts by weight of acrylic resin (Pararoid B-48N made by Rohm and Haas company)

Hexyl Calbitol 45 parts by weight

5 parts by weight of hydrogenated castor oil

Each material was mixed and melted at 120 degreeC according to the said prescription, and it cooled to room temperature, and prepared the viscous flux.

[Preparation of copper salt and activator mixed flux]

The metal salt selected previously, the active agent and the flux prepared according to the above formulation were mixed, heated to 100 ° C., and cooled to room temperature. Table 1 shows the types and mixing ratios (% by weight) of the used fluxes, metal salts and activators.

Table 1

Unit: weight%

Yes Bass flux Metal salt Active agent Example 1 Rosin Flux: 90 A: 10 - Example 2 Rosin Flux: 88 A: 10 F: 2 Example 3 Rosin Flux: 88 A: 10 G: 2 Example 4 Rosin Flux: 88 B: 10 E: 2 Example 5 Rosin Flux: 88 C: 10 G: 2 Example 6 Rosin Flux: 88 D: 10 F: 2 Example 7 Acrylic flux: 88 A: 10 F: 2 Example 8 Acrylic flux: 88 A: 10 G: 2 Comparative Example 1 Rosin Flux: 100 - - Comparative Example 2 Rosin Flux: 88 A: 10 E: 2 Comparative Example 3 Rosin Flux: 88 A: 10 H: 2 Comparative Example 4 Rosin Flux: 88 C: 10 F: 2 Comparative Example 5 Acrylic flux: 90 A: 10 - Comparative Example 6 Acrylic flux: 88 A: 10 E: 2 Comparative Example 7 Acrylic flux: 88 A: 10 H: 2

[Measurement of Insulation Resistance]                     

The flux obtained in each Example and Comparative Example of Table 1 was printed on the whole surface in 100 micrometer thickness on the board | substrate arrange | positioned by the comb pattern, and reflowed at the maximum temperature of 250 degreeC. Flux used for the measurement of insulation resistance is two types, the flux immediately after manufacture, and the flux left to stand at 40 degreeC for 1 month. After reflow, the insulation resistance between the lands was measured after 1000 hours in a temperature of 85 ° C. and a relative humidity of 85% with a voltage of DC 50 V applied to the substrate according to the test method of JIS Z 3197.

[Measuring Bonding Strength]

Electroless nickel plating was carried out on copper lands on the substrate, and gold was flash-plated thereon to form lands with a diameter of 0.4 mm, and the fluxes of the examples and comparative examples in Table 1 (right after production) on the substrate. Was printed on the entire surface to a thickness of 100 μm.

Then, a Sn-3.5 Ag-0.5 Cu solder ball having a diameter of 0.6 mm was mounted on the land, rippled off, and the solder ball was bonded to the land. Subsequently, the board | substrate was immersed in the ultrasonic cleaner which put the 60 degreeC butyl carbitol solution, and wash | cleaned, and the flux was removed.

Subsequently, the bonding strength of the solder ball was measured by DAGE-SERIES-4000P manufactured by DAGE Corporation (heating collision strength). The measurement was carried out for 30 points, and the average value was made the bonding strength and the minimum value was made the minimum bonding strength.

 [Cum yunsung evaluation]

0.025g of each flux of each Example and the comparative example of Table 1 (it immediately after manufacture) was raised on the copper plate oxidized at 150 degreeC for 1 hour, and Sn-Pb solder ball of diameter 1mm was mounted thereon, and 230 degreeC Heated for 1 minute on a hot plate of. Then, the height of the solder was measured, and the wet expansion rate was calculated from the following equation. The wet expansion rate evaluates the active force of the active agent, and indicates that the higher the wet expansion rate, the higher the active force of the active agent.

Wet Expansion Rate = (1-Solder Height) X 100

These test results are shown in Table 2.

TABLE 2

Insulation Resistance (Ω) Bond strength (N) Bonding strength (N) Wet growth rate (%) Immediately after manufacture At 40 ℃ for 1 month Example 1 1.8 x ^{10 12} 1.5 x ^{10 12} 18.5 15.5 78% Example 2 2.0 x ^{10 12} 1.8 x ^{10 12} 19.0 14.8 87% Example 3 1.5 x ^{10 12} 1.7 x ^{10 12} 18.0 16.0 85% Example 4 ^1.2 x ^{10 12} 1.0 x ^{10 12} 17.8 14.0 84% Example 5 1.4 x ^{10 12} 1.5 x ^{10 12} 18.3 14.7 81% Example 6 1.7 x ^{10 12} 1.5 x ^{10 12} 18.6 15.8 86% Example 7 1.5 x ^{10 12} 1.8 x ^{10 12} 18.2 14.3 82% Example 8 1.8 x ^{10 12} 1.3 x ^{10 12} 17.9 15.0 83% Comparative Example 1 3.0 x ^{10 12} 2.0 x ^{10 12} 15.1  6.3 76% Comparative Example 2 1.8 x ^{10 11} <1 x ^{17 7} 17.0 13.9 85% Comparative Example 3 1.5 x ^{10 10} <1 x 10 ⁷ 16.8 14.2 87% Comparative Example 4 2.0 x ^{10 11} <1 x 10 ⁷ 17.8 14.5 82% Comparative Example 5 2.0 x ^{10 12} 1.8 x ^{10 12} 16.5 14.5 65% Comparative Example 6 1.3 x ^{10 11} <1 x 10 ⁷ 17.2 14.0 80% Comparative Example 7 1.2 x ^{10 10} <1 x 10 ⁷ 16.4 13.8 82%

As shown in Table 2, the flux of Examples 1-8 did not significantly reduce insulation resistance even after 1 month standing at 40 degreeC. On the other hand, in Comparative Examples 2, 3, 4, 6, and 7, the metal salts were poor in stability, and when the flux after use at 40 ° C. for 1 month was used, a decrease in insulation resistance was confirmed.

In addition, all of the fluxes of Examples 1 to 8 maintained high bonding strength. In contrast, in Comparative Example 1, since the metal salt is not contained, there is a point that the average bond strength is weak and extremely low bond strength. In addition, Comparative Example 5 showed a low wet expansion rate because the active force is weak.

According to the present invention, even when the flux is stored for a long time, since a specific organic acid is used as the activator, the safety of the organic acid metal salt in the flux is improved. For this reason, the diffusion of nickel to the solder in the soldered portion of the electroless nickel plated substrate is suppressed by the organic acid metal salt and the concentration of phosphorus is prevented, whereby the bonding strength of the solder can be suppressed from being lowered. In addition, since metal salts can be prevented from being decomposed during long-term storage, the deposition of metals can be suppressed, so that the insulation resistance between the lands can be prevented from significantly decreasing. Moreover, since solderability is favorable even if the flux of this invention is used, the fall of solderability by applying this invention is not seen.

In addition, since the flux of the present invention does not contain a halogen compound such as hydrochloric acid, the stability of the organic acid metal salt can be improved.

Claims (12)

A flux containing a resin having an ability to form a film, an activator, and a solvent, and used for soldering to a substrate electroless nickel plated, containing from 0.1 to 20% by weight of an organic acid metal salt based on the total amount of the flux, A soldering flux, wherein the activator is an organic acid having the same organic acid or lower acidity as the organic acid constituting the organic organic acid metal salt. The soldering flux according to claim 1, wherein the electric organic acid metal salt is a metal salt selected from gold, silver, copper, lead, zinc, bismuth, indium, antimony and nickel. The soldering flux according to claim 2, wherein the electric organic acid metal salt is a copper salt of an organic acid. The soldering flux according to claim 1, wherein the organic organic acid metal salt is a metal salt of saturated fatty acid having 7 to 21 carbon atoms of a hydrocarbon group excluding a carboxyl group. The soldering flux according to any one of claims 1 to 4, wherein the resin having an electric film forming ability is a rosin or an acrylic resin. The soldering flux according to any one of claims 1 to 5, wherein the electroactive agent is rosin. The soldering flux according to claim 5 or 6, wherein the resin having an electric film-forming ability is a rosin, and the rosin also serves as an electric activator. The soldering flux according to any one of claims 1 to 7, which does not contain a halogen compound. The soldering flux of any one of claims 1 to 8 is printed on a substrate having a copper land coated with electroless nickel plating on the surface, and then the solder balls are placed on an electric land and heated to reflow the solder balls. And soldering the solder balls to the lands. 10. The method of claim 9, wherein the electrical solder balls are zinc free (lead free). A paste in which the solder flux of any one of claims 1 to 8 is mixed with a solder powder is printed on a substrate having a copper land with electroless nickel plating on the surface thereof, and then heated to reflow the paste to form a land. A soldering method comprising forming a braze alloy. The printed circuit board by which soldering was joined by the soldering method of any one of Claims 9-11.