Flux and soldering method

Abstract

Hitherto, there has been no flux with which an enameled aluminum wire can be soldered to an adherend without removal of the enamel.　The present invention provides a flux comprising a rosin ester, a rosin that is not the rosin ester, a solvent which is diethylene glycol monophenyl ether and / or propylene glycol monophenyl ether, and an organic salt of hydrofluoric acid (as an activator). The flux enables an enameled aluminum wire to be wetted with a solder and soldered to an adherend without necessitating removal of the enamel.

Description

Flux and Soldering Methods

[0001] The present invention relates to a flux used in soldering, and in particular to a flux and soldering method that can solder enamel-coated aluminum wire without peeling off the enamel, as well as electric and electronic components soldered using the flux.

[0002] Enamel-coated coil wire (hereafter referred to as "enameled wire") is a conductor wire that is coated with a resin such as polyurethane, preventing electrical continuity even when the wires touch each other. The coating is very thin, so even if the wires touch each other when winding the coil, they will not short out. Furthermore, the volume of the wire when wound is not too large. Therefore, enameled wire is suitable for use in coils, and is also called magnet wire.

[0003] Enamelled wire is basically joined by removing the enamel from the surface and then soldering as usual. The flux used in this process is the same as usual. This flux is composed of rosin, which is mainly made of abietic acid, a solvent, mainly isopropyl alcohol, an activator, and other additives.

[0004] There are two types of enameled wire: one that uses copper for the conductor (hereafter referred to as "enameled copper wire") and one that uses aluminum for the conductor (hereafter referred to as "enameled aluminum wire"). Enameled aluminum wire, which uses aluminum for the conductor, has a lighter specific gravity than copper, so it can be made lighter even when coils are wound many times. In addition, enameled aluminum wire can be made at a lower product price by using inexpensive aluminum.

[0005] Patent Document 1 (Japanese Patent No. 6177383) discloses a method of removing enamel by ultrasonic vibration and then soldering.

[0006] Furthermore, Patent Document 2 (Japanese Patent Laid-Open Publication No. 2002-059293) discloses a flux for aluminum soldering that is a mixture of 3.0 to 5.0 mass % of a fluorinated metal salt, 10.0 to 30.0 mass % of a metal salt of an organic acid, and the remainder being a hydrofluoride salt of an amino alcohol.

[0007] Japanese Patent No. 6177383 Japanese Patent Laid-Open No. 2002-059293

[0008] Enameled copper wire has very high solder wettability to copper, so the copper wire and solder can be wetted with just molten solder and regular flux. In other words, soldering is possible without stripping the enamel. However, in the case of enameled aluminum wire, even if the molten solder dissolves the surface enamel, it is not possible to sufficiently wet the solder and aluminum conductor wire. Furthermore, flux for aluminum conductor wire cannot strip the enamel, so the enameled aluminum wire and solder cannot be wetted with just molten solder and regular flux.

[0009] The present invention has been conceived in view of the above problems, and provides a flux that can wet solder and enameled aluminum wire without stripping the enamel.

[0010] More specifically, the flux according to the present invention contains rosin, specifically rosin ester, which has good affinity with enamel.

[0011] Furthermore, the ink contains 30 to 75 mass % of a glycol solvent having a phenyl group, specifically at least one of diethylene glycol monophenyl ether and propylene glycol monophenyl ether, and an organic hydrofluoric acid salt.

[0012] The flux of the present invention uses rosin ester and a glycol-based solvent having a phenyl group to melt the enamel, and the activator to dissolve the oxide film on the surface of the conductor. This allows for soldering using only the heat of the solder without stripping the enamel from the wire. In particular, the flux can be used to solder aluminum wires, even lightweight enamel-coated aluminum wires (enameled aluminum wires).

[0013] 1A and 1B are diagrams illustrating the appearance of objects to be joined used in an experiment.

[0014] The flux according to the present invention will be described below with reference to drawings and examples. Note that the following description exemplifies one embodiment of the present invention and one example, and the present invention is not limited to the following description. The following description can be modified within the scope of the present invention. Furthermore, "to" means greater than or equal to or less than. For example, "A to B" means greater than A (greater than or equal to A), including the value of A, and less than B (less than or equal to B), including the value of B.

[0015] <Rosin> The flux according to the present invention is composed of rosin, a solvent, and an activator. It is preferable to use a combination of rosin ester and a rosin other than rosin ester. The rosin ester is a rosin having a hydroxyl value, and whether or not the flux contains rosin ester can be detected by Fourier Transform Infrared Spectroscopy (FT-IR) or Gel Permeation Chromatography (GPC).

[0016] The rosin content of the flux is 20 to 55% by mass. Of this, the rosin ester content is preferably 5 to 45% by mass. If the rosin ester content is too low, it will not wet the enamel-coated aluminum wire. If the rosin ester content is too high, the viscosity will be too high and the flux will not be usable.

[0017] Suitable rosins other than rosin esters include conventionally used rosins made from abietic acid, hydrogenated rosin, polymerized rosin, acrylic-modified rosin, etc. The rosin other than rosin esters is preferably contained in an amount of 10 mass % based on the total mass of the flux.

[0018] <Solvent> The solvent should have a boiling point of less than 400°C and be a good solvent for resin. 400°C is the typical soldering temperature for lead-free solder. The boiling point of the solvent should be 220°C or higher. 220°C is the melting point of lead-free solder. If the solvent evaporates before the lead-free solder melts, its ability to wet the solder and conductor wires will be reduced. In other words, any good solvent for resin with a boiling point above the melting point of lead-free solder and below the working temperature can be used as a solvent for the flux according to the present invention.

[0019] Specifically, glycol solvents containing a phenyl group, more specifically, diethylene glycol monophenyl ether and propylene glycol monophenyl ether are suitable.

[0020] Furthermore, to aid in the removal of enamel, N-methyl-2-pyrrolidone, 3-methylphenol, trichloromethane, hexafluoro-2-propanol, 2-chlorophenol, and the like, which are good solvents for enamel, may be added.

[0021] The solvent should be 25 to 75% by mass of the total amount of flux. If it is less than this, the rosin will not dissolve sufficiently, and the flux will crystallize during storage or operation.

[0022] <Activator> The activator dissolves the enamel, removes the metal oxide film from the exposed surface of the conductor, and makes it easier for the solder to wet. In particular, when the conductor is made of aluminum, it is desirable to use an activator that can remove the strong oxide film and that works only at the high temperature during soldering and not at room temperature. Among these, hydrofluoric acid salts of organic amines are preferably used.

[0023] Specifically, hydrofluoric acid salts of amines are suitable, such as hydrofluoric acid salts of cyclohexylamine, 1,3-diphenylguanidine, N,N'-diethylaniline, diethylamine, and the like.

[0024] If amine hydrochloride or hydrobromide is used instead of amine hydrofluoride, the oxide film removal ability is weak, and the activator cannot complete the removal of the oxide film on the aluminum surface and soldering.

[0025] Furthermore, when hydrofluoric acid, an inorganic acid, or sodium fluoride, a salt other than an amine, is used, they exhibit the ability to remove oxide films not only at high temperatures during soldering, but also at room temperature after soldering is completed, causing corrosion and subsequent destruction of the soldered area.

[0026] The amine hydrofluoride may be used alone or in combination. The activator is added in an amount of 1.2 to 5.0 mass% based on the total amount of flux. If the amount is less than 1.2 mass%, solderability will be poor, and if the amount added exceeds this amount, a large amount of fluorine will remain in the flux residue, which may cause corrosion at the soldered portion and reduce electrical reliability.

[0027] <Co-activator> Furthermore, in the flux of the present invention, organic bromides that generate hydrobromic acid at soldering temperatures, such as 2,3-dibromo-1-propanol, 1,2,5,6,9,10-hexabromocyclododecane, tris(2,3-dibromopropyl)isocyanurate, and 2,2-bis(4-bromomethyl)-1,3-propanediol, can be suitably used as a co-activator.

[0028] These auxiliary activators continue to exhibit a gentle oxide removal effect even after the oxide film on the surface of the aluminum wire has been removed with amine hydrofluoric acid salt, preventing the re-oxidation of aluminum and ensuring good solderability.

[0029] The auxiliary activator is preferably added in an amount of 0.5 to 5 mass % based on the total amount of flux, because if the amount added is less than this amount, the oxide removal effect will not be obtained, and if the amount added is more than this amount, a large amount of halogen will remain in the flux residue, which may cause problems with corrosiveness and electrical reliability.

[0030] Next, we will explain a soldering method using the flux of the present invention. The flux of the present invention contains rosin, which gives it an appropriate viscosity. Therefore, soldering can be performed by bringing an enameled wire and an object to be joined into contact with each other, immersing the contact parts in the flux to adhere the flux, and then immersing them in molten solder. After these steps, the soldered objects may be cleaned.

[0031] In order to adjust the viscosity and thixotropy of the flux in order to control the amount of the flux adhered to the contact portion, wax, gelling agent, etc. may be added, as in the case of general liquid fluxes and paste-like fluxes.

[0032] Here, the object to be joined is a conductive metal. It is usually a material typically used as a conductor or terminal material in electric or electronic circuits, such as copper, iron, aluminum, gold, silver, or an alloy of these. The enameled wire may be enameled copper wire or enameled aluminum wire. Bringing the enameled wire into contact with the object to be joined means that the enameled wire and the object to be joined are in contact, even if only partially. Alternatively, the object to be joined and the enameled wire are very close to each other, so long as they are not in contact at all.

[0033] The flux of the present invention can wet even enameled aluminum wire with solder. Therefore, if the objects to be joined and the enameled wire are very close to each other, they can be electrically joined using solder. The distance is approximately 0.1 mm. In other words, when we say that the enameled wire and the objects to be joined are in contact with each other, it includes not only cases where they are actually in contact, but also cases where the enameled wire and the objects to be joined are placed close to each other. The enameled wire and the objects to be joined that are in contact with each other are called "objects to be joined."

[0034] Next, the objects to be joined are immersed in the flux according to the present invention. It is sufficient to immerse the portion of the objects to be joined where the object to be joined and the enameled wire are in contact and fixed in the flux. In other words, the portion of the object to be joined where the enameled wire and the enameled wire are to be soldered is immersed in the flux.

[0035] Next, the objects to be joined with the flux attached are immersed in molten solder. The flux does not need to be dry when immersing in the molten solder. In other words, the objects to be joined may be immersed in flux and then immediately immersed in molten solder.

[0036] In the step of immersing in molten solder, the object to be joined to which the flux is attached does not need to be kept in the molten solder for a while, and can be pulled out immediately after the entire portion to which the flux is attached is immersed in the molten solder.

[0037] Immersion in flux and molten solder may be performed not only once but also multiple times. In other words, the objects to be joined are immersed in flux and then in molten solder. This is considered one set, and this set may be performed multiple times. However, the flux according to the present invention can solder objects to be joined, consisting of an enameled wire and objects to be joined, in just one set, i.e., immersion in flux and then in molten solder. The soldered objects to be joined are called a "completely joined object."

[0038] The joining method using flux according to the present invention requires the operation of immersing the objects to be joined, to which the flux has been applied, in solder. That is, the operation of the objects to be joined passing through the interface between the solder and the flux on its surface removes the enamel and simultaneously wets the objects to be joined and the solder.

[0039] After immersion in the molten solder, the joined object may be washed. Since the flux according to the present invention is composed of components with a boiling point of 400°C or less, all components evaporate when immersed in the molten solder. However, if any components of the flux remain, this is to avoid corrosion of the joined object or the joined object.

[0040] The joining method using the flux according to the present invention can be suitably used for joining enameled wire to electrical or electronic components. That is, the object to be joined can be an electrical or electronic component that uses enameled wire. In particular, the method can be suitably used for joining enameled wire to terminals of components such as electromagnets, motor rotors and stators, and inductors, which are made by winding enameled wire.

[0041] The following experiment was carried out to confirm the effect of the flux according to the present invention. <Solderability Test> An enamel-coated aluminum coil wire was wound around a wiring terminal (0.64 × 0.64 × 20 mm, tin-plated over nickel), and then the test flux was applied and the terminal was immersed in molten solder in a solder bath (solder temperature: 400°C, solder composition: 96.1% tin, 3.5% silver, 0.4% nickel by mass).

[0042] FIG. 1 shows the appearance of the sample used. FIG. 1( a) shows a motor rotor 10. The rotor 10 has a main body 10a formed of a cylindrical insulating material and two wiring terminals 10b (10ba and 10bb) attached to it. Referring to FIG. 1( b), an enameled aluminum wire 12 was wound around the rotor 10, starting from one wiring terminal 10ba. The enameled aluminum wire 12 was also wound around the main body 10a and continued to the other wiring terminal 10bb. Here, the wiring terminal 10b is the object to be joined 14, and the wiring terminal 10b around which the enameled aluminum wire 12 is wound is the object to be joined 16.

[0043] Referring now to Figure 2, first, objects to be joined 16 were immersed in the above-mentioned test flux 18 (P100). Then, objects to be joined 16 were immersed in molten solder 20 prepared in a solder bath 20a (P102). Objects to be joined 16 were then removed from molten solder 20 (P104). When flux 18 according to the present invention was used, this single set (one process of immersion in flux 18 and then immersion in solder 20) resulted in no unwetted areas of objects to be joined 16, i.e., wiring terminals 10b to which enameled aluminum wire 12 was fixed, and the solder was completely wetted, resulting in a completed joint 16a.

[0044] The soldered portion of the completed joint 16a was visually evaluated, and a rating of "◎" (meaning an excellent pass) was given if the solder had sufficiently wetted the wiring terminal 10b and the enameled aluminum wire 12 to form a single unit; a rating of "◯" (meaning pass) was given if the wettability was slightly poor but still good enough to be used as a product; and a rating of "×" (meaning fail) was given if the wettability was insufficient and the product was not usable as a product.

[0045] At the same time, an experiment was also conducted in which an aluminum plate without enamel was coated with flux and immersed in molten solder.

[0046] The composition of the test flux is shown below: (Example 1) The rosin was 20.0 mass% purified rosin, 25.0 mass% rosin ester, 51.7 mass% PhDG as a solvent, 2.3 mass% CHAH as an activator, and 1.0 mass% TAIC6B as a co-activator. The above materials were mixed to prepare the flux of Example 1.

[0047] The rosin ester used was Pine Crystal KE-359 (also referred to as "PCKE-359"). PCKE-359 is a rosin derivative (rosin ester) manufactured by Arakawa Chemical Industries, Ltd. PhDG is diethylene glycol monophenyl ether, CHAH is cyclohexylamine hydrofluoride, and TAIC6B is tris(2,3-dibromopropyl)isocyanurate.

[0048] (Example 2) The flux of Example 2 was prepared by mixing the following materials: 20.0 mass% purified rosin as rosin, 25.0 mass% rosin ester, 51.7 mass% PhDG as solvent, 2.3 mass% CHAH as activator, and 1.0 mass% TAIC6B as co-activator.

[0049] The rosin ester used was Pine Crystal KE-100 (also referred to as "PCKE-100"), a rosin derivative (rosin ester) manufactured by Arakawa Chemical Industries, Ltd.

[0050] (Example 3) The flux of Example 3 was prepared by mixing the following materials: 20.0 mass % of polymerized rosin as rosin, 25.0 mass % of rosin ester, 51.7 mass % of PhDG as solvent, 2.3 mass % of CHAH as activator, and 1.0 mass % of TAIC6B as co-activator.

[0051] The rosin ester used was Pine Crystal KE-359 (PCKE-359).

[0052] (Example 4) The flux of Example 4 was prepared by mixing the following materials: 20.0 mass % of purified rosin as rosin, 25.0 mass % of rosin ester, 51.7 mass % of PhFG as solvent, 2.3 mass % of CHAH as activator, and 1.0 mass % of TAIC6B as co-activator.

[0053] The rosin ester used was Pine Crystal KE-359 (PCKE-359), and PhFG is propylene glycol monophenyl ether.

[0054] (Example 5) The flux of Example 5 was prepared by mixing the following materials: 20.0 mass% purified rosin as rosin, 25.0 mass% rosin ester, 51.7 mass% PhDG as solvent, 2.3 mass% CHAH as activator, and 1.0 mass% TAIC6B as co-activator.

[0055] The rosin ester used was Pine Crystal KE-311 (also referred to as "PCKE-311"), a rosin derivative (rosin ester) manufactured by Arakawa Chemical Industries, Ltd.

[0056] (Example 6) The flux of Example 6 was prepared by mixing the following materials: 20.0 mass% purified rosin as rosin, 25.0 mass% rosin ester, 51.7 mass% PhDG as solvent, 2.3 mass% CHAH as activator, and 1.0 mass% TAIC6B as co-activator.

[0057] The rosin ester used was Pine Crystal D-6011 (also referred to as "PCD-6011"), a rosin derivative (rosin ester) manufactured by Arakawa Chemical Industries, Ltd.

[0058] (Example 7) The flux of Example 7 was prepared by mixing the following materials: 20.0 mass% purified rosin as rosin, 25.0 mass% rosin ester, 51.7 mass% PhDG as solvent, 2.3 mass% CHAH as activator, and 1.0 mass% TAIC6B as co-activator.

[0059] The rosin ester used was Ester Gum 105 (also referred to as "EG105"), a rosin derivative (rosin ester) manufactured by Arakawa Chemical Industries, Ltd.

[0060] (Example 8) The flux of Example 8 was prepared by mixing the following materials: 40.0 mass% purified rosin as rosin, 5.0 mass% rosin ester, 51.7 mass% PhDG as solvent, 2.3 mass% CHAH as activator, and 1.0 mass% TAIC6B as co-activator.

[0061] The rosin ester used was Pine Crystal KE-359 (PCKE-359).

[0062] (Example 9) The flux of Example 9 was prepared by mixing the following materials: 10.0 mass% purified rosin as rosin, 45.0 mass% rosin ester, 41.7 mass% PhDG as solvent, 2.3 mass% CHAH as activator, and 1.0 mass% TAIC6B as co-activator.

[0063] The rosin ester used was Pine Crystal KE-359 (PCKE-359).

[0064] Comparative Example 1 The flux of Comparative Example 1 was prepared by mixing the following materials: 45.0 mass% purified rosin as rosin, 51.7 mass% PhFG as solvent, 2.3 mass% CHAH as activator, and 1.0 mass% TAIC6B as co-activator.

[0065] Comparative Example 1 does not contain rosin ester.

[0066] Comparative Example 2 The flux of Comparative Example 2 was prepared by mixing the following materials: 20.0 mass % of purified rosin as rosin, 25.0 mass % of rosin ester, 51.7 mass % of IPA as solvent, 2.3 mass % of CHAH as activator, and 1.0 mass % of TAIC6B as co-activator.

[0067] The rosin ester used was Pine Crystal KE-359 (PCKE-359), and IPA is isopropyl alcohol.

[0068] Comparative Example 3 The flux of Comparative Example 3 was prepared by mixing the following materials: 20.0 mass % of purified rosin as rosin, 25.0 mass % of rosin ester, 51.7 mass % of BZA as solvent, 2.3 mass % of CHAH as activator, and 1.0 mass % of TAIC6B as co-activator.

[0069] The rosin ester used was Pine Crystal KE-359 (PCKE-359), and BZA is benzyl alcohol.

[0070] Comparative Example 4 The flux of Comparative Example 4 was prepared by mixing the following materials: 44.0 mass% purified rosin as rosin, 1.0 mass% rosin ester, 51.7 mass% PhDG as solvent, 2.3 mass% CHAH as activator, and 1.0 mass% TAIC6B as co-activator.

[0071] The rosin ester used was Pine Crystal KE-359 (PCKE-359).

[0072] Comparative Example 5 The following materials were mixed to prepare the flux of Comparative Example 5. Comparative Example 5 did not contain any rosin other than the rosin ester: 45.0 mass% rosin ester, 51.7 mass% PhDG as a solvent, 2.3 mass% CHAH as an activator, and 1.0 mass% TAIC6B as a co-activator.

[0073] The rosin ester used was Pine Crystal KE-359 (PCKE-359). The rosin in Comparative Example 5 consisted of only rosin ester.

[0074] Table 1 shows the composition of each sample of the examples and the evaluation of the experimental results. Table 2 shows the composition of each sample of the comparative examples and the evaluation of the experimental results. In the table, examples may be represented as "Ex" and comparative examples as "CEx".

[0075]

[0076]

[0077] With reference to Comparative Example 1, the solder wetted well to the uncoated aluminum plate, but hardly wetted the enameled aluminum wire (referred to in the table as "enamel-coated aluminum coil wire"). That is, the activator cyclohexylamine hydrofluorate (CHAH) and the co-activator tris(2,3-dibromopropyl)isocyanurate (TAIC6B) were able to wet the aluminum well, but the refined rosin was unable to strip the enamel and was unable to wet the solder well.

[0078] On the other hand, in Examples 1 and 2, the solder was able to wet not only the uncoated aluminum plate but also the enameled aluminum wire well. That is, the rosin esters such as Rosin Ester Pine Crystal KE-359 and Rosin Ester Pine Crystal KE-100 were able to strip the enamel.

[0079] Furthermore, with reference to Examples 3 and 5 to 7, as long as the composition contained a rosin ester such as Rosin Ester Pine Crystal KE-359, Rosin Ester Pine Crystal KE-100, Rosin Ester Pine Crystal KE-311, Rosin Ester Pine Crystal D-6011, or Rosin Ester Ester Gum 105, it was possible to strip the enamel and achieve good solder wetting even when other rosins such as purified rosin or polymerized rosin were used.

[0080] Furthermore, with reference to Comparative Examples 2 and 3, solvents with boiling points lower than the melting point of lead-free solder, such as isopropyl alcohol (IPA: boiling point 82.4°C) and benzyl alcohol (BZA: boiling point 206°C), volatilized instantly when heated during soldering, and volatilized before the enamel could be peeled off, failing to properly wet the solder.

[0081] On the other hand, referring to Examples 1 and 4, glycol solvents containing phenyl groups, such as diethylene glycol monophenyl ether and propylene glycol monophenyl ether (PhFG), were able to strip the enamel and wet the solder well.

[0082] With reference to Examples 8 and 9, the effects of the present invention were achieved when the rosin ester was 5% by mass or more and 45% by mass or less of the total amount of flux. Even in this case, it is preferable that the other rosin be contained in an amount of at least 10% by mass of the total amount of flux (Example 9). Furthermore, when the rosin ester was less than 5% by mass of the total amount of flux, it was not possible to wet the enamel-coated aluminum coil wire (comparison between Example 8 and Comparative Example 4).

[0083] In addition, all of the examples were also evaluated as "Excellent" (meaning excellent pass) for the enameled copper wire.

[0084] As described above, the flux according to the present invention can be suitably used for soldering enamel-coated conductor wires without stripping the enamel, and the conductor wires may be made of either copper or aluminum.

[0085] REFERENCE SIGNS LIST 10 rotor 10a main body 10b wiring terminal 12 enameled aluminum wire 14 object to be joined 16 object to be joined 16a completed joined object 18 flux 20 molten solder 20a solder bath 22 portion not wetted with solder

Claims

1. A flux comprising: a rosin ester; a rosin other than the rosin ester; at least one of diethylene glycol monophenyl ether and propylene glycol monophenyl ether as a solvent; and an organic hydrofluorate (as an activator).

2. The flux according to claim 1, wherein the organic hydrofluoride is at least one of cyclohexylamine hydrofluoride, 1,3-diphenylguanidine hydrofluoride, N,N'-diethylaniline hydrofluoride, and diethylamine hydrofluoride.

3. A flux as claimed in claim 1 or 2, further comprising at least one of 2,3-dibromo-1-propanol, 1,2,5,6,9,10-hexabromocyclododecane, tris(2,3-dibromopropyl)isocyanurate, and 2,2-bis(4-bromomethyl)-1,3-propanediol as a co-activator.

4. A flux according to any one of claims 1 to 3, wherein the rosin is 20% by mass or more and 55% by mass or less of the total amount of the flux, the rosin ester is 5% by mass or more and 45% by mass or less of the total amount of the flux, and the other rosin is 10% by mass or more of the total amount of the flux.

5. A method for soldering an enameled wire, comprising the steps of: bringing an enameled wire and an object to be joined into contact and fixing them to form a joint; immersing the object to be joined in a flux as defined in any one of claims 1 to 3; and immersing the object to be joined in molten solder to form a joint in which the enameled wire and the object to be joined are welded together.

6. The method for soldering enameled wire according to claim 4, further comprising the step of cleaning the joint.