Manufacturing methods for welded products

Abstract

The soldered product is manufactured by performing a solder supply process, a heating process, and a curing process. In the solder supply process, a cylindrical soldering iron (2, 21) with a through hole (22) is brought into contact with the part to be soldered (11). Then, a wire bond (3) is supplied to the part to be soldered (11) through the through hole (22). In the heating process, the wire bond (3) is heated using the soldering iron (2, 21) and melted in the part to be soldered (11). In the curing process, the molten material (34) of the wire bond (3) is cured. The wire bond (3) consists of a core and a coating. The core contains flux, and the coating contains a solder alloy. The flux is mainly composed of rosin with a substantially zero acid value.

Description

[0001] Cross-reference to related applications

[0002] This application is based on Japanese Application No. 2020-205781 filed on December 11, 2020 and Japanese Application No. 2021-154163 filed on September 22, 2021, the contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to a method for manufacturing welded products by so-called sleeve welding. Background Technology

[0004] Soldered products, such as electronic products, are manufactured by soldering electronic components to terminals or to the electronic circuitry of a substrate. Sensors, actuators, inverters, power windows, motors, and other soldered products are manufactured through this process. Soldering electronic components to the substrate primarily employs methods known as surface mount soldering, such as reflow soldering or jet soldering. The soldering that connects the completed electronic circuitry to connectors, actuators, sensors, etc., is called post-soldering, and post-soldering can be done using soldering irons, lasers, or sleeves.

[0005] The sleeve welding method is superior in terms of suppressing the scattering of solder and flux during welding and thus providing a stable amount of solder to the joined objects (see Patent Document 1).

[0006] In sleeve soldering, a cylindrical soldering iron and solder wire are typically used. The solder wire contains a solder alloy and flux; the flux can be a resin such as rosin (specifically, a resin). Such solder is also known as resin-core solder.

[0007] In the field of welding technology, to leverage the aforementioned advantages, continuous advancements are being made in the development of solders and fluxes suitable for sleeve welding methods. For example, Patent Document 2 discloses a technique using a flux primarily composed of volatile rosin. According to Patent Document 2, this technique can suppress welding defects caused by the flux. Specifically, it is believed that welding defects can be suppressed while reducing the frequency of cleaning.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent No. 5184359

[0011] Patent Document 2: Japanese Patent No. 6516053 Summary of the Invention

[0012] For example, in the flux disclosed in Patent Document 2, since the flux is volatile, although it can inhibit the accumulation of dirt inside the soldering iron, a portion of the flux remains inside the soldering iron, and the flux residue accumulates inside the soldering iron in the form of carbide dirt.

[0013] This disclosure provides a method for manufacturing a soldering product that can prevent dirt from accumulating inside a cylindrical soldering iron.

[0014] One aspect of this disclosure is a method for manufacturing a welded product, which manufactures the welded product by welding the welded parts, and has the following characteristics:

[0015] In the solder supply process, a cylindrical soldering iron with a through hole is brought into contact with the part to be soldered, and a wire solder piece is supplied to the part to be soldered through the through hole.

[0016] In the heating process, the soldering iron is used to heat the solder wire piece, melting the solder wire piece at the soldering area; and

[0017] The curing process involves welding the welded parts by solidifying the molten material from the aforementioned wire bonding sheets.

[0018] The aforementioned wire bonding sheet consists of a core containing flux and a coating containing a solder alloy covering the core.

[0019] The above flux is mainly composed of rosin with an actual acid value of 0.

[0020] According to the above method, a method for manufacturing a welding product can be provided that provides good wettability between the welded part and the solder, inhibits the accumulation of dirt into the cylindrical soldering iron, and has high insulation reliability.

[0021] It should be noted that the symbols in parentheses in the scope of the request represent the correspondence between the specific means described in the embodiments described later, and do not limit the technical scope of this disclosure. Attached Figure Description

[0022] The above and other objects, features, and advantages of this disclosure will become more apparent from the accompanying drawings and the following detailed description. The drawings are as follows:

[0023] Figure 1 This is a schematic diagram illustrating the sleeve welding method in Embodiment 1.

[0024] Figure 2 This is a schematic diagram showing the cross-section of the bonding wire in Embodiment 1.

[0025] Figure 3 (a) is a schematic diagram of the part being soldered when the inside of the cylindrical soldering iron is free of dirt. Figure 3(b) is a schematic diagram of the part being soldered when the inside of the cylindrical soldering iron is filled with dirt.

[0026] Figure 4 This is an explanatory diagram showing the criteria for determining wettability in the experimental examples.

[0027] Figure 5 This is a graph showing the results of thermogravimetric determination in Example 1 and Comparative Example 1 of the experimental examples.

[0028] Figure 6 This is a graph showing the relationship between the total acid value and the number of blocked injections in Examples 1-3, Example 5, and Comparative Example 1 of the experimental examples.

[0029] Figure 7 This is a graph showing the relationship between the content of acid-free rosin and the total acid value in the flux of Examples 1-3, Example 5, and Comparative Example 1 in the experimental examples.

[0030] Figure 8 This is a graph showing the relationship between the thermogravimetric analysis results at 400°C and the number of sluggish injections in Examples 1-3, 5, and Comparative Example 1 of the experimental examples.

[0031] Figure 9 It is a graph showing the relationship between the halogen content in the flux and the insulation resistance test results. Detailed Implementation

[0032] (Implementation Method 1)

[0033] Reference Figures 1-3 The implementation method for manufacturing the welded product is described. It should be noted that in this specification, the use of tildes such as “~” is intended to encompass the numerical or physical values ​​described before or after them. In this specification, “wt%” and “mass%” have essentially the same meaning.

[0034] Welded product 1 refers to a product having a welded part. Specifically, as welded product 1, such as... Figure 1 As shown in (a) to (c), examples can be given of products having a printed circuit board 12 and electronic components 13 soldered to the printed circuit board 12. The printed circuit board 12 may have through holes 120. More specifically, the soldered portion 11 is composed of the through holes 120 of the printed circuit board 12 and terminals 14 (e.g., metal pins), and as soldered product 1, examples can be given of products with such soldered portions 11. Although the configuration is not illustrated, the printed circuit board 12 may be a so-called multilayer board. There are no particular limitations on the soldered product 1 as long as it has soldered portions formed by soldering.

[0035] In the above manufacturing method, a solder supply step, a heating step, and a curing step are performed. In a soldering method having these steps, the solder wire is heated with a soldering iron to a temperature exceeding the melting point of the solder (i.e., solder alloy), the objects to be joined are heated, and the solder wire melts. In other words, a soldering method in which solder wire is supplied into a through-hole of the soldering iron, the soldering iron is kept at a temperature exceeding the melting point of the solder, and the solder wire supplied to the through-hole is heated is called a sleeve type. For example... Figure 1 As shown in (a) to (c), the sleeve welding method is carried out, for example, using a sleeve welding machine 2 (i.e., soldering iron 2).

[0036] In the solder supply process, such as Figure 1 As shown in (a), the front end of the welding machine 2 abuts against the part 11 to be welded. The welding machine 2 has a cylindrical main body 21, in which a through hole 22 is formed. Figure 1 As shown in (a), for example, the front end of the main body 21 abuts against the welding part 11. The main body 21 abuts against the welding part 11 in such a way that at least a portion or all of it is disposed inside the through hole 22. The cylindrical main body 21 is made of a material containing ceramics with excellent thermal conductivity, for example, and more specifically, of aluminum nitride, silicon carbide, etc.

[0037] In the solder supply process, such as Figure 1 As shown in (a), a bonding wire piece 3 is supplied to the welded portion 11 through the through hole 22 of the main body 21. The bonding wire piece 3 can be supplied to the welded portion 11, for example, by moving within the through hole 22 under its own weight. Figure 2 As shown, the shape of the bonding wire 30 is, for example, rod-shaped or cylindrical, and the bonding wire consists of a core 31 and a coating 32. The same applies to the bonding wire sheet 3. The core 31 is made of flux. The coating 32 covers the core 31 and is made of solder alloy. The bonding wire 30 is cut, for example, to a size (specifically, length) suitable for welding the portion 11 to be welded, becoming the bonding wire sheet 3. This bonding wire sheet 3 is supplied to the portion 11 to be welded.

[0038] The composition of solder alloys is not particularly limited as long as it is an alloy composition commonly used for soldering. For example, solder known as soft solder can be used as a solder alloy. The melting point of solder alloys is typically 180°C to 280°C.

[0039] Flux contains at least rosin. Flux may further contain activators, etc. Activators will be discussed later.

[0040] The flux contains at least rosin with a substantially zero acid value (e.g., rosin ester), with the substantially zero acid value rosin as the main component. In this specification, "substantially zero" means that during the esterification of the carboxylic acids present in the rosin, the rosin may sometimes have a slight acid value due to the reaction residues (specifically, carboxyl groups), thus including such cases. Specifically, substantially zero acid value rosin refers to rosin with an acid value less than 10 mg / g of KOH. The substantially zero acid value rosin is appropriately referred to as "acid-free rosin" in this specification. When acid-free rosin is not the main component, flux residue tends to accumulate inside the cylindrical soldering iron body 21. That is, there is a concern that the accumulation of contaminants inside the soldering iron body 21 cannot be adequately suppressed. Figure 3 As shown in (b), if a large amount of dirt 39 accumulates inside the soldering iron body 21, there are concerns that even if the solder wire 3 melts during the heating process, it will be difficult to adequately supply flux and solder alloy to the part 11 to be soldered. Furthermore, there are concerns that the thermal conductivity of the cylindrical soldering iron (i.e., the body 21) will be reduced, making it difficult to supply flux and solder alloy to the part 11 to be soldered. Moreover, there are concerns that the frequency of dirt removal operations to avoid these adverse conditions will increase, thus increasing the manufacturing cost of the soldered product 1. It should be noted that the main component refers to the component that constitutes the flux in the largest proportion, preferably 50% by mass or more.

[0041] In addition, such as Figure 3 As shown in (a), when no dirt has accumulated, it will not hinder the supply of the welding wire sheet 3 to the part being welded 11, nor will it hinder heat conduction from the heater 25, for example.

[0042] In this specification, the acid value is measured for, for example, the base resin (specifically rosin) and flux. The acid value is determined according to JIS Z 3197:2012 8.1.4.1.1. Details of the measurement conditions will be described later.

[0043] In this specification, cases where the acid value is less than 10 KOH mg / g (including 0) in the above determination method are defined as having an actual acid value of 0. For acid values ​​above 10 KOH mg / g, the acid value is expressed as the actual measured value.

[0044] The acid value of the flux is preferably 20–60 KOH mg / g. The acid value of the flux refers to the overall acid value of the flux, and this acid value is called the "total acid value." A total acid value of 20 KOH mg / g or higher improves wettability. Furthermore, a total acid value of 60 KOH mg / g or lower prevents fouling. From the viewpoint of further improving wettability and preventing flux fouling from accumulating inside the cylindrical soldering iron, a total acid value of 23–57 KOH mg / g is more preferable, and 25–54 KOH mg / g is even more preferable.

[0045] The total acid value of the flux can be adjusted, for example, as follows. For instance, by adding rosin with an acid value substantially greater than 0 (i.e., rosin other than acid-free rosin) to the flux and adjusting the proportion of this rosin, the total acid value of the flux can be adjusted. Specifically, by adding rosin with a high acid value and increasing its proportion, the total acid value tends to increase. On the other hand, by increasing the proportion of acid-free rosin, the total acid value tends to decrease. It should be noted that hydrogenated rosin, acid-modified rosin, disproportionated rosin, phenol-modified rosin, etc., can be used as rosin with an acid value substantially greater than 0.

[0046] Alternatively, activators and other components other than rosin can be added to the flux. Examples of activators include organic acids, halogenated activators, and amines. These activators are selected from, for example, those commonly used in fluxes for wire bonding. Furthermore, when using organic acids as activators, the total acid value of the flux can be adjusted by changing their proportions.

[0047] As organic acids, glutaric acid, adipic acid, azelaic acid, eicosanoic acid, citric acid, glycolic acid, succinic acid, salicylic acid, diethylene glycol, pyridine dicarboxylic acid, dibutylaniline diethylene glycol, octanoic acid, sebacic acid, thioglycolic acid, phthalic acid, isophthalic acid, terephthalic acid, dodecanoic acid, p-hydroxyphenylacetic acid, pyridine carboxylic acid, phenyl succinic acid, fumaric acid, maleic acid, malonic acid, lauric acid, benzoic acid, and tartaric acid can be used. Acids, tris(2-carboxyethyl) isocyanurate, glycine, 1,3-cyclohexanedicarboxylic acid, 2,2-bis(hydroxymethyl)propionic acid, 2,2-bis(hydroxymethyl)butyric acid, 4-tert-butylbenzoic acid, 2,3-dihydroxybenzoic acid, 2,4-diethylglutaric acid, 2-quinolinecarboxylic acid, 3-hydroxybenzoic acid, malic acid, p-anestic acid, palmitic acid, stearic acid, 12-hydroxystearic acid, oleic acid, linoleic acid, linolenic acid, etc.

[0048] Organic bromine compounds can be used as halogen-based surfactants. Specifically, trans-2,3-dibromo-1,4-butenediol, triallyl isocyanurate hexabromide, 1-bromo-2-butanol, 1-bromo-2-propanol, 3-bromo-1-propanol, 3-bromo-1,2-propanediol, 1,4-dibromo-2-butanol, 1,3-dibromo-2-propanol, 2,3-dibromo-1-propanol, 2,3-dibromo-1,4-butanediol, 2,3-dibromo-2-buten-1,4-diol, trans-2,3-dibromo-2-buten-1,4-diol, cis-2,3-dibromo-2-buten-1,4-diol, tetrabromophthalic acid, bromosuccinic acid, and 2,2,2-tribromoethanol can be used. Alternatively, organochlorine compounds can be used as halogen-based surfactants. Specifically, chlorinated alkanes, chlorinated fatty acid esters, chlorinated brittle acids, and chlorinated brittle anhydrides can be used. Additionally, as halogen-based surfactants, fluorinated surfactants (organofluorine compounds), surfactants with perfluoroalkyl groups, and polytetrafluoroethylene can be used.

[0049] As amines, monoethanolamine, diphenylguanidine, ethylamine, triethylamine, ethylenediamine, triethylenetetramine, 2-methylimidazole, 2-undecylimidazole, 2-heptadecanylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole Trimeric ester, 1-cyanoethyl-2-phenylimidazolium Trimethicone ester, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-triazine isocyanuric acid adduct, 2-phenylimidazolyl isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazolium, 2-phenyl-4-methyl-5-hydroxymethylimidazolium, 2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole, 1-dodecyl-2-methyl-3-benzyl chloride imidazolium 2-Methylimidazoline, 2-Phenylimidazolin, 2,4-Diamino-6-vinyl-triazine, 2,4-Diamino-6-vinyl-triazine isocyanuric acid adduct, 2,4-Diamino-6-methacryloyloxyethyl-triazine, epoxy-imidazolium adduct, 2-Methylbenzimidazole, 2-Octylbenzimidazole, 2-Pentylbenzimidazole, 2-(1-Ethylpentyl)benzimidazole, 2-Nonyl Benzimidazole, 2-(4-thiazolyl)benzimidazole, benzimidazole, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2-(2'-hydroxy-3',5'-di-tert-pentylphenyl)benzotriazole, 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole, 2,2'-methylenebis[ 6-(2H-benzotriazol-2-yl)-4-tert-octylphenol, 6-(2-benzotriazolyl)-4-tert-octyl-6'-tert-butyl-4'-methyl-2,2'-methylenebisphenol, 1,2,3-benzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]benzotriazole, carboxybenzotriazole, 1-[N,N-bis(2-ethylhexyl)aminomethyl]methylbenzotriazole 2,2'-[[(methyl-1H-benzotriazol-1-yl)methyl]imino]diethanol, 1-(1',2'-dicarboxyethyl)benzotriazole, 1-(2,3-dicarboxypropyl)benzotriazole, 1-[(2-ethylhexylamino)methyl]benzotriazole, 2,6-bis[(1H-benzotriazol-1-yl)methyl]-4-methylphenol, rosin amine, N,N-diethylaniline, etc.

[0050] The content of activator in the flux is preferably 10% by mass or less. In this case, the insulation reliability is further improved. From the viewpoint of further improving the insulation reliability, the content of activator in the flux is more preferably 4% by mass or less, and even more preferably 3.5% by mass or less. It should be noted that in the flux of this disclosure, even with the reduction of the activator content as described above, the wettability is sufficiently excellent. In addition, from the viewpoint of ensuring wettability, the flux preferably contains activator, and its content is preferably 1% by mass or more, and more preferably 1.5% by mass or more.

[0051] The flux may further contain halogen-based activators comprising halides. The halogen content in the flux is preferably 4% by mass or less. In this case, for example, it is possible to prevent the degradation of insulation resistance in high humidity environments. From the viewpoint of improving this effect, the halogen content in the flux is more preferably 3.5% by mass or less, and even more preferably 3% by mass or less.

[0052] The flux preferably further contains rosin with an acid value of 150 mg / g or higher. In this case, adjusting the total acid value becomes easier, and compared to acid-free rosin, the total acid value can be increased to, for example, 20 mg / g or higher with a sufficiently small amount of addition. Thus, both improved wettability and inhibition of dirt buildup can be achieved. From the same point of view, the flux is more preferably containing rosin with an acid value of 200 mg / g or higher.

[0053] The content of acid-free rosin in the flux is preferably 60% by mass or more. In this case, the effect of suppressing flux accumulation inside the cylindrical soldering iron body 21 is further improved. From the viewpoint of further improving this effect, the content of acid-free rosin in the flux is more preferably 70% by mass or more, and even more preferably 75% by mass or more.

[0054] Typically, in sleeve soldering, to shorten soldering time and increase productivity, for example, to rapidly transfer heat from the heated cylindrical soldering iron to the solder wire and the part to be soldered inside the cylindrical soldering iron, the temperature of the soldering iron is heated to a temperature much higher than the melting temperature of the solder (specifically, the melting point of the solder alloy) (e.g., 400°C). The weight loss of the flux at the heating temperature of 400°C during soldering is preferably 55% by mass or less. That is, the weight reduction rate of the flux when heated at 400°C is preferably 55% by mass or less. In this case, the flux hardly volatilizes inside the heated soldering iron and is discharged as a liquid to the soldering part. Therefore, it has the effect of suppressing the volatile components of the flux from becoming flux fumes and adhering as dirt to the outer periphery of the soldering iron body and other parts of the soldering machine. A detailed method for measuring the weight loss during heating is shown in the experimental examples.

[0055] It should be noted that the accumulation of contaminants occurs as follows. Rosin, due to its carboxyl groups, possesses tackifying properties (specifically, adhesive or bonding properties). Therefore, rosin is considered to accumulate as flux residue (i.e., contaminants). On the other hand, residues accumulated on the inner wall are removed, for example, through periodic cleaning. Since the residues are firmly accumulated, cleaning is performed using, for example, a superhard drill bit for physical removal. Consequently, fine irregularities easily form on the inner wall surface of the cylindrical soldering iron 2. It is believed that these irregularities on the inner wall surface enhance the so-called anchoring effect, further facilitating residue accumulation.

[0056] In the process of realizing this disclosure, the inventors discovered a correlation between the acid value of rosin and its build-up of dirt. As shown in this disclosure, it is believed that by using acid-free rosin, which is largely free of carboxyl groups and therefore has difficulty exerting its tackifying properties, as the main component, it is possible to reduce the amount of rosin with an acid value greater than 0, such as acrylic rosin, and thus reduce dirt build-up.

[0057] like Figure 1As shown in (a) to (c), the soldering iron 2 has a built-in heater 25, for example. The heating method and configuration of the heater 25 are not particularly limited, but it is configured to heat the through hole 22 using the heater 25.

[0058] Next, in the heating process, the soldering iron 2 is used to heat the wire bond 3. Heating melts the wire bond 3. Specifically, it softens or melts the flux, causing the solder alloy to melt. Heating is performed, for example, by a heater 25.

[0059] The heating temperature in the heating process is, for example, above the melting point of the solder alloy, a temperature that allows the solder alloy to melt rapidly. Specifically, the heating temperature is preferably 400°C or higher. Furthermore, from the viewpoint of preventing heat damage and scorching around the soldered portion 11, such as the substrate, the heating temperature is preferably, for example, 550°C or lower.

[0060] In the curing process, the molten material 34 of the wire bonding sheet 3 is cured. Curing is carried out by cooling such as air cooling. By welding the welded parts 11 in this way, a welded product 1 with a welded part 35 (weld corner 35) can be manufactured.

[0061] As described above, in this embodiment, soldered product 1 can be manufactured. During manufacturing, by using a flux with acid-free rosin as the main component, the accumulation of contaminants caused by flux residue inside the cylindrical soldering iron 2 can be suppressed. If flux residue accumulates inside, heat transfer from the high-temperature state of the soldering iron 2 during soldering to the solder wire supplied inside is hindered. However, in the manufacturing method of this disclosure, the accumulation of flux residue is suppressed as described above, and thus the heat transfer obstacle is suppressed. Therefore, the cleaning frequency of the inside of the soldering iron 2 can be significantly reduced, and soldered product 1 with stable performance and quality can be manufactured continuously without stopping the production line of soldered product 1 for cleaning, for example. Cleaning is performed periodically, for example. Generally, it is appropriate to use either or both of the following methods: stopping soldering when the contaminant reaches a specified amount and inserting an ultra-hard drill bit into the barrel for physical removal, or heating the sleeve itself to, for example, 600°C or higher to carbonize the organic matter (specifically flux residue) for weight reduction.

[0062] Furthermore, the welding product 1 is preferably for automotive applications. Examples of welding products 1 for automotive applications include sensors, actuators, inverters, power windows, and motors.

[0063] It should be noted that, unless otherwise specified, the symbols used in the following description that are the same as those used in the above embodiments represent the same constituent elements as those in the above embodiments.

[0064] (Experimental Example)

[0065] This example demonstrates the manufacture of welded product 1 using solder wires containing the fluxes shown in Table 1 (Examples 1-5, Comparative Example 1), and the subsequent testing and evaluation. It should be noted that welded product 1 is manufactured by performing a solder supply process, a heating process, and a curing process, as described in Embodiment 1.

[0066] In Table 1, the composition of the solder alloy is common in all examples and comparative examples: Sn - 3.0 wt% Ag - 0.5 wt% Cu. Furthermore, the measurements and evaluations in Table 1 are performed as follows.

[0067] "Acid-free rosin content in flux"

[0068] The analysis was performed using GC-FID (i.e., gas chromatography-quantitative analysis). An Agilent Technologies 7890A gas chromatograph was used, and the determination was performed according to JIS K 0123:2018. GC conditions were: sample injection volume 2 μL, injection port temperature 260 °C, carrier gas He (linear velocity 25 cm / sec); FID conditions were: aspiration rate 5 Hz, detector temperature 300 °C, air flow rate 400 mL / min, H₂ flow rate 30 mL / min, and make-up gas flow rate 25 mL / min.

[0069] "Acid value (total acid value) of flux"

[0070] The acid value was determined by acid value testing. A Kyoto Electronics AT-710 potentiometric titration apparatus was used, and the determination was performed according to JIS Z3197:2012 8.1.4.1.1. A composite glass electrode was used, and 0.5N potassium hydroxide was used as the titrant.

[0071] Weight loss of flux at 400℃

[0072] Thermogravimetric analysis (TG) was performed according to JIS K 7120:1987. The weight loss of flux at 400°C was measured as the heating weight loss. It should be noted that the results of Example 1 and Comparative Example 1 are shown below. Figure 5 It should be noted that, in Figure 5 In the figure, the vertical axis represents the weight residual rate R (unit: %), and the weight loss due to heating D (unit: %) is calculated by the following formula (1). It should be noted that in sleeve welding, the temperature in the heating process is generally above 400°C, so the weight loss due to heating of the flux at the minimum temperature of 400°C is measured.

[0073] D = 100 - R···(1)

[0074] Halogen content

[0075] The determination was performed by combustion ion chromatography. A Nittoseiko Analytech AQF-2100H combustion apparatus and a Thermo Fisher ICS-1100 ion chromatography apparatus were used, and the determination was performed according to BS EN 14582:2016. The combustion apparatus conditions were: inlet temperature 900℃, outlet temperature 1000℃, air flow rate 200 mL / min, O2 flow rate 400 mL / min, WSAG flow rate 100 mL / min; the IC conditions were: flow rate 1.2 mL / min, sample injection volume 25–100 μL, and determination time 23 min.

[0076] "Dirty Assessment"

[0077] As in Implementation 1 Figure 1 (a)~ Figure 1 As shown in (c), continuous soldering is performed on the printed circuit board 12 having through holes 120. An Apollo Seiko J-CAT 300SLV is used as the sleeve-type soldering machine 2. Dirt accumulates on the inner wall of the sleeve (i.e., the cylindrical main body 21) (see reference). Figure 3 (b) If the tip of the soldering iron becomes clogged with dirt, poor soldering results. As a result, a good solder joint cannot be formed. By letting the pin fall into the sleeve, the change in inner diameter caused by dirt accumulation is confirmed. A change in inner diameter of 0.5 mm within 1.3 mm is defined as the clogging life, and the number of consecutive soldering shots up to the clogging life is defined as the clogging shot count. A clogging shot count of 15,000 or more is considered good (i.e., ○), and less than 15,000 is considered poor (i.e., ×). The higher the clogging shot count, the less likely dirt is to accumulate. If it is 15,000 or more, for example, if the time required for soldering at each point (specifically, including the time from the sleeve soldering device to the processing point) is 2 seconds, the limit is reached at 30,000 seconds (i.e., 8.3 hours). Therefore, for example, if the operation is divided into two days, since the operation time is about 8 hours, there is no need for a mid-operation stop for cleaning during one operation.

[0078] It should be noted that the evaluation criteria of this method are strict, and the number of clogging ejections, even at a level of, for example, 12,000 or higher, is considered sufficiently high, which can be said to fully exert the effect of inhibiting dirt accumulation. That is, the number of clogging ejections is preferably 12,000 or higher, more preferably 13,000 or higher, even more preferably 14,000 or higher, and even more preferably 15,000 or higher.

[0079] "Wetting properties"

[0080] Similar to the contamination evaluation, the printed circuit board 12 with through-holes 120 was soldered using soldering machine 2. Wetting performance was then evaluated by the red-eye rate on both sides of the pads. Red-eye refers to the phenomenon where, during soldering, the solder fails to wet and spread across the entire pad, leaving exposed copper foil on a portion of the pad. The evaluation is based on… Figure 4 The indicators shown are used. Based on 80 points... Figure 4 Evaluation of red-eye rate. Compared with ECO-SOLDER RMA02 manufactured by Senju Metal Industries, if the result is better than ECO-SOLDER RMA02, it is judged as ◎; if it is equal, it is judged as 0; if the result is worse than ECO-SOLDER RMA02, it is judged as ×. It should be noted that ECO-SOLDER RMA02 manufactured by Senju Metal Industries meets JIS AA level (JIS Z3197:2012).

[0081] "Insulation resistance"

[0082] The procedure was performed according to JIS Z3197:20128.5.3. Specifically, the resin core solder was soldered to a comb-shaped substrate, and the substrate was subjected to high temperature and high humidity conditions of 85°C and 85% RH. An ion migration evaluation system, Espec AMI-150-U-5, was used, and a voltage of 100V was applied to measure the resistance. JIS Z 3283:2017 specifies that the insulation resistance value after 168 hours should be used for measurement; however, in this application, the lowest value (minimum value) of the insulation resistance during 168 hours under conditions more stringent than the JIS standard will be used as the evaluation benchmark. JIS AA grade specifies 1×10⁻⁶. 9 Ω or higher, therefore the minimum insulation resistance value is set to 1×10. 9 Conditions with an insulation resistance of Ω or higher are considered acceptable (i.e., marked "○"), and the minimum insulation resistance value is less than 1×10⁻⁶. 9 When the value is Ω, it is evaluated as unqualified (i.e., "×").

[0083] [Table 1]

[0084] Table 1

[0085]

[0086] As can be seen from Table 1, when the flux is mainly composed of rosin with a substantially zero acid value (specifically Examples 1 to 5), it is possible to suppress the accumulation of dirt inside the cylindrical soldering iron body 21. Furthermore, the wettability is good, and the insulation resistance is sufficiently high, resulting in excellent insulation reliability. In contrast, when rosin without an acid value, i.e., when rosin with a substantially zero acid value is not the main component (specifically Comparative Example 1), dirt tends to accumulate.

[0087] In addition, by Figure 6 It is understood that the total acid value of the flux is correlated with the number of blocked injections; when the total acid value is below 60 mg KOH / g, the number of blocked injections becomes sufficiently high. Furthermore, by further reducing the total acid value as described above, the number of blocked injections can be increased to, for example, 15,000 or more. It should be noted that... Figure 7 It is understandable that the total acid value is correlated with the content of acid-free rosin in the flux.

[0088] In addition, by Figure 8 It is understandable that when the flux weight loss upon heating at 400°C is less than 55% by mass, the number of blocked injections increases. Furthermore, due to... Figure 9 It is understandable that when the halogen content in the flux is below 4% by mass, the insulation resistance becomes sufficiently high, enabling the manufacture of welded products with excellent insulation reliability. It should be noted that... Figure 9 In addition to Examples 1-5 and Comparative Example 1, flux was also prepared separately, and the insulation resistance was evaluated. The evaluation results were also recorded.

[0089] This disclosure is not limited to the above-described embodiments, and can be applied to various embodiments without departing from its spirit.

[0090] Although this disclosure has been described with reference to embodiments, it should be understood that the invention is not limited to those embodiments or structures. This disclosure also includes various modifications and equivalent variations. Furthermore, various combinations, forms, and other combinations and forms comprising only one element, or more or less thereof, also fall within the scope and spirit of this disclosure.

Claims

1. A method for manufacturing a welded product, comprising manufacturing a welded product (1) by welding a welded part (11), comprising: In the solder supply process, a cylindrical soldering iron (2, 21) with a through hole (22) is brought into contact with the part to be soldered, and a solder wire piece (3) is supplied to the part to be soldered through the through hole. The heating process involves heating the wire bond piece with the soldering iron to melt the wire bond piece at the soldering location; and The curing process involves welding the welded parts by solidifying the molten material (34) of the bonding wire pieces. The wire bonding sheet consists of a core (31) containing flux and a coating (32) containing solder alloy covering the core. The flux is mainly composed of rosin with an acid value of less than 10 KOH mg / g. The total acid value of the flux is 20-60 KOH mg / g.

2. The method for manufacturing the welded product according to claim 1, wherein, The flux contains rosin with an acid value of less than 10 KOH mg / g at a rate of 60% or more by mass.

3. The method for manufacturing the welded product according to claim 1 or 2, wherein, The flux further comprises rosin with an acid value of 150 KOH mg / g or higher.

4. The method for manufacturing the welded product according to claim 1 or 2, wherein, The flux loses less than 55% by mass when heated at 400°C.

5. The method for manufacturing the welded product according to claim 3, wherein, The flux loses less than 55% by mass when heated at 400°C.

6. The method for manufacturing a welded product according to claim 1 or 2, wherein, The flux further contains halogen-based activators, and the halogen content in the flux is less than 4% by mass.

7. The method for manufacturing a welded product according to claim 3, wherein, The flux further contains halogen-based activators, and the halogen content in the flux is less than 4% by mass.

8. The method for manufacturing a welded product according to claim 4, wherein, The flux further contains halogen-based activators, and the halogen content in the flux is less than 4% by mass.

9. The method for manufacturing a welded product according to claim 5, wherein, The flux further contains halogen-based activators, and the halogen content in the flux is less than 4% by mass.

10. The method for manufacturing a welded product according to claim 1 or 2, wherein, The welded product is for vehicle use.

11. The method for manufacturing a welded product according to claim 3, wherein, The welded product is for vehicle use.

12. The method for manufacturing a welded product according to claim 4, wherein, The welded product is for vehicle use.

13. The method for manufacturing a welded product according to claim 5, wherein, The welded product is for vehicle use.

14. The method for manufacturing a welded product according to claim 6, wherein, The welded product is for vehicle use.

15. A method for manufacturing a welded product according to any one of claims 7 to 9, wherein, The welded product is for vehicle use.

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