JP2005021975A - Flux for joining unleaded solder, and solder paste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide flux for joining unleaded solder, and solder paste. <P>SOLUTION: The flux for joining unleaded solder contains phenolic hydroxyl compound selected from the group consisting of quercetin, myricetin, anthocyanidin, pro-anthocyanidin, caffeic acid, chlorogenic acid, protocatechuic acid, and ferulic acid. The solder paste contains this flux for joining unleaded solder and unleaded solder powder. A tin-zinc alloy solder powder is applicable for unleaded solder powder. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a lead-free solder joining flux and solder paste for forming electrical, electronic, or mechanical component joining with solder containing no lead. Specifically, the present invention relates to a lead-free soldering flux and solder paste capable of forming electrical and electronic components such as circuit boards by tin-zinc alloy solder.

  Soldering is a technique for joining objects using a metal having a relatively low melting point and has been used for a long time. In the modern industry, soldering is widely used for joining and assembling electronic equipment. In the mounting substrate, it is used for joining for mounting electronic components such as a semiconductor, a microprocessor, a memory, and a resistor on the substrate. The advantage of soldering is not only that the component is fixed to the board, but also that electrical connection is formed by the conductivity of the metal that constitutes the solder.

  Commonly used solder is a eutectic solder of tin and lead, and its theoretical eutectic point is 183 ° C., which is lower than the temperature at which many thermosetting resins are gasified. Solder is used for bonding substrates or the like, and has a feature that a printed circuit board or the like is not damaged by heat.

  Tin-lead eutectic solder with such features is indispensable for joining and assembling parts in the manufacture of electronic equipment, and it is a fine soldering process such as thick film formation, conductor circuit formation and semiconductor mounting. Is used as a paste-like solder paste in which solder powder and flux are mixed according to a screen printing method or the like.

  With the recent rapid spread of electronic devices such as personal computers and personal devices of portable terminals, the demand for solder in electronic component mounting technology is increasing. The widespread use of electronic devices makes people's lives rich, but a large amount of electronic devices that are no longer used are discarded, and environmental problems caused by these wastes have become a major debate. Therefore, it is desired to establish a manufacturing method that does not recycle waste or use harmful substances. In the manufacture of electronic equipment, the development of manufacturing technology that does not use hazardous substances is an urgent task.

Tin-lead eutectic solder has a property that the wettability with respect to the base material is superior to other metal mixtures. However, the lead contained in this solder, when discarded electronic equipment is disposed of in landfills, is exposed to acid rain for many years, leading to the release of lead ions into the soil and toxicity to living organisms including humans. There is a strong concern. In order to solve this problem, lead immobilization technology has been studied, but has not reached the practical range. Therefore, establishment of solder joint and electronic equipment mounting technology that does not discharge harmful lead ions is required, and joint technology using lead-free solder (lead-free solder) is required. For this reason, use of solder in which lead is replaced with another metal or a combination of another metal has been studied (for example, Patent Documents 1 and 2 below).
Japanese Patent No. 2805595 JP-A-10-58190

  However, in lead-free solder, there are many problems that hinder the generalization. Specifically, a tin-silver alloy solder proposed as a lead-free solder is difficult to use in a large amount as a general-purpose product because silver itself is a noble metal and is expensive. Furthermore, the use of silver is regulated in some countries (states) due to the toxicity of the emitted silver ions. In addition, most lead-free solders have a high melting point as an alloy, so the soldering temperature has to be raised, and due to the relationship with the heat resistance temperature of the thermosetting board, it brings great difficulty to specific mounting technology. ing. In other words, it is necessary to solve problems such as poor wettability with the base material and not exhibiting satisfactory jointability, and easily damaging electronic components to be joined due to high melting temperature.

  Also, a solder-free solder paste using screen printing is strongly desired. In recent years, technological improvements have been promoted, and lead-free solder, for example, tin-silver-bismuth or the like, solder paste is practically used. However, it is said that it is difficult to make a general use of tin-zinc eutectic solder having the same melting point as that of tin-lead eutectic solder.

  An object of the present invention is to solve the above-mentioned environmental problems caused by lead in waste, and to establish a lead-free soldering technique capable of realizing both workability and bonding performance when mounting electronic equipment.

  In addition, the present invention provides a solder bonding flux using tin-zinc alloy solder and a tin-zinc alloy solder paste suitable for practical use as a substitute for the conventional solder paste of tin-lead alloy solder. The purpose is to provide.

  The inventor of the present application is an antioxidant compound having a phenolic hydroxyl group in a flux to be mixed for preparing a solder paste of tin-zinc alloy solder or a flux used in advance when joining with a tin-zinc alloy solder. It has been found that the problem that a special working environment is required at the time of reflow and flow, and that heating at a temperature that damages the thermosetting substrate is necessary can be solved by adding.

  According to one aspect of the present invention, the lead-free solder joining flux contains a phenolic hydroxyl compound selected from the group consisting of quercetin, myricetin, anthocyanidins, proanthocyanidins, caffeic acid, chlorogenic acid, protocatechuic acid and ferulic acid. Is the gist.

  Moreover, according to one aspect of the present invention, a solder paste contains the above-mentioned lead-free solder bonding flux and lead-free solder powder.

  ADVANTAGE OF THE INVENTION According to this invention, the mixing | blending of a phenolic hydroxyl compound provides the solder paste which has favorable preservability and can form the joining by a tin-zinc solder favorable. Moreover, the flux which activates solder and expresses favorable wettability by using when forming the joint by a tin-zinc solder is provided. Accordingly, it is possible to promote lead-free bonding materials widely used in the manufacturing industry, which is extremely useful for industrial and environmental measures.

  The role of the flux in the solder paste used for soldering is to remove and clean the natural oxide film on the surface of the solder powder and the surface of the component to be soldered and to prevent reoxidation during the reflow process. In addition, there is a role of supporting and temporarily fixing members to be soldered until bonding is formed. Therefore, basically, the component (activator) that dissolves, decomposes or reduces the metal oxide to clean the metal surface and the binder component (binding agent) are essential components of the solder paste flux. However, in the case of a flux used for flow type soldering, the binder component is not essential. Such a flux is configured by blending various substances as required in order to efficiently express chemical action and mechanical action.

  Generally, the main component constituting the flux is a resin that covers the surface of the solder powder and the member to be soldered. For example, rosin resin (pine resin) mainly composed of abietic acid, polyester resin, acrylic resin, etc. These thermoplastic synthetic resins are used. The rosin resin is responsible not only for the mechanical action of the flux (action as a binder component) but also for the chemical action (action as an activator). In addition to these resin components, it retains the activator for supplementing chemical action such as detergency and improving solder bonding, auxiliary activator for assisting activator action, and printability as paste. The flux is prepared by appropriately selecting and mixing the thixotropic agent for the purpose, the solvent for dissolving and mixing them, and the like.

  When a solder paste is prepared by applying a flux for a tin-lead alloy solder to a tin-zinc alloy solder, a significant increase in viscosity occurs over time, and the solder paste tends to harden. In order to prevent this, it is effective to reduce the addition amount of a substance having a high acidity, but this also causes insufficient solder wetting due to a decrease in cleaning power. Thus, if the solder composition is different, it is necessary to optimize the blending of the flux accordingly, and it is extremely difficult to adjust the blending balance particularly in the case of solder containing zinc having strong oxidizing properties.

  Therefore, the present invention proposes a flux containing a phenolic hydroxyl compound, and when a solder paste of tin-zinc solder is prepared using the flux, deterioration of the flux due to active oxygen species, organic or inorganic peroxide, etc. In addition, since it is possible to suppress a decrease in solder wetting, the paste state can be stably maintained for a long period of time, and a good solder joint can be formed.

  Further, in the method of applying flux to a base material (member to be soldered) in advance and joining with solder (flow), if a flux containing a polyphenol compound is used, wetting of the base material, which is a drawback of tin-zinc solder, is performed. By improving the properties and preventing oxidation of the flux and the solder surface, reliable soldering becomes possible.

  The above effectiveness is naturally exhibited for lead-free alloy solders other than tin-zinc solder.

  Lead-free solders typically require bonding at high temperatures (eg, about 240 ° C. or more for tin-silver-copper solders), but according to the present invention, tin-zinc has a melting point very close to that of tin-lead eutectic solder. Bonding using solder is simplified. This facilitates the elimination of harmful lead from electronic devices, making it safe to recycle electronic components and discharging harmful lead ions into the soil even when the electronic components are discarded. Disappears. Furthermore, the working environment for mounting electronic components is improved, which is extremely useful for industrial and environmental measures.

(Phenolic hydroxyl compound used in the present invention)
In the present invention, quercetin, myricetin, anthocyanidin, proanthocyanidin, caffeic acid, chlorogenic acid, protocatechuic acid and ferulic acid are used as the phenolic hydroxyl compound (compound having a phenolic hydroxyl group). The above compound excluding ferulic acid is a polyphenol having two phenolic hydroxyl groups (polyhydric phenol), and ferulic acid is a compound in which one of the two hydroxyl groups of caffeic acid is methyl etherified. Quercetin, myricetin, anthocyanidin and proanthocyanidin are similar to flavonoids, and caffeic acid, chlorogenic acid and protocatechuic acid have a catechol structure.

  The above-mentioned compounds are all strong antioxidant substances contained in plants, quercetin is contained in a large amount in onions, peas, asparagus, etc., myricetin is contained in strawberries, cranberries, etc., anthocyanidins and proanthocyanidins are Shiso, etc., caffeic acid is contained in coffee, chlorogenic acid is contained in olives, soybeans, protocatechuic acid is contained in buckwheat, and ferulic acid is contained in rice bran.

  Phenolic hydroxyl groups are highly reactive with metals and oxygen, and all of the above phenolic hydroxyl compounds are antioxidants having a strong action as scavengers for active oxygen, and they also act on metals to form chelate complexes. Has the property of forming Therefore, when blended in the solder paste, it coordinates to the surface of the solder powder and exhibits antioxidant properties, and also coordinates to active metal species to reduce its activity, and the action of metal species and flux components Suppress.

  The antioxidant properties of the phenolic hydroxyl compounds are synergistically increased when used in combination with amino acids and vitamins, and these can be used in combination with the phenolic hydroxyl compounds in the flux of the present invention. Examples of amino acids include L-methionine, and examples of vitamins include vitamin C and vitamin E. Vitamin D, vitamin K, and the like also have actions similar to these.

(Action of phenolic hydroxyl compounds)
The active metal species has the property of acting as a catalyst in the solder paste to cause a polymerization reaction of organic components in the flux and increase the viscosity of the flux. However, the above-mentioned phenolic hydroxyl compounds, and amino acids and vitamins used in combination therewith have a function of coordinatingly acting on metals, and this property is due to the oxidation property of the solder powder surface due to its antioxidant properties. And the activity of the metal species eluted from the solder metal oxide can be reduced, and the progress of the polymerization reaction of the flux component by the metal species can be suppressed. Therefore, the stability of the solder paste in the non-heated state is improved. This action involves phenolic hydroxyl groups.

  In addition, oxidation of metal species is likely to proceed rapidly due to temperature rise, and in the heated state, direct oxidation reaction of solder with active oxygen species in the atmosphere, and organic or inorganic components in the flux due to active oxygen species The indirect oxidation reaction of the solder is caused by the peroxide generated by the oxidation of the phenol, but the phenolic hydroxyl compound can suppress the direct oxidation and the indirect oxidation as described above due to its antioxidant action. Therefore, the solder surface is protected until the above compound is decomposed, and oxidation promotion by heating is prevented.

  When the solder paste according to the present invention is heated to the melting temperature of the solder, the flux is vaporized and decomposed, and the phenolic hydroxyl compound is decomposed. The function of the activator component is more heat-resistant than the other flux components including the antioxidant component, and the activator of the flux reacts with the metal on the surface of the solder powder, and the purification of the metal surface proceeds and is activated. The original wettability is exhibited and good soldering is performed. Amino acids and vitamins that can be used in combination also contribute to the progress of soldering by the same reaction.

  In the tin-zinc alloy solder, zinc is an active metal species, and zinc has a property of forming a thin layer with a high concentration on the solder surface in the tin-zinc system. In other words, zinc is not only easily oxidized but also has the property of being concentrated on the most oxidized surface, so it is extremely important to be able to suppress the action of zinc on oxidation and flux components. For this, the action of phenolic hydroxyl compounds is very effective.

(Flux and solder paste)
The flux according to the present invention is obtained by blending a phenolic hydroxyl compound with a flux main material, and the flux main material includes a commonly used flux or its components (the aforementioned activator, auxiliary activator, etc.). Can be selected and used as appropriate. For example, polymerized rosin, organic acid, organic amine compound, glycerin, ethylene glycol, various alcohols, water, and the like can be used as components of the flux main material.

  The solder paste of the present invention is prepared by preparing solder powder and mixing with the above-prepared flux, that is, a flux containing a phenolic hydroxyl compound. The solder powder is prepared by granulating a molten solder alloy. For example, tin-zinc solder powder is prepared by granulating a molten tin-zinc alloy. When the solder paste is applied to a soldering member and reflowed (heated), the flux reacts, vaporizes or decomposes, and a bond is formed by the molten solder. As an effective aspect of the solder paste manufacturing process considering the action of the phenolic hydroxyl compound, the solder powder is contacted with the phenolic hydroxyl compound and surface-treated, and then mixed with the flux main material or the flux containing the phenolic hydroxyl compound. There is a form to do.

  You may use the flux which mix | blended the phenolic hydroxyl compound of this invention, apply | coating as it is to the member surface to join to solder, and activating a member surface, without preparing a solder paste. It is also possible to perform flow bonding by placing ball-shaped solder, granular solder, solder pellets or the like on the member to which the flux is applied. Also, flux may be applied to the surface of a solder material such as wire solder, ball-shaped solder, solder pellets, etc., and used for soldering. In this case, a paste-like physical property for holding the members to be joined is not essential, and it is not necessary to use a component having a binder (binding agent) function. Preferably there is. Furthermore, the flux of the present invention can also be used as a protective agent for solder materials.

(Flux composition)
As the main component of the flux, a rosin resin (pine resin) mainly composed of abietic acid or a thermoplastic synthetic resin can be used as a binder component. Specific examples of the rosin resin include gum rosin, wood rosin, tall rosin and these There are modified rosins and rosin esters obtained. Examples of the thermoplastic synthetic resin include polyester resins and acrylic resins. The rosin resin also functions as an activator. The content of the resin in the flux is preferably about 10 to 60% by mass.

  As an activator for cleaning the metal surface by dissolving, decomposing or reducing the metal oxide and improving the bonding property of the solder, in addition to the rosin resin, a hydrohalide of amines or the like can be used. The content of the activator in the flux is preferably about 0 to 10% by mass.

  The content of the auxiliary activity flux that assists the action of the activator is preferably about 0.1 to 20% by mass.

  As a thixotropic agent for maintaining the printability of the solder paste, stearamide or the like can be used. The content of the thixotropic agent in the flux is preferably about 5 to 60% by mass.

  As a solvent for dissolving and mixing the above components, glycerin, isopropanol, butanol and the like can be used. The content of the solvent in the flux is preferably about 5 to 60% by mass.

  An organic acid is added to give the solder a gloss. For example, there are citric acid, lactic acid, adipic acid, stearic acid and the like. The amount of such organic acid used is preferably about 0.5 to 30% by mass of the flux.

  An organic amine compound is added in order to prevent sagging by adjusting the pH of the flux or to form a good round solder joint. Examples of commonly used ones include monoethanolamine, stearylamine, diphenylamine, ethylamine, propylamine, diethylamine, aniline, and salts thereof. The amount of such an organic amine compound used depends on the content of the organic acid, activator, etc., but is generally preferably about 0.5 to 30% by mass of the flux.

  The flux of the present invention is obtained by adding a phenolic hydroxyl compound to a flux main material blended by appropriately selecting the above components.

  The phenolic hydroxyl compound is added in the flux so as to be about 1 ppm to 5 mass%, preferably about 3 ppm to 2 mass%. When amino acids or vitamins are used in combination, the addition amount of amino acids is preferably about 100 ppm to 5 mass%, and the addition amount of vitamins is preferably about 100 ppm to 10 mass%. Both amino acids and vitamins may be used. These additives are added and mixed together with other blending components when preparing the flux according to a conventional method.

(Preparation and use of solder paste)
A solder paste with excellent performance is prepared by mixing the flux with a solder powder for paste prepared to have a particle size of about 4 to 100 μm, preferably about 10 to 50 μm. The solder powder and the flux are usually mixed at a ratio (mass ratio) of about 9: 1. When soldering, the solder paste applied on the metal is reduced in volume by about 1/2 due to reflow. The amount of the solder paste applied to the member to be soldered is preferably an amount that provides a thickness of about 150 to 200 μm.

  Lead-free solder includes tin-silver-copper ternary alloy, tin-copper alloy system, tin-bismuth alloy system, tin-zinc alloy system, etc., and any of these can be used, but among these, the melting point is tin- A tin-zinc alloy system close to a lead eutectic alloy is particularly preferable for mounting. In the present invention, the tin-zinc alloy solder can contain a trace amount of silver, bismuth, nickel, aluminum, magnesium, indium and the like.

  The flux to which the phenolic hydroxyl compound of the present invention is added is particularly suitable for producing a solder paste of tin-zinc alloy solder. It is not limited to alloy particles having a tin-zinc eutectic composition, but may be alloy particles other than the eutectic composition, or may be a mixture of simple powders of tin and zinc. In particular, a mixture of simple powders of tin and zinc with a eutectic composition has particular advantages. That is, when the heating temperature reaches the eutectic temperature in the reflow operation, the solder powder particles of the eutectic composition start to melt on the entire outer surface, whereas the single particles of tin and zinc have a contact interface between the tin particles and the zinc particles. From this, a liquid that is susceptible to air oxidation is generated inside the lump of solder powder, and a decrease in wettability due to solder oxidation can be suppressed. Furthermore, considering that zinc is susceptible to oxidation, a solder powder in which zinc is coated with tin and the composition of the entire solder powder becomes a eutectic composition is a preferred form. The solder powder having such a multi-layer structure can be easily manufactured through the rolling of metal ingots and the pressing and cutting process.

  Since the melting temperature is increased and the wettability is remarkably lowered due to the oxidation of the solder, the solder powder to be used preferably has a low content of oxygen and oxide. If the solder powder used contains a large amount of oxygen or oxide, even if the surface of the solder powder is activated and melted by the flux, the melting temperature is increased by the oxide inside, so it does not melt and the reflow temperature is increased. There must be. As a result, air oxidation on the surface of the liquid layer is more likely to proceed, and sufficient wettability cannot be obtained even when a strong flux is used. Tin-zinc solder refined so that the inevitable metal impurities other than tin and zinc are 0.1 mass% or less and the oxygen concentration is 1,000 ppm or less, preferably 100 ppm or less, has good wettability and is active as a flux. Does not require expensive materials.

  After the solder paste prepared according to the above is applied onto a metal member to be soldered using a screen printing technique, the metal member to be joined is brought into contact with the metal member to be reflowed. In the reflow process, by heating to a temperature of about 100 to 170 ° C., the above-described flux activates the surface of the solder powder, and the solder powder and the metal member surface come into contact with each other. Subsequently, the solder powder is melted by heating to a reflow temperature at which the solder melts. Thereafter, the metal member is joined by soldering by cooling. The heating time to the reflow temperature is preferably 200 ° C. or less and 30 seconds or less, and 240 ° C. is preferably 10 seconds or less. If the heating is continued more than necessary, the oxidation of the solder easily proceeds.

  The reflow process is preferably performed in a non-oxidizing atmosphere, but can also be performed in an air atmosphere. In reflow in a non-oxidizing atmosphere, the solder powder is prevented from being oxidized, and the tin-zinc alloy breaks in the molten state or maintains low viscosity, and can be used to form dense bonds such as bonding of high-density mounting boards. Easy.

  The solder paste of the present invention can be applied not only to single-type metal members such as copper, gold, silver, nickel, aluminum, and SUS stainless steel, but also to bonding of alloy materials and composite metal materials. Further, it can sufficiently cope with fine soldering, and a thin metal member having a narrow gap can cope with soldering of a member having a line width and a line gap of about 0.3 mm. Therefore, it can be used for soldering for mounting a substrate and joining various electric and electronic parts. Examples of electrical and electronic parts include semiconductors, hard disks built into personal computers, liquid crystal panel electrical circuits, IC cards, cable connectors used for connecting personal computers and printers, optical connectors used for communication cables, Examples include automobile radiators.

  Examples of substrate mounting modes include single-sided surface mounting, double-sided surface mounting, double-sided surface-mounted leaded component mounting, single-sided surface-mounted leaded component mounting, and lead-through mounting. can do. Examples of the mounted parts include ceramic capacitors, inductors, jumpers, transistors, diodes, aluminum electrolytic capacitors, tantalum semi-fixed resistors, trimmers, coils, and the like as passive components. Typical examples of active components include IC and SI. Examples of the package shape include SOIC, SOP, QIP, QFP, PLCC, LCC, SOJ, MSP, PC-BGA, CSP, PLC, MCM, OE-MCM, and a high-density chip in which a plurality of chips are stacked.

  Depending on the material of the member to be joined, the member may be pre-coated in advance, and the pre-coating composition and pre-coating method can be appropriately selected.

  In the reflow process, it is more effective to use a reducing atmosphere. Examples of the reducing atmosphere include an atmosphere in which an inert gas such as nitrogen appropriately contains a reducing gaseous substance. Examples of reducing gaseous substances include hydrogen, alcohol vapors such as methanol, ethanol, and propanol, and acid vapors such as phosphoric acid and acetic acid.

  Since the solder paste of the present invention can be soldered using the solder paste apparatus and equipment used in the current electrical / electronic assembly manufacturing process, it is highly versatile and has a tin-zinc alloy. It is extremely useful in promoting lead-free joining of parts by solder. In addition, the use of tin-zinc binary alloy solder having a simple composition makes it easy to collect and recycle poorly joined parts and used parts, which is advantageous for metal recovery and reuse.

  Hereinafter, details of the present invention will be described by way of examples.

  (Test A) 91.2 parts by mass of metal tin and 8.8 parts by mass of metal zinc were heated and melted under reduced pressure, and the composition was 91.1 mass% or more of tin, 8.8 mass% of zinc, and the total amount of other trace elements of 0.1 mass. A tin-zinc solder containing less than% and containing 10 ppm of oxygen was prepared. The solder was granulated in a nitrogen atmosphere to obtain a solder powder having a particle size distribution of 20 to 40 μm. On the other hand, a flux main material comprising 54 parts by mass of polymerized rosin (pine resin), 35 parts by mass of hexylene glycol as a solvent, 5 parts by mass of hardened castor oil (thixotropic agent), 4 parts by mass of citric acid, and 1 part by mass of ethylamine hydrochloride is prepared. did. Using this flux main material as a flux, 89 parts by mass of the aforementioned solder powder was added to 11 parts by mass of the flux, and the mixture was stirred and mixed in a nitrogen atmosphere to prepare a solder paste.

  (Test B) A flux having a quercetin content of 0.2 mass% was prepared by adding quercetin to the flux main material prepared in test A, and a test was performed using this flux and the tin-zinc solder powder prepared in test A. A solder paste was prepared by stirring and mixing in a nitrogen atmosphere at the same mass ratio as A.

  (Test C) Myricetin was added to the flux main material prepared in Test A to prepare a flux having a myricetin content of 0.2 mass%, and this flux and the tin-zinc solder powder prepared in Test A were used for testing. A solder paste was prepared by stirring and mixing in a nitrogen atmosphere at the same mass ratio as A.

  (Test D) Anthocyanidin was added to the flux main material prepared in Test A to prepare a flux having an anthocyanidin content of 0.15 mass%, and this flux and the tin-zinc solder powder prepared in Test A were used for testing. A solder paste was prepared by stirring and mixing in a nitrogen atmosphere at the same mass ratio as A.

  (Test E) Proanthocyanidin was added to the flux main material prepared in Test A to prepare a flux having a proanthocyanidin content of 0.15 mass%, and this flux and the tin-zinc solder powder prepared in Test A were used. A solder paste was prepared by stirring and mixing in a nitrogen atmosphere at the same mass ratio as in Test A.

  (Evaluation of Solder Paste) For each of the solder pastes of Tests A to E, the viscosity and the spreading ratio in soldering according to JIS Z 3197 were measured. The remaining solder paste was stored for 1 month in a refrigerator set at 0 to 10 ° C., and the viscosity and the spreading rate in soldering were measured in the same manner. From these measured values, the rate of change in spreading was determined as a measure of wettability, and the rate of change in viscosity was determined as a measure of storage stability. The rate of change in expansion (%) is [100 × (expansion rate after storage−initial expansion rate) / initial expansion rate], and the rate of change in viscosity (%) is [100 × (viscosity after storage−initial viscosity) / [Initial Viscosity]], and numerical values of less than 1% were evaluated as A, 1% or more and less than 5% as B, and 5% or more as C. The results are shown in Table 1.

(Table 1)
Effects of adding phenolic hydroxyl compounds
Additives Initial spreading rate Initial viscosity Wet storability Shelf life
(%) (Pa · s)
Test A None 61 440 C C
Test B Quercetin 81 230 B A
Test C Myricetin 79 245 B A
Test D Anthocyanidin 76 244 B A
Test E Proanthocyanidins 77 242 B A

  (Test a) 91.1 parts by mass of metal tin and 8.8 parts by mass of metal zinc were heated under reduced pressure, the composition was 91.1 mass% tin, 8.8 mass% zinc, and the total amount of other trace elements was 0.1 mass%. A tin-zinc solder having an oxygen content of less than 10 ppm was prepared. On the other hand, a flux main material composed of 5 mass% urea, 10 mass% diethanolamine, 20 mass% triethanolamine, and 65 mass% water was prepared.

  (Test b) Caffeic acid was added to the flux base material prepared in Test a to prepare a flux having a caffeic acid content of 0.5 mass%.

  (Test c) Chlorogenic acid and vitamin C were added to the flux main material prepared in test a to prepare a flux having a chlorogenic acid content of 0.5 mass% and a vitamin C content of 1.0 mass%.

  (Test d) Protocatechuic acid was added to the flux main material prepared in Test a to prepare a flux having a protocatechuic acid content of 0.5 mass%.

  (Test e) Ferulic acid was added to the flux base material prepared in Test a to prepare a flux having a ferulic acid content of 0.5 mass%.

  (Evaluation of flux I) On the copper base plate, the flux main material and flux of each of tests a to e and the tin-zinc solder piece prepared in test a are placed, and in a furnace in an air atmosphere according to JIS method. After heating to 220 ° C., the spreading rate that is a measure of wetting was measured. As a result, the spreading rate is the largest when the flux of test c is used (spreading rate = 78%), then test b (75%), test d (73%), and test e (70%) in that order. Test a in which no polyphenol compound was added showed the smallest value (56%). This result shows that the flux to which caffeic acid, chlorogenic acid, protocatechuic acid or ferulic acid, which are phenolic hydroxyl compounds, is added improves the wettability of the tin-zinc solder to the base material.

  (Evaluation of Flux II) Tin prepared in Example 1 while applying the flux main material and the flux of each of the tests a to e to a copper base material in advance on a copper base plate and heating to 220 ° C. in an air atmosphere. After soldering with the zinc solder piece in contact, a weight was attached and a creep test was performed at a temperature of 80 ° C., and the time until the soldered portion was broken (breakage time) was measured. When the fracture time in test a is 1, the fracture time in each test was test b (3.1), test c (3.5), test d (3.0), and test e (3.1). It was. This result shows sufficient bonding strength with respect to the base material of the tin-zinc solder when the flux added with the phenolic hydroxyl compound is used, and indicates that the occurrence of poor bonding of the solder is suppressed.

Claims (7)

  A lead-free solder bonding flux comprising a phenolic hydroxyl compound selected from the group consisting of quercetin, myricetin, anthocyanidin, proanthocyanidin, caffeic acid, chlorogenic acid, protocatechuic acid and ferulic acid.   The lead-free soldering flux according to claim 1, further comprising an activator for dissolving, decomposing or reducing the metal oxide.   The solder bonding flux according to claim 1 or 2, further comprising a compound selected from the group consisting of methionine, vitamin C, and vitamin E, wherein the lead-free solder joint is a tin-zinc alloy solder joint.   A solder paste comprising the lead-free solder bonding flux according to claim 1 and a lead-free solder powder.   The solder paste according to claim 4, wherein the lead-free solder powder is a tin-zinc alloy solder powder.   The tin-zinc alloy solder powder is a tin-zinc eutectic alloy solder powder or contains at least one metal selected from the group consisting of bismuth, silver, copper, aluminum, nickel, magnesium, and indium. The solder paste according to claim 5. The solder paste according to any one of claims 4 to 6, wherein the lead-free solder bonding flux contains a binder component, an auxiliary activator, a thixotropic agent, and a solvent.