JP4079026B2 - No residue solder paste - Google Patents

Description

【００６６】
本発明のソルダペーストは、従来のロジン系フラックスを用いた比較例２のソルダペーストに近い流動特性 (粘度およびチキソ比) を示し、保存安定性、印刷性、ぬれ性のいずれも良好であった。また、リフロー後は無残渣であり、無洗浄で樹脂コーティングして、密着性のよい樹脂皮膜を形成できた。
【００６７】
これに対し、比較例１のソルダペーストは、無残渣で樹脂コーティングの密着性はよかったが、流動特性が不良である (粘度とチキソ比のいずれも低い) ため、保存安定性が悪く、印刷にも適していなかった。比較例２の従来のロジン系フラックスから調製したソルダペーストは、大量のフラックス残渣が残り、無洗浄では樹脂コーティングの密着性が悪かった。比較例３の低残渣ペーストも、無洗浄では樹脂コーティングの密着性を得ることができなかった。
【００６８】
【発明の効果】
本発明にかかるソルダペーストは、印刷性が良いにも関わらず、リフロー時にフラックス成分のほとんどが蒸発してしまい、フラックス残渣が残らないことから、フラックス残渣による問題、具体的には、外観、ピンコンタクト性、防湿保護コーティング剤との密着性が良好で、信頼性が要求される電子機器に組み込まれるワークのはんだ付けに無洗浄で使用できる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solder paste that allows a resin coating or a resin molding to be performed without washing and that has little or no flux residue after reflow soldering.
[0002]
[Prior art]
Solder paste is a bonding material obtained by mixing powder solder and paste-like flux. Solder paste is applied to the soldering part of a work such as a printed circuit board or silicon wafer (workpiece, the same shall apply hereinafter) by printing or discharging, and then heated in a heating furnace to melt the solder for soldering. Adhere to the part. This soldering method is generally called a reflow method. Various heating means such as infrared rays, laser beams, hot air, and hot plates can be employed for the heating furnace (also called a reflow furnace). The solder paste is required to have a viscosity suitable for a printing method or a discharge method.
[0003]
In general, the solder paste flux is obtained by dissolving solid components such as rosin (pine resin), thixotropic agent and activator with a liquid solvent to obtain an appropriate viscosity. Since the conventional solder paste is obtained by dissolving a solid component with a solvent, a large amount of the solid component remains as a flux residue in the soldered portion after reflow. In this way, if a large amount of flux residue remains in the soldered part, the appearance will be poor and the pin contact will be hindered, and the flux residue will absorb moisture, reducing the insulation resistance between the work circuits, and corrosion products. May occur, causing the problem of disconnecting the circuit. For this reason, after reflowing a workpiece incorporated in an electronic device that requires high reliability, the flux residue on the soldered portion must be cleaned and removed with a cleaning liquid.
[0004]
In addition, in an electronic device or the like mounted on a car, resin coating or molding is performed in which a soldering portion is coated with a resin serving as a moisture-proof protective agent or the entire workpiece is molded in order to ensure reliability. Since the flux residue hinders the adhesiveness of the resin, it was necessary to remove the flux residue by washing the workpiece in advance.
[0005]
Cleaning to remove the flux residue requires using fluorinated or chlorinated solvents that easily dissolve rosin. When these solvents evaporate and reach the sky, they destroy the ozone layer surrounding the earth. Since harmful UV rays from the sun can reach the earth in large quantities and cause human skin cancer, its use is now regulated.
[0006]
In addition, since electronic devices are mounted at high density and the interval between components is narrow, it has become difficult to perform complete cleaning.
One of the applicants of this patent has proposed a low-residue solder paste that does not require cleaning after reflow for soldering a workpiece incorporated in an electronic device that requires high reliability (Japanese Patent No. 2500018). . Since this low-residue solder paste contains rosin, it does not eliminate the flux residue, and it remains a quantity of flux that does not cause harm in normal use.
[0007]
The flux residue after reflowing with the low-residue solder paste does not cause a problem in general electronic devices that require high reliability. However, today's ultra-reliable electronic devices are not perfect. Further, since a small amount of residual flux residue impairs the adhesiveness of the resin, it could not be used without washing in the case of resin coating or resin molding.
[0008]
Accordingly, a residue-free solder paste is required which has a flux residue remaining after reflow of 1% or less of the flux and does not cause any adverse effects due to the flux residue even without washing.
[0009]
Rosin is a natural resin based on abietic acid and its isomers. Rosin has been considered to be an indispensable component for solder paste fluxes for viscosity adjustment, electronic component adhesion retention, and reduction and removal of oxides by abietic acid. However, if rosin is present in the solder paste flux, the rosin component always remains as a flux residue after reflow. Therefore, rosin cannot be used for a flux for a residue-free solder paste in which 99% or more of the flux does not remain after reflow.
[0010]
Several residue-free solder pastes that do not contain rosin have been proposed.
In Japanese Patent Laid-Open No. 2-25291, reflow is performed in a reducing atmosphere in which powder solder and a binder made of polyhydric alcohol having a boiling point between the solid phase line and liquid phase line of the powder solder are mixed. A solder paste containing no flux is described.
[0011]
Similarly, Japanese Patent Application Laid-Open No. 2-290693 describes a solder paste comprising solder fine particles and an alcohol having a boiling point higher than the melting point of the solder. This solder paste may contain an activator, a fatty acid amide, and the like that can be vaporized above the melting point of the solder.
[0012]
Japanese Patent Application Laid-Open No. 9-94691 discloses a residue containing an organic polyhydroxy compound having an evaporation temperature of 170 ° C. or higher and a solder solid phase temperature or higher as determined by thermal gravimetry (TG method). There are no solder pastes.
[0013]
[Patent Document 1]
Japanese Patent No. 2500018
[Patent Document 2]
JP-A-2-290693
[Patent Document 3]
Japanese Patent Laid-Open No. 2-25291
[Patent Document 4]
Japanese Patent Laid-Open No. 9-94691
[0014]
[Problems to be solved by the invention]
Residue-free solder paste does not contain rosin and has the same good component retention (adhesiveness), storage stability, and printability as conventional solder paste using rosin-based flux In addition, when ensuring properties such as dischargeability (transferability) and wettability, and further containing a solid or highly viscous component such as a thixotropic agent or an activator in the flux, it is also necessary to evaporate them during reflow.
[0015]
None of the residue-free solder pastes described in Patent Documents 2 to 4 described above have good flow characteristics. That is, the viscosity is low and the thixotropy is insufficient. For this reason, the solder powder is easily separated from the flux, the storage stability is poor, the printability in screen printing using a metal mask is poor, and the discharge from the syringe may be difficult. Furthermore, the component retention is not sufficient.
[0016]
Although the present invention does not contain rosin and is non-residue, it can impart optimal flow characteristics to the flux, and has component retention, storage stability, printability, dischargeability, and wettability. It is an object of the present invention to provide a residue-free solder paste that can perform resin coating and resin molding without washing after reflow soldering.
[0017]
[Means for Solving the Problems]
The present inventors use a combination of a solid solvent and a highly viscous solvent in addition to a commonly used liquid solvent as a flux solvent, so that the optimum flow for the flux can be achieved without using any rosin. It has been found that characteristics can be imparted. It has also been found that some thixotropic agents and activators do not evaporate alone at the reflow temperature, but evaporate together with them in the presence of a solid solvent and a highly viscous solvent. If necessary, by using such a thixotropic agent and / or activator, printability, ejection property, component retention, wettability, storage stability are good, and little or no flux residue remains after reflow. It was found that no residue-free solder paste was obtained and the present invention was completed.
[0018]
  Here, the present invention is a solder paste for reflow soldering in which powder solder and paste-like flux are mixed, and the flux is a solid at room temperature and evaporates at the reflow temperature.Ten ~ 40 mass%Evaporates at reflow temperature with a highly viscous fluid at room temperatureIs isobornylcyclohexanolHigh viscosity solvent20 ~ 50 mass%When,The rest,At least one liquid solvent that is liquid at room temperature and evaporates at reflow temperatureConsist ofThis is a residue-free solder paste.
[0019]
In the present invention, the term “highly viscous solvent” means that the solvent has a viscosity at 30 ° C. of 10,000 cps or more and is a syrupy fluid at room temperature. Further, “no residue” means that the amount of flux residue is 1% by mass or less in the flux.
[0020]
In order to increase the thixotropy and wettability of the solder paste, the flux may further contain at least one additive component selected from a thixotropic agent and an active agent. Use one that evaporates with the ingredients.
[0021]
In a particularly preferred embodiment of the invention, the flux has the following composition in mass%:
20-50% highly viscous solvent consisting of isobornylcyclohexanol,
10-40% of at least one solid solvent selected from 2,5-dimethylhexane-2,5-diol and trimethylolpropane;
From a mixture of at least one carboxylic acid amine salt selected from oxalic acid monoethanolamine salt and malonic acid monoethanolamine salt and at least one carboxylic acid selected from adipic acid and substituted or unsubstituted benzoic acid 1-20% active agent,
Optionally, 5-12% stearamide and / or bis (p-methylbenzylidene) sorbitol as a thixotropic agent is 1% or less,
A liquid solvent in which the balance is selected from octanediol and tetraethylene glycol.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
In the residue-free solder paste of the present invention, the flux contains three types of solvents having different properties at room temperature: at least one solid solvent, at least one high-viscosity solvent, and at least one liquid solvent. . Each solvent can be evaporated at the reflow temperature, that is, its boiling point or decomposition temperature is lower than the reflow temperature.
[0023]
Solid solvent and highly viscous solvent replace rosin in conventional solder paste, and by using both together, the flow characteristics are the same as when rosin is used, and therefore good transferability and parts retention. And storage stability can be imparted to the solder paste. This flow characteristic can be evaluated by viscosity and thixo ratio according to JIS Z3284-6. In this test method, the thixo ratio is preferably in the range of 0.35 to 0.60, more preferably 0.4 to 0.6, and most preferably 0.5 to 0.6.
[0024]
The total content of the highly viscous solvent and the solid solvent in the flux is preferably 30 to 90% by mass. If the content is less than 30% by mass, the thixo ratio is low and printing may be difficult. On the other hand, when the content exceeds 90% by mass, the viscosity becomes too high to form a paste. This total content is preferably 40 to 70% by mass, more preferably 45 to 65% by mass.
[0025]
The mass ratio between the solid solvent and the highly viscous solvent is selected according to the types of both solvents so that the flow characteristics of the flux approach those of a conventional rosin flux. Generally, the mass ratio of solid solvent: high viscosity solvent is in the range of 5: 1 to 1:10.
[0026]
Preferred solid solvents for use in the present invention are 2,5-dimethylhexane-2,5-diol and trimethylolpropane, and the high viscosity solvent is isobornylcyclohexanol. In this case, the mass ratio of solid solvent: high viscosity solvent is preferably in the range of 2: 1 to 1: 5. Specifically, the amount of the solid solvent is preferably 10 to 40% by mass, and the amount of the highly viscous solvent is preferably 20 to 50% by mass.
[0027]
In addition to the solid solvent and the high-viscosity solvent, a liquid solvent is also used for the purpose of dissolving an additive component such as an activator and a thixotropic agent that can be added to the flux and adjusting the viscosity so that proper flow characteristics can be obtained.
[0028]
Preferred liquid solvents for use in the present invention are octanediol and tetraethylene glycol. These liquid solvents exhibit thixotropic properties and can improve the flow characteristics of the flux.
[0029]
The preferred solid solvents, high viscosity solvents, and liquid solvents listed above are all monovalent or polyvalent hydroxy compounds, and exhibit a reducing action similar to that of rosin during reflow, thus improving wettability.
[0030]
In this way, in the present invention, only three kinds of solvents, solid, high viscosity and liquid, used for the flux can give the solder paste proper flow characteristics and wettability to some extent. Even when only these solvents are used, they can be used for soldering depending on the reflow conditions and applications.
[0031]
However, an additive such as a thixotropic agent or an activator is preferably included in the flux in order to further improve the flow characteristics and wettability of the flux to the level of the rosin flux. In order for the solder paste to be “residue free” which is the object of the present invention, these additives must also be evaporated during reflow. In the conventional residue-free solder paste, since the active agent and thixotropic agent are difficult to evaporate, they are not included at all, or even if they are included, they are limited to those that vaporize at the reflow temperature, and have sufficient activity or fluidity Those with improved characteristics could not be used.
[0032]
In the present invention, the flux contains a large amount of a solid solvent and a highly viscous solvent that evaporate at the reflow temperature. In that case, it was found that even when the additive does not evaporate alone at the reflow temperature, the additive may evaporate together with these solvents when the solid solvent and the highly viscous solvent evaporate. In the present invention, materials that can evaporate together with other components at the reflow temperature can be used as additives such as thixotropic agents and activators. This is meant to include both compounds that evaporate alone at the reflow temperature and compounds that cannot evaporate without a solid solvent or a highly viscous solvent.
[0033]
The thixotropic agent has a function of improving the flow characteristics so as to prevent the separation of the solder powder and the flux having different specific gravities in the solder paste and to improve the storage stability and to improve the transferability at the time of printing and discharging.
[0034]
Fatty acid amides such as hydrogenated castor oil and stearamide that have been mainly used as a thixotropic agent in rosin-based flux remain together with rosin as a flux residue after reflow. However, among these thixotropic agents, certain fatty acid amides evaporate with these solvents in accordance with the present invention in the absence of rosin and under conditions where large amounts of solid and highly viscous solvents evaporate. Therefore, it was found that it can be used for a residue-free solder paste. Accordingly, the preferred thixotropic agent used in the present invention is a fatty acid amide, and stearic acid amide is particularly preferable.
[0035]
The content of stearamide in the flux is preferably 3 to 12% by mass. When the amount is less than 3% by mass, the effect of suppressing separation of the flux and the powder solder does not appear, and when the amount exceeds 12% by mass, it is not completely evaporated together with other components, and a part thereof may remain as a flux residue.
[0036]
The activator has the action of reducing and removing oxides on the soldered portion and the surface of the powder solder to improve the wettability of the molten solder and to adhere to the soldered portion metallically. As flux activators, amines, amine hydrohalides, organic acids, amine salts of organic acids, phosphate esters, and the like have been used.
[0037]
Common solder pastes have used strong activators such as amine hydrohalides. However, this type of activator is not only difficult to evaporate at the reflow temperature, but also causes problems such as a decrease in insulation resistance and generation of corrosion products as described above when remaining in the flux residue.
[0038]
The active agent used in the present invention needs to evaporate alone or together with other ingredients at the reflow temperature. Such activators include carboxylic acids and amine salts of carboxylic acids. At least one of them may be used, but in general, the carboxylic acid amine salt has a higher activating effect, and therefore, when only one kind is used, it is preferable to use the carboxylic acid amine salt. However, since the carboxylic acid also has the advantageous feature of little change over time, it is more preferable to use a mixture of at least one carboxylic acid amine salt and at least one carboxylic acid as the activator.
[0039]
Preferred carboxylic acids as activators are adipic acid and substituted or unsubstituted benzoic acid. The substituent of benzoic acid is preferably one or more alkyl groups and / or alkoxy groups. Specific examples of the substituted benzoic acid include 4-butylbenzoic acid and 3,4-dimethoxy-benzoic acid. Preferred examples of the carboxylic acid amine salt as the activator include oxalic acid monoethanolamine salt and malonic acid monoethanolamine salt.
[0040]
The content of the activator in the flux is preferably 1 to 20% by mass, more preferably 3 to 15% by mass. If the amount is too small, the activation (removing action of the oxide) is insufficient. If the amount is too large, the powder solder in the solder paste may be chemically adversely affected. When the activator contains a carboxylic acid amine salt, the content of the carboxylic acid amine salt is preferably in the range of 1 to 6% by mass.
[0041]
In the solder paste of the present invention, the flux may contain an additive component that does not evaporate during reflow as long as the amount is 1% by mass or less. Even if all the components remain as a flux residue, if all other components are evaporated, the flux residue becomes 1 mass% or less of the flux. In the present invention, since the flux contains a large amount of a solid solvent and a highly viscous solvent, such non-evaporable components can also evaporate during reflow, so the actual flux residue may be further reduced. There is. Preferably, the content of the non-evaporable component in the flux is 0.5% by mass or less. This non-evaporable component is preferably one that does not adversely affect wettability or adhesion even if a trace amount remains as a flux residue.
[0042]
One example of such a non-evaporable component is bis (p-methylbenzylidene) sorbitol, a thixotropic agent that is effective in improving the drooling properties upon heating. This thixotropic agent is effective in a small amount of 1% or less, and by using this thixotropic agent, even if the stearamide is not contained, an appropriate flow characteristic can be imparted to the flux. Of course, these two types of thixotropic agents may be used in combination. The content of bis (p-methylbenzylidene) sorbitol in the flux is 1% by mass or less, preferably 0.5% by mass or less.
[0043]
The solder paste of the present invention is obtained by mixing powder solder with the flux having the above-described composition. The alloy composition of the powder solder used for the solder paste of the present invention is not particularly limited. Various solder alloys used today for bump formation and printed circuit board mounting can be used. Particularly preferred solder alloys are those having a liquidus temperature of 320 ° C. or lower. In this case, the reflow temperature is generally 350 ° C. or lower. The solder paste of the present invention is particularly suitable for use in reflow soldering where the reflow temperature is 200-350 ° C, preferably 240-320 ° C.
[0044]
The particle size of the powder solder may be, for example, in the range of 5 to 15 μm, but may be larger or smaller. The blending ratio of the powder solder and the flux varies depending on the particle size of the powder solder, but generally the flux may be 5 to 15% by mass. In the case of powder solder having the above particle size range, the flux amount is preferably 8 to 12% by mass.
[0045]
The solder paste of the present invention can be used in either a reducing atmosphere or a non-reducing atmosphere (including an inert gas atmosphere such as a nitrogen atmosphere and an air atmosphere). The reducing atmosphere may be, for example, an atmosphere containing hydrogen radicals described in JP-A-2001-58259 in addition to a general reducing atmosphere containing hydrogen gas.
[0046]
Reflow soldering in an atmosphere containing hydrogen radicals can be performed using a reflow furnace that is equipped with a hydrogen gas supply device and a plasma generator and that can be evacuated to a vacuum.
[0047]
When reflow soldering is performed in a reducing atmosphere using the solder paste of the present invention, the atmosphere gas exhibits an oxide removing action, and therefore it is not necessary to contain any activator in the flux. Alternatively, it may be a flux containing only one kind of carboxylic acid or carboxylic acid amine salt as an activator. When the reflow atmosphere is non-reducing, it is preferable to use both carboxylic acid and carboxylic acid amine salt as activators.
[0048]
【Example】
In the following Examples and Comparative Examples, a solder paste was prepared by thoroughly mixing the flux having the composition and amount described and powder solder. % Is% by mass unless otherwise specified.
[0049]
(Example 1)
Flux: 11%
Isobornyl cyclohexanol 42%
Trimethylolpropane 13%
Stearic acid amide 5%
4-Butylbenzoic acid 5%
3,4-dimethoxybenzoic acid 5%
Succinic acid monoethanolamine salt 3%
Octanediol 16.3%
Tetraethylene glycol 10.7%
Powder solder: 89%
Sn-3Ag-0.5Cu (particle size: 5-15 μm).
[0050]
(Example 2)
Flux: 11%
Isobornyl cyclohexanol 30%
Trimethylolpropane 20%
Stearic acid amide 8%
4-Butylbenzoic acid 5%
Malonic acid monoethanolamine salt 3%
Tetraethylene glycol 34%
Powder solder: 89%
Sn-3Ag-0.5Cu (particle size: 5-15 μm).
[0051]
Example 3
Flux: 10.5%
Isobornyl cyclohexanol 42%
2,5-dimethylhexane 2,5-diol 10%
Stearic acid amide 10%
Bis (p-methylbenzylidene) sorbitol 0.5%
Benzoic acid 9.5%
Succinic acid monoethanolamine salt 3%
Octanediol 15%
Tetraethylene glycol 10%
Powder solder: 89.5%
Sn-3Ag-0.5Cu (particle size: 5-15 μm).
[0052]
Example 4
Flux: 10%
Isobornyl cyclohexanol 30%
Trimethylolpropane 25%
Stearic acid amide 8%
Adipic acid 3%
Malonic acid monoethanolamine salt 3%
Octanediol 31%
Powder solder: 90%
Sn-37Pb (particle size: 5-15 μm).
[0053]
(Example 5)
Flux: 10%
Isobornyl cyclohexanol 42%
Trimethylolpropane 14%
3,4-dimethoxybenzoic acid 5%
4-Butylbenzoic acid 5%
Bis (p-methylbenzylidene) sorbitol 0.5%
Succinic acid monoethanolamine salt 2%
Octanediol 16.3%
Tetraethylene glycol 15.2%
Powder solder: 90%
Sn-3Ag-0.5Cu (particle size: 5-15 μm).
[0054]
(Comparative Example 1)
This comparative example exemplifies the solder paste described in JP-A-9-94691.
Flux: 11.7%
Trimethylolpropane 66.5%
Tetraethylene glycol 33.5%
Powder solder: 88.3%
Sn-2Ag-36Pb (particle size: 5-15 μm).
[0055]
(Comparative Example 2)
This comparative example illustrates a solder paste using a conventional rosin flux. Flux: 9.5%
Polymerized rosin 65%
Hydrogenated castor oil 7%
Diethanolamine HBr 2%
Diethylene glycol monobutyl ether 26%
Powder solder: 90.5%
Sn-3Ag-0.5Cu (particle size: 5-15 μm).
[0056]
(Comparative Example 3)
This comparative example illustrates a low residue solder paste.
Flux: 9.5%
Polymerized rosin 30%
Trimethylolpropane 30%
Hydrogenated castor oil 4%
Bis (p-methylbenzylidene) sorbitol 2%
Diethanolamine HBr 2%
Octanediol 32%
Powder solder: 90.5%
Sn-37Pb (particle size: 5-15 μm).
[0057]
The flow characteristics, storage stability, printability, wettability, appearance, and resin adhesion of the solder pastes of Examples 1 to 5 and Comparative Examples 1 to 3 were evaluated by the following test methods. The test results are summarized in Table 1.
[0058]
[Test method]
1. Flow characteristics (JIS Z3284-Appendix 6)
The viscosity and thixo ratio of the solder paste one day after production were measured with a PCU-505 viscometer (Malcom).
[0059]
2. Storage stability
The solder paste was stored at room temperature, the change with time in viscosity after 90 days was examined, and the storage stability was judged according to the following criteria:
A: The fluctuation range of the viscosity change is within 20%.
○: The fluctuation range of the viscosity change is 20% or more, but printing is possible.
X: The flux and the solder powder are separated, or the paste is so soft that it cannot be printed.
[0060]
3. Printability
Using a metal mask for an 8-inch wafer, solder paste was continuously screen-printed on 11 8-inch semiconductor wafers under the following conditions:
Printing speed: 0.8 mm / min,
Printing pressure: 1.0 kg / cm²,
Squeegee: Metal squeegee,
Metal mask thickness: 0.1 mm (laser processing)
Clearance width: 0.15 mm (dot shape) (34992 pieces).
[0061]
The dot missing rate of the 11th wafer was measured (JIS Z 3284-Appendix 7), and the printability was judged according to the following criteria:
A: Dot drop rate is over 90%,
○: Dot drop rate is 50 to 90%,
×: Dot drop rate is less than 50%.
[0062]
4. Wettability
A peak of about 20-50 ° C higher than the liquidus temperature of powder solder in an 8-inch semiconductor wafer printed with solder paste by a printability test in a hydrogen radical supply type reflow furnace described in JP-A-2001-58259 Soldering was performed at a temperature, and the wettability of the solder was judged according to the following criteria:
A: Solder is 100% spread on the land of the wafer.
○: The solder spreads to the land of the wafer by 99% or less.
X: Solder does not spread on the land of the wafer.
[0063]
5. Appearance
The soldered part of the work (wafer) after soldering was observed with a stereomicroscope to check for the presence of flux residue:
A: No or no flux residue (1% or less)
○: A small amount of flux residue is observed,
X: A large amount of flux residue is observed.
[0064]
6. Adhesion
The workpiece after appearance observation was returned to room temperature, and a coating solution for resin coating (Tuffy TF-1159 manufactured by Hitachi Chemical Co., Ltd.) was applied without washing. The resin-coated workpiece was subjected to 1000 cycles of thermal shock in a thermal shock bath of −30 ° C. to + 85 ° C., and then the state of peeling and cracking of the resin film was confirmed with a stereomicroscope and judged as follows:
A: The resin film is not peeled off from the workpiece, and no cracks are seen in the film.
○: The resin film is not peeled from the workpiece, but cracks are seen in the film.
X: The resin film has peeled from the workpiece.
[0065]
[Table 1]

[0066]
The solder paste of the present invention exhibited flow characteristics (viscosity and thixo ratio) similar to those of Comparative Example 2 using a conventional rosin flux, and had good storage stability, printability, and wettability. . Moreover, it was residue-free after reflowing, and it was possible to form a resin film with good adhesion by resin coating without washing.
[0067]
In contrast, the solder paste of Comparative Example 1 had no residue and good adhesion of the resin coating, but the flow characteristics were poor (both viscosity and thixo ratio were low), so the storage stability was poor and printing was difficult. Was also not suitable. The solder paste prepared from the conventional rosin flux of Comparative Example 2 left a large amount of flux residue, and the adhesion of the resin coating was poor without washing. The low-residue paste of Comparative Example 3 also failed to obtain resin coating adhesion without washing.
[0068]
【The invention's effect】
Although the solder paste according to the present invention has good printability, most of the flux components evaporate at the time of reflow, and the flux residue does not remain. It has good contact properties and adhesion to moisture-proof protective coating agents, and can be used without soldering for soldering workpieces incorporated in electronic devices that require reliability.

Claims (14)

A solder powder and a paste flux and the solder paste for reflow soldering mixed, flux, at least one and a solid solvent from 10 to 40% by weight is evaporated in a reflow temperature in solid state at normal temperature, high viscosity at room temperature evaporating the reflow temperature fluid, characterized with high viscosity solvent 20-50 wt%, which is the isobornyl cyclohexanol, balance, in that it consists of at least one liquid solvent to evaporate at reflow temperature is liquid at ordinary temperature, No residue solder paste. The residue-free solder paste according to claim 1, wherein the total amount of the solid solvent and the highly viscous solvent in the flux is 30 to 90% by mass. The residue-free solder according to claim 1 or 2, wherein the flux further contains at least one additive component selected from a thixotropic agent and an activator, and each additive component evaporates together with other components at a reflow temperature. paste. The residue-free solder paste according to any one of claims 1 to 3, wherein the solid solvent is selected from 2,5-dimethylhexane-2,5-diol and trimethylolpropane. The residue-free solder paste according to any one of claims 1 to 4 , wherein the liquid solvent is selected from alkanediols and polyalkylene glycols. The residue-free solder paste according to claim 5 , wherein the liquid solvent is selected from octanediol and tetraethylene glycol. The residue-free solder paste according to any one of claims 3 to 5 , wherein the thixotropic agent is selected from fatty acid amides. The residue-free solder paste according to claim 7 , wherein the thixotropic agent is stearamide. The residue-free solder paste according to any one of claims 3 to 8 , wherein the activator is at least one selected from a carboxylic acid and a carboxylic acid amine salt. The residue-free solder paste according to claim 9, wherein the activator contains both a carboxylic acid and a carboxylic acid amine salt. The residue-free solder according to claim 9 or 10 , wherein the carboxylic acid amine salt is selected from oxalic acid monoethanolamine salt and malonic acid monoethanolamine salt, and the carboxylic acid is selected from adipic acid and substituted or unsubstituted benzoic acid. paste. The residue-free solder paste according to any one of claims 1 to 11 , wherein the flux contains a component that does not evaporate at a reflow temperature in an amount of 1% by mass or less. A solder paste for reflow soldering in which powder solder and paste-like flux are mixed, wherein the flux has a composition of the following in mass%:
20-50% by mass of a highly viscous solvent comprising isobornylcyclohexanol,
10 to 40% by weight of at least one solid solvent selected from 2,5-dimethylhexane-2,5-diol and trimethylolpropane;
From a mixture of at least one carboxylic acid amine salt selected from oxalic acid monoethanolamine salt and malonic acid monoethanolamine salt and at least one carboxylic acid selected from adipic acid and substituted or unsubstituted benzoic acid 1 to 20% by mass of an active agent,
As a thixotropic agent, stearic acid amide is 3 to 12% by mass or bis (p-methylbenzylidene) sorbitol is 1% by mass or less,
A liquid solvent in which the balance is selected from octanediol and tetraethylene glycol. The residue-free solder paste according to any one of claims 1 to 13 , wherein the reflow temperature is 350 ° C or lower.