JP2019072724A - Powder for joining and paste for joining using the powder - Google Patents

Abstract

To provide a powder for joining and a paste for joining where comparatively high temperature reflow and high joining strength in a comparatively high temperature using environment are obtained even when the utilization ratio of rosin in a flux is reduced and the residue of the flux after reflowing is reduced.SOLUTION: In a tin-based powder for joining, the surface of a base powder containing tin and copper where the content of tin is 40 mass% or more and 60 mass% or less and the content of copper is 40 mass% or more and 60 mass% or less is coated with the layer of tin formate and copper formate. The base powder is desirably made of an intermetallic compound of tin and copper or desirably constituted with a coating layer made of a copper core and the intermetallic compound of tin and copper coating the core. A paste for joining contains the powder for joining and a flux and the content of rosin in the flux is 0 mass% or more and 2 mass% or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a bonding powder suitably used for mounting electronic parts and the like, and a bonding paste using the powder. More specifically, a bonding powder which achieves high bonding strength in a relatively high temperature reflow and relatively high temperature use environment even if the proportion of rosin used in the flux is reduced, and a flux residue after reflow, The present invention relates to a bonding paste using powder.

  The bonding paste is widely used for mounting of electronic parts, bonding of other parts, and the like at the time of manufacturing information electronic devices such as mobile phones and personal computers and vehicles, etc. The characteristics required of the bonding paste vary depending on the application of the apparatus to be produced, the environment of use, and the like. For example, since information electronic devices such as mobile phones are required to be thin and lightweight with emphasis on portability, the fine pitch of bonding parts is also used for bonding paste used for mounting as well as miniaturization of mounting parts. Characteristics and the like suitable for (narrow pitch) and high density mounting are required. On the other hand, in automotive applications and the like, since the mounted components are exposed to relatively high temperatures, it is necessary to prevent the solder after mounting from being remelted in a high temperature atmosphere and the bonding strength being lowered. Therefore, the bonding paste to be used is required to have high heat resistance and the like to the solder after reflow (melting).

  The bonding paste used for mounting such an electronic component is prepared in the form of a paste by mixing the bonding powder and the flux. The flux generally contains an activator and other components in addition to the resin component and the solvent component, and the resin component generally includes rosin which is excellent in electrical insulation, moisture resistance, and soldering performance at melting. It is widely used.

  In mounting using a bonding paste, cleaning is usually performed to remove active components and the like adhering to the bonding surface after reflow, but in the case of a bonding paste prepared using a flux containing rosin as a main component However, this washing can not be performed with water alone, and it is necessary to wash with an organic solvent. However, cleaning with an organic solvent causes the fire to occur as the organic solvent volatilizes in the atmosphere, or causes pollution of the atmosphere and drainage, so it is not safe in terms of safety and health during installation, or the environment. There was a problem.

  In order to solve this problem, conventionally, it is possible to prepare a paste which is excellent in printability and meltability, can be washed only with alkaline ionized water after reflow, and has excellent viscosity stability over time (for bonding Paste) has been proposed (see, for example, Patent Document 1). This solder paste contains an acrylic resin having a carboxyl group, a thixo agent, a solvent and an activator, and the above acrylic resin has a (meth) acrylic acid ester monomer with an SP value of 9.4 to 12, (Meth) acrylic acid monomer, (meth) acrylic acid ester monomer and other vinyl group copolymerizable with (meth) acrylic acid monomer, containing the above acrylic resin Acid value is 50 to 250 mg KOH / g, and the weight average molecular weight is 1,000 to 20,000.

JP, 2016-150344, A (claim 1, paragraph [0001])

  In the solder paste (paste for bonding) shown in Patent Document 1, although it is assumed that active components and the like attached to the bonding surface after reflow can be washed only with alkaline ionized water, acrylic resin which is a resin component in flux It was necessary to select from among (meth) acrylate monomers having an SP value in the range of 9.4 to 12, and the like. And, even if the use ratio of rosin in the conventional flux is reduced, a high bonding strength can be obtained, and a bonding powder and a bonding paste using this powder are desired in which the residue of the flux after reflow is reduced.

  It is an object of the present invention to provide a bonding powder in which high bonding strength can be obtained in a relatively high temperature reflow and relatively high temperature use environment even if the proportion of rosin used in the flux is reduced, and flux residue after reflow is reduced. And it is providing the paste for joining using this powder.

  The inventors of the present invention are configured such that the matrix powder is an intermetallic compound of copper and tin, or a central core made of copper and a coating layer made of an intermetallic compound of copper and tin covering the central core. The effect of protecting the surface of the base powder with the tin formate and copper formate layer even with relatively high temperature reflow, by covering the surface of the base powder with the tin format bonding powder, with the surface of the base powder coated with the tin formate and copper formate layer. It has been found that high bonding strength can be obtained even if the proportion of rosin used in the flux is reduced, and the present invention has been achieved.

  The first aspect of the present invention is the surface of a base powder containing tin and copper in which the content of tin is 40% by mass to 60% by mass and the content of copper is 40% by mass to 60% by mass. Is a tin-based bonding powder coated with a layer of tin formate and copper formate.

  A second aspect of the present invention is the invention based on the first aspect, wherein the base powder is a tin-based bonding powder which is an intermetallic compound of copper and tin.

  A third aspect of the present invention is the invention based on the first aspect, wherein the base powder is composed of a central core consisting of copper and a covering layer consisting of an intermetallic compound of copper and tin for covering the central core. The tin-based bonding powder (also referred to as Cu core CuSn shell powder).

A fourth aspect of the present invention is the invention based on the second or third aspect, wherein the intermetallic compound of copper and tin is Cu ₆ Sn ₅ and / or Cu ₃ Sn. It is.

  According to a fifth aspect of the present invention, there is provided a junction including the powder for bonding and the flux according to any one of the first to fourth aspects, wherein the flux contains rosin at a ratio of 0% by mass or more and 2% by mass or less. Paste.

The bonding powder according to the first aspect of the present invention is reduced to tin and copper when the outermost tin formate and copper formate layer covering the base powder is heated at 200 ° C. or higher during reflow, Because it fuses with the copper and tin intermetallic compound covered with the outermost shell, removal of the oxide remaining due to the flux in the bonding paste after reflow is not necessary, or its removal is reduced It is possible to reduce the use ratio of rosin contained in the flux in the bonding paste. In other words, the components generated when the tin formate and copper formate layers are reduced at 200 ° C. or higher during reflow do not remain on the bonding surface as CO ₂ and H _2, and the problem as a residue on the bonding surface is also obtained. Resolved. In addition, high bonding strength can be obtained in relatively high temperature reflow and relatively high temperature use environments.

  In the bonding powder according to the second and third aspects of the present invention, in addition to the features of the bonding powder according to the first aspect, the outermost tin formate and copper formate layers are copper and tin In the composition after reflow, only the intermetallic compound having a high melting point or the intermetallic compound becomes a main component, and such an intermetallic compound has an increase in solidification initiation temperature. This makes remelting less likely to occur. For this reason, this bonding powder can be suitably used as a bonding powder used to mount an electronic component or the like that is particularly exposed to a high temperature atmosphere. Further, since copper and tin are contained in one metal particle constituting the powder, it is possible to prevent a decrease in bonding strength due to uneven melting at the time of reflow and compositional deviation.

  The bonding powder according to the second aspect, in which the matrix powder is an intermetallic compound of copper and tin, is a brittle substance because the intermetallic compound is a brittle substance, so the stress relaxation capability of the bonding layer after melting is not high. It has the feature of becoming a uniform composition. In the third bonding powder, which is a Cu core CuSn shell powder, copper remains in the bonding layer after melting, so the bonding layer has a non-uniform composition, but copper remains in the bonding layer to cause thermal conduction of the bonding layer. As compared with the bonding powder of the second aspect, the bonding layer has a feature that the stress relaxation capability of the bonding layer is high.

In the bonding powder of the fourth aspect of the present invention, the intermetallic compound of copper and tin is Cu ₆ Sn ₅ and / or Cu ₃ Sn. Among these intermetallic compounds, the melting point of the ε phase (Cu ₃ Sn) is 676 ° C., and the melting point of the (phase (Cn ₆ Sn ₅ ) is very high at 415 ° C., so the solidification start temperature rises to about 300 to 640 ° C. By doing this, remelting does not occur easily.

  The paste for bonding according to the fifth aspect of the present invention contains the powder for bonding and the flux, and contains rosin at a ratio of 0% by mass or more and 2% by mass or less in the flux. While having the features of the bonding powder of the first to fourth aspects after reflow, the residue of the flux after reflow is reduced.

It is the figure which represented typically the cross-section of the powder for joining of this invention embodiment. FIG. 1 (a) shows the cross-sectional structure of the bonding powder in which the base powder is an intermetallic compound of copper and tin, and FIG. 1 (b) shows the core of the base powder made of copper and copper covering this core. The cross-section of the powder for joining comprised with the coating layer which consists of an intermetallic compound of and tin is shown. It is a block diagram of the manufacturing apparatus of the powder for joining of this invention. It is a block diagram of the experimental apparatus for forming the layer of a tin formate and a copper formate on the base powder of this invention.

First Embodiment
[Powder for bonding]
First, a first embodiment for carrying out the present invention will be described based on the drawings. As shown in FIG. 1 (a), in the bonding powder 10 of this embodiment, the base powder 11 is made of an intermetallic compound of copper and tin (CuSn intermetallic compound), and the surface of the base powder 11 is tin formate. And coated with a layer 12 of copper formate. Examples of the intermetallic compound of copper and tin in the base powder 11 include one or more compounds selected from the group consisting of Cu ₃ Sn, Cu ₆ Sn ₅ , Cu ₁₀ Sn ₃ and Cu ₄₁ Sn ₁₁ In practice, however, the base powder 11 is mainly represented by the chemical structure of either one or both of Cu ₃ Sn and Cu ₆ Sn ₅ depending on the composition ratio of copper and tin.

  The content of copper is 40% by mass or more and 60% by mass or less based on 100% by mass of the total amount of the bonding powder. The preferable content rate of copper is 40 mass% or more and 50 mass% or less. By including the proportion of copper of the bonding powder in the above range, a Sn—Cu alloy having a high solidification start temperature of about 300 to 640 ° C. is formed after reflow. Note that, by containing copper, after reflow, an Sn—Cu alloy having a solidification start temperature higher than that of tin is formed. Thereby, in the bonding bump formed by the reflow of the bonding paste containing the bonding powder, the heat resistance can be greatly improved, and the remelting and the decrease in the bonding strength can be prevented. For this reason, it can be suitably used as a bonding powder used to mount an electronic component or the like that is particularly exposed to a high temperature atmosphere.

  Moreover, the content rate of tin is 40 mass% or more and 60 mass% or less which become remainder parts other than the said copper in powder with respect to 100 mass% of whole quantity of the powder for joining. The preferable content rate of tin is 50 mass% or more and 60 mass% or less. When the content ratio of tin is less than the lower limit value, molten tin is insufficient at the time of bonding, causing melting failure and causing bonding failure. When the content of tin exceeds the upper limit, the content of copper decreases as a result, and the tin component remains in the bonding layer to lower the heat resistance, and bonding with a substrate or the like in a high temperature atmosphere of 200 ° C. or higher. The strength is reduced.

The bonding powder preferably has an average particle diameter in the range of 1 μm to 30 μm. If the average particle diameter of the bonding powder is limited to 30 μm or less, if it exceeds 30 μm, coating unevenness occurs when the bonding pattern surface is printed with the bonding paste, and it becomes difficult to print the entire pattern uniformly. It is from. When the thickness is less than 1 μm, the specific surface area is increased, and the outermost tin formate and copper formate layer 12 may not sufficiently cover the base powder 11. The bonding powder preferably has an average particle diameter of about 3 to 20 μm as long as it is mainly composed of Cu ₆ Sn ₅ which is an intermetallic compound of copper and tin, and is an intermetallic compound of copper and tin If Cu ₃ Sn is the main component, it is preferable to have an average particle diameter of about 2 to 5 μm. In the present specification, the average particle diameter of the powder is measured with a particle size distribution measuring apparatus (laser diffraction / scattering particle size distribution measuring apparatus LA-950 manufactured by Horiba, Ltd.) using a laser diffraction scattering method. Volume cumulative median diameter (Median diameter, D ₅₀ ).

  The thickness of the tin formate and copper formate layer is preferably 10 nm or more and 30 nm or less. The thickness of the tin formate and copper formate layers is more preferable in this range. The formation mechanism of the layer of tin formate and copper formate is based on the fact that the natural oxide film formed on the surface of the base powder is chemically changed to a layer of tin formate and copper formate by contacting with a formic acid containing nitrogen gas described later. When the thickness of the tin formate and copper formate layer is 10 nm or less, the natural oxide film is not completely chemically converted to tin formate and copper formate, and the effect of the present invention is not exhibited. The effect of the present invention is hardly changed even if it exceeds 30 nm.

[Method of producing bonding powder]
In the matrix powder of the first embodiment, a Cu core Sn shell powder with a core core of copper and a coating layer of tin is dispersed by adding a high boiling point solvent having a boiling point of 100 ° C. or higher, and under an inert gas atmosphere, a predetermined temperature And the copper of the central core and the tin of the covering layer are completely fused. As high boiling point solvents to be used, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, castor oil and the like can be mentioned. The heat treatment is preferably performed at a temperature of 100 to 130 ° C. for 2 to 3 hours, depending on the size of the average particle diameter of the bonding powder and the like. Instead of heat treatment using the high-boiling point solvent, the Cu core Sn shell powder is maintained in an inert gas atmosphere at 200 to 220 ° C. for 1 to 2 hours to coat the copper core and the core nucleus. The coating layer of tin can be reacted to obtain a matrix powder of an intermetallic compound of copper and tin. If the treatment temperature or the holding time is less than the lower limit value, the intermetallic compound may not be formed in the central nucleus. Within the above range, if the heating temperature and the heating time are short, a base powder composed of the intermetallic compound of Cu ₆ Sn ₅ is obtained, and if the heating temperature and the heating time are long, Cu ₆ Sn ₅ and Cu ₃ Sn are mixed. A base powder made of an intermetallic compound or Cu ₃ Sn is obtained.

  In order to form a layer of tin formate and copper formate on the surface of the matrix powder, the matrix powder is placed in a closed reaction vessel, a formic acid-containing nitrogen gas is flowed into the reaction vessel, The base powder is heated at a temperature of 180 ° C., preferably at a temperature of 160-180 ° C. for 30 to 60 minutes. The formic acid-containing nitrogen gas is a mixed gas of formic acid gas and nitrogen gas. The content ratio of formic acid gas in the mixed gas is preferably 2 to 10% by volume. If it is less than 2% by volume, it takes too long to form a tin formate and copper formate layer, and even if it exceeds 10% by volume, there is no difference in the coating effect. As a result, a bonding powder having a tin formate and a copper formate layer formed on the surface of the base powder is obtained. After the bonding powder is taken out of the reaction vessel, if the bonding powder is stored in the atmosphere, the tin formate and copper formate layers may react with oxygen in the atmosphere and disappear, so as a bonding paste It is preferable to store the bonding powder in an inert atmosphere until it is used.

  FIG. 2 shows an example of a manufacturing apparatus for bonding powder. As shown in FIG. 2, the apparatus 30 for producing a bonding powder includes a reaction vessel 30 of a fluidized bed. The reaction container 30 has a cylindrical cylinder main body 31 closed at both ends and extending in the vertical direction, a raw material introduction pipe 32 connected to the side surface of the cylinder main body 31 and introducing the base powder 11 into the cylinder main body 31, Slide gate type current plate 33 provided near the lower end in 31 to receive base powder 11 and rectify gas in the cylinder main body vertically, nitrogen gas 34 or formic acid from bottom of cylinder main body 31 to cylinder main body 31 And a gas inlet pipe 37 for introducing a formic acid-containing nitrogen gas, which is a mixed gas of a gas 36 and a nitrogen gas 34. In the middle of the gas introduction pipe 37, a switching valve 37a for mixing formic acid gas into nitrogen gas is provided. Below the cylinder main body 31, a recovery tank 38 maintained in an inert gas atmosphere is provided. An outlet pipe 39 is provided between the bottom of the cylinder main body 31 and the recovery tank 38 to connect them. The outer periphery of the cylindrical tube body 31 has a jacket structure through which the heat medium passes. An exhaust pipe 40 for discharging the exhaust gas is connected to the top of the cylinder main body 31.

  In order to produce the bonding powder with the device 30 configured as described above, the switching valve 37a of the gas introduction pipe 37 is switched to replace the atmosphere in the reaction vessel 30 of the fluidized bed with nitrogen gas 34, and the cylinder main body 31 Is heated to 100 to 180.degree. C., preferably 160 to 180.degree. C., with a heat medium. In this state, the base powder 11 which is a raw material powder is introduced by the raw material introduction pipe 32, and is brought into a fluidized state in the cylinder main body. The switching valve 37 a is further switched to mix the formic acid gas 36 into the nitrogen gas 34, and the formic acid-containing nitrogen gas is made to flow into the inside of the cylinder main body 31 from the gas introduction pipe 37. The base powder 11 in a fluid state is contacted with formic acid-containing nitrogen gas, and the formic acid and the intermetallic compound of copper and tin of the base powder react to form a layer 12 of tin formate and copper formate on the surface of the base powder. . The reaction time is set in the range of 30 to 60 minutes depending on the content (less than volume%) of formic acid gas in the mixed gas. After the layer 12 of tin formate and copper formate is formed, the switching valve 37a is switched to introduce only nitrogen gas 34 into the inside of the cylinder main body 31 and cool the inside of the cylinder main body. The base powder in which the tin formate and copper formate layers are formed is collected in the collection tank 38 from the bottom of the cylinder main body 31 through the pipe 39, that is, the bonding powder 10 is collected.

Second Embodiment
[Powder for bonding]
Next, a second embodiment for carrying out the present invention will be described based on the drawings. As shown in FIG. 1 (b), in the bonding powder 20 of this embodiment, the core powder 22 of the base powder 21 is made of copper, and the intermetallic compound of copper and tin (CuSn intermetallic compound covering the core core 22) And the surface of the matrix powder 21 is coated with a layer 25 of tin formate and copper formate. The intermetallic compound of copper and tin is the same as the intermetallic compound of copper and tin in the first embodiment. Further, the content ratio of copper to the total amount 100% by mass of the powder for bonding, the content ratio of tin similarly, the average particle diameter of the powder for bonding and the thickness of the tin formate and copper formate layer are in the same range as the first embodiment. is there.

[Method of producing bonding powder]
In the base powder of the second embodiment, if the copper and tin content of the Cu core Sn shell powder whose core is copper and the coating layer is tin is the same as that of the first embodiment, this Cu core Sn As in the first embodiment, the shell powder is dispersed by adding a high boiling point solvent having a boiling point of 100 ° C. or higher, and heated at a predetermined temperature in an inert gas atmosphere, or the Cu core Sn shell powder is inert Maintain at 200 to 220 ° C. for 30 minutes to 1 hour in a gas atmosphere. The difference from the first embodiment is that the heating time or the maintenance time is shorter than in the first embodiment, or the heating temperature or the maintenance temperature is lowered to make the core nucleus copper and the coating layer tin The heating conditions or maintenance conditions are adjusted so that copper of the central core remains without completely fusing. In addition, if each content rate of copper and tin of Cu core Sn shell powder is higher than that of 1st Embodiment than the content rate of Sn (if it is Cu rich), 1st implementation Heat treatment as in the form. By doing this, the core nucleus copper is covered with the intermetallic compound of Cu ₆ Sn ₅ , the intermetallic compound covering layer in which Cu ₆ Sn ₅ and Cu ₃ Sn are mixed, or the coating layer of Cu ₃ Sn, respectively. A coated base powder is obtained.

  Similar to the first embodiment, layers of tin formate and copper formate are formed on the surface of the obtained base powder using the manufacturing apparatus shown in FIG. 2 or the like, and the bonding of the second embodiment is performed. Powder is obtained.

[Preparation of paste for bonding]
The bonding powder manufactured in the above first and second embodiments is prepared as a bonding paste by the following method. The preparation of the bonding paste is performed by mixing the bonding powder and the flux at a predetermined ratio to form a paste. The flux used for preparing the bonding paste is not particularly limited, and a flux prepared by mixing each component such as a known solvent, rosin, thixo agent and activator can be used. Viscosity stabilizers may be added as additives.

  The bonding flux is obtained by mixing the above-mentioned components at a predetermined ratio. A characteristic feature of the present embodiment is that the rosin is contained at a ratio of 0% by mass or more and 2% by mass or less with respect to 100% by mass of the flux. The proportion of solvent which is a component other than rosin is 30 to 60% by mass, the proportion of thixo agent is 1 to 10% by mass, and the proportion of activator is 0.1 to 10% by mass with respect to 100% by mass of flux Is preferred. By making the rosin 0% by mass, that is, rosin-free, it is possible to eliminate the residue of the flux at the junction after reflow, and if it is 2% by mass or less, washing of the residue can be alleviated.

  If the proportion of the solvent is less than the lower limit value, the viscosity of the flux becomes too high, so the viscosity of the bonding paste using it also becomes high accordingly, and the filling property of the bonding powder decreases frequently and coating unevenness occurs, printability May cause problems that cause On the other hand, if the upper limit value is exceeded, the viscosity of the flux becomes too low, and the viscosity of the bonding paste using it also decreases accordingly, which may cause a problem that the bonding powder and the flux component precipitate and separate. In addition, when the ratio of the thixotropic agent is less than the lower limit value, the viscosity of the bonding paste is too low, which may cause a problem that the bonding powder and the flux component precipitate and separate. On the other hand, if the upper limit value is exceeded, the viscosity of the bonding paste becomes too high, which may cause problems such as a decrease in the fillability of the paste and a decrease in printability such as uneven coating. In addition, if the ratio of the activator is less than the lower limit, the bonding powder may not be melted, which may cause a problem that a sufficient bonding strength can not be obtained. On the other hand, if the ratio exceeds the upper limit, the activator is bonded during storage. Since it becomes easy to react with, there may occur a problem that storage stability of the bonding paste is lowered.

  The mixing amount of the bonding flux at the time of preparing the bonding paste is preferably such that the ratio of the flux in 100% by weight of the prepared paste is 5 to 30% by mass. If it is less than the lower limit, the flux will be insufficient and it will become difficult to paste, while if it exceeds the upper limit, the content of the flux in the paste will be too high and the content of the metal will decrease, which is desirable when the bonding powder is melted. It is because it becomes difficult to obtain a bump of a size.

  Since this bonding paste is made of the bonding powder of the first and second embodiments, after reflow, the bonding powder to be melted forms an intermetallic compound having a high melting point, and the heat resistance is increased. Therefore, remelting by heat does not easily occur. For this reason, the paste for joining using the powder for joining of the 1st and 2nd embodiment can be used suitably for mounting of electronic parts etc. which are especially exposed to high temperature atmosphere.

  Next, an example of the present invention will be described in detail along with a comparative example.

  An experiment for forming a tin formate and a copper formate layer on a CuSn intermetallic compound-based sample was performed using the apparatus shown in FIG. As shown in FIG. 3, the experimental apparatus 50 is provided with a plurality of heating lamps 52 and a pedestal 53 on which a test sample is placed in a sealed reaction container 51. A gas introduction pipe 56 for introducing nitrogen gas or nitrogen gas containing formic acid is connected to one side wall 54 of the reaction vessel 51, and an exhaust pipe 58 for discharging exhaust gas is connected to the other side wall 57 of the reaction vessel 51. In the vicinity of the gas introduction pipe 56, a liquid tank 59 containing a formic acid aqueous solution 55 having a formic acid concentration of 98% by mass is disposed. In the liquid tank 59, a nitrogen gas introduction pipe 59a and a formic acid gas discharge pipe 59b are provided. The lower end of the nitrogen gas introduction pipe 59a extends to the bottom of the liquid tank in the formic acid aqueous solution, and the lower end of the formic acid gas discharge pipe 59b is disposed at the top of the liquid tank above the liquid surface of the formic acid aqueous solution. The nitrogen gas inlet pipe 59a and the formic acid gas outlet pipe 59b are connected to the gas inlet pipe 56 via the switching valves 56a and 56b, respectively. The liquid tank 59 is provided with a heater (not shown). In FIG. 3, a tray 60 in which the base powder 21 of the bonding powder is placed on the pedestal 53.

[Production of matrix powder and formation of tin formate and copper formate layer on matrix powder]
Next, as a CuSn intermetallic compound-based sample, the base powder of the bonding powder shown in FIG. 1 (b) is placed in a tray 60 on the pedestal 53 of the reaction container 51 shown in FIG. Layers of tin and copper formate were formed.

[Production of matrix powder]
First of all, the base powder No. 1 is a Cu core Sn shell powder having an average particle diameter of 8 μm and an average particle diameter of 8 μm, with a central core of copper and a central core of copper as a target composition. Were heated at a temperature of 200 ° C. in a nitrogen gas atmosphere for 1 hour to produce a central core made of copper and a coating layer made of an intermetallic compound of copper and tin covering the central core. Next, for the base powder part 2, a Cu core Sn shell having an average particle diameter of 8 μm and an average particle diameter of 8 μm of a core nucleus of copper and a core nucleus of copper with a content ratio of 60 mass% and 40 mass% of Cu as a target composition The powder was manufactured by heating the powder at a temperature of 220 ° C. for 1.5 hours under a nitrogen gas atmosphere so that the copper of the central core disappeared and all consisted of an intermetallic compound of copper and tin.

[Evaluation of properties of matrix powder]
With respect to the base powder part 1 and part 2, the metal element content is measured by inductively coupled plasma emission spectrometry (ICP emission analyzer: ICPS-7510 manufactured by Shimadzu Corporation), and the content ratio of Sn in the base powder part 1 is 40 mass %, The content ratio of Cu was 60 mass%, it was confirmed that the content ratio of Sn of the base powder part 2 was 60 mass%, and the content ratio of Cu was 40 mass%. Furthermore, base powder part 1 and part 2 are cross-section processed by focused ion beam (Forcused Ion Beam: FIB), and identification and quantification of central core and covering layer elements are carried out by Auger Electron Spectroscopy (AES). The base powder No. 1 had a core composed of Cu and a covering layer composed of Cu ₆ Sn ₅ of an intermetallic compound formed on the periphery of the Cu core. The base powder No. 2 was all composed of Cu ₆ Sn ₅ .

[Formation of Tin Formate and Copper Formate Layer on Base Powder (Production of Bonding Powder)]
<Powder No. 1>
The base powder No. 1 (Sn 40 Cu 60 (% by mass)) produced by the above method was used as powder for bonding of powder No. 1.

<Powder No. 2, Powder No. 3>
10 g of the base powder No. 1 (Sn 40 Cu 60 (mass%)) manufactured by the above method is put in the tray 60 on the pedestal 53 of the reaction container 51 shown in FIG. Was introduced at a rate of 0.5 mL / min, the atmosphere in the reaction vessel 51 was replaced with nitrogen gas, and the reaction vessel 51 was heated by a heating lamp 52 from room temperature to 180 ° C. at a rate of 3 ° C./sec. After the atmosphere in the reaction vessel 51 was replaced with nitrogen gas, as shown in Table 1, the content of formic acid gas in the formic acid-containing nitrogen gas was changed to continue exposing the formic acid-containing nitrogen gas to the base powder surface for 60 minutes. . As a result, powders for bonding of powder No. 2 and powder No. 3 were obtained. The average particle diameter of these bonding powders was 8 μm as shown in Table 1 as measured by the above-described particle size distribution analyzer.

<Powder No. 4>
The base powder No. 2 (Sn60Cu40 (% by mass)) produced by the above method was used as powder for bonding of powder No. 4.

<Powder No. 5, Powder No. 6>
10 g of the base powder 2 (Sn 60 Cu 40 (mass%)) manufactured by the above method is the same as the base powder 1 and, as shown in Table 2, the content of formic acid gas in the formic acid containing nitrogen gas is changed, The surface of the base powder was kept exposed to formic acid-containing nitrogen gas for 60 minutes. Thus, a bonding powder of powder No. 5 and powder No. 6 was obtained. The average particle diameter of these bonding powders was 8 μm as shown in Table 2 as measured by the above-described particle size distribution analyzer.

[Preparation of paste for bonding using powder for bonding]
Example 1
A bonding paste was prepared by the following method using powder No. 3 for bonding. First, rosin is not included, the other components are mixed with alpha terpineol as a solvent, 1.0% by mass of cyclohexylamine hydrobromide as an activator, and 3.0% by mass of hydrogenated castor oil as a thixotropic agent. The flux was prepared. The paste for bonding was prepared by mixing the flux and the powder for bonding such that the content of the flux was 12 mass% and the obtained powder for bonding was 88 mass%.

Examples 2 to 8 and Comparative Examples 1 to 10
As shown in Table 3, using the bonding powder of powder No. 1 to powder No. 6, the flux of the solvent and rosin ratio is fixed at 12 mass% as compared with Example 1, The powders were mixed at a ratio of 88% by mass to prepare bonding pastes. When rosin was contained, polymerized rosin (softening point 95 ° C.) was used as the rosin, and the solvent was reduced by the amount of rosin contained.

<Comparison evaluation>
[Evaluation of bonding strength]
Using 18 metal pastes obtained in Examples 1 to 8 and Comparative Examples 1 to 10, using a metal mask having a thickness of 50 μm at 3 mm square openings, using a metal squeegee on a copper plate Each printed so as to be 50 μm. A 2.5 mm □ Si element was mounted on the printed paste. In the surface of the Si element in contact with the paste, Au sputtering is performed in advance. Heat treatment was performed for 60 seconds at a maximum holding temperature of 300 ° C. for 60 seconds in a bonding furnace (Falcon 8500 manufactured by SIKAMA) (not shown) to obtain 18 types of bonded samples by bonding the Si element and the copper plate. The bonding shear strength (MPa) was measured at room temperature for the bonding strength between the bonded copper plate and the Si element.

[Evaluation of molten state of joint surface, amount of flux residue]
The fractured surface of the joined sample after the measurement of the joint shear strength was observed with an electron microscope. The melting condition of the bonding powder was confirmed from each of the fracture surfaces on the Si element side and the substrate side. The material for which the bonding powder was melted was referred to as “melted”, the material not melted was referred to as “unmelted”, and the case where the substrate was exposed was referred to as “base exposure”. Furthermore, after reflow, the presence or absence of the residue of the flux in a joining location was investigated. The presence of the residue is regarded as "present" as the washing of the conventional flux residue is required, and the case where the residue which needs only a slight washing is slight is regarded as "slightly present". The case where there was no residue which was not required at all was regarded as "none". The results are shown in Table 4.

  As apparent from Table 4, in Comparative Example 1 and Comparative Example 6, since the bonding powder in the flux had no tin formate and copper formate layers but had a sufficient amount of rosin, each of the Si element side and the substrate side The bonding powder was molten at the bonding surface, and the bonding shear strength was high, but there was a residue of flux.

  In Comparative Example 2 and Comparative Example 7, the bonding powder in the flux had no layer of tin formate and copper formate and had an insufficient amount of rosin, so the bonding powder was formed on each bonding surface on the Si element side and the substrate side. It became unmelted, the bonding shear strength was extremely low, and there was a slight residue of flux.

  In Comparative Example 3 and Comparative Example 8, since the bonding powder in the flux has no layer of tin formate and copper formate and does not contain rosin, an oxide film remains on each bonding surface on the Si element side and the substrate side, and bonding is performed. The powder was unmelted, the bonding shear strength was extremely low, and there was no flux residue.

  In Comparative Example 4 and Comparative Example 9, since the bonding powder in the flux has a thick layer of tin formate and copper formate but has a sufficient amount of rosin, bonding is performed on each bonding surface on the Si element side and the substrate side. The powder for use was molten, and although the bonding shear strength was high, there was a residue of flux.

  In Comparative Example 5 and Comparative Example 10, since the bonding powder in the flux had thin tin formate and copper formate layers but had a sufficient amount of rosin, bonding was performed on each bonding surface on the Si element side and the substrate side. The powder for use was molten, and although the bonding shear strength was high, there was a residue of flux.

  On the other hand, in each of Examples 1 to 8, since the bonding powder in the flux has a thin layer of tin formate and copper formate, even if the amount of rosin is zero or 2% by mass in the flux The bonding shear strength was 15 MPa or more, which was practically acceptable, and the residue of the flux was either absent or slightly present. In Examples 1, 3, 5, and 7, since there was no flux residue, post-cleaning was unnecessary. In Examples 1, 2, 5 and 6, the bonding powder was melted at each bonding surface on the Si element side and the substrate side. In Examples 3, 4, 7 and 8, the bonding powder was not melted at the bonding surface on the Si element side, but the bonding powder was melted at the bonding surface on the substrate side.

  The bonding powder of the present invention can be used as a lead-free bonding powder for fine pitch, and the bonding paste obtained using this bonding powder as a raw material can be suitably used for mounting of fine electronic components.

10 Bonding powder 11 Base powder (CuSn intermetallic compound)
12 layer of tin formate and copper formate 20 bonding powder 21 base powder 22 central core (Cu)
23 Coating layer (CuSn intermetallic compound)
25 Layer of tin formate and copper formate

Claims (5)

  The surface of the base powder containing tin and copper having a tin content of 40% to 60% by mass and a copper content of 40% to 60% by mass is a layer of tin formate and copper formate Coated tin-based bonding powder.   The tin-based bonding powder according to claim 1, wherein the base powder is an intermetallic compound of copper and tin.   The tin-based bonding powder according to claim 1, wherein the base powder comprises a central core made of copper and a coating layer made of an intermetallic compound of copper and tin for coating the central core. The tin-based bonding powder according to claim 2 or 3, wherein the intermetallic compound of copper and tin is Cu ₆ Sn ₅ and / or Cu ₃ Sn.   A bonding paste comprising the bonding powder according to any one of claims 1 to 4 and a flux, wherein the flux contains rosin in a proportion of 0% by mass or more and 2% by mass or less.

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