JP2008214678A - Tin powder, tin paste and method for producing tin powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide tin powder having excellent shape stability when being worked into tin paste and also having excellent connection reliability, to provide tin paste, and to provide a method for producing the tin powder. <P>SOLUTION: Tin powder in which the grains have flake shape, and the average equivalent circle diameter in the plane direction of the grains is 1 to 10 μm is used. Then, using this tin powder, tin paste is produced. Further, upon the production of this tin powder, the method where tin powder in which the grains have granular shape is dispersed into a dispersion medium, and the dispersed slurry is treated in a media agitating mill is used. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a flaky tin powder, a tin paste using the tin powder, and a method for producing tin powder, and is particularly suitable for use as a bonding material for fine high-density mounting.

  With respect to a wiring board such as a semiconductor, soldering is performed in order to mount an electronic component on a substrate. In the past, tin-lead eutectic solder was used to solder electronic components to the board. However, in order to consider the effects of lead on the human body and the environment, the need for alternative materials has increased. Various so-called “lead-free solder” materials have been put into practical use. And various improvement is examined for the tin paste using a tin powder in order to provide the performance equivalent to a tin-lead eutectic solder as one of the alternative materials of a tin-lead eutectic solder.

  For example, Patent Document 1 discloses a solder paste using tin as a material in which the surface of tin powder is coated with a surface treatment agent, dried, and improved in corrosion resistance, oxidation resistance and alteration resistance. ing. Further, in Patent Document 2, attention is paid to the stress generated in the printed wiring board in which the electronic component is soldered to the conductor layer using lead-free solder, due to the deviation of the thermal expansion coefficient of the components of the printed wiring board. A technique is disclosed in which lift-off is suppressed by suppressing the thermal expansion coefficient of the substrate on which the layer is disposed, and the quality and reliability of the soldered portion are improved. Patent Document 3 discloses a technique relating to a circuit board in which unnecessary solder balls are not generated beside the substrate electrode when a chip component or a semiconductor device is mounted on the board using lead-free solder (Pb-free solder). It is disclosed.

JP 2004-339583 A JP 2002-368362 A JP 2003-298220 A

  In recent years, with the miniaturization and high density of wiring patterns, dimensional errors in via-hole connection of laminated wiring boards and mounting of lead-free solder paste (tin paste) used as a bonding agent for mounting components on wiring boards are smaller. It is demanded. Further, as disclosed in Patent Document 2, it is desired to improve the connection reliability with a substrate or a component terminal. However, conventional lead-free solder has physical characteristics and handleability that are higher than those of tin-lead eutectic solder. There is a need for improved mounting accuracy equivalent to tin-lead eutectic solder in terms of inferior shape stability and connection reliability. In particular, the wettability of lead-free solder after melting is poor, and it is a problem that it flows out and falls out of the soldering position. The physical properties of the paste itself must be taken into account. Therefore, a lead-free solder paste that can be soldered to a target position with higher dimensional accuracy is demanded in relation to the allowable range of the dimensional design of the soldering part and the higher density. Further, as the shape of the conventional solder powder, spherical powder is mainly used, but the average particle size is as large as several tens of μm, which is not suitable for forming a fine circuit.

  As a result of intensive studies, the present inventors have come up with the following invention that has good shape stability and improves connection reliability in order to solve the above-mentioned problems.

Tin powder according to the present invention: The tin powder according to the present invention is characterized in that the particles have a flake shape, and the average equivalent circle diameter in the plane direction of the particles is 1 μm to 10 μm.

The tin powder according to the present invention preferably has a volume cumulative average particle diameter D ₅₀ (hereinafter referred to as “D ₅₀ ”) measured by a laser diffraction / scattering particle size distribution measurement method of 1.5 μm to 15 μm.

  Furthermore, the tin powder according to the present invention preferably has an aspect ratio ([average equivalent circular diameter (μm) in the plane direction (μm)] / [average thickness (μm)]) of 5 to 40.

Moreover, tin powder according to the present invention is preferably a tap density is ^{3g / cm 3 ~5g / cm 3} .

Moreover, tin powder according to the present invention is more preferably a specific surface area of 0.3m ² / g~1m ² / g.

Tin paste according to the present invention: The tin paste according to the present invention is characterized by containing the above tin powder.

Production method of tin powder according to the present invention: The production method of tin powder according to the present invention is characterized in that tin powder having a granular shape is dispersed in a dispersion medium, and the dispersion slurry is processed in a medium mill. And

  Moreover, it is preferable that the manufacturing method of the tin powder which concerns on this invention is that the primary particle average diameter by the scanning electron microscope (SEM) of the tin powder which the said particle | grain shape exhibits granular form is 0.5 micrometer-7 micrometers.

  In the method for producing tin powder according to the present invention, the medium mill is preferably a bead mill.

  Furthermore, in the manufacturing method of the tin powder which concerns on this invention, it is preferable that the medium used for the said medium mill is a media bead with a particle size of 0.3 mm or less.

  When the tin powder of the present invention is used as a tin paste, the rheological properties are improved and the circuit formability is excellent due to the flake shape of the particles. Therefore, the tin powder of the present invention is supplied on the substrate as a tin paste, and is excellent in the shape stability of the paste when forming the joint. In addition, the balance between the dimensional design tolerance of the soldering part and the high density can be maintained, and soldering to a target position can be performed with higher dimensional accuracy, thereby improving connection reliability. Moreover, according to the manufacturing method of the tin powder of this invention, the tin powder which can eliminate the said subject can be manufactured efficiently.

Tin powder according to the present invention: The tin powder according to the present invention is characterized in that the shape of the constituting particles is flaky. The present inventor has found that the thixotropy is higher in the case where the tin powder has a flake shape than in the case where the tin powder has a spherical shape, with respect to the thixotropy which is an index representing the rheological characteristics of the tin paste before melting. Although the reason for this is not known, the flake powder has a larger contact area between the particles than the contact point between the spherical particles. As a result, the frictional resistance between the stationary state and the fluid state is spherical. It may be larger than the powder. Further, regarding the filler concentration, it was found that the connection reliability can be obtained even if the flaky powder has a lower filler concentration than the spherical powder. Therefore, the resin addition ratio of the tin paste can be increased, and the bonding strength can be increased. About this reason, it is thought that it is easy to ensure the contact of particle | grains by setting it as flake-shaped particle | grains, and can obtain connection reliability efficiently. Hereinafter, the tin powder according to the present invention will be described in detail.

  First, the tin powder according to the present invention has a flake shape, and the average equivalent circle diameter in the particle surface direction is 1 μm to 10 μm. By using tin powder having such characteristics, good shape stability can be obtained when it is made into a paste and used for circuit formation. The average equivalent circle diameter in the particle plane direction is more preferably 3 μm to 8 μm. The average equivalent circle diameter in the particle plane direction is to analyze a 2000 times scanning electron micrograph using an image analyzer IP-1000PC (Asahi Engineering Co., Ltd.) with a circularity threshold of 10 and an overlap of 20. Is required.

Then, for good dimensional stability of the tin paste, since it also involved agglomerated particles of _{approximately,} preferably _{D 50} is 1.5Myuemu～15myuemu, more preferably 3Myuemu～10myuemu. If D ₅₀ is in this range, it is possible to produce a glue with a proper viscosity state more stably. D ₅₀ can be measured using a MicroTrac HRA9320-X100 type (Leeds + Northrup), which is a laser diffraction / scattering particle size distribution measuring device (sample 0.1 g is a 0.1% aqueous solution of SN Dispersant 5468 (San Nopco) And using a sample dispersed for 5 minutes with an ultrasonic homogenizer (US-300T, manufactured by Nippon Seiki Seisakusho).

  Moreover, it is preferable that the aspect ratio of the tin powder of this invention is 5-40, and it is more preferable that it is 10-30. This aspect ratio indicates the degree of flaking of the flaky powder, and is calculated by [average equivalent circular diameter (μm)] / [average thickness (μm)] of the particles. Here, the average thickness is obtained by first preparing a sample in which tin powder is hardened with an epoxy resin, and then directly observing the cross section of the sample with a scanning electron microscope (magnification 10,000 times). The total sum of the thicknesses of more than one is divided by the number of particles. When the aspect ratio is in the range of 5 to 40, the shape stability of the conductor formed using the paste is not impaired, the viscosity is increased when the paste is formed, and the circuit forming ability of the paste is maintained. Can do.

Furthermore, tin powder of the present invention, it is preferred tap density of the particles is ^{3g / cm 3 ~5g / cm 3} . The tap density is a constant index in considering the powder characteristics of the tin powder according to the present invention, and the tap density of the particles that can obtain the desirable rheological characteristics as described above falls within the above range. The tap density was measured using a powder star PT-E (manufactured by Hosokawa Micron Corporation).

Further, it is preferable that the specific surface area of tin powder of the present invention is 0.3m ² /g~1.0m ² / g. When the specific surface area is in such a range, a paste having a viscosity that does not impair the handleability while ensuring the thixotropy of the paste can be obtained. In addition, the specific surface area in this specification is measured by BET 1-point method using a monosorb (manufactured by Kantachrome Co., Ltd.) after subjecting a sample of 3.00 g to deaeration treatment at 70 ° C. for 10 minutes. The tin powder according to the present invention having the above-mentioned powder characteristics shows a fine and good particle size distribution, and further has a flake-like shape showing a suitable aspect ratio, so that the conventional particle size is large. It can be said that the tin powder is suitable for screen printing performance and fine pitch bonding, overcoming the problems of spherical solder powder.

Production form of tin powder according to the present invention: In the method for producing tin powder according to the present invention, tin powder having a granular particle shape is dispersed in a dispersion medium, and the dispersion slurry is processed in a medium mill. Originally, tin is a soft metal and is very easily plastically deformed. Therefore, it has been considered difficult to produce a practical tin powder because the particles are excessively deformed when a flaky tin powder is produced using a medium mill. However, the present inventor has found that the granular tin powder can be formed into a desired flake shape under the following production conditions.

  First, tin powder having a granular shape (hereinafter referred to as “granular tin powder”) is dispersed in a dispersion medium to prepare a dispersion slurry. As the granular tin powder, any shape can be used as long as it is granular, but if it is substantially spherical, it is preferable because uniform particles are easily obtained when flaked. The granular tin powder preferably has an SEM primary particle average particle diameter of 0.5 μm to 7 μm because it does not require excessive flaking and can produce tin powder having the desired particle size. In addition, although the means is not limited about manufacture of a granular tin powder, In order to obtain a substantially spherical powder, it is preferable to employ | adopt a dry atomization method.

  As the dispersion medium used in producing the dispersion slurry, water, an organic solvent, or a mixed solvent of water and an organic solvent can be used, but considering that the dispersion medium component remains on the particle surface. It is preferable to employ water. On the other hand, it is preferable to use an organic solvent if the main purpose is to increase the dispersibility of particles in the slurry or to suppress oxidation of tin powder. This selection may be performed according to the application. Examples of organic solvents that are suitable include alcohols such as methanol, ethanol, and ethylene glycol. These are easy to volatilize, have high air diffusion efficiency during drying after flaking, and have little residue on the particle surface.

  Moreover, in the manufacturing method of the tin powder of this invention, it is preferable to adjust so that the density | concentration of the granular tin powder in a dispersion | distribution slurry may be 5 vol%-90 vol%. By adjusting to such a granular tin powder concentration, it is possible to prevent the particles in the slurry from aggregating and to obtain a tin powder that is excellent in particle dispersibility and suitable for paste production.

  In addition, before the granular tin powder is slurried, the particle shape can be reduced during flaking by releasing the particle aggregation as much as possible using an appropriate pulverization device (wind circulator, etc.) or dispersion device (homogenizer, etc.). It is preferable that it can be processed without impairing the quality.

  The granular tin powder-dispersed slurry thus obtained is flaked using a medium mill. The medium mill to be used is not particularly limited, but a bead mill suitable for pulverizing fine particles is preferably used. As the medium used in the medium mill, it is preferable to use fine media beads, and specifically, a medium having a particle diameter of preferably 0.3 mm or less, more preferably 0.2 mm or less is used. The lower limit of the bead particle size is not particularly limited, but the industrially used level is 0.05 mm or more. The material of the beads may be selected from commonly used materials such as zirconia beads, alumina beads, and glass beads. By appropriately selecting the medium used for flake processing in this way, it is possible to obtain a flake powder having an optimum aspect ratio by suppressing bond aggregation due to particle coarsening, and without using a lubricant. Generation of coarse flake particles in which particles are bonded to each other can be prevented.

  The mixing ratio of the granular tin powder and the media beads in the slurry is in the range of [amount of granular tin powder in the slurry (wt%)]: [amount of media beads (wt%)] = 1: 1 to 1:10. It is preferable to set. When the blending ratio is set in such a range, the balance between the granular tin powder that is the object to be crushed and the media beads becomes appropriate, and an excessive load on the tin particles that are the soft metal can be suppressed. As a result, the processing can be performed efficiently and stably without impairing the particle size distribution of the obtained flake powder.

  Moreover, when the excessive load to the tin particle which is a soft metal is considered, it is preferable that the time which performs a flaking process is 3 hours or less. When the flaking process is performed for more than 3 hours, plastic deformation proceeds excessively, making it difficult to obtain preferable flaky tin particles. That is, it is suitable for producing tin powder having a flaky particle shape, which has been conventionally considered difficult to perform flaking treatment under weak plastic deformation conditions in a short time.

  In this way, the slurry containing tin powder that has been flaked is subjected to conventional washing and drying after removing the medium to obtain tin powder. In washing, alcohols such as ethanol and methanol are preferably used in order to avoid oxidation, and drying may be performed at about 50 ° C. to 80 ° C. for several tens of minutes to several hours. Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

  Production of tin powder according to the present invention: As the raw material powder, a substantially spherical granular tin powder produced by a dry atomization method and having powder characteristics shown in Table 1 is used. The granular tin powder is obtained by classifying tin powder obtained by a disk atomization method which is a dry atomization method. This granular tin powder is mixed with a dispersion medium to produce a dispersion slurry. The granular tin powder was deagglomerated as much as possible using a wind circulator before slurrying.

  0.4 kg of the above granular tin powder was put in 0.04 kg of methanol as a dispersion medium and stirred well to produce a slurry having a tin powder concentration of 58 vol% (91 wt%). Subsequently, the obtained granular tin powder-dispersed slurry is flaked using a medium mill. In this example, a bead mill was used, and zirconia beads having a diameter of 0.1 mm were used. That is, 0.8 kg of zirconia beads having a diameter of 0.1 mm were prepared, and [spherical powder amount in slurry (wt%)]: [media bead amount (wt%)] = 1: 2 was set. Filled. And the rotational speed was set to 2000 rpm, the solution was circulated for 60 minutes, and the particles were physically plastically deformed to form flakes.

  In the slurry containing tin powder thus flaked, zirconia beads were removed with a 45 μm sieve mesh, and then the slurry was allowed to stand for a certain period of time to precipitate the flake tin powder, and the supernatant was discarded to remove the medium. In the state of discarding the supernatant, the water washing operation of adding water to wash and discarding the supernatant is repeated twice (repulp washing), and then washing with ethanol three times to enhance washing, Contaminants were removed as much as possible. And it dried at 70 degreeC * 5 hours, and obtained the flaky tin powder.

  FIG. 1 shows a scanning electron microscope observation image (magnification 2000 times) of the flaky tin powder obtained in the examples. The powder characteristics of the flaky tin powder are shown in Table 1. From FIG. 1, it can be seen that the flake-shaped particles are thinly stretched and have a flat surface with few irregularities and a flake shape having a smooth surface. Moreover, when it sees as a whole, it can be said that there is little aggregation.

Production of tin paste: 12.0 g of bisphenol F type epoxy resin (Nippon Kayaku Co., Ltd .: RE-303SL), 2.1 g of acid anhydride type curing agent (Kayahard MCD manufactured by Nippon Kayaku Co., Ltd.), and amine adduct type curing agent The flake tin powder obtained after kneading 0.7 g (Ajinomoto Fine Techno Co., Ltd .: Amicure MY-24) and 15.2 g α-terpineol (manufactured by Yasuhara Chemical Co., Ltd.) as a viscosity modifier in a paddle type kneader for 5 minutes. 130 g was added and kneaded for an additional 10 minutes. And after kneading | mixing a kneaded material with 3 rolls continuously, the bubble contained in a kneaded material was removed using the defoaming machine (made by Shinki: AR-250), and the tin paste was obtained.

  In order to measure the thixo ratio of the tin paste of this example, first, the viscosity of the tin paste having a filler concentration of 90 wt% was set to a temperature of 20 ° C. using RE-105U which is a rotary viscometer manufactured by Toki Sangyo Co., Ltd. Measurements were made at 1.0 rpm and 10 rpm, respectively. The thixo ratio was calculated from the measured 1.0 rpm data and 10 rpm data. The results are shown in Table 1.

Comparative example

  As a comparative example, the granular tin powder obtained by classifying the disk atomized powder, which is the raw material powder of the example, was evaluated as it was. Since the manufacturing method of a tin paste is the same method as an Example, description is omitted. And the result of having computed the thixo ratio of the tin paste of the comparative example by the method similar to an Example is shown in Table 1.

Rheological properties of tin paste: Evaluation of the rheological properties of tin paste will be described. The viscosity of the tin paste is thought to affect the shape stability, but generally the viscosity of the paste changes with the number of rotations of stirring, and the viscosity tends to increase with stirring. The shape stability of a circuit or the like cannot be shown. Therefore, the thixo ratio is adopted as an index indicating the shape stability before the tin paste is landed at a predetermined position and melted. The thixo ratio is a physical property value indicating the fluidity of a substance, and is shown as a ratio of viscosities measured at different rotational speeds using a rotary viscometer. That is, the thixo ratio is a numerical value represented by the formula ([viscosity at 1.0 rpm] / [viscosity at 10 rpm]), and is the viscosity ratio of the tin paste accompanying the change in the rotational speed of the rotor of the viscometer. In the above formula, it is the ratio of the viscosity at low speed stirring (hereinafter referred to as “low speed stirring viscosity”) to the viscosity at high speed stirring (hereinafter referred to as “high speed stirring viscosity”). It is considered that thixotropy is improved. That is, when the high-speed stirring viscosity and the low-speed stirring viscosity of the tin paste are compared, the relationship of [high-speed stirring viscosity] <[low-speed stirring viscosity] may be established. In this case, the larger the difference between the high-speed stirring viscosity and the low-speed stirring viscosity, the more accurately the circuit shape can be drawn when fluidizing the tin paste to form a circuit, and the stationary shape formed as a circuit on the substrate. In this state, the apparent viscosity increases and the circuit shape can be easily maintained.

  From the results shown in Table 1, the tin paste of the example has a higher thixo ratio than the comparative example. Therefore, it can be said that the flake-shaped particles have a greater thixotropy than the spherical powder. The above-mentioned tin powder has powder characteristics in a range that does not affect the practical viscosity such as printing performance and processing performance when processed into a paste, has excellent rheological characteristics, and the supplied paste is It can be said that the shape stability before melting is improved. And it can be said that the tin paste using this tin powder is easy to supply the paste in a screen printing method or the like and has excellent shape stability after supply.

  The following is considered as a reason why the tin powder according to the present invention has good shape stability through Examples and Comparative Examples. That is, it is difficult to obtain thixotropy with a paste containing only spherical powder, and it is difficult to control the rheological properties of the paste such as printability and shape stability. The contact surface between the particles can be sufficiently secured even if the amount of tin powder in the paste is small, and the amount of binder added can be increased accordingly. Therefore, by increasing the amount of binder added to improve paste shape stability and adhesion, paste supply performance, shape stability and adhesion performance can be improved, and as a result, connection reliability can be improved. Can do. As a result, it is possible to improve handling and connection reliability, which have been problems with conventional lead-free solder.

  The tin powder of the present invention described above is excellent in shape stability when processed into a tin paste containing the tin powder and supplied onto the substrate. And it was possible to realize tin powder flaking by plastic deformation, which has been considered difficult in the past. When the tin powder according to the present invention is applied to a fine and high-density wiring board or the like, it is excellent in handleability and shape stability. Furthermore, when a tin paste is placed on a substrate, the paste can be prevented from protruding from a predetermined position, and a tin paste that can be mounted with high accuracy can be supplied to the market at a low cost. Such tin paste is effective for application to uses such as via connection, wiring, and mounting adhesive.

It is an observation image by the scanning electron microscope (magnification 2000 times) of the tin powder obtained in Example 1.

Claims (10)

The shape of the particles is flaky,
A tin powder having an average equivalent-circle diameter of 1 μm to 10 μm in the planar direction of the particles. The tin powder according to claim 1, wherein the volume cumulative average particle diameter D ₅₀ measured by a laser diffraction / scattering particle size distribution measurement method is 1.5 μm to 15 μm. The tin powder according to claim 1 or 2, wherein the aspect ratio ([average circular equivalent diameter (μm)] / [average thickness (μm)] in the planar direction) is 5 to 40. The tin density according to any one of claims 1 to ³ , wherein the tap density is 3 g / cm ^{3 to} 5 g / cm ³ . Tin powder according to any one of claims 1 to 4 having a specific surface area of 0.3m ² / g~1m ² / g. A tin paste comprising the tin powder according to any one of claims 1 to 5. The tin powder production method according to any one of claims 1 to 5, wherein tin powder having a granular shape is dispersed in a dispersion medium, and the dispersion slurry is treated in a medium mill. The method for producing a tin powder according to claim 7, wherein the average particle size of the tin powder having a particle shape of a granular shape with a scanning electron microscope (SEM) is 0.5 μm to 7 μm. The method for producing tin powder according to claim 7 or 8, wherein the medium mill is a bead mill. The method for producing tin powder according to any one of claims 7 to 9, wherein a medium used in the medium mill is media beads having a particle size of 0.3 mm or less.