JP3925792B2 - Method for producing metal sphere for conductive spacer - Google Patents

Description

【００３５】
（実施例２）
図１に記載のRFプラズマ装置を用いて、実質的にCu（不可避的不純物含む）からなる金属片を用い、目標直径が300.0μmの導電性スペーサ用金属球を以下に示す製造条件で作製した。この際、金属片のCV値が異なる２条件で製造を行った。なお、金属片の作製、及びCV値の測定は実施例１と同様にして行った。
【００３６】
（製造条件）
金属片寸法：φ0.2mm×L0.450mm（体積0.0141mm³、L/φ=2.25）
プラズマ動作ガス：Ar 30L/min
プラズマトーチ：水冷式石英管φ50mm、高周波誘導コイルφ70mm
チャンバ：最大内径φ800mm、最大内高1500
チャンバ内雰囲気：Arガス雰囲気
原料供給装置：電磁フィーダー
高周波誘導コイル入力条件：4MHz、12kW
【００３７】
上述の製造条件により得られた導電性スペーサ用金属球について実施例１と同様の分級を行ない、プラズマ炎に導入した金属片の重量に対して、約40％の重量の金属球を回収した。分級後の金属球から無作為に約60球を抽出し、実施例１と同様の方法により金属球の平均粒径、金属球のCV値、酸素含有量の測定を行った。結果を表２に示す。
【００３８】
【表２】

【００３９】
表２に示すように、プラズマ炎中に導入した金属片のCV値と、分級後の金属球のCV値は一致している。よって、金属片のばらつきを小さくすることにより、分級後の金属球における直径のばらつきを小さくすることが可能である。
【００４０】
【発明の効果】
本発明によれば電子機器の製造における加熱工程等での接合寸法の変動が小さく、またアウトガスの発生を抑制することが可能な導電性スペーサ用金属球の製造方法を提供することができ、電子部品の製造において欠くことのできない技術となる。
【図面の簡単な説明】
【図１】本発明の製造方法を実施する製造装置の一例を示す模式図である。
【符号の説明】
１．原料供給装置、２．原料供給位置、３．プラズマ炎、４．チャンバ、５．金属球回収部、６．プラズマ動作ガス供給位置、７．コイル、８．RFプラズマトーチ、９．導電性スペーサ用金属球、１０．水冷管、１１．プラズマ動作ガス供給装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a metal sphere for a conductive spacer that is excellent in high-temperature strength, has a clean surface, and is suitable for use as a conductive spacer in an electronic component.
[0002]
[Prior art]
In recent years, electronic devices are required to be smaller, lighter, and higher performance. As a manufacturing method suitable for reduction in size and weight, a bonding method called BGA (Ball Grid Array) or CSP (Chip Size Package) has been widely used. Both BGA and CSP are IC packages in which input / output pads are arranged on the back side of the package. A package in which metal balls are mounted in advance is placed on the mounting substrate, and the package and the mounting substrate are separated by batch reflow. This is a technique for joining.
In these joinings, Sn-based solder, which has been widely used in the past, has become the mainstream, and metal balls obtained by spheroidizing this solder are used.
[0003]
Solder spheroidization is performed by a cooling method in oil or the like. In this oil-cooling method, metal strips cut to a fixed size are poured into oil with the upper part higher than the melting point of the metal pieces and the lower part below the melting point, and spheroidized using surface tension. It is a method to make it. In addition, a method has also been proposed in which a metal strip is freely dropped into a vertically arranged furnace core tube and heated above the melting point of the metal used in the metal strip to make it spherical. This method is disclosed in, for example, Japanese Patent Laid-Open No. 4-066601.
[0004]
On the other hand, as another bonding method that does not use metal balls such as BGA and CSP, bonding with a conductive resin is also performed. For example, Japanese Patent Application Laid-Open No. 9-167934 provides a crystal resonator holding structure that is electrically conductive by using a conductive resin for bonding the crystal resonator and the holding electrode. As such a conductive resin, an epoxy Ag adhesive or the like is used.
[0005]
[Problems to be solved by the invention]
Along with the improvement in performance of electronic devices, high-accuracy bonding dimensions are required when the components constituting the electronic device are bonded. Conventionally, the required bonding dimensions have been in the vertical and horizontal plane directions. However, in the case of electronic components used in some electronic devices, in addition to the plane direction, the height direction, that is, the substrate and the component to be bonded With respect to the distance between them, a highly accurate joint dimension is required. In other words, in such an electronic device, the bonding portion is required not only to function as an electrically conductive portion but also to function as a conductive material.
[0006]
However, in conventional joints using Sn-based alloy metal balls, there are cases where it is difficult to achieve high precision in the joint dimension in the height direction. This is due to the following reason.
The manufacturing process has become more complicated with higher performance of electronic devices, and some electronic devices are completed through a plurality of heat treatment steps. In this case, the joint part joined at the initial stage of the manufacturing process is heated again in a later process. A joint portion such as a BGA using a Sn-based alloy metal ball is softened every time the heating process is performed, but the softening of the joint portion causes a reduction in dimensional accuracy in the height direction. In addition, when a conductive resin is used, it is difficult to accurately control the required height in the first place.
[0007]
In order to improve the dimensional accuracy in the height direction described above, it is effective to use a metal ball such as Cu or Cu alloy having a higher melting point than that of solder for the joint. However, in the conventional manufacturing method, since it is difficult to increase the heating temperature until a high melting point metal such as Cu can be melted in a short time, it is not suitable for efficient spheroidization of a high melting point metal. Met.
[0008]
This invention provides the manufacturing method of the metal sphere for conductive spacers which can suppress the fluctuation | variation of the joining dimension in the heating process etc. in manufacture of an electronic device.
[0009]
[Means for Solving the Problems]
The inventor of the present invention has solved the above problem by forming a metal sphere for a conductive spacer by a plasma process.
That is, the present invention is a method for producing a metal sphere for a conductive spacer in which a single metal piece formed by cutting into a predetermined size is introduced into a plasma flame, and melting and solidification are performed with the single metal piece .
The metal piece is preferably a metal or alloy of Cu, Ag, or Au.
[0010]
Further, the metal piece preferably has a volume CV value calculated by the following formula from the average volume V _ave of the metal piece and the standard deviation σ _V of the volume distribution of the metal piece of 5% or less.
Formula: CV value = σ _V / V _ave × 100 (%)
The metal piece is obtained by cutting a wire material, and the ratio of the diameter φ of the wire material and the length L after cutting is preferably 0.5 ≦ L / φ ≦ 3.0.
The metal piece preferably has an average volume of 0.0005 mm ³ or more.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
As described above, an important feature of the present invention is that a configuration in which a metal piece cut into a predetermined size is introduced into a plasma flame.
In the present invention, a metal or alloy having a higher melting point than that of solder, which has been conventionally used, is used for the metal piece. Specifically, it is preferable to use a metal or an alloy of Cu having a small specific resistance, Ag, or Au, which is an element of the same. These metal pieces are introduced into a plasma flame in an inert atmosphere to be melted and spheroidized.
[0012]
A plasma flame is an ionized gas that dissociates molecules in the gas into atomic states by applying energy to the gas, and further ionizes the atoms into ions and electrons. Compared to the conventional manufacturing method described earlier, It can be heated to a high temperature, and the temperature is 5000 ° C. or higher in the high temperature part. If metal pieces to a high temperature of the plasma flame Ru is introduced, the metal pieces are dissolved instantaneously, it is possible to efficiently spheroidized refractory metal so spheronized by its own surface tension. When the molten and spheroidized metal pieces are discharged from the plasma flame, they solidify to form metal spheres.
[0013]
In the process of melting to solidification in such a plasma flame, the volume fluctuation hardly occurs when the melting and solidification are performed with a single metal piece. The melting and solidification process is not performed with a single piece of metal, and some of the metal spheres fluctuate in contact with other pieces of metal during melting, but with these metal balls, a single piece of metal solidifies. Since the volume and shape are significantly different from those of, it can be easily removed by classification. Therefore, by using metal pieces cut into a predetermined size and having the same volume, it is possible to efficiently obtain metal balls for conductive spacers having a uniform diameter.
By the manufacturing method described above, it is possible to efficiently manufacture metal balls for conductive spacers that have a high melting point and are not easily softened.
[0014]
In addition, in the production method of the present invention, the oxide formed on the metal piece can be reduced during melting and spheroidization. For this reason, the manufacturing method of the present invention is also effective for the problems described below, which are included in conventional metal balls for conductive spacers.
[0015]
In the joining using the metal balls for conductive spacers and the conductive resin using the conventional solder, outgas from the joint is also a problem. This is a problem mainly in electronic parts whose members are vacuum-sealed, for example, electronic parts using a crystal resonator. An electronic component using a crystal unit is one in which a crystal unit is bonded to a substrate in a housing using metal balls for conductive spacers or conductive resin, and then the inside of the housing is evacuated and vacuum-sealed. is there.
[0016]
In electronic parts in which members such as crystal units are vacuum-sealed, if the joint is heated after vacuum-sealing, a volatile solvent in the resin is generated as an outgas when it is joined by a conductive resin. To do. In addition, when bonded by conductive spacer metal spheres, surface oxidation is inevitable during the spheroidization of Sn-based solder. In addition to the formation of an oxide film on the surface of the metal sphere for the conductive spacer, adhesion of contaminants is inevitable. These oxide films and contaminants cause outgassing during heating at the joint portion formed of the conductive spacer metal spheres. In an electronic component in which a member is vacuum-sealed, if outgas is generated inside the vacuum-sealed casing, the accuracy and reliability of the electronic component is impaired, which is a serious problem.
[0017]
In the manufacturing method of the present invention, as described above, the temperature reaches 5000 ° C. or higher in the high temperature part of the plasma flame. When the metal piece is heated to a high temperature such as 5000 ° C. in the plasma flame, the oxygen forming the oxide on the surface of the metal piece is dissociated and scattered in the atmosphere. As a result, it is possible to obtain a metal sphere for a conductive spacer in which oxidation on the surface is suppressed.
By performing melting, spheroidization, and solidification of the metal piece in an inert atmosphere, a metal sphere for a conductive spacer having a lower oxygen content can be obtained. In the present invention, as the inert gas atmosphere, a nitrogen gas atmosphere, an argon gas atmosphere, or the like can be used.
[0018]
As described above, according to the production method of the present invention, since the melting point is high, a high-melting-point metal piece, which has been difficult to spheroidize in the past, can be efficiently processed in a state where surface oxidation and contamination are suppressed. It becomes possible to spheroidize. Therefore, according to the manufacturing method of the present invention, it is possible to obtain a conductive spacer metal sphere that hardly generates outgas.
[0019]
In the present invention, the metal piece preferably has a volume CV value of 5% or less.
The CV value used in the present invention is a value representing the uniformity of the volume of the metal piece, and is a value calculated from the following formula from the average volume V _ave of the metal piece and the standard deviation σ _V of the volume distribution of the metal piece: It is.
CV value = σ _V / V _ave × 100 (%)
[0020]
As described above, in the method for producing a metal sphere for a conductive spacer according to the present invention, in the process from melting to solidification, when the melting to solidification is performed with a single metal piece, the volume is almost changed. Absent. In other words, the process from melting to solidification is not performed with a single piece of metal, and the dispersion of the metal sphere after removing the metal sphere with greatly different volumes and shapes by classification is the metal piece before being introduced into the plasma flame. Depends on the variation of Therefore, in order to obtain metal balls for conductive spacers having a uniform diameter in the present invention, it is preferable to use metal pieces having a uniform volume.
[0021]
In addition, if there are metal pieces with a very small volume, these metal pieces evaporate in the plasma flame. Since the evaporated metal is solidified as a fine powder, the fine powder is mixed into the metal sphere. The mixed fine powder adheres to the surface of the metal sphere, and the surface cleanliness is lost with the metal sphere. Since the metal spheres for conductive spacers are used for electronic parts and the like, the surface is required to be clean, but once the fine powder adhering to the metal spheres is difficult to remove, as a result, the metal spheres Would be unsuitable for conductive spacer applications.
[0022]
By using a metal piece having a CV value of 5% or less, which is a value representing the uniformity of the volume of the metal piece, it is possible to obtain a metal sphere for a conductive spacer having a more uniform diameter, and in addition, on the surface of the metal sphere. The adhesion of fine powder can be reduced and surface cleaning can be achieved. It is more preferable to use a metal piece having a CV value of 1% or less. More preferably, it is 0.5% or less.
[0023]
As a simple method for obtaining metal pieces of a predetermined size with a uniform volume, there is a method of cutting a wire material with a cutter or the like. In this case, the cut metal piece preferably has a ratio of diameter φ and length L such that 0.5 ≦ L / φ ≦ 3.0.
When the ratio of the length L to the diameter φ is small, not only is the cutting difficult, but the ratio of the cut portion area to the surface area of the metal piece is increased. Since the cutting is due to plastic deformation, the shape of the cut portion and its periphery is non-uniform, and if the area ratio occupied by the cut portion is large, the volume of the metal piece becomes non-uniform. Therefore, in order to reduce the variation in volume in the metal piece after cutting, it is preferable to satisfy 0.5 ≦ L / φ.
On the other hand, if the ratio of the length L to the diameter φ is too large, the metal piece is easily divided into two or more in the longitudinal direction at the time of melting in the spheroidization in the plasma flame, and the metal for the conductive spacer having a uniform size It becomes difficult to obtain a sphere. Therefore, it is preferable that L / φ ≦ 3.0. More preferably, 1.0 ≦ L / φ ≦ 2.0.
[0024]
Furthermore, in the present invention, by setting the average volume of the metal pieces to 0.0005 mm ³ or more, metal balls for conductive spacers having an average diameter of 0.1 mm or more can be produced.
When a conductive spacer is used for an electronic component, in order to ensure the dimension in the height direction of the joint, the conductive spacer metal sphere before joining requires a predetermined diameter. In the conventional spheronization method as described in Japanese Patent No. 066601, the amount of heat at the time of heating is insufficient, and therefore, metal balls for conductive spacers having a diameter of 0.1 mm or more are used for metal pieces having a melting point higher than that of solder. Was particularly difficult.
According to the present invention, since the metal piece can be heated to a high temperature of 5000 ° C. or more, the conductive spacer having an average diameter of 0.1 mm or more suitable for the spacer application can be obtained by using the metal piece having an average volume of 0.0005 mm ³ or more. It is possible to produce metal balls for use.
[0025]
The manufacturing method of the metal sphere for conductive spacers of the present invention can be carried out, for example, by an apparatus shown in FIG.
In FIG. 1, an RF plasma torch 8 cooled by a water-cooled tube 10 has a plasma flame generated by a plasma operating gas supplied from a plasma operating gas supply position 6 by a plasma operating gas supply device 11 and high-frequency energy generated from a coil 7. 3 is generated.
The metal piece cut into a predetermined size that has been put into the raw material supply device 1 (for example, the electromagnetic vibration raw material supply device) is put into the high temperature part (5000 to 10000 ° C.) inside the plasma flame 3 from the raw material supply position 2 together with the carrier gas. Is done. The raw material thrown into the plasma flame melts instantly and becomes spherical due to surface tension.
[0026]
The raw material supplied from the raw material supply position 2 located upstream of the plasma flame passes through a highly refined plasma portion containing hydrogen gas in a sufficiently heated and melted state, and impurities such as oxides are reduced. Is done.
The metal pieces treated in the plasma flame are solidified in an inert gas atmosphere while falling in the chamber 4, and are collected and collected in the lower metal sphere collecting unit 5 as conductive metal balls 9.
As described above, the metal spheres for conductive spacers having a uniform diameter with less surface oxidation and contamination can be efficiently produced.
[0027]
Typical plasma flames that can be applied to the present invention include DC plasma and RF plasma. In the present invention, it is preferable to use RF plasma. This is because RF plasma, unlike DC plasma, does not require an electrode and contains less impurities due to electrode materials. In addition, with RF plasma, the gas flow rate of the plasma operating gas can be lowered compared to DC plasma, so it is possible to heat the metal pieces sufficiently by increasing the residence time of the metal pieces in the plasma flame. It is.
[0028]
In addition, as the plasma operating gas for generating the plasma flame, argon gas, nitrogen gas or the like generally used as the plasma operating gas can be used, but it is preferable to contain hydrogen gas therein.
In the present invention, the oxygen concentration on the surface of the metal sphere for the conductive spacer can be reduced by introducing the metal piece into the plasma flame. However, if hydrogen is introduced into the plasma working gas, hydrogen ions, excitation The oxygen concentration can be further reduced by the reduction reaction of atoms and the like. When hydrogen gas is contained in the plasma operating gas, the concentration of the hydrogen gas in the plasma operating gas is preferably 1 vol% or more in order to obtain a sufficient effect. More preferably, it is 3 vol% or more. If the hydrogen gas concentration is increased, the oxygen concentration can be further reduced. On the other hand, if the hydrogen gas is excessively contained, the plasma flame becomes unstable and spheroidization of the metal pieces cannot be achieved. There is. Therefore, it is preferable to contain hydrogen gas at 20 vol% or less.
[0029]
As a use of the metal sphere for conductive spacers of the present invention, for example, it can be used for electrical connection between spacers of printed boards and substrates.
Since the melting point is higher in BGA connection than in connection with a normal solder ball, the conductive spacer metal spheres of the present invention are installed on the periphery of the BGA substrate, and if these are melted and bonded in advance with EB or the like, When reflowing the BGA substrate for melting the solder balls, the metal ball of the present invention does not melt because of its high melting point, and as a result, a function to prevent crushing can be added. Therefore, the reliability of BGA connection by reflow can be improved.
Moreover, the metal sphere for conductive spacers of the present invention can be used by coating the surface with a low melting point metal such as solder or applying Au plating, if necessary.
[0030]
【Example】
Example 1
Using the RF plasma apparatus shown in FIG. 1, a metal sphere for conductive spacer having a target diameter of 300.0 μm using a metal piece containing 71% Ag by mass and the balance being substantially Cu is shown below. It was produced under manufacturing conditions. The Ag—Cu alloy (metal piece) to be introduced into the plasma flame was prepared by cutting a 0.2 mm diameter wire with a rotary blade to a certain size. The CV value is calculated from the measured values by measuring the length and diameter of the metal piece from the image of the side (surface parallel to the axis) of each metal piece using about 60pcs of metal pieces. Value.
[0031]
(Production conditions)
Metal piece dimensions: φ0.2mm × L0.450mm (volume ^{0.0141mm 3, L / φ = 2.25} )
CV value of metal piece: 0.47
Plasma operating gas: Ar 30L / min, H ₂ 1L / min, mixed gas plasma torch: water-cooled quartz tube φ50mm, high-frequency induction coil φ70mm
Chamber: Maximum inner diameter φ800mm, Maximum inner height 1500
Chamber atmosphere: Ar gas atmosphere Raw material supply device: Electromagnetic feeder High frequency induction coil Input conditions: 4MHz, 10kW
[0032]
Conductive spacer metal spheres obtained under the above-mentioned manufacturing conditions are classified by sieving and rolling (classification method that removes the metal spheres that have not been moved straight on the inclined flat plate) and introduced into the plasma flame. About 30% of the metal balls for conductive spacers were collected with respect to the weight of the metal pieces. 100 balls were randomly extracted from the classified metal balls for conductive spacers, and the average diameter and average roundness were measured. These images are analyzed for the extracted SEM images of the conductive spacer metal spheres, and the average diameter is calculated from the diameter (equivalent circle diameter) assuming the projected area is a circle, and the sphericity is calculated from the equivalent circle diameter / maximum diameter. The average roundness was calculated. The volume of the conductive spacer metal sphere was calculated from the equivalent circle diameter, and the volume CV value of the conductive spacer metal sphere was determined. In addition, the oxygen content in the metal balls for conductive spacers was analyzed by the ICP method. The results are shown in Table 1.
[0033]
As shown in Table 1, metal spheres for conductive spacers with a target diameter and high sphericity can be manufactured. Moreover, the CV value of the metal spheres for conductive spacers after classification is 0.47, which is the same value as the CV value of the metal pieces introduced into the plasma flame. In addition, the oxygen content has reached a very low value of 1 ppm or less, which is the detection limit of the device.
[0034]
[Table 1]

[0035]
(Example 2)
Using the RF plasma apparatus shown in FIG. 1, a metal sphere for a conductive spacer having a target diameter of 300.0 μm was produced under the manufacturing conditions shown below using a metal piece substantially made of Cu (including inevitable impurities). . At this time, the metal piece was manufactured under two conditions with different CV values. The production of the metal piece and the measurement of the CV value were performed in the same manner as in Example 1.
[0036]
(Production conditions)
Metal piece dimensions: φ0.2mm × L0.450mm (volume ^{0.0141mm 3, L / φ = 2.25} )
Plasma operating gas: Ar 30L / min
Plasma torch: Water-cooled quartz tube φ50mm, high-frequency induction coil φ70mm
Chamber: Maximum inner diameter φ800mm, Maximum inner height 1500
Chamber atmosphere: Ar gas atmosphere Raw material supply device: Electromagnetic feeder High frequency induction coil Input conditions: 4MHz, 12kW
[0037]
The metal balls for conductive spacers obtained under the above-described manufacturing conditions were classified in the same manner as in Example 1 to collect metal balls having a weight of about 40% with respect to the weight of the metal pieces introduced into the plasma flame. About 60 balls were randomly extracted from the classified metal spheres, and the average particle diameter of the metal spheres, the CV value of the metal spheres, and the oxygen content were measured in the same manner as in Example 1. The results are shown in Table 2.
[0038]
[Table 2]

[0039]
As shown in Table 2, the CV value of the metal piece introduced into the plasma flame matches the CV value of the metal sphere after classification. Therefore, by reducing the variation in the metal pieces, it is possible to reduce the variation in the diameter of the classified metal sphere.
[0040]
【The invention's effect】
According to the present invention, it is possible to provide a method for producing a metal sphere for a conductive spacer, in which the variation in the bonding dimension in the heating process or the like in the production of an electronic device is small, and the generation of outgas can be suppressed. This technology is indispensable in the production of parts.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of a production apparatus for carrying out a production method of the present invention.
[Explanation of symbols]
1. 1. Raw material supply device, 2. Raw material supply position; 3. Plasma flame, Chamber, 5. 5. Metal ball recovery unit, 6. Plasma operating gas supply position; Coil, 8. RF plasma torch, 9. 9. Metal spheres for conductive spacers Water-cooled tubes, 11. Plasma operating gas supply device

Claims (5)

A method for producing a metal ball for a conductive spacer, wherein a single metal piece cut into a predetermined dimension is introduced into a plasma flame, and melting and solidification are performed with the single metal piece .   The method for producing a metal ball for a conductive spacer according to claim 1, wherein the metal piece is a metal or alloy of any one of Cu, Ag, and Au. The metal piece has an average volume _Vave of the metal piece and a CV value of the volume calculated by the following formula from the standard deviation σ _V of the volume distribution of the metal piece is 5% or less. The manufacturing method of the metal sphere for conductive spacers of 2.
Formula: CV value = σ _V / V _ave × 100 (%)   The metal piece is formed by cutting a wire material, and the ratio of the diameter φ of the wire material and the length L after cutting is 0.5 ≦ L / φ ≦ 3.0. The manufacturing method of the metal sphere for conductive spacers as described in any one of. 5. The method for producing metal balls for conductive spacers according to claim 1, wherein the metal pieces have an average volume of 0.0005 mm ³ or more.

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