solder ball

Abstract

Provided is a solder ball capable of having increased sphericity. The solder ball contains 19 to 25 mass% of Sn with Au being the main component of the remainder, and further contains any one additive element from among Mg, Al, Si, Ti, V, Cr, Mn, and Ce. The concentration of the additive element in relation to the overall solder ball is 0.01 to less than 0.1 ppm by weight. A uniform lamellar structure is formed by a first phase (also referred to as an Au-rich phase) mainly composed of Au5Sn and a second phase mainly composed of AuSn, and thereby the occurrence of unevenness and shrinkage cavities in the surface is suppressed and sphericity is increased.

Description

[Technical Field]

[0001] The present invention relates to solder balls. [Background technology]

[0002] Solder paste and sheet-like brazing filler metal made of Au-Sn alloys are used as bonding materials for sealing packages that hermetically seal electronic devices such as semiconductor light-emitting devices in which semiconductor light-emitting elements are mounted on circuit boards, SAW (Surface Acoustic Wave) filters, FBAR (Film Bulk Acoustic Resonator) filters, and quartz oscillators, due to their high strength and high electrical conductivity.

[0003] Patent Document 1 discloses an Au-Sn-containing alloy paste, which is characterized by mixing an Au-Sn alloy powder having a particle size of 10 μm or less, containing 20 to 25 wt% Sn and the remainder Au, with 15 to 30 wt% of flux containing at least an activator.

[0004] Patent Document 2 discloses a method for providing solder bumps for use in flip-chip bonding technology using a solder composed of 80% Au and 20% Sn.

[0005] Patent Document 3 discloses a solder ball containing 19% by mass or more and 25% by mass or less of Sn, with the remainder being mainly Au, and containing one element of Fe, Cr, or Ni, wherein the concentration of Fe in the entire solder ball is 0.1 ppm by mass or more and 10 ppm by mass or less, if Fe is contained, the concentration of Cr in the entire solder ball is 0.1 ppm by mass or more and 100 ppm by mass or less, if Cr is contained, and the concentration of Ni in the entire solder ball is 1 ppm by mass or more and 5000 ppm by mass or less, if Ni is contained.

[0006] When solder balls formed from the Au-Sn alloy are mounted as a bonding material for the sealed package or other semiconductor devices, a large number of solder balls are processed using a ball mounter or a solder jetting device (manufactured by PacTech). When mounting solder balls using a ball mounter, it is necessary to place each solder ball in the appropriate position to prevent mounting defects. Furthermore, when mounting solder balls using a solder jetting device, it is necessary to process them without causing clogging. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-54653 [Patent Document 2] Japanese Patent Application Publication No. 5-136152 [Patent Document 3] International Publication No. 2020 / 217833 Summary of the Invention [Problem to be solved by the invention]

[0008] However, if the sphericity of the solder balls is not sufficiently high, they are more likely to cause mounting defects when using a ball mounter or clogging when using a solder jet device, resulting in reduced productivity. This effect is particularly pronounced when the solder ball diameter is 250 μm or less.

[0009] An object of the present invention is to provide a solder ball that can have improved sphericity. [Means for solving the problem]

[0010] The solder ball according to the present invention contains 19% by mass or more and 25% by mass or less of Sn, with the remainder being primarily Au, and contains one additive element selected from Mg, Al, Si, Ti, V, Cr, Mn, and Ce, with the concentration of the additive element relative to the entire solder ball being 0.01 ppm by weight or more and less than 0.1 ppm by weight. [Effects of the Invention]

[0011] According to the present invention, a uniform eutectic alloy of Au and Sn can be obtained, and the sphericity of the solder ball can be improved. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic diagram of a USD manufacturing device used to manufacture solder balls by the uniform droplet spray method. [Figure 2A] FIG. 2A is a plan view showing an example in which solder balls according to the embodiment are arranged in a closest-packed manner. [Figure 2B] FIG. 2B is a plan view showing an example in which solder balls according to the embodiment are arranged at intervals L. FIG. [Figure 3A] FIG. 3A is a schematic end view showing a state before melting of a solder ball according to an embodiment. [Figure 3B] FIG. 3B is a schematic end view showing the state of the solder ball according to the embodiment after melting. [Figure 4A] FIG. 4A is a perspective view showing an example of the arrangement of solder balls in a corner portion according to the embodiment. [Figure 4B] FIG. 4B is a schematic diagram showing an example of a joint at a corner according to the embodiment. [Figure 5] FIG. 5 is a schematic diagram showing an example of a linear joint according to the embodiment. [Figure 6] FIG. 6 is a partial cross-sectional view schematically showing an LED package manufactured using the solder ball according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Similar components are designated by similar reference numerals, and the description thereof will be omitted as appropriate.

[0014] 1. Embodiment (1) Solder ball configuration The solder ball 34 according to this embodiment is an Au-Sn alloy containing 19% to 25% by mass of Sn, with the remainder being primarily Au, and is a uniform eutectic alloy of Au5Sn1 and AuSn formed by adding one of the following additive elements: Mg, Al, Si, Ti, V, Cr, Mn, and Ce. The concentration of the additive element in the entire solder ball 34 is 0.01 ppm by weight or more but less than 0.1 ppm by weight.

[0015] Conventional Au-Sn alloy solder balls have the problem of having uneven surfaces and, in some cases, poor appearance due to shrinkage cavities. This is thought to be due to the formation of a non-uniform Au-rich phase near the surface of the solder ball during cooling during the solder ball manufacturing process.

[0016] In the solder ball 34 of this embodiment, trace amounts of Mg, Al, Si, Ti, V, Cr, Mn, and Ce are dispersed within the AuSn, providing numerous nucleation sites during solidification. This suppresses the formation of a non-uniform Au-rich phase during cooling, resulting in the formation of a uniform lamellar structure consisting of a first phase (also referred to as the Au-rich phase) primarily composed of AuSn and a second phase primarily composed of AuSn. This suppresses the occurrence of surface irregularities and shrinkage cavities, and improves sphericity. The improved sphericity is preferably 0.7% or less. This reduces mounting defects in ball mounters and clogging in solder jetting equipment.

[0017] If the concentration of the additive element relative to the entire solder ball 34 is less than 0.01 ppm by weight, the effect of increasing the sphericity of the solder ball is small, which is not preferable. Also, if the concentration of the additive element relative to the entire solder ball 34 is increased to 0.1 ppm by weight or more, the effect of increasing the sphericity is lost due to the influence of oxides, and the upper limit is 0.1 ppm by weight.

[0018] The diameter of the solder balls 34 in this embodiment is not limited as long as the effects of the present invention are exhibited, but is preferably 10 μm or more and 500 μm or less. This range allows for the production of solder balls with uniform diameter accuracy. A more preferred diameter range is 20 μm or more and 400 μm or less, and even more preferably 50 μm or more and 300 μm or less. In conventional technology, when the diameter of the solder balls is 500 μm or less, particularly 300 μm or less, poor sphericity of the solder balls can easily lead to mounting failures in a ball mounter or clogging in a solder jet device, resulting in reduced productivity. The solder balls 34 in this embodiment have enhanced sphericity, which can prevent mounting failures in a ball mounter or clogging in a solder jet device.

[0019] In the solder ball 34 of this embodiment, when the concentration of the additive element is within the above range, the oxide film on the surface is reliably dissolved when melted, resulting in good wettability. It is believed that the wettability is affected by the oxide film on the solder ball surface, and when the concentration of the additive element is outside the above range, the oxide film becomes difficult to dissolve, which can result in a decrease in wettability.

[0020] (2) Manufacturing method of solder balls To achieve uniform diameter accuracy, solder balls 34 are preferably formed using the uniform droplet spray method (UDS). A manufacturing apparatus for solder balls 34 using the UDS method is described with reference to FIG. 1. The USD manufacturing apparatus 31 shown in FIG. 1 includes a nozzle 35 that ejects molten solder 33 downward, a vibration device 37 that vibrates the nozzle 35, a nozzle stand 39 that slidably holds the nozzle 35, and a solder reservoir 41. The nozzle 35 has an outlet 47 below it. The nozzle 35 is connected to the vibration device 37 via a steel connecting rod 49. In the solder reservoir 41, the molten solder 33 is maintained at a temperature a predetermined temperature higher than its melting point. The nozzle 35 has a nozzle path 51. The tip of the nozzle path 51 is connected to the outlet 47 below the nozzle. The molten solder 33 stored in the solder reservoir 41 flows through the stand path 53 and the nozzle path 51 and flows out from the outlet 47. USD manufacturing apparatus 31 vibrates nozzle 35 with vibration device 37 while causing molten solder 33 to flow out from outlet 47, thereby separating the flowed-out molten solder 33 into droplets 55. With the exception of the above, the method for manufacturing solder balls can be the same as the method described in Patent Document 3. The method for manufacturing solder balls using USD manufacturing apparatus 31 produces solder balls 34 with uniform droplet sizes and highly accurate spherical diameters.

[0021] (3) Concentration analysis method This section explains the analytical method for elemental concentration. Elemental concentration is analyzed using either ICP-MS or ICP-OES depending on the concentration range. When the concentration range is less than 100 ppm by mass, analysis can be performed using inductively coupled plasma mass spectrometry (ICP-MS). When the concentration range is 100 ppm by mass or more, analysis can be performed using inductively coupled plasma optical emission spectrometry (ICP-OES).

[0022] (About ICP-MS) <Sample pretreatment method> The analytical equipment used is an Agilent Technologies Inc. (model number: Agilent 8800). The pretreatment procedure is as follows: 0.1 g of solder balls are weighed out, 20 ml of aqua regia (composition: a 3:1 mixture of hydrochloric acid and nitric acid) is added, and the mixture is heated to approximately 200°C to dissolve. After cooling, the mixture is transferred to a polypropylene (hereinafter referred to as "PP") measuring flask (volume: 100 mL) and made to volume with ultrapure water. A quartz glass beaker is used as the decomposition vessel to avoid the inclusion of impurities.

[0023] <Analysis method> The analytical method is the standard addition method. Specifically, 10 mL of the solution is poured into multiple PP measuring flasks (volume: 100 mL) and a solution of the target element (Mg, Al, Si, Ti, V, Cr, Mn, Ce) diluted to 100 μg / L is added in 2 mL increments to the PP measuring flasks. The analytical value of each solution is then extrapolated to the assumption that the amount added is zero, and the analytical value of the target element is determined. Kanto Chemical reagents are used for the single element standard solutions.

[0024] <measurement> In ICP-MS analysis, polyatomic ions generated interfere with the measurement, increasing the background. Therefore, cool plasma (output: 600 W) is used to suppress the influence of interfering ions.

[0025] (About ICP-OES) <Sample pretreatment method> The analytical equipment used is a Thermo Fisher Scientific model (iCAP6500). The pretreatment procedure is as follows: 1.0 g of solder balls are weighed out, and 20 mL of aqua regia (composition: a 3:1 mixture of hydrochloric acid and nitric acid) is added, and the mixture is heated to approximately 200°C to dissolve. After cooling, the mixture is transferred to a borosilicate glass (hereafter referred to as "glass") measuring flask (volume: 100 mL) and the volume is adjusted to the desired volume with heated and degassed aqua regia.

[0026] <Analysis method> The analytical method is the standard addition method. Specifically, 10 mL of the solution is poured into several glass measuring flasks (volume: 100 mL) and 0.1 mL of a single-element standard solution (1000 μg / L) of the target analyte (Sn) is added to the glass measuring flasks in increments of 0.1 mL. Based on the analytical values ​​of each solution, the extrapolated value assuming the added amount is zero is used as the analytical value of the target element. Reagents manufactured by Kanto Chemical are used for the single-element standard solution.

[0027] <measurement> Measure Sn at a wavelength of 226.8 nm using ICP-OES.

[0028] (4) Solder ball mounting and joining methods The solder ball 34 of this embodiment can be used as a bonding material for a sealing package that hermetically seals electronic devices such as a semiconductor light-emitting device in which a semiconductor light-emitting element is mounted on a circuit board, a SAW filter, an FBAR filter, and a quartz oscillator, or as a bonding material for other semiconductor devices.

[0029] When the solder balls 34 of this embodiment are mounted on a bonding surface as a bonding material for the above-mentioned sealed package or other semiconductor devices, they can be mounted using, for example, a ball mounter. The ball mounter may be, for example, that described in Japanese Patent Application Laid-Open No. 2012-256748. The ball mounter includes, for example, a ball array plate with suction holes at the mounting positions of the solder balls 34. After the solder balls 34 are suction-held on the ball array plate, the ball array plate is transported to the bonding surface and placed on the bonding surface coated with flux. The solder balls 34 adhere to the bonding surface due to the adhesive force of the flux. Using the ball mounter, multiple solder balls can be mounted at once.

[0030] When mounting the solder balls 34 of this embodiment as a bonding material for the above-mentioned sealed package or other semiconductor devices, they can be mounted using, for example, a solder jetting device (manufactured by PacTech). The solder jetting device loads the solder balls 34 into a microtube such as a capillary, irradiates them with laser light to melt the solder balls 34, and simultaneously extrudes them using an inert gas or the like to temporarily fix the solder balls 34 to the bonding surface, and then positions and mounts the solder balls 34 on the bonding surface. Using a solder jetting device allows the solder balls 34 to be temporarily fixed directly to the bonding surface without using flux, thereby reducing defects caused by flux, such as the occurrence of voids and bonding failures. Mounting the solder balls 34 using a solder jetting device may also be applied in combination with bumps or the like formed on the bonding surface.

[0031] 2A is a plan view showing an example in which the solder balls 34 according to the embodiment are arranged in a closest packed state. As shown in FIG. 2A, the solder balls 34 may be arranged in a closest packed state.

[0032] 2B is a plan view showing an example in which solder balls 34 according to the embodiment are arranged at intervals L. As shown in FIG. 2B, solder balls 34 may be arranged on the joining surface at intervals L expressed by the following formula (1): L=√(2R1 3 / 3t) (1)

[0033] 3A is a schematic end view showing an example of a state of a solder ball 34 according to an embodiment before melting, and FIG. 3B is a schematic end view showing an example of a state of a solder ball 34 according to an embodiment after melting. Here, a case will be described in which, for example, solder balls 34 are mounted on the joining surface of substrate 16, and the solder balls 34 are melted and spread to form joints 14. Before melting, solder balls 34, each having a spherical diameter R1, are arranged at a distance L. Upon melting, the solder balls 34 spread and become joints 14 having a diameter R2 and a thickness t.

[0034] 4A is a perspective view showing an example of the arrangement of solder balls 34 at a corner portion according to the embodiment. In this example, solder balls 34 are mounted on a conductive layer 46 provided on a flange portion 44 of a substrate 36 having a corner portion using a solder jet device, and the solder balls 34 are melted to form joints 14, with the surface of the conductive layer 46 serving as the joint surface.

[0035] 4B is a schematic diagram showing an example of a joint 14 at a corner according to an embodiment. The joint 14 shown in FIG. 4B is formed by aligning a mating surface (not shown) with the joining surface of the substrate 36 carrying the solder balls 34 as shown in FIG. 4A, heating the substrate 36 in this state to melt the solder balls 34, and then cooling the solder balls 34 to solidify them. The joint 14 electrically connects the joining surface of the substrate 36 with the mating surface to be joined to the joining surface. The joint 14 shown in FIG. 4B has a basic joint portion 59 and an extension portion 60.

[0036] 5 is a schematic diagram showing an example of a linear joint according to an embodiment. The extensions may be formed at regular intervals in areas other than the corners, for example, in linear portions as shown in FIG.

[0037] After the ball bumps 34 are mounted on the bonding surface as described above, the surface to be bonded to is aligned and placed opposite the bonding surface, and the solder balls are heated in this state to melt, and then cooled and solidified to form a bond, electrically connecting the bonding surface and the surface to be bonded to the other surface. Except for the above, the method of mounting and bonding the solder balls can be the same as the method described in Patent Document 3.

[0038] (5) Action and effect If an Au-rich phase precipitates in a solder ball made of an Au-Sn alloy, even if there are no shrinkage cavities, the ball will have a polyhedral shape like a mirror ball, and the sphericity will be low, which will result in poor mounting on the ball mounter or clogging in the solder jet device.

[0039] In the present embodiment, the solder ball 34 contains one of Mg, Al, Si, Ti, V, Cr, Mn, and Ce dispersed in the AuSn alloy at a concentration of 0.01 weight ppm or more but less than 0.1 weight ppm. This provides numerous nucleation sites during solidification, suppresses the formation of a non-uniform Au-rich phase during cooling, and forms a uniform lamellar structure consisting of a first phase (also referred to as the Au-rich phase) primarily composed of AuSn and a second phase primarily composed of AuSn. Therefore, the solder ball 34 of the present embodiment is a solder ball with a smooth, mirror-finished surface, suppressing the occurrence of surface irregularities and shrinkage cavities and improving sphericity. This reduces the occurrence of mounting defects in ball mounters and clogging in solder jetting equipment.

[0040] Any metal element that is more easily oxidized than Sn can be added to the Au-Sn alloy. The same effect can be achieved by adding 0.01 ppm by weight or more but less than 0.1 ppm by weight of any one of Mg, Al, Si, Ti, V, Cr, Mn, and Ce.

[0041] (6) A semiconductor light-emitting device manufactured using the solder balls of this embodiment The LED (Light Emitting Diode) package 10 shown in FIG. 6 includes a semiconductor light-emitting device 11 as a bonded structure. The semiconductor light-emitting device 11 includes an LED chip 12 as a first structure and a substrate 16 as a second structure bonded to the LED chip 12 via a joint 14 made of a solder alloy. The LED chip 12 is a light-emitting element having a substrate 20 and a crystal layer 18 including a light-emitting layer formed on the substrate 20. Electrodes 22 and 24 are formed on the surface of the substrate 20 opposite the surface on which the crystal layer 18 is formed. The electrodes 22 and 24 are made of a conductive material such as Au, Ag, Cu, or Al. The LED chip 12 is a flip-chip light-emitting element in which the electrodes 22 and 24 face downward. One of the electrodes 22 and 24 is an n-side electrode and the other is a p-side electrode. The bonding portion 14 is formed of an Au-Sn alloy containing 19% by mass or more and 25% by mass or less of Sn, with Au as the main component, and contains one additive element selected from Mg, Al, Si, Ti, V, Cr, Mn, and Ce at a concentration of 0.01 ppm by weight or more and less than 0.1 ppm by weight. Except for the above, the bonding portion 14 can have the same configuration as the semiconductor light-emitting device described in Patent Document 3.

[0042] The LED package 10 can be applied to light sources such as automobile headlights that require high brightness.

[0043] The solder ball 34 of this embodiment can be used as a bonding material for the LED package 10, as well as a bonding material for a sealing package that hermetically seals electronic devices such as a semiconductor light-emitting device in which a semiconductor light-emitting element is mounted on a circuit board, a SAW filter, an FBAR filter, and a quartz oscillator, or as a bonding material for other semiconductor devices.

[0044] 2. Working Example The present invention will be described in detail below based on the following examples, but these are merely examples of the present invention and the present invention is not limited to these examples in any way.

[0045] (sample) The solder balls shown in Table 1 were produced using the procedure described above in "(2) Solder Ball Manufacturing Method." First, Au, Sn, and additive elements were weighed, and ingots were produced by high-frequency melting. Because the additive elements are consumed as oxides during granulation, an amount 5 to 10 times the desired component concentration was added. The ingots were placed in a solder reservoir, which was heated to 385°C in an N2-5% by volume H2 atmosphere, and the frequency of the piezoelectric element was adjusted to 10 to 50 kHz to obtain solder balls with the desired diameter. More than 10,000 solder balls of each type were produced.

[0046] (Evaluation method) The Sn concentration of the fabricated solder balls was evaluated using ICP-OES, and the concentration of each added element was evaluated using ICP-MS, using 1g of each solder ball. The spherical diameter and sphericity (%) were measured using an image processing device based on the coordinate data of the outline of a 2D image of the solder ball taken from directly above. The spherical diameter was determined as the diameter of a reference circle (D1) using the least squares method. The sphericity (%) was calculated by finding the diameter of the circumscribed circle (D2) and the diameter of the inscribed circle (D3), as (D2 - D3) / D1 x 100, and was taken as a simple average of 50 solder balls. The results are shown in Table 1.

[0047] [Table 1]

[0048] (Evaluation results) In Comparative Examples 1 and 5 and Examples 2 to 4, the Sn concentration was 18 wt % to 26 wt % and the Mg concentration in the solder ball was 0.05 wt ppm. The Sn concentration was 19 wt % to 25 wt % and the sphericity was 0.58 to 0.65%, which was high.

[0049] In Examples 6 to 12, Al, Si, Ti, V, Cr, Mn, and Ce were investigated as additive elements for the solder balls. The concentration of the additive elements in the solder balls measured by ICP-MS was 0.05 ppm by weight, and the spherical diameter was 125 μm. The sphericity was high, ranging from 0.49 to 0.58%.

[0050] The solder balls were evaluated with a Si concentration of 0 to 0.1 ppm by weight and a sphere diameter of 50 μm for Comparative Examples 13 and 16 and Examples 14 and 15. When the concentration of the Si additive element was 0.01 ppm by weight or more and less than 0.1 ppm by weight, the sphericity was 0.63% and 0.64%, respectively, which were high in sphericity.

[0051] In Examples 17 to 20, the solder balls had an Sn concentration of 25 wt %, a V concentration of 0.08 wt ppm, and a spherical diameter of 10 μm to 500 μm. The sphericity was high, ranging from 0.58 to 0.65%.

[0052] In Examples 21 to 25, the solder balls had an Sn concentration of 19 wt %, a Cr concentration of 0.01 wt ppm to 0.09 wt ppm, and a spherical diameter of 100 μm. The sphericity was high, ranging from 0.52 to 0.64%.

[0053] In Example 26, the Sn concentration in the solder ball was 20 wt % and the Al concentration was 0.04 wt ppm, in Example 27, the Sn concentration in the solder ball was 19 wt % and the Ti concentration was 0.06 wt ppm, and in Example 28, the Sn concentration in the solder ball was 21 wt % and the Mn concentration was 0.07 wt ppm, and each sphere diameter was 150 μm. The sphericity was 0.52 to 0.55%, which was high. [Explanation of symbols]

[0054] 10 LED packages 11 Semiconductor light-emitting device 12 LED chips 14 Joint 16 boards 22,24 electrode 26,28 electrode 34 solder balls 36 PCB 44 Flange 46 Conductive layer 59 Basic joints 60 Extension 61 Basic joints 62 Extension

Claims

1. A solder ball containing 19% by mass or more and 25% by mass or less of Sn, with the remainder being Au, Contains one additive element selected from Mg, Al, Si, Ti, V, Cr, Mn, and Ce, the concentration of the additive element relative to the entire solder ball is 0.01 ppm by weight or more and less than 0.1 ppm by weight; Solder ball.

2. 2. The solder ball according to claim 1, wherein the diameter of the solder ball is 500 μm or less.

3. 3. The solder ball according to claim 1, wherein the sphericity is 0.7% or less.

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