Sn-Bi-In TERNARY SOLDER AND DEVICES USING IT

Abstract

One embodiment of the present invention provides a Sn-Bi-In ternary solder comprising tin (Sn), bismuth (Bi) and indium (In), wherein the Sn-Bi-In ternary solder has a melting point temperature of 140°C to 160°C.

Description

Technology Field

[0001] The present invention relates to a solder, and more specifically, to a ternary solder capable of soldering at low temperatures. Background Technology

[0003] In the past, flexible solder, an alloy of tin and lead, was primarily used as the solder material for bonding substrates within devices due to its advantages such as low process temperature and excellent wettability.

[0004] However, as the use of lead, which is harmful to the human body, has been regulated, research on lead-free solder has been actively conducted, and SAC305-based solder, which has excellent thermal and mechanical reliability, is currently widely used for bonding substrates.

[0005] However, as the increase in integration density in the packaging process determines the improvement of device performance, the thickness of the PCB substrate inside electronic products becomes increasingly thinner. Consequently, the high process temperature caused by the high melting point (217°C) of the existing SAC305 exacerbates the warpage problem where the substrate bends due to heat, and as the number of stacked substrates increases, the number of processes increases, leading to a problem of increased thermal damage caused by high process temperatures.

[0006] To solve these problems, Sn-58Bi solder with a low melting point is being studied as an alternative, but it exhibits mechanical reliability issues due to the brittleness of Bi.

[0007] Therefore, there is a need for research on the exploration of additional materials that can be used as low-temperature solders capable of solving the aforementioned problems. Prior art literature

[0009] Republic of Korea Published Patent Application No. 10-2022-0091404 The problem to be solved

[0010] The technical problem that the present invention aims to solve is to provide a Sn-Bi-In ternary solder capable of low-temperature soldering, which is intended to solve the problems of the aforementioned conventional technology.

[0011] In addition, the technical problem that the present invention aims to solve is to provide a method for mounting a device using Sn-Bi-In ternary solder.

[0012] The technical problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art to which the present invention belongs from the description below. means of solving the problem

[0014] To achieve the above technical problem, one embodiment of the present invention provides a Sn-Bi-In ternary solder.

[0015] In one embodiment of the present invention, the Sn-Bi-In ternary solder comprises tin (Sn), bismuth (Bi) and indium (In), and the melting point of the Sn-Bi-In ternary solder may be 140°C to 160°C.

[0016] In addition, in one embodiment of the present invention, the phase structure of the Sn-Bi-In ternary solder may include one or more of the group consisting of Bi, β-Sn, γ-InSn, and BiIn phases.

[0017] In addition, in one embodiment of the present invention, the Sn-Bi-In ternary solder can control the formation of the Bi phase and the γ phase.

[0018] In addition, in one embodiment of the present invention, the Sn-Bi-In ternary solder can reduce the brittleness of the Sn-Bi-In ternary solder by controlling the formation of the Bi phase and γ phase, which have relatively higher brittleness compared to the β-Sn and BiIn phases.

[0019] In addition, in one embodiment of the present invention, the tin content may be 48 wt% to 59 wt% relative to the total mass of the Sn-Bi-In ternary solder; the bismuth content may be 20 wt% to 35 wt%; and the remainder may be indium and other unavoidable impurities.

[0020] To achieve the above technical problem, one embodiment of the present invention provides a method for mounting a device using Sn-Bi-In ternary solder.

[0021] In one embodiment of the present invention, a method for mounting a device using Sn-Bi-In ternary solder may include the steps of: forming a solder layer containing Sn-Bi-In ternary solder on a substrate; positioning a device on the solder layer; and applying heat to the solder layer to mount the device.

[0022] In addition, in one embodiment of the present invention, the melting point of the solder layer may be 140°C to 160°C.

[0023] In addition, in one embodiment of the present invention, the phase structure of the Sn-Bi-In ternary solder may include one or more of the group consisting of Bi, β-Sn, γ-InSn, and BiIn phases.

[0024] In addition, in one embodiment of the present invention, the Sn-Bi-In ternary solder comprises tin (Sn), bismuth (Bi) and indium (In), and, relative to the total mass of the Sn-Bi-In ternary solder, the content of tin is 48 wt% to 59 wt%; the content of bismuth is 20 wt% to 35 wt%; and the remainder may comprise the indium and other unavoidable impurities. Effects of the invention

[0026] A Sn-Bi-In ternary solder according to one embodiment of the present invention can provide the effect of reducing thermal damage to substrates and devices as a low-temperature solder while simultaneously maintaining mechanical reliability equivalent to that of currently used solders.

[0027] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description of the invention or the claims. Brief explanation of the drawing

[0029] FIG. 1 is a flowchart showing the steps of a method for mounting a device using Sn-Bi-In ternary solder according to one embodiment of the present invention. Figure 2 is a phase diagram showing the region of the Sn-Bi-In ternary system having a melting point from 140°C to 160°C. Figure 3 is a phase diagram showing regions having the phases of Bi, Sn, γ-InSn, and BiIn in the Sn-Bi-In ternary system. Figure 4 is the result of EPMA cross-sectional analysis of PA1 to PA4 according to composition ratio in a Sn-Bi-In ternary system according to one embodiment of the present invention. Figure 5 is the result of EPMA cross-sectional analysis of PB1 to PB4 according to composition ratio in a Sn-Bi-In ternary system according to one embodiment of the present invention. Figure 6 is the result of EPMA cross-sectional analysis of PC1 to PC4 according to composition ratio in a Sn-Bi-In ternary system according to one embodiment of the present invention. FIG. 7 is the shear strength test result of PA1 to PA4, PB1 to PB4 and PC1 to PC4 in a Sn-Bi-In ternary system according to one embodiment of the present invention. Figure 8 shows the shear strength test results of conventional solders SAC305 and Sn-58Bi. Specific details for implementing the invention

[0030] The present invention will be described below with reference to the attached drawings. However, the present invention may be implemented in various different forms and is therefore not limited to the embodiments described herein. Furthermore, in order to clearly explain the present invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification have been given similar reference numerals.

[0031] Throughout the specification, when it is stated that a part is "connected (connected, in contact, combined)" with another part, this includes not only cases where they are "directly connected," but also cases where they are "indirectly connected" with other members interposed between them. Furthermore, when it is stated that a part "includes" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but rather allows for the inclusion of additional components.

[0032] The terms used herein are merely for describing specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising” or “having” are intended to indicate the presence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0033] Embodiments of the present invention will be described in detail below with reference to the attached drawings.

[0034] In the case of conventional lead-free solder, it could not be free from the problem of increasing thermal damage to the substrate by applying heat due to its high melting point.

[0035] To solve these problems, the present invention provides a Sn-Bi-In ternary solder capable of low-temperature soldering and a method for mounting a device using the same.

[0036] Hereinafter, the present invention will be described with reference to the drawings presented in this specification. For reference, the drawings may be partially exaggerated to illustrate the features of the present invention. In such cases, it is preferable to interpret them in light of the entire intent of this specification.

[0038] A Sn-Bi-In ternary solder according to one embodiment of the present invention is described.

[0039] According to one embodiment of the present invention In the Sn-Bi-In ternary solder comprising tin (Sn), bismuth (Bi) and indium (In), the melting point of the Sn-Bi-In ternary solder may be 140°C to 160°C.

[0040] The Sn-Pb solders used in the early days were flexible solders, and there were cases where they caused harm to the human body due to their lead content.

[0041] Therefore, the solder primarily used recently is lead-free solder, which does not use lead.

[0042] However, since these solders are soldered in a high-temperature region (around 240°C), there is a problem of thermal damage to the substrate, and as the integration density of the package process increases, it is becoming important to control this thermal damage.

[0043] As soldering is performed in a low-temperature range for the reasons mentioned above, and as it becomes important to have a solder that can maintain the same mechanical reliability as conventional solder, the present invention provides a Sn-Bi-In ternary solder, and the melting point of the Sn-Bi-In ternary solder may be 140°C to 160°C, which is a low-temperature range compared to the melting point of conventional solder.

[0044] The reason the soldering temperature of the Sn-Bi-In ternary solder of the present invention is 140°C to 160°C is that the phase of the Sn-Bi-In ternary system can be controlled in that temperature range to maintain the same mechanical reliability as conventional solder.

[0045] Figure 2 is a phase diagram showing the region of the Sn-Bi-In ternary system having a melting point from 140°C to 160°C.

[0046] Referring to Figure 2, the melting point of the Sn-Bi-In ternary alloy according to the content of each element can be confirmed.

[0047] This is a low-temperature range of 140°C to 160°C compared to conventional solder, and assuming that soldering is performed by heating to a temperature 30°C higher than the melting point, the temperature applied for soldering is 170°C to 190°C, which is also naturally known to be lower than the temperature applied for soldering conventional solder.

[0048] This allows for the reduction of thermal damage to the substrate and components during soldering.

[0049] Figure 3 is a phase diagram showing regions having the phases of Bi, Sn, γ-InSn, and BiIn in the Sn-Bi-In ternary system.

[0050] Referring to Figure 3, it can be seen that Sn-Bi-In alloys can exist in various phases at room temperature depending on the composition, specifically Bi phase, β-Sn phase, γ-InSn phase, and BiIn phase.

[0051] Accordingly, the phase structure of the Sn-Bi-In ternary solder of the present invention may include one or more of the group consisting of Bi phase, β-Sn phase, γ-InSn phase and BiIn phase, and as an example, two or three phases among Bi, BiIn, β-Sn and γ4 phases may exist.

[0052] At this time, the Sn-Bi-In ternary solder of the present invention can control the formation of the Bi phase and the γ phase.

[0053] At this time, the meaning that the Sn-Bi-In ternary solder can control the formation of the Bi phase and the γ phase may mean that the degree to which the Bi phase and the γ phase are formed inside the solder can be reduced or prevented from being formed.

[0054] For example, the Sn-Bi-In ternary solder may be composed of a β-Sn phase and a BiIn phase, as another example, a BiIn phase and a γ-InSn phase, as another example, a Bi phase, a β-Sn phase and a BiIn phase, and as yet another example, a γInSn phase, a β-Sn phase and a BiIn phase, but is not limited thereto.

[0055] However, since the γInSn phase exhibits high characteristics even in small amounts, it is desirable to set the composition so that the Bi phase and γInSn phase are not dominant.

[0056] Meanwhile, the reason it is important to control the formation of the Bi phase and γ phase in the Sn-Bi-In ternary solder of the present invention is that the Bi phase and γ phase have high brittleness.

[0057] Specifically, the Bi phase exhibits high brittleness due to its trigonal structure, which acts as a factor that reduces mechanical reliability in Sn-58Bi solder, one of the representative low-temperature solders.

[0058] In addition, γ also has a hexagonal structure and is relatively brittle.

[0059] Accordingly, in the Sn-In-Bi ternary system of the present invention, a solder with high mechanical properties can be manufactured by controlling the Bi phase and γ phase of the final solder through compositional change. Accordingly, the phases of the Sn-In-Bi ternary solder may include one or more of the group consisting of Bi, β-Sn, γ-InSn, and BiIn phases, but the formation of the Bi phase and γ phase is controlled to increase the proportion of the Bi and β-Sn phases.

[0060] Accordingly, the Sn-Bi-In ternary solder of the present invention can reduce the brittleness of the Sn-Bi-In ternary solder by controlling the formation of the Bi phase and γ phase, which have relatively higher brittleness compared to the β-Sn and BiIn phases.

[0061] At this time, the phase structure of the Sn-Bi-In ternary solder of the present invention includes one or more of the group consisting of Bi, β-Sn, γ-InSn, and BiIn phases, and the content of Sn, Bi, and In of the Sn-Bi-In ternary solder can be limited in order to control the formation of the Bi phase and γ phase of the Sn-Bi-In ternary solder.

[0062] Specifically, relative to the total mass of the Sn-Bi-In ternary solder, the tin content is 48 wt% to 59 wt%; the bismuth content is 20 wt% to 35 wt%; and the remainder may include indium and other unavoidable impurities.

[0063] At this time, if the content of the tin, bismuth, and indium falls outside the aforementioned content range, the Bi phase and γ phase may be formed as phases of the Sn-Bi-In ternary solder, so it may be important to satisfy the aforementioned content range.

[0065] A method for mounting a device using a Sn-Bi-In ternary solder according to one embodiment of the present invention is described.

[0066] The device mounting method using Sn-Bi-In ternary solder according to the present invention can apply all the contents described above regarding Sn-Bi-In ternary solder, and although detailed explanations of overlapping parts have been omitted, they can be applied in the same way even if such explanations are omitted.

[0067] FIG. 1 is a flowchart showing the steps of a method for mounting a device using Sn-Bi-In ternary solder according to one embodiment of the present invention.

[0068] Referring to FIG. 1, a device mounting method using a Sn-Bi-In ternary solder according to one embodiment of the present invention is The method may include the steps of: forming a solder layer comprising Sn-Bi-In ternary solder on a substrate; positioning a device on the solder layer; and applying heat to the solder layer to mount the device.

[0070] As a first step, the method may include the step of forming a solder layer comprising Sn-Bi-In ternary solder on a substrate. (S100)

[0071] At this time, the phase structure of the Sn-Bi-In ternary solder may include one or more types from the group consisting of Bi, β-Sn, γ-InSn, and BiIn phases.

[0072] In addition, the Sn-Bi-In ternary solder can control the formation of the Bi phase and the γ phase.

[0073] In addition, the phase structure of the Sn-Bi-In ternary solder may include one or more of the group consisting of Bi, β-Sn, γ-InSn, and BiIn phases, and the content of Sn, Bi, and In of the Sn-Bi-In ternary solder may be limited in order to control the formation of the Bi phase and γ phase of the Sn-Bi-In ternary solder.

[0074] At this time, the Sn-Bi-In ternary solder comprises tin (Sn), bismuth (Bi), and indium (In), and relative to the total mass of the Sn-Bi-In ternary solder, the content of tin is 48 wt% to 59 wt%; the content of bismuth is 20 wt% to 35 wt%; and the remainder may comprise indium and other unavoidable impurities.

[0075] Meanwhile, the above substrate can be used without limitation as long as it is a substrate for mounting conventionally used components.

[0076] In addition, the thickness formed when forming a solder layer containing the Sn-Bi-In ternary solder is not particularly limited.

[0078] A second step may include a step of positioning a device on the solder layer. (S200)

[0079] The device positioned on the above solder layer can be positioned without limitation as a device to be mounted.

[0081] As a final step, the method may include a step of applying heat to the solder layer to mount the device. (S300)

[0082] At this time, the heat applied to the solder layer may be lower than the temperature applied to solder conventional solder.

[0083] This is because, in the case of conventional solder, the melting point is about 217°C, and a temperature higher than that of about 240°C or higher was applied to solder it, but the present invention has a lower melting point than conventional solder.

[0084] Specifically, the melting point of the solder layer containing the solder of the present invention is 140 to 160°C, and the device can be mounted by applying heat at a temperature approximately 30°C higher than the melting point temperature to solder the device.

[0085] At this time, since the melting point temperature of the solder layer of the present invention is 140°C to 160°C, soldering can be performed by heating to a lower temperature than conventional solder, which means that the degree of thermal damage to the substrate and device can be reduced.

[0087] The present invention will be explained in more detail below through examples, comparative examples, and experimental examples. These examples, comparative examples, and experimental examples are solely for the purpose of illustrating the present invention, and the scope of the present invention is not limited by these examples, comparative examples, and experimental examples.

[0089] Examples

[0090] Includes tin, bismuth, and indium To manufacture Sn-Bi-In ternary solder, a uniform alloy was produced by mixing and melting Sn, Bi, and In metal powders according to compositional ratios.

[0091] Afterwards, the material was ground back into powder through a milling process, mixed with flux to produce a paste, and finally, solder balls were manufactured on an OSP substrate through screen printing.

[0092] The composition ratio (wt%) of Sn, Bi, and In of the solder produced at this time is as shown in Table 1 below.

[0093] Sn Bi In PA1 55 30 15 PA2 55 27 18 PA3 55 24 21 PA4 55 20 25 PB1 50 35 15 PB2 50 31 19 PB3 50 28 22 PB4 50 25 25 PC1 48 35 17 PC2 48 32 20 PC3 48 29 23 PC4 48 26 26

[0095] Comparative example

[0096] Conventional SAC305 and Sn-58Bi solders were prepared.

[0098] Experimental Example 1: EPMA Cross-sectional Analysis

[0099] Figure 4 is the result of EPMA cross-sectional analysis of PA1 to PA4 according to composition ratio in a Sn-Bi-In ternary system according to one embodiment of the present invention.

[0100] Figure 5 is the result of EPMA cross-sectional analysis of PB1 to PB4 according to composition ratio in a Sn-Bi-In ternary system according to one embodiment of the present invention.

[0101] Figure 6 is the result of EPMA cross-sectional analysis of PC1 to PC4 according to composition ratio in a Sn-Bi-In ternary system according to one embodiment of the present invention.

[0102] Referring to Figures 4 to 6, EPMA cross-sectional analysis results show that as the ratio of Sn is fixed and the ratio of In increases, the Bi, β-Sn phase disappears and the γ-InSn phase is formed.

[0104] Experimental Example 2: Shear Strength Test

[0105] The shear strength test of the solder balls produced according to the composition ratios listed in Table 1 above was performed 20 times each, and brittle fracture and ductile fracture were distinguished using a stress-displacement graph.

[0106] Table 2 below shows the rate of ductile fracture occurrence based on the shear strength test results for each composition.

[0107] Through this, it can be confirmed that avoiding the Bi phase and γ-InSn phase improves the ductility of the composition.

[0108] In addition, the shear strength test results of the comparative compositions SAC305 and Sn-58Bi showed ductile failure rates of 100% and 0%, respectively, which confirms that they show results similar to the existing SAC305, which exhibits high reliability through the control of the Bi phase and γ-InSn phase.

[0110] Ductile fracture ratio (%) PA1 15 PA2 40 PA3 65 PA4 15 PB1 0 PB2 75 PB3 80 PB4 40 PC1 15 PC2 85 PC3 100 PC4 30 SAC305 100 Sn-58Bi 0

[0111] FIG. 7 is the shear strength test result of PA1 to PA4, PB1 to PB4 and PC1 to PC4 in a Sn-Bi-In ternary system according to one embodiment of the present invention.

[0112] Figure 8 shows the shear strength test results of conventional solders SAC305 and Sn-58Bi.

[0113] Comparing Figures 7 and 8, it can be confirmed through a shear strength test that the Sn-Bi-In ternary system according to one embodiment of the present invention has excellent mechanical properties and reliability even when compared to conventional solders such as SAC305 and Sn-58Bi.

[0114] Through this, it can be confirmed that the Sn-Bi-In ternary solder of the present invention exhibits mechanical reliability at the level of conventional solders such as SAC305 and Sn-58Bi, and through these mechanical properties, it can be confirmed that it is applicable to low-temperature packaging processes.

[0116] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical spirit or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single unit may be implemented in a distributed manner, and components described as distributed may likewise be implemented in a combined form.

[0117] The scope of the present invention is defined by the claims set forth below, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention.

Claims

Claim 1 A Sn-Bi-In ternary solder comprising tin (Sn), bismuth (Bi), and indium (In), wherein, relative to the total mass of the Sn-Bi-In ternary solder, the content of tin (Sn) is 48 wt% to 59 wt%, the content of bismuth (Bi) is 20 wt% to 35 wt%, and the remainder comprises indium (In) and other unavoidable impurities; the melting point of the Sn-Bi-In ternary solder is 140°C to 160°C; the phase structure of the Sn-Bi-In ternary solder comprises one or more phases selected from the group consisting of Bi, β-Sn, γ-InSn, and BiIn phases; and wherein, in the phase structure of the solder, the formation of the phases is controlled such that the ratio of the β-Sn phase and the BiIn phase to the Bi phase and the γ-InSn phase is greater, thereby forming the main phase. Sn-Bi-In ternary solder. Claim 2 delete Claim 3 delete Claim 4 A Sn-Bi-In ternary solder according to claim 1, characterized in that the Sn-Bi-In ternary solder controls the formation of Bi phase and γ phase, which have relatively higher brittleness compared to β-Sn and BiIn phases, thereby reducing the brittleness of the Sn-Bi-In ternary solder. Claim 5 delete Claim 6 A step of forming a solder layer comprising Sn-Bi-In ternary solder on a substrate; a step of positioning a device on the solder layer; A method for mounting a device using a Sn-Bi-In ternary solder, comprising the step of applying heat to the solder layer to mount the device; wherein the melting point of the solder layer is 140°C to 160°C, the content of tin (Sn) is 48 wt% to 59 wt% relative to the total mass of the Sn-Bi-In ternary solder, the content of bismuth (Bi) is 20 wt% to 35 wt%, and the remainder comprises indium (In) and other unavoidable impurities, the phase structure of the Sn-Bi-In ternary solder comprises one or more of the group consisting of Bi, β-Sn, γ-InSn, and BiIn phases, and in the phase structure of the solder, the formation of the phase is controlled such that the ratio of the β-Sn phase and BiIn phase to the Bi phase and γ-InSn phase is greater, thereby forming the main phase. Claim 7 delete Claim 8 delete Claim 9 delete

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