Solder joint and method for producing same, and bonded body

Abstract

The present application discloses a kind of solder joint and its preparation method, joint, the solder joint of the present application is the solder joint (100) of the first component (151) and second component (152) joint, with first metal layer (110) and second metal layer (120) arranged in the surface of first metal layer (110).Characterized in that, first metal layer (110) is the solder layer containing Sn, second metal layer (120) is the solder layer containing Sn and Bi, the liquidus temperature of second metal layer (120) is lower than the solidus temperature of first metal layer (110) temperature.According to the present application, the reliability of the joint of the joint of each component can be further improved, the preparation method of the solder joint can be easily prepared, the joint of the reliability improvement is realized.

Description

Technical Field

[0001] This invention relates to solder joints, methods for preparing the same, and joint bodies. This application claims priority based on Japanese Patent Application No. 2021-179530, filed on November 2, 2021, the contents of which are incorporated herein by reference. Background Technology

[0002] Components are typically attached to a substrate and electrically connected to it by soldering. Soldering uses flux, solder powder, and solder paste, a mixture of flux and solder powder.

[0003] Flux has the ability to chemically remove metal oxides present on the metal surfaces of the objects being welded and on the solder, and to allow metal elements to move at the boundary between them. Therefore, by using flux for welding, an intermetallic compound is formed between the two materials, resulting in a strong bond.

[0004] In welding, processes such as reflow welding and flow welding are used depending on the size of the objects to be joined.

[0005] In reflow soldering, solder paste is first printed onto a substrate. Then, components are mounted, and the substrate with the components mounted is soldered in a heated furnace called a reflow oven (see, for example, Patent Document 1).

[0006] In flow soldering, flux is first applied to a substrate on which the component is mounted. Then, while conveying the substrate on which the component is mounted, molten solder jetted from below is brought into contact with the soldering surface, thereby performing soldering (see, for example, Patent Document 2).

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Invention Patent Publication No. 2002-126893

[0010] Patent Document 2: Japanese Patent No. 6617848 Summary of the Invention

[0011] The problem to be solved by the present invention

[0012] In the past, Sn-Pb solder alloys were used in almost all mounting configurations. However, with the requirement for lead-free soldering, solder alloys with various properties in soldering installations have been developed and put into practical use.

[0013] The requirements for solder alloy properties include: properties related to operating temperature, properties related to wettability indicating the ease of solder joint fabrication, joint strength, fatigue life, etc., with various properties and required levels depending on the application of the solder alloy joint.

[0014] Therefore, the range that can be covered by standard solder alloys is narrow. Although various solder alloys have been tried in each process, it is difficult to simultaneously meet the requirements of ease of joint preparation and reliability.

[0015] The present invention was made in view of the above circumstances, and its object is to provide a solder joint with further improved reliability of the joint of the connecting components, a method for preparing the solder joint with ease, and a joint body with improved reliability.

[0016] Problem-solving methods

[0017] To solve the above problems, the present invention adopts the following solution.

[0018] [1] A solder joint for joining a first component and a second component, comprising: a first metal layer in contact with both the first component and the second component, and a second metal layer disposed on the surface of the first metal layer, wherein the first metal layer is a solder layer containing Sn, the second metal layer is a solder layer containing Sn and Bi, and the liquidus temperature of the second metal layer is a temperature lower than the solidus temperature of the first metal layer.

[0019] [2] A method for preparing a solder joint, which is a method for preparing a solder joint for joining a first component and a second component, wherein the method includes: a reflow soldering step in which a first solder material containing Sn is melted and a first metal layer in contact with the first component and the second component is formed in a manner that is configured to contact both the first component and the second component; and a flow soldering step in which a second metal layer is formed on the surface of the first metal layer by contacting the first metal layer with a second solder material containing Sn and Bi in a molten state, wherein the first solder material and the second solder material are selected in such a manner that the liquidus temperature of the second metal layer is lower than the solidus temperature of the first metal layer, and the flow soldering step is performed at a temperature condition lower than the solidus temperature of the first metal layer.

[0020] [3] A joint comprising a first member, a second member, and a solder joint for joining the first member and the second member, wherein the solder joint includes the solder joint described in [1].

[0021] Effects of the present invention

[0022] According to the present invention, a solder joint with improved reliability of the joint of the components can be provided, a method for preparing the solder joint can be easily prepared, and a joint body with improved reliability is achieved. Attached Figure Description

[0023] Figure 1 This is a cross-sectional view showing one embodiment of the solder joint in a bonding assembly of a leaded electronic component and a substrate.

[0024] Figure 2 This is a cross-sectional view showing one embodiment of the solder joint in the bonding assembly of the chip component and the substrate.

[0025] Explanation of reference numerals in the attached figures

[0026] 10. Connector, 20. Connector, 100. Solder joint, 110. First metal layer, 120. Second metal layer, 151. Substrate, 152. Lead, 200. Solder joint, 210. First metal layer, 220. Second metal layer, 251. Substrate, 252. Chip component Detailed Implementation

[0027] The solder joint of this embodiment will be described in detail below with reference to the accompanying drawings. Furthermore, for ease of reading, the dimensions and proportions of the constituent elements in all the following drawings have been appropriately adjusted.

[0028] (Solder joint)

[0029] According to one aspect of the invention, a solder joint joins a first component and a second component.

[0030] The solder joint has a first metal layer that contacts both the first component and the second component, and a second metal layer disposed on the surface of the first metal layer.

[0031] The first metal layer is a solder layer containing Sn. The second metal layer is a solder layer containing Sn and Bi.

[0032] In this solder joint, the liquidus temperature of the second metal layer is lower than the solidus temperature of the first metal layer.

[0033] <First Implementation>

[0034] Figure 1 This is a cross-sectional view showing one embodiment of the solder joint in a bonding assembly of a leaded electronic component and a substrate.

[0035] exist Figure 1In the assembly 10, the substrate 151 serves as a first component, a lead-type electronic component (not shown) serves as a second component, and a solder joint 100 joins the first and second components.

[0036] With the lead 152 inserted into the through hole 151h provided on the substrate 151, the solder joint 100 joins the substrate 151 and the lead 152. An electronic component (not shown) is disposed on the substrate surface 151s on the side opposite to the solder joint 100.

[0037] The solder joint 100 has a first metal layer 110 and a second metal layer 120.

[0038] The first metal layer 110 contacts and bonds the substrate 151 and the lead 152. The second metal layer 120 is disposed on the surface of the first metal layer 110.

[0039] Regarding the first component

[0040] In the bonding body 10, the first component (substrate 151) can be, for example, a printed circuit board.

[0041] The thickness of the substrate 151 is, for example, 0.8 to 1.6 mm.

[0042] The diameter of the through hole 151h provided on the substrate 151 can be appropriately determined according to the thickness (diameter) of the lead wire, for example, 0.8 to 1.5 mm.

[0043] Regarding the second component

[0044] In the junction 10, as a second component (lead-type electronic component), examples include integrated circuits, transistors, diodes, resistors, capacitors, etc.

[0045] The thickness (diameter) of lead 152 is, for example, 0.5 to 1.2 mm.

[0046] First Metal Layer 110

[0047] In the solder joint 100, the first metal layer 110 contacts both the substrate 151, which is a first component, and the lead 152, which is a lead-type electronic component, which is a second component. Furthermore, the first metal layer 110 can fully cover the entire portion of the lead 152 that protrudes from the substrate 151 through the insertion through-hole 151h.

[0048] The first metal layer 110 is a solder layer containing Sn.

[0049] The solder layer constituting the first metal layer 110 may be a layer containing Sn monomers, a layer containing Sn and metals other than Sn, or a layer containing unavoidable impurities in the solder powder used as raw material.

[0050] Examples of layers containing Sn and metals other than Sn include layers containing Sn-Ag alloys, Sn-Cu alloys, Sn-Ag-Cu alloys, Sn-Pb alloys, or solder alloys containing solder alloys made by adding at least one metal selected from Sb, In, Zn, As, Cd, Fe, Ni, Co, Au, Ge, P, and Pb to any of these alloys.

[0051] The first metal layer 110 is preferably a solder layer that does not contain Pb.

[0052] The solidus temperature of the first metal layer 110 is, for example, 175 to 250°C, preferably 215 to 230°C.

[0053] The liquidus temperature of the first metal layer 110 is, for example, 190–265°C, preferably 218–232°C.

[0054] The following are specific examples of the metals contained in the solder layer constituting the first metal layer 110. The numerical values ​​in the alloy indicate the proportion (mass %) of that alloy.

[0055] (Example 1) An alloy with Sn 96.5% by mass, Ag 3.0% by mass and Cu 0.5% by mass: solidus temperature 217℃, liquidus temperature 220℃

[0056] (Example 2) An alloy of 99.25% by mass Sn and 0.75% by mass Cu: solidus temperature 227°C, liquidus temperature 229°C

[0057] (Example 3) An alloy with 99.0% by mass of Sn, 0.3% by mass of Ag, and 0.7% by mass of Cu: solidus temperature 217°C, liquidus temperature 227°C

[0058] Second Metal Layer 120

[0059] In the solder joint 100, the second metal layer 120 is configured to cover the entire surface of the first metal layer 110.

[0060] The thickness of the second metal layer 120 is, for example, several μm to tens of μm.

[0061] The second metal layer 120 is a solder layer containing Sn and Bi.

[0062] The solder layer constituting the second metal layer 120 may be a layer containing only Sn and Bi, a layer containing Sn, Bi and metals other than Sn and Bi, or a layer containing unavoidable impurities in the solder used as raw material.

[0063] As a layer containing only Sn and Bi, an example that can be cited is a layer composed of Sn-Bi alloy.

[0064] As a layer containing Sn, Bi and metals other than Sn and Bi, for example, a layer containing a solder alloy in which at least one metal selected from Sb, In, Cu, Zn, As, Ag, Cd, Fe, Ni, Co, Au, Ge, P and Pb is added to a Sn-Bi alloy.

[0065] The second metal layer 120 is preferably a solder layer that does not contain Pb.

[0066] The solidus temperature of the second metal layer 120 is, for example, 137–140 °C.

[0067] The liquidus temperature of the second metal layer 120 is, for example, 140–205°C.

[0068] The following are specific examples of the metals contained in the solder layer constituting the second metal layer 120. The numerical values ​​in the alloy indicate the proportion (mass %) of that alloy.

[0069] (Example 4) An alloy of Sn 42% by mass and Bi 58% by mass: solidus temperature 139℃, liquidus temperature 141℃

[0070] (Example 5) An alloy of Sn 42% by mass, Bi 57% by mass and Ag 1% by mass: solidus temperature 138℃, liquidus temperature 204℃

[0071] (Example 6) An alloy with 42.7% by mass Sn, 57% by mass Bi, and 0.3% by mass Ag: solidus temperature 138℃, liquidus temperature 141℃

[0072] In the solder joint 100, the liquidus temperature (T) of the second metal layer 120 L The solidus temperature (T) is lower than that of the first metal layer 110. S (temperature).

[0073] The liquidus temperature (T) of the second metal layer 120 L ) and the solidus temperature (T) of the first metal layer 110 S The difference (ΔT=T) S -T LThe temperature is preferably 50°C or higher, more preferably 70°C or higher, even more preferably 70-90°C, and particularly preferably 70-80°C.

[0074] The difference (ΔT=T) S -T L When the value is above the lower limit of the preferred range, the bonding between the substrate 151 and the lead 152 can be easily and stably performed when preparing the solder joint 100. On the other hand, when the value is below the upper limit of the preferred range, the adhesion between the first metal layer 110 and the second metal layer 120 can be easily improved.

[0075] Suitable combinations of the metal contained in the solder layer constituting the first metal layer 110 and the metal contained in the solder layer constituting the second metal layer 120 can be, for example, the combination of (Example 1) and (Example 4) (ΔT = 76°C), the combination of (Example 2) and (Example 4) (ΔT = 88°C), and the combination of (Example 3) and (Example 4) (ΔT = 76°C).

[0076] exist Figure 1 In the solder joint 100 shown, the cross-sectional shape of the solder leg is such that the solder leg is at approximately 45 degrees and widens downwards in a smooth concave curve. That is, the first metal layer 110 has high wettability relative to the substrate 151 and the lead 152, and the first metal layer 110 and the second metal layer 120 also have high adhesion, resulting in a good solder joint 100.

[0077] The height H1 of the solder joint 100 is, for example, 0.5 to 1.0 mm.

[0078] [Preparation method of solder joint 100]

[0079] The solder joint 100, which joins the substrate 151 as the first component and the lead-type electronic component as the second component, can be prepared by using a preparation method including the following steps (P1) and (P2).

[0080] Process (P1): A reflow soldering process in which a first welding material containing Sn is melted and a first metal layer 110 in contact with both the first component and the second component is formed, and the material is configured to contact both the first component and the second component.

[0081] Process (P2): A flow welding process in which a second metal layer 120 is formed on the surface of the first metal layer 110 by contacting the second solder material containing Sn and Bi in a molten state with the first metal layer 110 formed in process (P1).

[0082] However, the flow welding process is performed at a temperature below the solidus temperature of the first metal layer 110.

[0083] Regarding solder materials

[0084] In the method for preparing the solder joint 100, the first solder material and the second solder material are selected in such a way that the liquidus temperature of the second metal layer 120 is lower than the solidus temperature of the first metal layer 110.

[0085] As a first solder material, for example, solder paste containing solder alloy powder containing Sn and flux can be used.

[0086] As a second solder material, a solder alloy containing Sn and Bi can be used, for example.

[0087] When using such a first solder material and a second solder material, the liquidus temperature (T) of the second metal layer 120 is brought to a certain level. L The solidus temperature (T) below the first metal layer 110 S The solder alloy powder (containing Sn) of the first solder material and the solder alloy (containing Sn and Bi) of the second solder material are selected by means of selection.

[0088] As the solder alloy powder in the first solder material, examples of solder alloy powder exemplified in the above description of "solder layer constituting the first metal layer 110" can be cited. Among them, Sn-Ag alloy powder, Sn-Cu alloy powder, and Sn-Ag-Cu alloy powder are preferred, and powders selected from the alloys in (Example 1), (Example 2) and (Example 3) above are particularly preferred.

[0089] As a solder alloy in the second solder material, examples of solder alloys exemplified in the description of "solder layer constituting the second metal layer 120" above can be cited. Among them, Sn-Bi alloy and Sn-Bi-Sb alloy are preferred, and alloys selected from (Example 4), (Example 5) and (Example 6) above are particularly preferred.

[0090] The flux contained in the solder paste, which is the first welding material, can be, for example, a composition containing rosin, activator, thixotropic agent and solvent as resin components.

[0091] Additionally, in process (P2), flux is typically applied to the first metal layer 110 before the solder alloy, which serves as the second solder material, comes into contact with the metal in a molten state. This flux can be, for example, a composition containing rosin as a resin component, an activator, and a solvent.

[0092] Details about this flux will be described later.

[0093] • Regarding the process (P1)

[0094] In process (P1), lead 152 is inserted into through hole 151h, and on the substrate surface opposite to the substrate surface 151s on which electronic components are disposed, insertion mounting is performed by reflow soldering to solder substrate 151 and lead 152.

[0095] First, solder paste, serving as the first solder material, is supplied in such a way that it covers the entire portion of the insertion through-hole 151h and the lead 152 protruding from the substrate 151. For example, a dedicated machine is used to supply the solder paste. Thus, the solder paste is positioned in contact with both the substrate 151 and the lead 152.

[0096] Next, the reflow oven is used for heat treatment and reflow operation.

[0097] The heating conditions in the reflow oven are, for example, a temperature of 220–230°C and a holding time of about 10 seconds.

[0098] During the reflow soldering operation, the solder alloy powder in the first soldering material melts to form a first metal layer 110 that contacts both the substrate 151 and the lead 152.

[0099] • Regarding the process (P2)

[0100] In process (P2), a second metal layer 120 is applied to the surface of the first metal layer 110 formed in process (P1) by flow welding.

[0101] First, flux is applied to the surface of the first metal layer 110, and then the substrate 151 with flux applied to the surface of the first metal layer 110 is preheated.

[0102] Examples of flux coating devices include spray-type flux coating devices and foam-type flux coating devices.

[0103] Next, the solder alloy containing Sn and Bi, which is the second solder material, is brought into contact with the surface of the first metal layer 110 coated with flux in a molten state.

[0104] There are no particular limitations on the method of bringing the solder alloy of the second solder material into contact with the surface of the first metal layer 110 in a molten state; for example, spraying or immersion methods can be used.

[0105] In process (P2), the preheating operation and the operation of bringing the second solder material into contact with the surface of the first metal layer 110 are both performed at a temperature below the solidus temperature of the first metal layer 110.

[0106] Preheating operations, for example, are carried out at temperatures of 80–130°C.

[0107] The operation of bringing the second solder material into contact with the surface of the first metal layer 110 is performed, for example, at a temperature of 150°C to 200°C.

[0108] The solder joint 100 of the second metal layer 120 is thinly formed by the flow welding operation in a manner that covers the entire surface of the first metal layer 110.

[0109] In addition, through the above-described processes (P1) and (P2), a bonding body 10 is prepared, which is formed by bonding the substrate 151 and the lead-type electronic component via the solder joint 100.

[0110] According to the first embodiment described above, a solder joint 100 is provided that further improves the reliability of the joint where the components are joined.

[0111] Previously, solder alloys used for solder layers containing Sn (first metal layer 110), such as Sn-Ag-Cu alloys, have excellent ductility. However, from the viewpoint of joint reliability, higher strength properties (tensile strength, etc.) are sometimes required.

[0112] On the other hand, solder alloys used for solder layers (second metal layer 120) containing Sn and Bi, such as Sn-Bi eutectic alloys, have high strength properties (tensile strength, etc.), but poor ductility, and are therefore brittle under impact loads.

[0113] In the solder joint 100 of the first embodiment, a solder layer (second metal layer 120) containing Sn and Bi is provided on the surface of a solder layer (first metal layer 110) containing Sn. That is, the solder joint 100 has a laminated structure comprising solder layers with opposite characteristics. Therefore, the solder joint 100 having this laminated structure possesses both ductility and strength characteristics (tensile strength, etc.). Furthermore, since the liquidus temperature of the second metal layer 120 is lower than the solidus temperature of the first metal layer 110, the adhesion between the first metal layer 110 and the second metal layer 120 is high, making peeling difficult. Thus, the reliability of the solder joint 100 in joining the components is further improved.

[0114] Furthermore, according to the first embodiment described above, a method for preparing a solder joint 100 that can be easily prepared and whose reliability is further improved can be provided.

[0115] In the method for preparing the solder joint 100 in the first embodiment, two conventional mass production methods (process (P1) and process (P2)) are used to produce a solder foot with a stacked structure composed of solder layers with different properties.

[0116] First, a solder containing Sn, such as a standard medium-temperature melting point solder, is used as the metal material and reflow soldered to form a first metal layer 110 (step (P1)). In the first embodiment, this step (P1) is a so-called insert mounting process, and therefore can be performed in the same production environment as in the present.

[0117] Next, on the surface of the first metal layer 110, a solder containing Sn and Bi, such as a relatively low-melting-point solder, is used as the metal material for flow soldering (wave soldering) to form the second metal layer 120 (process (P2)). In the first embodiment, this process (P2) can also be performed in the same production environment as in the present invention.

[0118] In the first embodiment, the flow welding performed in step (P2) is specified to be carried out at a temperature below the solidus temperature of the first metal layer 110. Therefore, the previously installed components will not detach, and a second metal layer 120 with different properties can be stably added and formed on the first metal layer 110.

[0119] As described above, the solder joint 100 can be easily prepared by a preparation method including process (P1) and process (P2).

[0120] According to this preparation method, as a miniaturized solder pad, a solder joint 100 having a laminated structure including solder layers with opposite characteristics can be fabricated at the current production level.

[0121] Furthermore, according to the first embodiment described above, a joint with improved reliability can be provided.

[0122] In particular, in the joint body 10 having a solder joint 100 having a second metal layer 120 provided in such a way that it covers the entire surface of the first metal layer 110, the mounting strength of the lead 152 relative to the substrate 151 is improved, and the reliability of the joint is further improved.

[0123] The first embodiment described above describes a solder joint 100 for bonding a substrate 151 as a first component and a lead-type electronic component as a second component, a method for preparing the same, and a bonding body 10 having the solder joint 100. However, the description is not limited to the content described herein, and other embodiments may also be described.

[0124] For example, in the above-described process (P2), flow soldering can be performed while a third component is further mounted on the substrate 151 side where the first metal layer 110 is formed. Preferably, the third component is an electronic component with weaker heat resistance than the second component. According to this embodiment, the second and third components can be mounted together on the first component.

[0125] <Second Implementation>

[0126] Figure 2 This is a cross-sectional view showing one embodiment of the solder joint in the bonding assembly of the chip component and the substrate.

[0127] exist Figure 2 In the process, the bonding body 20 includes: a substrate 251 having pads 251L as a first component, a chip component 252 as a second component, and a solder joint 200 for bonding the first component and the second component.

[0128] Chip component 252 is mounted on pad 251L.

[0129] Solder joint 200 joins the pad 251L located on the surface of substrate 251 with chip component 252.

[0130] The solder joint 200 has a first metal layer 210 and a second metal layer 220.

[0131] The first metal layer 210 is in contact with both the substrate 251, the pads 251L, and the chip component 252. The second metal layer 220 is disposed on the surface of the first metal layer 210.

[0132] Regarding the first component

[0133] In the bonding body 20, the first component (the substrate 251 having the pads 251L) can be, for example, a printed circuit board.

[0134] The thickness of the substrate 251 is, for example, 0.8 to 1.6 mm.

[0135] Regarding the second component

[0136] In the assembly 20, the second component (chip component 252) can be, for example, an integrated circuit, a transistor, a diode, a resistor, a capacitor, etc.

[0137] First Metal Layer 210

[0138] In the solder joint 200, the first metal layer 210 contacts the pad 251L located on the surface of the substrate 251, which is a first component, and the chip component 252, which is a second component.

[0139] The first metal layer 210 is a solder layer containing Sn.

[0140] The description of the metal material constituting the solder layer of the first metal layer 210 is the same as the description of the metal material constituting the solder layer of the first metal layer 110 in the first embodiment described above.

[0141] The solidus temperature of the first metal layer 210 is, for example, 175 to 250°C, preferably 215 to 230°C.

[0142] The liquidus temperature of the first metal layer 210 is, for example, 190–265°C, preferably 218–232°C.

[0143] Second metal layer 220

[0144] In the solder joint 200, a second metal layer 220 is provided in such a way that it covers the entire surface of the first metal layer 210.

[0145] The thickness of the second metal layer 220 is, for example, several μm to tens of μm.

[0146] The second metal layer 220 is a solder layer containing Sn and Bi.

[0147] The description of the metal material constituting the solder layer of the second metal layer 220 is the same as the description of the metal material constituting the solder layer of the second metal layer 120 in the first embodiment described above.

[0148] The solidus temperature of the second metal layer 220 is, for example, 137–140 °C.

[0149] The liquidus temperature of the second metal layer 220 is, for example, 140–205°C.

[0150] In the solder joint 200, the liquidus temperature (T) of the second metal layer 220 L The solidus temperature (T) is lower than that of the first metal layer 210. S (temperature).

[0151] The liquidus temperature (T) of the second metal layer 220 L ) and the solidus temperature (T) of the first metal layer 210 S The difference (ΔT=T) S -T L The temperature is preferably 50°C or higher, more preferably 70°C or higher, and even more preferably 70-80°C.

[0152] The difference (ΔT=T) S -T L When the value is above the lower limit of the preferred range, the bonding between the substrate 251 and the chip component 252 can be easily and stably performed when the solder joint 200 is prepared. On the other hand, when the value is below the upper limit of the preferred range, the adhesion between the first metal layer 210 and the second metal layer 220 can be easily improved.

[0153] exist Figure 2In the solder joint 200 shown, the cross-sectional shape of the solder pads is such that the pad angle is approximately 45 degrees, and the solder pads widen downwards in a smooth concave curve. That is, the first metal layer 210 has high wettability with respect to the substrate 251 and the chip component 252, and the adhesion between the first metal layer 210 and the second metal layer 220 is also high, resulting in good soldering in the solder joint 200.

[0154] The height H2 of the solder joint 200 is approximately 0.3 to 0.6 mm when the chip component 252 is a chip resistor, and approximately 0.8 to 1.6 mm when the chip component 252 is a chip capacitor.

[0155] [Preparation method of solder joint 200]

[0156] The solder joint 200 for bonding a substrate 251 with pads 251L as a first component and a chip component 252 as a second component can be prepared by using a preparation method including process (P3) and process (P4).

[0157] Process (P3): A reflow soldering process in which a first welding material containing Sn is melted and a first metal layer 210 in contact with both the first component and the second component is formed, and the material is configured to contact both the first component and the second component.

[0158] Process (P4): A flow welding process in which a second metal layer 220 is formed on the surface of the first metal layer 210 by contacting the second solder material containing Sn and Bi in a molten state with the first metal layer 210 formed in process (P3).

[0159] However, the flow welding process is performed at a temperature below the solidus temperature of the first metal layer 210.

[0160] Regarding welding materials

[0161] In the method for preparing the solder joint 200, the first solder material and the second solder material are selected in such a way that the liquidus temperature of the second metal layer 220 is lower than the solidus temperature of the first metal layer 210.

[0162] The description of the first welding material is the same as that in the first embodiment described above.

[0163] The description of the second welding material is the same as that in the first embodiment described above.

[0164] • Regarding the process (P3)

[0165] In process (P3), surface mount of the substrate 251 with solder pads 251L and the chip component 252 is performed by reflow soldering. The soldering area (solder joint 200) and the chip component 252 are disposed on the same surface 251s of the substrate 251.

[0166] First, solder paste, serving as the first solder material, is printed onto the pads 251L in such a way that it contacts the side of the chip component 252. Thus, the solder paste is configured to contact both the substrate 251 having the pads 251L and the chip component 252.

[0167] Next, the reflow oven is used for heat treatment and reflow operation.

[0168] The heating conditions in the reflow oven are, for example, a temperature of 220–230°C and a holding time of about 10 seconds.

[0169] During the reflow soldering operation, the solder alloy powder in the first soldering material melts to form a first metal layer 210 that contacts both the pad 251L and the chip component 252.

[0170] • Regarding the process (P4)

[0171] In process (P4), a second metal layer 220 is applied to the surface of the first metal layer 210 formed in process (P3) by flow welding.

[0172] First, flux is applied to the surface of the first metal layer 210, and then the substrate 251 on which flux has been applied to the surface of the first metal layer 210 is preheated.

[0173] Examples of flux coating devices include spray-type flux coating devices and foam-type flux coating devices.

[0174] Next, a solder alloy containing Sn and Bi, which is the second solder material, is brought into contact with the surface of the first metal layer 210 coated with flux in a molten state.

[0175] There are no particular limitations on the method of bringing the solder alloy of the second solder material into contact with the surface of the first metal layer 210 in a molten state; for example, spraying or immersion methods can be used.

[0176] In process (P4), the preheating operation and the operation of bringing the second solder material into contact with the surface of the first metal layer 210 are both performed at a temperature below the solidus temperature of the first metal layer 210.

[0177] Preheating operations, for example, are carried out at temperatures of 80–130°C.

[0178] The operation of bringing the second solder material into contact with the surface of the first metal layer 210 is performed, for example, at a temperature of 150°C to 200°C.

[0179] The solder joint 200 of the second metal layer 220 is prepared by the flow welding operation in such a way that it covers the entire surface of the first metal layer 210.

[0180] Furthermore, through the above-described processes (P3) and (P4), a bonding body 20 is prepared by bonding a substrate 251 having pads 251L and a chip component 252 via a solder joint 200.

[0181] According to the second embodiment described above, a solder joint 200 is provided that further improves the reliability of the joint where the components are joined.

[0182] In the solder joint 200 of the second embodiment, a solder layer (second metal layer 220) containing Sn and Bi is provided on the surface of a solder layer (first metal layer 210) containing Sn. That is, the solder joint 200 has a laminated structure comprising solder layers with opposite characteristics. Therefore, the solder joint 200 having this laminated structure possesses both ductility and strength characteristics (tensile strength, etc.). Furthermore, since the liquidus temperature of the second metal layer 220 is lower than the solidus temperature of the first metal layer 210, the adhesion between the first metal layer 210 and the second metal layer 220 is high, making peeling difficult. Thus, the reliability of the joint where the solder joint 200 connects the components is further improved.

[0183] Furthermore, according to the second embodiment described above, a method for preparing a solder joint 200 with improved reliability can be provided, which allows for easy preparation of joints that connect various components.

[0184] In the method for preparing the solder joint 200 in the second embodiment, two conventional mass production methods (step (P3) and step (P4)) are used to produce a solder foot with a stacked structure composed of solder layers with different properties.

[0185] In the second embodiment, process (P3) is a so-called surface mount process, and therefore can be carried out in the same production environment as the present.

[0186] Furthermore, process (P4) can also be performed in the same production environment as currently. The flow welding performed in process (P4) is specified to be carried out at a temperature below the solidus temperature of the first metal layer 210. Therefore, previously installed components will not detach, and a second metal layer 220 with different properties can be stably added and formed on the first metal layer 210.

[0187] As described above, the solder joint 200 can be easily prepared by a preparation method including process (P3) and process (P4).

[0188] According to this preparation method, as a miniaturized solder pad, a solder joint 200 having a laminated structure including solder layers with opposite characteristics can be fabricated at the current production level.

[0189] Furthermore, according to the second embodiment described above, a joint with improved reliability can be provided.

[0190] In particular, in the bonding body 20 having a solder joint 200 having a second metal layer 220 provided in such a way as to cover the entire surface of the first metal layer 210, the plastic deformation of the substrate 251 or the chip component 252 is suppressed, and the reliability of the bonding body is further improved.

[0191] The second embodiment described above describes the solder joint 200, which joins a substrate 251 having a pad 251L as a first component and a chip component 252 as a second component, as well as the method for preparing the solder joint 200 and the joint body 20 having the solder joint 200. However, it is not limited to the description and other embodiments are also possible.

[0192] For example, in the second embodiment described above, the chip component 252 is soldered to only one side 251s of the substrate 251, but it is not limited to this and can also be soldered to other sides of the substrate 251. According to this embodiment, the chip component 252 can be mounted on both sides of the substrate 251.

[0193] Alternatively, in the second embodiment described above, surface mounting of the substrate 251 with pads 251L and the chip component 252 is performed via steps (P3) and (P4), but this is not a limitation. Alternatively, after step (P3), leads for a lead-type electronic component can be inserted into a through-hole in the substrate 251, followed by step (P4). According to this embodiment, the second metal layer 220 can be configured to cover both the first metal layer 210 formed in step (P3) that contacts both the pads 251L and the chip component 252, and the lead portion protruding from one surface 251s of the substrate 251. This allows the chip component 252 to be bonded on one surface 251s of the substrate 251, while simultaneously bonding the lead-type electronic component on the other surface of the substrate 251.

[0194] • About flux

[0195] In the first or second embodiment described above, a flux having a composition in which the components are designed and their proportions are used, depending on the welding process method, etc.

[0196] In this embodiment, examples of components that can be used in flux include rosin, activator, thixotropic agent, and solvent, which are resin components.

[0197] About rosin:

[0198] The term "rosin" as used here includes natural resins containing a mixture of abrasive acid and its isomers, with abrasive acid as the main component, as well as substances obtained by chemically modifying natural resins (sometimes called rosin derivatives).

[0199] "Main component" refers to the component that constitutes a compound and whose content in the compound is 40% or more by mass.

[0200] As an example, the rosin acid content in natural resin is between 40% and 80% by mass relative to the total mass of natural resin.

[0201] Representative isomers of rosin acid include neorosin acid, longleaf rosin acid, and L-rosinic acid.

[0202] Examples of "natural resins" include resin rosin, wood rosin, and oil rosin.

[0203] "Substances obtained by chemically modifying natural resins (rosin derivatives)" include substances prepared by subjecting the "natural resins" to one or more treatments selected from hydrogenation, dehydrogenation, neutralization, alkyl epoxide addition, amination, dimerization and polymerization, esterification and Diels-Alder cycloaddition.

[0204] Examples of rosin derivatives include purified rosin and modified rosin.

[0205] Examples of modified rosin include, for example, hydrogenated rosin, polymerized rosin, polymerized hydrogenated rosin, disproportionated rosin, acid-modified rosin, rosin ester, acid-modified hydrogenated rosin, acid anhydride-modified hydrogenated rosin, acid-modified disproportionated rosin, acid anhydride-modified disproportionated rosin, phenol-modified rosin, and α,β-unsaturated carboxylic acid modified products (acrylated rosin, maleated rosin, fumarated rosin, etc.), as well as purified products, hydrogenated products, and disproportionated products of the polymerized rosin, purified products, hydrogenated products, and disproportionated products of the α,β-unsaturated carboxylic acid modified products, rosin alcohol, rosin amine, hydrogenated rosin alcohol, rosin ester, hydrogenated rosin ester, rosin soap, hydrogenated rosin soap, acid-modified rosin soap, etc.

[0206] Examples of active agents include organic acids, halogen compounds, and amine compounds.

[0207] Regarding organic acids:

[0208] Examples of organic acids include organic carboxylic acids and organic sulfonic acids.

[0209] Examples of organic carboxylic acids include aliphatic carboxylic acids and aromatic carboxylic acids. Examples of aliphatic carboxylic acids include aliphatic monocarboxylic acids and aliphatic dicarboxylic acids.

[0210] In addition, examples of organic carboxylic acids include tris(2-carboxyethyl) isocyanurate, 1,3-cyclohexanedicarboxylic acid; dimer acids, trimer acids, hydrogenated dimer acids as hydrides of hydrogenated dimer acids, and hydrogenated trimer acids as hydrides of hydrogenated trimer acids.

[0211] Examples of organic sulfonic acids include aliphatic sulfonic acids and aromatic sulfonic acids. Examples of aliphatic sulfonic acids include alkyl sulfonic acids and alkanol sulfonic acids.

[0212] Regarding halogen compounds:

[0213] Examples of halogenated compounds include, for example, aminohydrohalides and halogenated aliphatic compounds.

[0214] Amino halides are compounds formed by reacting amines with hydrogen halides. Examples of amines include aliphatic amines, azoles, and guanidines. Examples of hydrogen halides include the hydrides of chlorine, bromine, and iodine.

[0215] Halogenated aliphatic compounds are compounds in which some or all of the hydrogen atoms constituting the aliphatic hydrocarbon group are replaced by halogen atoms. Examples of halogenated aliphatic compounds include halogenated fatty alcohols and halogenated heterocyclic compounds.

[0216] Regarding amine compounds:

[0217] Examples of amines include rosin amines, azoles, guanidines, alkylamine compounds, and amino alcohol compounds.

[0218] Regarding thixotropic agents:

[0219] Examples of thixotropic agents include ester-based thixotropic agents, amide-based thixotropic agents, and sorbitol-based thixotropic agents.

[0220] Examples of ester-based thixotropic agents include ester compounds such as hydrogenated castor oil and ethyl myristate.

[0221] Examples of amide-based thixotropic agents include monoamides, diamides, and polyamides.

[0222] As monoamides, they can be lauryl amide, palmitamide, stearamide, behenamide, hydroxystearamide, saturated fatty acid amide, oleamide, erucamide, unsaturated fatty acid amide, 4-methylbenzamide (p-toluamide), tolueneformamide, aromatic amide, hexamethylene hydroxystearamide, substituted amide, hydroxymethylstearamide, hydroxymethylamide, fatty acid ester amide, etc.

[0223] Examples of diamides include ethylene difatty acid (fatty acid with 6-24 carbon atoms) amides, ethylene dihydroxy fatty acid (fatty acid with 6-24 carbon atoms) amides, hexamethylene difatty acid (fatty acid with 6-24 carbon atoms) amides, hexamethylene dihydroxy fatty acid (fatty acid with 6-24 carbon atoms) amides, and aromatic diamides. Examples of fatty acids used as raw materials for these diamides include stearic acid (C18 carbon atoms), oleic acid (C18 carbon atoms), and lauric acid (C12 carbon atoms).

[0224] Examples of polyamides include saturated fatty acid polyamides, unsaturated fatty acid polyamides, aromatic polyamides, 1,2,3-propanetricarboxylic acid tris(2-methylcyclohexylamide), cyclic amide oligomers, and non-cyclic amide oligomers.

[0225] Examples of sorbitol-based thixotropic agents include dibenzylidene-D-sorbitol, di(4-methylbenzylidene)-D-sorbitol, (D-)sorbitol, monobenzylidene(-D-)sorbitol, and mono(4-methylbenzylidene)-(D-)sorbitol.

[0226] Regarding solvents:

[0227] Examples of solvents include water, alcohols, glycol ethers, and terpineols.

[0228] Regarding other compounding components:

[0229] In this embodiment, in addition to the rosin, activator, thixotropic agent and solvent mentioned above, the flux may also contain other compounding components as needed.

[0230] Other contributing components include resins other than rosin, metal passivators, surfactants, silane coupling agents, antioxidants, colorants, etc.

[0231] In the first and second embodiments described above, preferred fluxes for the flux contained in the solder paste in the first welding material include, for example, a composition containing rosin as a resin component, an organic acid as an activator, a halogen compound and an amine compound, a thixotropic agent and a solvent (F1).

[0232] The rosin content in the composition (F1) is, for example, more than 5% and less than 50% by mass relative to the total mass (100% by mass) of the composition (F1).

[0233] The organic acid content in the composition (F1) is, for example, more than 5% by mass and less than 25% by mass relative to the total mass (100% by mass) of the composition (F1).

[0234] The content of halogen compounds in the composition (F1) is, for example, more than 0.01% by mass and less than 2% by mass relative to the total mass (100% by mass) of the composition (F1).

[0235] The content of the amine compound in the composition (F1) is, for example, more than 1% and less than 10% by mass relative to the total mass (100% by mass) of the composition (F1).

[0236] The thixotropic agent content in the composition (F1) is, for example, 3% or more and 20% or less relative to the total mass (100% by mass) of the composition (F1).

[0237] The solvent content in the composition (F1) is, for example, more than 30% and less than 80% by mass relative to the total mass (100% by mass) of the composition (F1).

[0238] The content of the composition (F1) in the solder paste is, for example, more than 5% and less than 30% by mass relative to the total mass of the solder paste (100% by mass).

[0239] In the first and second embodiments described above, in the flow welding process, a preferred flux used as a commonly used flux can be, for example, a composition (F2) containing rosin as a resin component, an organic acid and an amine compound as an activator, and a solvent. Preferably, a composition further containing polyalkylene glycol can be included.

[0240] The rosin content in the composition (F2) is, for example, more than 2% and less than 30% by mass relative to the total mass (100% by mass) of the composition (F2).

[0241] The content of organic acids in the composition (F2) is, for example, more than 1% and less than 10% by mass relative to the total mass (100% by mass) of the composition (F2).

[0242] The content of the amine compound in the composition (F2) is, for example, more than 0.05% by mass and less than 2% by mass relative to the total mass (100% by mass) of the composition (F2).

[0243] The solvent content in the composition (F2) is, for example, 60% or more and 95% or less relative to the total mass (100% by mass) of the composition (F2).

[0244] Examples of polyalkylene glycols include polyethylene glycol, polypropylene glycol, and polyethylene glycol-polypropylene glycol copolymers. The average molecular weight of the polyalkylene glycol is preferably between 100 and 4000. Here, average molecular weight refers to exponential average molecular weight.

[0245] When polyalkylene glycol is also contained, the content of polyalkylene glycol in the composition (F2) relative to the total mass (100% by mass) of the composition (F2) is, for example, 0.1% by mass or more and 6% by mass or less. By further containing polyalkylene glycol, slag adhesion to the weld surface can be suppressed during flow welding.

[0246] The preferred embodiments of the present invention have been described above with reference to the accompanying drawings; however, the present invention is not limited to these embodiments. In these drawings, for convenience, some features are sometimes shown enlarged, and the dimensional proportions of each component are not limited to the illustrated proportions. The shapes and combinations of the constituent components shown in the above examples are merely examples, and various modifications can be made based on design requirements, etc., without departing from the spirit of the present invention.

Claims

1. A solder joint for joining a first component and a second component, the solder joint comprising: a first metal layer in contact with both the first component and the second component, and a second metal layer disposed on the surface of the first metal layer. The first metal layer is a solder layer containing Sn. The second metal layer is a solder layer containing Sn and Bi. The solidus temperature of the first metal layer is 215~230℃. The liquidus temperature of the second metal layer is lower than the solidus temperature of the first metal layer.

2. A solder joint for joining a first component and a second component, the solder joint comprising: a first metal layer in contact with both the first component and the second component, and a second metal layer disposed on the surface of the first metal layer. The first metal layer is a solder layer containing Sn. The second metal layer is a solder layer containing Sn and Bi. The liquidus temperature of the second metal layer is lower than the solidus temperature of the first metal layer. The difference between the liquidus temperature of the second metal layer and the solidus temperature of the first metal layer is greater than 50°C.

3. A method for preparing a solder joint, comprising a method for preparing a solder joint for joining a first component and a second component, wherein, The method includes: A reflow soldering process in which a first solder material containing Sn is melted and forms a first metal layer in contact with both the first and second components, configured to contact both the first and second components; and A flow soldering process is performed by bringing a second solder material containing Sn and Bi into contact with the first metal layer in a molten state, thereby creating a second metal layer on the surface of the first metal layer. The first solder material and the second solder material are selected in such a way that the liquidus temperature of the second metal layer is lower than the solidus temperature of the first metal layer. The flow welding process is performed at a temperature below the solidus temperature of the first metal layer.

4. A joint comprising a first member, a second member, and a solder joint for joining the first member and the second member, wherein, The solder joint includes the solder joint as described in claim 1 or 2.

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