Sheet solder

Abstract

To provide sheet-like solder that hardly causes electromigration, a solder joint part using the same, and a semiconductor device.SOLUTION: There are provided: sheet-like solder which consists principally of Sn and includes additive elements and inevitable impurities, and is pressed, the pressed surface being a surface perpendicular to the principal surface and a c axis of crystal of Sn being aligned in a direction perpendicular to a thickness of the sheet; and a solder joint part which comprises a solder joint layer formed by fusing the sheet-like solder between a semiconductor element and a conductive joint member.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sheet solder, a solder joint, and a semiconductor device equipped with the same. In particular, the present invention relates to a sheet solder, a solder joint, and a highly reliable semiconductor device equipped with the same that are applied to semiconductor devices and are resistant to electromigration even when a large current is passed through them. [Background technology]

[0002] Power semiconductor modules are widely used in fields that require efficient power conversion. For example, their application range is expanding to power electronics fields such as industrial equipment, electric vehicles, and home appliances. These power semiconductor modules contain built-in switching elements and diodes, and the elements use Si (silicon) semiconductor elements or SiC (silicon carbide) semiconductor elements.

[0003] In recent years, the current density flowing through semiconductor elements has been increasing. 2 When the current reached a large value, electromigration (EM) occurred at the solder joints, which could cause localized electrical conductivity failure.

[0004] Conventionally, SnSb-based solders and SnSbAg-based solders have been used to bond semiconductor elements because of their melting point and strength. These solder materials are primarily composed of tin (Sn) and have a structure in which Sn crystals are randomly oriented. It is known that the Sn constituting the solder material is more likely to cause EM depending on the direction of current relative to the orientation (see, for example, Patent Document 1). EM can also occur in structures in which Sn crystals are randomly oriented, but EM is more likely to occur when current flows along the c-axis of the Sn crystal lattice, and less likely to occur when current flows perpendicular to the c-axis. Patent Document 1 discloses a technique for bonding elements in the manufacture of semiconductor devices, in which the c-axis of the solder is made perpendicular to the current flow direction by applying an electric or magnetic field to molten solder. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-51844 Summary of the Invention [Problem to be solved by the invention]

[0006] According to the technology disclosed in Patent Document 1, it is theoretically possible to align the c-axis of the Sn crystal lattice in a predetermined direction. However, the process is complicated and requires expensive equipment, making it unsuitable for practical use. [Means for solving the problem]

[0007] Current density is 800A / cm 2 There is a need for a solder that can realize a semiconductor device that is less susceptible to electromigration even when a large current of this magnitude is passed through it.

[0008] As a result of extensive research, the inventors discovered that compressing solder with randomly oriented Sn crystals in a predetermined direction can cause plastic deformation and orient the c-axis of the Sn crystal lattice parallel to the compression direction, leading to the completion of the present invention.

[0009] That is, according to one embodiment, the present invention relates to a pressed sheet solder containing a solder alloy having Sn as a main component and containing additional elements and unavoidable impurities, wherein the pressed surface is perpendicular to the main surface and the c-axis of the Sn crystal is oriented in a direction perpendicular to the thickness direction of the sheet.

[0010] In the sheet solder, the c-axis orientation ratio, which is an index of the c-axis orientation of Sn crystals, on the press-processed surface is preferably 0.3 or more.

[0011] In the solder sheet, the c-axis orientation ratio is preferably 0.95 or less.

[0012] In the solder sheet, the additive element is preferably selected from Sb, Cu, Ag, Ni, Ge, or a combination thereof.

[0013] According to another embodiment, the present invention provides a semiconductor device and a conductive connection The present invention relates to a solder joint having a solder joint layer formed between a member and any one of the above-described sheet solders melted therein.

[0014] In the solder joint, the conductive connection Preferably, the member is a lead frame.

[0015] According to yet another embodiment, the present invention relates to a semiconductor device including the above-described solder joint.

[0016] According to yet another embodiment, the present invention is a method for manufacturing a semiconductor device, the method comprising the steps of: pressing a solder alloy containing Sn as a main component and containing additional elements and unavoidable impurities to produce a sheet solder in which the pressed surface is perpendicular to the main surface and the c-axis of the Sn crystal is oriented perpendicular to the thickness direction of the sheet; connection The present invention relates to a method for manufacturing a semiconductor device, comprising the steps of: laminating a substrate and a member; and melting the sheet-like solder.

[0017] In the method for manufacturing a semiconductor device, the press working step is preferably a step of applying pressure until a c-axis orientation ratio, which is an index of c-axis orientation of Sn crystals, becomes 0.3 or more. [Effects of the Invention]

[0018] In the solder sheet according to the present invention, the c-axis of the Sn crystal lattice is oriented perpendicular to the thickness direction, so by joining semiconductor elements using this solder sheet, electromigration can be prevented, making it possible to manufacture highly reliable semiconductor devices. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a conceptual explanatory diagram showing a sheet solder according to a first embodiment of the present invention, where (a) is a conceptual plan view and (b) is a conceptual cross-sectional view. [Figure 2] Figure 2 shows an overview of electron backscatter diffraction (EBSD) measurements to identify the c-axis orientation of sheet solder, where (a) is a diagram explaining the projection sphere display, and (b) is a diagram showing an example of a crystal orientation map in which crystals with a specific orientation are extracted. [Figure 3] FIG. 3 is a conceptual perspective view showing an example of a press mold that can be used in the manufacturing process of the sheet solder according to the first embodiment of the present invention. [Figure 4] FIG. 4 is a conceptual diagram showing a cross-sectional structure of a solder joint according to a second embodiment of the present invention. [Figure 5] FIG. 5 is a conceptual diagram showing a cross-sectional structure of a semiconductor device according to a third embodiment of the present invention. [Figure 6] FIG. 6 is a conceptual diagram showing a cross-sectional structure of a solder joint according to the prior art. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the embodiments described below.

[0021] [First embodiment: sheet solder] According to a first embodiment, the present invention relates to a solder sheet. The solder sheet according to this embodiment contains a solder alloy containing Sn as a main component, additional elements, and inevitable impurities, and is press-formed so that the c-axis of the Sn crystal is oriented perpendicular to the thickness direction of the sheet.

[0022] In this specification, sheet solder refers to solder processed into a sheet having a predetermined length, width, and thickness, and having a thickness that is small relative to the length and width. More specifically, the thickness t is approximately 500 μm or less, but may be approximately 5 μm or more, and preferably approximately 300 μm or less, but approximately 10 μm or more. The thickness t of the sheet solder typically corresponds to the thickness when cut from a pressed solder block in the manufacturing method described below. The length and width of the sheet solder are not particularly limited, and as long as it is sheet-shaped, it may be a plate or a roll. It may also be cut into a shape that fits the product to be joined. The length and width of the sheet solder vary depending on the product to which it is applied and are not particularly limited, but may be at least 500 μm or more, and generally 2000 μm or more. The length and width of the sheet solder can also be determined by the dimensions and shape of the mold used in the manufacturing method described below.

[0023] The sheet solder contains a solder alloy, and preferably consists of a solder alloy. The composition of the solder alloy may be Sn-based, containing additional elements and inevitable impurities. The composition of the solder alloy is preferably a lead-free solder alloy that does not contain Pb except as an inevitable impurity. "Based on Sn as the main component" means that, when the total mass of the solder alloy is taken as 100%, 80% by mass or more of the solder alloy is composed of Sn. In a solder alloy that is composed of 80% by mass or more of Sn, the c-axis of the Sn crystal lattice can be oriented by plastic deformation such as pressing, similar to a solder that is essentially composed of only Sn. Specifically, the Sn solder alloy is pressed. processingWhen compressed by this method, the material undergoes plastic deformation, and the c-axis is oriented in a direction parallel to the pressing surface. Pressing is a process in which the workpiece is pressed against a die and deformed by applying pressure from a specific direction (press direction).

[0024] The additive elements are not particularly limited as long as they are elements other than Sn that are commonly used in solder alloys. Examples include, but are not limited to, Sb, Cu, Ag, Ni, Ge, P, Bi, In, Si, V, Au, Pt, Mo, Zn, Co, Fe, Mn, Cr, and Ti. The additive elements may be one or more, but the total mass of the additive elements may not exceed 20 mass% of the total mass of the solder alloy. Inevitable impurities include, but are not limited to, Cu, Ni, Zn, Fe, Al, As, Cd, Au, In, P, and Pb. The content of inevitable impurities may be within the range specified for each alloy system by the International Organization for Standardization or industrial standards of each country. Furthermore, in accordance with the RoHS Directive, it is preferable that Hg is not included, and hexavalent Cr is less than 0.1 mass% and Cd is less than 0.01 mass% of the total mass of the solder alloy.

[0025] More specific solder alloy compositions include, but are not limited to, Sn-Ag-Cu, Sn-Sb, Sn-Sb-Ag, Sn-Cu, Sn-Sb-Ag-Cu, Sn-Cu-Ni, and Sn-Ag alloys, all of which contain 80% or more by mass of Sn. More specifically, Sn-Ag-Cu solders preferably contain 0.5 to 5.0% by mass of Ag and 0.1 to 3.0% by mass of Cu. Sn-Sb solders preferably contain 2.0 to 20% by mass of Sb. Sn-Sb-Ag solders preferably contain 6.0 to 8.0% by mass of Sb and 2.0 to 4.0% by mass of Ag. In the case of an Sn-Cu system, it is preferable to contain Cu in the range of 0.1 to 10.0 mass%. In the case of an Sn-Sb-Ag-Cu system, it is preferable to contain Sb in the range of 5.0 to 10 mass%, Ag in the range of 2.0 to 4.0 mass%, and Cu in the range of 0.1 to 1.2 mass%. In the case of an Sn-Cu-Ni system, it is preferable to contain Cu in the range of 0.1 to 6.0 mass% and Ni in the range of 0.1 to 0.5 mass%. In the case of an Sn-Ag system, it is preferable to contain Ag in the range of 1.0 to 6.0 mass%.

[0026] In one embodiment, the sheet solder may be composed of a solder alloy having a substantially uniform composition throughout the sheet. In another embodiment, the sheet solder may contain high-melting-point metal particles in an alloy having the composition specified above. The high-melting-point metal particles may be particles containing, for example, Ni, Ag, Cu, Fe, stainless steel, or an alloy thereof, and the high-melting point metal particles may be particles containing, for example, Ni, Ag, Cu, Fe, stainless steel, or an alloy thereof. point The metal particles may have an average particle size of about 1 to 50 μm. The content of the high-melting point metal particles in the sheet solder may be about 1 to 40 mass %. In yet another embodiment, the sheet solder may contain a high-melting point metal wire in an alloy having the composition specified above. The high-melting point metal wire can be selected from the same composition as the high-melting point metal particles, and the diameter aboutThe thickness may be about 1 to 50 μm. The content of the high-melting point metal wire in the sheet-shaped solder may be about 1 to 40 mass %.

[0027] FIG. 1(a) is a conceptual plan view and a cross-sectional view showing an example of a sheet solder according to this embodiment. X, Y, and Z in FIG. 1 represent the length, width, and thickness directions of the sheet solder, respectively. The sheet solder is pressed in one direction and cut along a plane parallel to the pressing direction. It has a main surface m defined by the length and width directions and an opposing surface f. FIG. 1(b) is a conceptual diagram showing a cross section of the sheet solder cut perpendicular to the main surface m. Referring to FIG. 1(b), the sheet solder is made of a solder alloy with a thickness t, and the c-axis of the Sn crystal is oriented perpendicular to the thickness direction Z of the solder. The c-axis of the Sn crystal constituting the solder alloy is oriented parallel to the main surface m of the sheet solder. Of the side surfaces perpendicular to the main surface m of the sheet solder, one pair of opposing surfaces is the surface P that was pressed during manufacturing. In this specification, the pressed surface P is also referred to as the pressed surface. In Figure 1(b), the area surrounded by the solid line represents Sn crystal grains, and the arrows in the area represent the orientation direction of the c-axis of the Sn crystals. The solid line representing the Sn crystal lattice is for explanatory purposes and is significantly different from the actual scale. The area surrounded by the solid line can also be interpreted as a single crystal region. A single crystal region is a region with the same orientation direction and does not contain twins, etc.

[0028] In the sheet solder according to this embodiment, the c-axis of the Sn crystals can be confirmed to be oriented in a predetermined direction using EBSD. EBSD is a commonly known surface analysis method that determines crystal orientation by irradiating a sample surface with accelerated electrons in a vacuum and analyzing the Kikuchi pattern obtained by the backscattering of the electrons. Irradiating the sample surface (measurement surface) with an electron beam determines the crystal orientation at that location. Scanning the electron beam within a predetermined range allows for the acquisition of a crystal orientation map of the crystal grains in the scanned area. The range of one measurement point of the electron beam is approximately 10 nmφ. The c-axis orientation of Sn in the sheet solder can be evaluated by irradiating the electron beam at an angle of approximately 20° with respect to the press-processed surface P or the main surface m shown in Figure 1.

[0029] At temperatures between approximately 13°C and 200°C, Sn crystals are tetragonal (β-Sn structure) with lattice constants a = b = 5.832 Å and c = 3.181 Å, with four Sn atoms per unit cell. The c-axis refers to the aforementioned 3.181 Å long axis. This section explains how to evaluate the orientation of this c-axis. Crystal orientation is expressed by the inclination of the normal to the crystal plane relative to the reference plane. The orientation plane of each crystal can be described as the inclination of the normal radiating from a point within the crystal and the reference plane. The crystal orientation plane at a measurement point can be represented by the intersection of this normal and a virtual sphere (projected sphere) centered at a point within the crystal. Figure 2(a) illustrates the virtual projected sphere representation used in EBSD. In Figure 2(a), S represents the projected sphere, and B represents the reference plane.

[0030] This section explains the case where the measurement target is a single Sn crystal particle (single crystal particle). If the c-axis of the Sn crystal particle is oriented perpendicular to the reference plane, the orientation point is plotted directly above the projection sphere. Here, "directly above the projection sphere" refers to the point where the perpendicular to the reference plane passing through the center of the projection sphere intersects with the projection sphere above the reference plane, i.e., on the side of the reference plane where the electron beam is irradiated. If the c-axis of the Sn crystal particle is tilted relative to the reference plane, the orientation point is plotted at a point tilted from directly above the projection sphere, depending on the tilt. A diagram showing the crystal orientation in this way is called a "pole figure." Using the EBSD method, the surface of the measurement sample is used as the reference plane, and the crystal orientation of the sample is measured at the position where the electron beam is irradiated on the surface of the measurement sample. This allows the location of the orientation point on the projection sphere to be determined. For example, if a region on the surface of a Sn crystal with its c-axis oriented perpendicular to the reference plane is measured using the EBSD method, a crystal orientation map showing the entire measurement region as being (001)-oriented is obtained. In this case, the crystal orientation is displayed on the projection sphere as a single point K, which represents the c-axis orientation with the (001) plane facing the measurement surface. On the other hand, if a polycrystalline region with non-single crystal orientation is measured using the EBSD method, numerous orientation points will be displayed scattered across almost the entire surface above the reference plane of the projection sphere. Examples of orientation points in this case are indicated by x. If points are concentrated in a specific region of the projection sphere, it can be said that the c-axis of Sn is oriented in the direction from the center of the projection sphere toward the point. For example, the orientation point when measuring a sample with many crystals having c-axis orientation is indicated by ▲.

[0031] Next, we will explain the c-axis orientation ratio A, an index of c-axis orientation. For example, when EBSD measurement is performed on Sn polycrystals, a crystal orientation map can be obtained for the measurement area, as described above. EBSD allows for the extraction and mapping of only crystal grains within the measurement area whose c-axes are tilted within a specific angle θ from the normal to the reference plane passing through the center of the projection sphere, as shown by the dashed line within the projection sphere. Figure 2(b) shows an example of a crystal orientation map in which crystals with a specific orientation are extracted. In Figure 2(b), crystals a1 with a specific c-axis orientation are indicated by dots. Crystals a2 with no specific c-axis orientation are indicated by white. Based on the crystal orientation map, the area of ​​the portion with a specific c-axis orientation can be calculated and its ratio to the area of ​​the measurement area (the entire area scanned by the electron beam). This area ratio can then be used to extract the area ratio of crystals with a specific orientation, which can be defined as the c-axis orientation ratio A. That is, A is defined by the following equation (1): c-axis orientation ratio A = area where the c-axis is oriented in a specific direction on the crystal orientation map obtained by EBSD measurement / area of ​​the measurement region (1)

[0032] When the press-processed surface P, which is the side surface of the sheet solder 1 shown in Figure 1(b), is used as the measurement surface, the ratio Av of the Sn c-axis oriented in the direction perpendicular to the press-processed surface (measurement surface) is defined by the following formula (1a). Av = Area where the c-axis is oriented perpendicular to the measurement surface on the crystal orientation map obtained by EBSD measurement with the measurement surface being the pressed surface / Area of ​​the measurement region (1a) The press-processed surface is not limited to the surface that comes into contact with the press tool, but also includes surfaces perpendicular to the pressing direction.

[0033] In the present invention, EBSD measurement is performed using the press-processed surface P of the sheet solder 1 in Figures 1(a) and 1(b) as the reference plane B on the projection sphere in Figure 2(a). Crystals with a c-axis whose inclination θ is within 26° from the c-axis indicated by the arrow c in Figure 2(a) can be said to be crystals whose c-axis is oriented in a direction perpendicular to the thickness direction of the sheet solder, and are defined as crystals with c-axis orientation. In the sheet solder according to the present invention, if the inclination θ of the c-axis on the press-processed surface of the Sn crystal, which is the main component of the solder, is within 26°, it can be determined that the c-axis is nearly perpendicular to the press surface, and when the main surface m of the sheet solder is incorporated into a semiconductor module so that it is parallel to the top surface of the semiconductor element (Figure 2). 5 ), because electromigration can be prevented.

[0034] For example, the measurement conditions for the c-axis orientation ratio A are as follows: the measurement surface is the pressed surface P of the solder material, and the measurement area is, for example, 400 μm × 400 μm. The incident angle of the electron beam is approximately 20° relative to the measurement surface, and the electron beam scans in 2.5 μm increments. For sheet solder, if the measurement surface is the pressed surface (side surface) and the measurement area cannot be 400 μm × 400 μm, a measurement area of ​​the same area, such as a rectangle, can be used. Note that if the measurement area contains alloy phases such as Sn-Ag, or high-melting-point metal particles or high-melting-point metal wires, these can be excluded from the calculation of the c-axis orientation ratio A. Because alloy phases and Cu have different crystalline structures from Sn, their electron diffraction patterns (Kikuchi patterns) are also different, making their presence easy to identify. If the Sn content is 80 wt% or more, Sn crystals account for the majority, allowing for control of the orientation of the Sn crystal grains. Furthermore, if the Sn content is 80 wt % or more, the alloy exhibits ductility similar to Sn, and as will be described in detail later, Sn crystals can be oriented by pressing.

[0035] For example, when the c-axis orientation ratio Av of the press-processed surface P is measured, the Sn crystal is defined as randomly oriented when the c-axis has no specific orientation. When Av is greater than 0.2, the c-axis of the Sn crystal is said to be oriented perpendicular to the thickness direction. Av is preferably 0.3 or greater and 0.95 or less. The thickness direction is the Z direction in Figure 1(b). When sheet solder with a c-axis orientation ratio A within this range is used to bond semiconductor elements, with the principal surface m parallel to the back electrode or laminate substrate of the semiconductor device, it prevents EM and increases power cycle resistance.

[0036] The preferable c-axis orientation ratio of the solder sheet according to this embodiment can also be confirmed by performing EBSD measurement using the principal surface m as the measurement surface. Specifically, by evaluating the proportion of c-axes oriented in a direction parallel to the principal surface m, it can be confirmed that the c-axes of the Sn crystals are oriented in a direction perpendicular to the thickness direction of the solder sheet, and preferably that the c-axis orientation ratio Av, which is an index of the c-axis orientation of the Sn crystals, is 0.3 or more. In this case, if the principal surface m is the measurement surface and Ap is the proportion of c-axes oriented in a direction parallel to the measurement surface and perpendicular to the side surface (press-processed surface P), Ap is defined by the following formula (1b): Ap = Area where the c-axis is parallel to the measurement surface and perpendicular to the side surface (pressed surface) on the crystal orientation map obtained by EBSD measurement with the measurement surface as the main surface / Area of ​​measurement region (1b)

[0037] In the sheet solder according to the present invention shown in FIGS. 1(a) and 1(b) and the solder joint according to a second embodiment shown in FIG. 4 (described later), the c-axis of Sn is parallel to the main surface m and oriented perpendicular to the pressed surface. In this case, Ap is essentially the same as Av, the ratio of the c-axis oriented perpendicular to the pressed surface when the measurement surface is the side surface (pressed surface). EBSD is a technique that can uniquely determine the crystal orientation. Therefore, it is possible to measure the pressed surface P as in Av and derive the orientation ratio of the Sn crystal in the measurement coordinate system viewed from the pressed surface P. Also, it is possible to measure the main surface m as in Ap and obtain the orientation ratio of the Sn crystal in the measurement coordinate system viewed from the pressed surface P. Therefore, the c-axis orientation of the sheet solder according to this embodiment can be obtained by the above formula (1a) or (1b) using the EBSD method with the pressed surface P or the main surface m as the measurement surface.

[0038] It is sufficient that the c-axis of the Sn crystal is oriented perpendicular to the thickness direction, and the orientation direction of the c-axis may be random within the XY plane shown in FIG. 1(a).

[0039] Next, a method for manufacturing the sheet solder according to this embodiment will be described. The method for manufacturing the sheet solder includes the following steps. (1) Preparing the solder block (2) The process of pressing the prepared solder block (3) Cutting the pressed solder block

[0040] In step (1), a solder block is prepared. Commercially available solder blocks can be used. Alternatively, the solder block can be prepared by melting raw materials selected from Sn and additive elements, or a master alloy containing these raw materials, in an electric furnace according to a conventional method. A purchased or prepared solder block with a predetermined composition is preferably melted at a temperature above its liquidus temperature and then rapidly cooled. The melting temperature is preferably in the range of the liquidus temperature or higher and up to 100°C above the liquidus temperature. Rapid cooling refers to cooling to 100°C at a rate of 5°C / min or higher. This allows for the production of a solder block in which the c-axes of the Sn crystal lattice are randomly oriented in the initial state. In step (1), the c-axis orientation of the Sn crystal lattice in the obtained initial solder block is preferably measured and confirmed using the EBSD method. This EBSD measurement can be performed on the surface to be pressed in the next step. Furthermore, the step (1) may include a step of cutting the solder block into a shape and size that fits the mold for the next step.The quenched block was analyzed by electron beam diffraction using a TEM (transmission electron microscope) and was found to have no specific orientation but was randomly oriented.

[0041] In step (2), the solder block in its initial state is placed in a mold and pressed. The mold is not particularly limited as long as it is a common mold used in press processing; for example, a metal mold can be used. It is preferable to use a mold capable of applying a pressure of approximately 0.1 to 40 MPa, preferably 0.3 to 25 MPa. Furthermore, it is preferable to equip the mold surface that contacts the solder block with a heater or the like capable of heating the surface to a temperature of approximately solidus temperature (K) × 0.7 to solidus temperature (K) × 0.95, preferably approximately solidus temperature (K) × 0.8 to solidus temperature (K) × 0.9, at which the βSn phase can be maintained. By maintaining the mold temperature within the aforementioned range, the sheet solder material can be formed well without cracking. The mold is preferably shaped to obtain a substantially rectangular prism-shaped solder block after pressing. Therefore, the press surface P of the mold is preferably rectangular when viewed from above. Considering the subsequent cutting process, it is preferable that the side lengths be the same as the dimensions of the sheet shape to be actually used.

[0042] FIG. 3 is a conceptual perspective view showing an example of a press mold and a pressed solder block that can be used in step (2). In the figure, L indicates the vertical direction, M indicates the short-side direction of the mold, and N indicates the long-side direction of the mold. In this step, the initial solder block is placed in the groove of the lower mold (bottom) 3, and the mold is heated to a predetermined temperature using a heater (not shown). Next, the upper mold is placed in contact with the solder block, and pressure is applied in the direction of L in the figure. The pressure and compression ratio during pressing are within the above-mentioned pressure range, and can be determined by conducting a preliminary experiment on a solder alloy of the desired composition to achieve the desired c-axis orientation ratio A. In one embodiment, if it is confirmed in step (1) that the initial solder block has a random orientation, the thickness of the solder block after pressing can be in the range of 5% to 95% of the initial thickness. The pressed surface P, which is used as the EBSD measurement surface when measuring the c-axis orientation ratio A, is a surface perpendicular to the direction of pressure applied during pressing. Of the surfaces perpendicular to the direction of pressure during press working, both the surface that comes into contact with the upper die and the surface that comes into contact with the lower die during press working can be referred to as the press working surface P. In the embodiment shown in FIG. 3, the upper and lower surfaces of the solder block 2 that are parallel to the MN plane are the press working surfaces P. The mold is designed so that the pressed solder block 2 has a rectangular column shape, and the shape of the solder block before being placed in the mold is adjustment It is possible.

[0043] In step (2), pressure is applied in a predetermined direction L, thereby plastically deforming the Sn-based solder alloy and orienting the c-axis in a direction parallel to the pressure direction L. The c-axis direction of the Sn crystal lattice in the compressed solder block 2 after press working is indicated by arrow c in Figure 3. It is preferable to further include a step at the end of step (2) of measuring and confirming the c-axis orientation ratio A by the EBSD method. In this case, the electron beam incident surface can be the press-worked surface P.

[0044] In step (3), the pressed, rod-shaped solder block 2 is cut in a direction parallel to the direction of pressure, i.e., parallel to the c-axis. In the embodiment shown in FIG. 3, the cut can typically be parallel to the LM plane or the LN plane. The cutting means is not particularly limited, but a wire saw or an electric discharge machine can be used. In FIG. 3, the dashed-two-dot lines show an example of a cut point 5 when the compressed solder block 2 is cut in a plane parallel to the LM plane. By cutting in a plane parallel to the LM plane at the positions shown by the dashed-two-dot lines, multiple sheet solder pieces can be cut from one solder block 2, with the resulting cut surfaces (cut edges) as the main surfaces and the cutting width t corresponding to the thickness. In the cut rectangular solder sheet, one of the two pairs of opposing surfaces other than the main surfaces is the pressed surface. This step allows the sheet solder shown in FIG. 1 to be obtained, in which the c-axis of the Sn crystal is oriented perpendicular to the thickness direction of the sheet.

[0045] The sheet solder thus obtained can be used for joining electronic devices, and in particular for joining semiconductor elements and conductive materials. connection In this case, the surface parallel to the XY plane shown in Figure 1 is the main surface m of the sheet solder, and the main surface m and the surface f opposite thereto are the electrode surfaces of a semiconductor element or conductive surfaces such as a lead frame. connection This allows the c-axis to be oriented in a direction perpendicular to the thickness direction of the sheet solder even before joining. The sheet solder according to this embodiment is particularly suitable for use at current densities of 500 A / cm 2 or more than 1000A / cm 2 It can be preferably used for manufacturing solder joints for passing large currents as described above.

[0046] [Second embodiment: solder joint] According to a second embodiment, the present invention relates to a solder joint. The solder joint according to this embodiment is a solder joint comprising a semiconductor element and a conductive connection A solder joint layer is provided between the member and the sheet solder according to the first embodiment.

[0047] 4 is a conceptual cross-sectional view showing an example of a solder joint according to this embodiment. Referring to FIG. 4, a semiconductor element 11, a molten sheet solder 1, a conductive connection Lead frames 18, which are an example of components, are laminated on the substrate 1. The molten sheet solder refers to a solid state in which the solder material is heated and melted, and joined to the materials to be joined.

[0048] The solder joint according to this embodiment is formed by joining the front surface electrodes of the semiconductor element 11 and the lead frame 18 with the molten sheet solder 1. As described in the first embodiment, the sheet solder 1 has a main surface m shown in FIG. 1 and an opposing surface f that are connected to the electrodes of the semiconductor element 11 or the conductive connection The solder alloy is placed in contact with a component (such as lead frame 18) and melted. The c-axis orientation of the Sn crystals that make up the solder alloy does not substantially change when heated and melted during joining, and the c-axis of the Sn crystals is oriented perpendicular to the thickness direction Z of the sheet, even in the solder joint. In FIG. 4, the c-axis orientation direction is indicated by arrow c. In the illustrated solder joint, current flows from the semiconductor element 11 to the lead frame 18 in the direction indicated by arrow I, or in the opposite direction. In other words, because the orientation direction c is perpendicular to the current direction I, the solder joint is less susceptible to electromigration. The solder joint may be formed by joining the semiconductor element 11 and the second conductive plate 123a of the laminated substrate with sheet solder 1.

[0049] FIG. 6 is a conceptual cross-sectional view showing an example of a solder joint using a conventional solder material. The solder joint is formed by joining a front surface electrode of a semiconductor element 111 and a lead frame 118 with molten solder 101. In a solder joint layer formed by melting a conventional solder material, the c-axis of the Sn crystal lattice does not have a fixed orientation with respect to the thickness direction Z of the sheet, but is randomly oriented. In other words, the direction of current indicated by arrow I and the c-axis of the Sn crystal lattice indicated by arrow c are not perpendicular. This results in a problem where, for example, a current density of 500 A / cm 2 When a current as large as this is applied, atoms move due to electromigration, causing defects that can lead to breakage. According to the present invention, by orienting the c-axis of the Sn crystal lattice in the solder joint, defects such as breakage are less likely to occur, and the current density is 500 A / cm. 2 or more than 1000A / cm 2 When a large current is passed through the solder joint, a particularly reliable solder joint can be obtained.

[0050] The conductive member is not limited to the lead frame 18, but may be any conductive member used in semiconductor devices, such as aluminum wire or pins.

[0051] Next, a method for manufacturing a soldered joint will be described. The method for manufacturing a soldered joint simply requires that the contact surfaces between the sheet solder and the semiconductor element and lead frame (the members to be joined) are as described above, and that the contact surfaces between the sheet solder and the semiconductor element and second conductive plate of the laminated substrate (the members to be joined) are as described above. Other conditions can be the same as those for a normal joining method. This method includes a pretreatment step of etching the sheet solder using an acid or the like to remove the oxide film, and a step of heating the sheet solder in a reducing atmosphere to perform solder joining. The reducing atmosphere may be an atmosphere containing hydrogen or the like. The temperature for solder joining can be determined appropriately depending on the composition of the solder alloy.

[0052] While not intending to be bound by theory, it is known that local randomization of the Sn crystal lattice orientation occurs when solder melts. However, since the solder solidifies into large crystals of several hundred micrometers, it is thought that the average orientation direction of the solder before melting determines the orientation after melting. The c-axis orientation of the solder joint layer formed after melting and joining a solder alloy can be confirmed by cutting out the solder joint layer and performing EBSD measurement. More specifically, the solder joint layer is cut out from a manufactured semiconductor device to prepare a sample with a surface parallel to the press-processed surface during processing as the measurement surface, and EBSD measurement of the sample can be performed to obtain the c-axis orientation ratio A.

[0053] [Third embodiment: semiconductor device] According to a third embodiment, the present invention relates to a semiconductor device, which includes the solder joint according to the second embodiment.

[0054] 5 is a conceptual cross-sectional view of a power semiconductor module, which is an example of a semiconductor device according to a third embodiment of the present invention. The illustrated power semiconductor module has a laminated structure in which a semiconductor element 11 and a laminated substrate 12 are bonded to a heat sink 13 by a bonding layer 17, and a solder bonding layer 1 in which sheet-like solder according to the first embodiment is melted between the semiconductor element 11 and a lead frame 18. A case 16 incorporating external terminals 15 is bonded to the heat sink 13. The electrodes of the semiconductor element 11 and the laminated substrate 12 are connected by a lead frame 18, which is a conductive connecting member, and the semiconductor element 11 and the external terminals 15 are connected by aluminum wires 14. A sealing material 20 is filled in contact with the semiconductor element 11, the laminated substrate 12, the lead frame 18, the aluminum wires 14, and other members to be sealed.

[0055] The semiconductor element 11 is a power chip such as an IGBT (Insulated Gate Bipolar Transistor) or a diode chip. The semiconductor element may be a Si device, or a wide-gap semiconductor device such as a SiC device, a GaN device, a diamond device, or a ZnO device, or a combination of these. For example, a hybrid module using a Si-IGBT and a SiC-SBD may be used. The number of semiconductor elements 11 mounted may be one or more.

[0056] The laminated substrate 12 can be composed of an insulating substrate 122, a first conductive plate 121 having a predetermined shape (pattern) formed on one main surface of the insulating substrate 122, and second conductive plates 123a, 123b formed on the other main surface. The insulating substrate 122 can be made of a material with excellent electrical insulation and thermal conductivity. Examples of materials for the insulating substrate 122 include Al2O3, AlN, and SiN. For high-voltage applications, a material that combines electrical insulation and thermal conductivity is preferable, such as AlN or SiN, but is not limited to these. The first conductive plate 121 and the second conductive plates 123a, 123b can be made of metal materials such as Cu and Al, which are easy to process. The conductive plates may also be Cu or Al that have been treated with Ni plating or other treatments for rust prevention. The conductive plates 121, 123a, 123b can be mounted on the insulating substrate 122 by a direct copper bonding method or an active metal brazing method. In the illustrated embodiment, two second conductive plates 123a, b are discontinuously provided on an insulating substrate 122, one 123a serving as an electrode to be bonded to the semiconductor element 11, and the other 123b serving as an electrode to be connected to the lead frame 18.

[0057] The lead frame 18 is a conductive connecting member that connects the semiconductor element 11 to the second conductive plate 123b and the like. Specifically, it is bonded to the electrodes (front electrodes) of the semiconductor element 11 with a bonding layer 1 formed by melting the sheet-like solder according to the first embodiment. The wiring portions of the second conductive plate 123b and the like can also be bonded with a bonding layer 17 made of a general solder material, but may also be bonded using the sheet-like solder 1 according to the first embodiment. The lead frame 18 may be made of a metal such as copper or a copper alloy. A Ni or Ni alloy layer, or a Cr or Cr alloy layer may be formed on the surface of the lead frame 18 by plating or the like. In this case, the film thickness of the Ni or Ni alloy layer or the Cr or Cr alloy layer can be approximately 20 μm or less. In addition to the lead frame, the conductive connecting member that connects the semiconductor element 11 to the second conductive plate 123b and the like can be a pin-shaped take-out terminal, or a wire made of aluminum or copper used for wire bonding.

[0058] Metals with excellent thermal conductivity, such as copper and aluminum, are used for the heat sink 13. To prevent corrosion, the heat sink 13 may be coated with Ni or a Ni alloy. The heat sink may also be a cooler having a water-cooling or air-cooling function.

[0059] The bonding layer 17 can be formed using a common lead-free solder. Examples of suitable materials include, but are not limited to, Sn-Ag-Cu, Sn-Sb, Sn-Sb-Ag, Sn-Cu, Sn-Sb-Ag-Cu, Sn-Cu-Ni, and Sn-Ag solders. Alternatively, the bonding layer can be formed using a connecting material containing minute metal particles, such as a sintered body of nano-silver particles. Instead of a common lead-free solder, a bonding layer formed by melting the sheet solder according to the first embodiment can also be used.

[0060] The case 16 may be made of a thermoplastic resin such as polyphenylene sulfide (PPS) or polybutylene terephthalate (PBT).

[0061] In this embodiment, the components including the semiconductor element 11, the laminated substrate 12, and the conductive connecting members such as the lead frame 18 and the aluminum wire 14 are also referred to as the encapsulated components. The encapsulated components are filled with an encapsulant 20. The encapsulant 20 comes into contact with the semiconductor element 11, the laminated substrate 12, and the conductive connecting members, and covers the peripheries of these encapsulated components.

[0062] The sealing material 20 includes a cured product of a thermosetting resin composition that includes a thermosetting resin base, a curing agent, and an inorganic filler, and may optionally include a curing accelerator and additives.

[0063] The thermosetting resin base is not particularly limited, and examples thereof include epoxy resins, phenolic resins, maleimide resins, and the like, which have heat resistance and high insulating properties. Among these, epoxy resins having at least two epoxy groups per molecule are particularly preferred due to their high dimensional stability, water resistance, chemical resistance, and electrical insulating properties. Specifically, it is preferred to use aliphatic epoxy resins such as bisphenol A epoxy resins, bisphenol F epoxy resins, and bisphenol AD ​​epoxy resins; alicyclic epoxy resins such as monofunctional epoxy resins, bifunctional epoxy resins, and trifunctional or higher polyfunctional epoxy resins; or mixtures of these resins in any desired mixing ratio.

[0064] The inorganic filler may be a metal oxide or metal nitride having high thermal conductivity and a low linear expansion coefficient, such as, but not limited to, fused silica, silica (silicon oxide), alumina, aluminum hydroxide, titania, zirconia, aluminum nitride, talc, clay, mica, and glass fiber. The inorganic filler preferably has an average particle size of approximately 0.2 to 20 μm. The amount of inorganic filler added to the encapsulant 20 is preferably 100 to 600 parts by mass, and more preferably 200 to 400 parts by mass, based on 100 parts by mass of the matrix resin. If the amount of inorganic filler added is less than 100 parts by mass, the thermal expansion coefficient of the encapsulant 20 may increase, potentially leading to peeling or cracking. If the amount added is more than 600 parts by mass, the viscosity of the composition may increase, potentially resulting in poor extrusion moldability.

[0065] The curing agent is not particularly limited as long as it can react with a thermosetting resin base, preferably an epoxy resin base, and harden, but it is preferable to use an acid anhydride curing agent. The amount of curing agent is preferably 50 parts by mass or more and 170 parts by mass or less, and more preferably 80 parts by mass or more and 150 parts by mass or less, per 100 parts by mass of the epoxy resin base. If the amount of curing agent is less than 50 parts by mass, the glass transition temperature may decrease due to insufficient crosslinking, while if it is more than 170 parts by mass, the moisture resistance, high heat distortion temperature, and heat resistance stability may decrease.

[0066] A curing accelerator can be added as an optional component to the thermosetting resin composition constituting the encapsulant 20. The amount of the curing accelerator added is preferably 0.01 parts by mass or more and 50 parts by mass or less, and more preferably 0.1 parts by mass or more and 20 parts by mass or less, per 100 parts by mass of the main thermosetting resin.

[0067] The thermosetting resin composition constituting the encapsulant 20 may also contain optional additives to the extent that the additives do not impair its properties. Examples of additives include, but are not limited to, flame retardants, pigments for coloring the resin, and plasticizers and silicone elastomers for improving crack resistance. These optional components and their amounts can be appropriately determined by those skilled in the art depending on the specifications required for the semiconductor device and / or the encapsulant 20.

[0068] Next, a method for manufacturing the illustrated power semiconductor module will be described. The heat sink 13, laminated substrate 12, and semiconductor element 11 are bonded together, and the case 16 is attached to the heat sink 13. Then, the sheet-like solder according to the first embodiment is placed on the front electrodes of the semiconductor element 11, and the lead frame 18 is bonded. Detailed bonding conditions are the same as those described in the second embodiment. Wire bonding is performed using aluminum wire 14. Next, a thermosetting resin composition constituting the encapsulant 20 is injected into the case 16 and heat-cured. The heat-curing process can be, for example, a two-stage curing process. When an epoxy resin is used as the thermosetting resin base, the composition is heated at 90 to 120°C for 1 to 2 hours to achieve a semi-cured state (pre-curing). Then, heating can be further performed at 175 to 185°C for 1 to 2 hours (main curing). Main curing can be performed by continuously increasing the temperature from the pre-curing stage. However, the temperature and time are not limited to specific values, and two-stage curing may not be necessary.

[0069] As a variation of the illustrated power semiconductor module, a primer layer may be further provided. The primer layer may be formed at the interface between the sealing material 20 and the members to be sealed, including the laminated substrate, the semiconductor element, and the conductive connecting member. The primer layer may be preferably used in some cases from the viewpoint of providing a stress relief effect at the interface between the sealing material 20 and the members to be sealed and ensuring adhesion. The primer layer may be a layer made of a resin containing polyamide, polyimide, or polyamideimide.

[0070] The encapsulant 20 may further be formed from one or more thermosetting resin layers of different compositions, or may include a resin encapsulating layer other than a thermosetting resin encapsulating layer. For example, the encapsulant 20 may include a thermoplastic resin layer covering the surface that comes into contact with the atmosphere. In this case, a primer layer may or may not be included.

[0071] In a method for manufacturing a power semiconductor module with a primer layer, a primer layer is formed after assembling the sealed components and before injecting the thermosetting resin composition constituting the sealing material 20. The primer layer can be applied to the entire surface of the sealed components, including the semiconductor element 11, lead frame 18, laminated substrate 12, aluminum wire 14, and case 16 shown in FIG. 5, by, for example, spray coating, dipping, or dispenser application. After the primer layer is formed, the assembly is heated in an inert oven containing nitrogen gas in stages at 70 to 100°C for approximately 60 to 80 minutes, and then preferably at 200 to 220°C for 60 to 80 minutes. This heating process heats the Cu constituting the lead frame 18, vaporizes the solvent, and solidifies the primer. After the primer layer is formed, insulation and sealing can be performed using the sealing material 20, similar to the method for manufacturing a power semiconductor module shown in FIG. 5. If an additional resin sealing layer is optionally provided, the additional resin sealing layer can be formed using a conventional method.

[0072] The illustrated configuration of the power semiconductor module is an example, and the present invention is not limited to this configuration. For example, any conductive connecting member may be used, and implant pins may also be used. The conductive connecting member may also be configured to consist of only a lead frame or only a wire. When a primer layer is provided in a module in which the conductive connecting member includes an implant pin, the primer layer can also be formed on the surface of the implant pin. When a primer layer is provided in a module in which the conductive connecting member is configured to consist of only a wire, the primer layer can also be formed on the surface of the wire.

[0073] The power semiconductor module may also be a caseless power semiconductor module. Although not shown, the caseless power semiconductor module may include, for example, implant pins and a printed circuit board bonded to the implant pins instead of the lead frame and aluminum wires shown in FIG. 5 , and the components including these are sealed with a thermosetting resin sealing layer. The printed circuit board may be a polyimide film substrate or an epoxy film substrate with a conductive layer of Cu, Al, or the like formed thereon. The implant pins may be copper pins made of copper. The conductive layer of the printed circuit board and the implant pins may be Cu or Al plated with Ni for rust prevention or other purposes. The printed circuit board and the implant pins electrically connect semiconductor elements to each other or between the semiconductor element and the laminated substrate. The implant pins can be joined to the laminated substrate or semiconductor element by a solder joint layer. The implant pins can also be used as external connection terminals by extending them from the laminated substrate to the outside of the thermosetting resin sealing layer. The power semiconductor module of this embodiment is manufactured by assembling the encapsulated components including the laminated substrate, the semiconductor element, the implant pin, and the printed circuit board, optionally forming a primer layer on the surfaces of the laminated substrate, the semiconductor element, the implant pin, and the printed circuit board by a method such as spray coating, placing the encapsulated components in an appropriate mold, filling the mold with a thermosetting resin composition that constitutes the thermosetting resin encapsulating layer, and curing it. Examples of molding methods for such an encapsulated body include vacuum casting, transfer molding, liquid transfer molding, potting, etc., but are not limited to the specified molding method.

[0074] According to this embodiment, the sheet solder according to the first embodiment is used to electrically connect a semiconductor element to the solder. connection By providing a solder joint connecting the components, electromigration can be prevented, and a highly reliable semiconductor device can be obtained. The semiconductor device according to this embodiment is particularly suitable for applications where the current density is 500 A / cm 2 or more than 1000A / cm 2High reliability can be expected in applications where large currents are required. [Example]

[0075] The present invention will be described in more detail below with reference to examples of the present invention, but the present invention is not limited to the scope of the following examples.

[0076] 1. Manufacturing of sheet solder In Examples 1 to 6 and Comparative Examples 1 and 2, sheet solder was produced using a solder block made of a Sn3.5Ag solder alloy containing 3.5 mass% Ag, with the remainder consisting of Sn and unavoidable impurities. First, the solder block was heated to 300°C to melt it, and then cooled to 100°C at a rate of 5°C / min or more to produce a solder block in which the c-axes of the Sn crystals were randomly oriented. The c-axis orientation of the Sn crystals in this solder block was measured using the EBSD method, and the c-axis orientation ratio A was obtained. The value of A was 0.1, confirming random orientation. The solder block with randomly oriented c-axes was cut, without compression, into a size of 5000 μm long, 5000 μm wide, and 100 μm thick, which was used as Comparative Example 1.

[0077] This solder block was placed in a mold shown in Figure 3 and pressed to obtain six types of solder blocks with different pressing rates. The pressing rate is defined as follows: Thickness is the thickness of the solder block. Processing rate = (initial thickness - processed thickness) / initial thickness The pressed solder block was cut in a direction parallel to the pressing direction. More specifically, it was cut parallel to the LM plane along cutting point 5 shown in Figure 3 to obtain sheet solder pieces with a length of 5000 μm, a width of 5000 μm, and a thickness of 100 μm, with the cut surface being the main surface. These were designated Examples 1 to 6.

[0078] The solder block is pressed at a processing rate of 75%, PThe solder was processed so that the thickness was in the direction parallel to the direction of the processing. More specifically, the MN plane shown in Figure 3 was the main surface, and the L direction was cut out so that the thickness was in the direction of the L direction, obtaining a sheet solder measuring 5000 μm in length, 5000 μm in width, and 100 μm in thickness. This was designated Comparative Example 2.

[0079] Except for changing the composition of the solder alloy, the sheet solders of Examples 7 to 14 were obtained in the same manner as in Example 1. Note that Example 8 is the same sample as Example 1. The composition notation in the table, SnX[element A]Y[element B], represents a composition containing X mass% of element A and Y mass% of element B, with the remainder consisting of Sn and unavoidable impurities.

[0080] 2. Semiconductor device manufacturing The manufactured sheet solder was applied to the solder joints that joined the semiconductor element and lead frame in the power semiconductor module according to the third embodiment, and its reliability was evaluated. The semiconductor element was a Si IGBT, and the lead frame was made of copper. The bonding was performed at 310±5°C for 5 minutes in a hydrogen reducing atmosphere containing 10% hydrogen by volume (volume ratio of N2 to H2 was 9:1).

[0081] 3.Continuous current test The fabricated semiconductor device was subjected to a current density of 800 A / cm 2 A continuous current-voltage test was conducted for 500 hours. After that, the current-voltage characteristics were evaluated, and if they were normal, they were marked with a "O", and if they were abnormal, they were marked with an "X". A normal value is one in which the increase or decrease from the initial (pre-test) current-voltage characteristics (voltage when the rated ON current is passed, and leakage current when the rated withstand voltage is applied to the element) is within 20%, and an abnormal value is one in which the increase or decrease is greater than that.

[0082] 4. Reliability evaluation Reliability is T j Power cycle resistance (T j The power cycle test was performed at 40 to 175°C (ΔT jThe number of cycles required for the electrical properties to reach abnormal values ​​was investigated, with one cycle consisting of one second of current operation and four seconds of rest, at a temperature of 135°C. The current density was 300 A / cm. 2 It was decided.

[0083] The working ratios of the solder alloys of Examples 1 to 6 and Comparative Examples 1 and 2, the c-axis orientation ratios Ap (Av) of the sheet solders, the results of the continuous current test, and T j The P / C resistance is shown in Table 1. The processing direction of Comparative Example 2 was 90° different from that of Examples 1 to 6 and Comparative Example 1, and the surface pressed at a processing rate of 75% was positioned parallel to the bonding surface of the element and lead frame. Table 1 shows that a c-axis orientation ratio Ap of 0.25 to 0.98, more preferably 0.32 to 0.94, suppressed EM and resulted in a highly reliable semiconductor device. A processing rate of the solder block of 5 to 99% was found to be effective, more preferably 25 to 90%. A c-axis orientation ratio Ap value of 0.1 in Comparative Example 1 indicates that the c-axes were randomly oriented, while a c-axis orientation ratio Ap value of 0.01 in Comparative Example 2 indicates that the c-axes were oriented parallel to the thickness direction of the sheet solder. Comparative Examples 1 and 2 showed abnormal values ​​in the current-voltage characteristic evaluation after a continuous current test after 1k cycles. In other words, the P / C resistance was less than 1k cycles.

[0084] These results suggest that EM was suppressed when the c-axis of the Sn crystal was oriented parallel to the bonding surface and the c-axis orientation ratio A was set to a value close to 1. However, when the c-axis was oriented too parallel to the bonding surface, the power cycle life was slightly reduced (Example 6). Without intending to be bound by theory, it is speculated that when the c-axis was oriented too parallel to the bonding surface, it became weak against shear stress.

[0085] [Table 1]

[0086] The composition of the solder alloys of Examples 7 to 14, the mass % of Sn content in each composition, the processing rate, the c-axis orientation ratio Ap of the sheet solder, the results of the continuous current test of the semiconductor device, and T j P / C tolerance2 Table 2 shows that various solder materials containing Sn as the main component can be plastically deformed in almost the same way and the c-axis can be oriented in a predetermined direction if the Sn content is 80% or more. Example 14, which contains 82% Sn, had a slightly worse P / C resistance than the others. In other words, when the c-axis orientation ratio Ap is 0.2 or more, is preferred It can be seen that a c-axis orientation ratio Ap of 0.23 or more is more preferable. When combined with the results in Table 1, the c-axis orientation ratio Ap is preferably 0.2 to 0.98, more preferably 0.32 to 0.94. Even in the case of Sn6Sb4Ag.2Ni0.001Ge in Example 12, which forms intermetallic compounds at the grain boundaries, plastic deformation occurred and no EM occurred.

[0087] [Table 2]

[0088] According to this embodiment, it is possible to provide a sheet solder that prevents electromigration, and to provide a highly reliable solder joint and a semiconductor device. [Explanation of symbols]

[0089] 1 sheet solder, m main surface, f surface opposite to the main surface, p pressed surface 2 solder block, 3 lower mold (bottom), 4 upper mold 11 semiconductor element, 12 laminated substrate, 121 conductive plate, 122 insulating substrate 123a, b conductive plate, 13 heat sink, 14 aluminum wire, 15 external terminal 16 case, 17 bonding layer, 18 lead frame, 20 encapsulant

Claims

1. A pressed sheet solder containing a solder alloy containing Sn as a main component and containing additional elements and inevitable impurities, The pressed surface is perpendicular to the main surface of the solder sheet, and the c-axis of the Sn crystal is oriented in a direction perpendicular to the thickness direction of the sheet.

2. 2. The sheet solder according to claim 1, wherein the c-axis orientation ratio, which is an index of the c-axis orientation of Sn crystals, on the pressed surface is 0.3 or more.

3. The solder sheet according to claim 2 , wherein the c-axis orientation ratio is 0.95 or less.

4. 4. The solder sheet according to claim 1, wherein the additive element is selected from the group consisting of Sb, Cu, Ag, Ni, Ge, and combinations thereof.

5. A solder joint comprising a solder joint layer formed by melting the sheet solder according to any one of claims 1 to 4 between a semiconductor element and a conductive connecting member.

6. The solder joint of claim 5 , wherein the conductive connecting member is a lead frame.

7. A semiconductor device comprising the solder joint according to claim 5 or 6.

8. a step of press-forming a solder alloy containing Sn as a main component and containing additional elements and inevitable impurities to produce a sheet-shaped solder in which the pressed surface is perpendicular to the main surface and the c-axis of the Sn crystal is oriented perpendicular to the thickness direction of the sheet; a step of laminating a semiconductor element, the sheet-like solder, and a conductive connecting member; melting the sheet solder; A method for manufacturing a semiconductor device, comprising:

9. 9. The method for manufacturing a semiconductor device according to claim 8, wherein the step of pressing is a step of applying pressure until a c-axis orientation ratio, which is an index of c-axis orientation of Sn crystals, becomes 0.3 or more.

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