Semiconductor device

Abstract

To provide a semiconductor device which can sufficiently secure the quality of connection between a semiconductor substrate and a lead frame in a case where the semiconductor substrate and the lead frame are connected by a solder material including a spherical filler.SOLUTION: In a semiconductor device in which a lead frame and a pellet are connected with a solder material including a spherical filler, the lead frame has a protruding part and a recessed part in a surface facing the pellet, and the spherical filler is arranged in the space between the recessed part and the pellet.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a semiconductor device that maintains a predetermined solder film thickness between components by using a solder material containing spherical fillers. [Background technology]

[0002] The semiconductor device disclosed in Patent Document 1 is known as a semiconductor device that maintains a predetermined solder film thickness or more between components by using a solder material mixed with spherical fillers.

[0003] For example, the abstract of the document states that the purpose is to "obtain a solder material that enables two components to be soldered together with a required and uniform gap between them," and that the composition is "The solder material 3 used to solder the metal surfaces of two components (semiconductor substrate 1 and heat sink 2) is composed of a solder material such as hard solder or soft solder and an additive material 5 contained therein. The additive material 5 is formed into a spherical (granular) shape with a particle size approximately equal to the gap required between the two components, a higher melting point than the solder material, and good thermal conductivity."

[0004] Furthermore, paragraph 0007 of the same document states, "The solder material 3...contains a large number of spherical (granular) additives 5 inside the solder material. The additives 5 are formed as particles with a particle size approximately equal to the required spacing between the bottom surface of the semiconductor substrate 1 and the top surface of the heat sink 2, i.e., a spacing that ensures high connection strength by the solder material and does not cause cleavage of the semiconductor substrate 1 due to stress distortion. The additives 5 have a higher melting point than the solder material and also have high thermal conductivity." Paragraph 0008 states, "Therefore, if the semiconductor substrate 1 is soldered to the heat sink 2 using solder material 3 containing such additives 5, the spherical shape of the additives 5 is maintained due to their high melting point, and even if the thickness of the solder is reduced due to the weight of the components or the weight of the jig, etc., the additives 5 can maintain the spacing between the semiconductor substrate 1 and the heat sink 2."

[0005] In this way, by using the solder material of Patent Document 1, the action of the spherical additive material (spherical filler) contained in the solder material makes it possible to ensure a predetermined distance between two components during soldering (i.e., solder film thickness after soldering) or more. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 6-685 Summary of the Invention [Problem to be solved by the invention]

[0007] However, as is evident from the flatness of both the bottom surface of the semiconductor substrate and the top surface of the heat sink in Figure 1 of Patent Document 1, the semiconductor device in this document does not have any structure to restrict the movement of the spherical filler particles in the molten solder during soldering. In addition, since spherical fillers generally have manufacturing errors, a certain degree of variation in the size of the spherical filler particles is allowed.

[0008] 1 of Patent Document 1, during solder melting, the relatively large spherical filler particles are sandwiched between the upper and lower parts and their movement is restricted, while the relatively small spherical filler particles are able to move freely in conjunction with the flow of the molten solder, which can cause uneven distribution of the spherical filler particles within the molten solder and can result in an inability to achieve a uniform solder film thickness after soldering. Therefore, when the solder material of Patent Document 1 is used at the connection point between the semiconductor substrate and lead frame in a semiconductor device, there is a risk that the solder film thickness between the semiconductor substrate and lead frame cannot be made uniform, and the connection quality between the two cannot be fully guaranteed.

[0009] Therefore, the present invention aims to provide a semiconductor device that can fully ensure the connection quality between a semiconductor substrate and a lead frame, even when a solder material containing spherical fillers is used to connect the two. [Means for solving the problem]

[0010] In order to solve the above problem, the semiconductor device of the present invention is a semiconductor device in which a lead frame and a pellet are connected with a solder material mixed with spherical fillers, the lead frame has a recess and a protrusion on the surface facing the pellet, and the spherical fillers are arranged in the space between the recess and the pellet. [Effects of the Invention]

[0011] According to the semiconductor device of the present invention, when a solder material containing spherical fillers is used to connect a semiconductor substrate and a lead frame, the quality of the connection between the two can be sufficiently ensured. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view of a semiconductor device according to a first embodiment. [Figure 2] FIG. 2 is a bottom view of an upper lead frame according to the first embodiment. [Figure 3] 4A to 4C are diagrams illustrating the function of the protrusions of the upper lead frame in the first embodiment. [Figure 4] FIG. 10 is an enlarged cross-sectional view of a protrusion of an upper lead frame in Example 2. [Figure 5] 10A and 10B are diagrams illustrating the function of the protrusions of the upper lead frame in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the semiconductor device of the present invention will be described with reference to the drawings. [Example]

[0014] First, a semiconductor device 100 according to a first embodiment of the present invention will be described with reference to FIGS.

[0015] FIG. 1 is a cross-sectional view of a semiconductor device 100 according to this embodiment. As shown in the figure, the semiconductor device 100 is a device in which an upper lead frame 1, an upper solder layer 2, a pellet 3, a lower solder layer 4, and a lower lead frame 5 are stacked, with a large number of spherical fillers 6 disposed inside the upper solder layer 2 and the lower solder layer 4. Although not shown in the figure, the semiconductor device 100 also has support parts that hold the upper lead frame 1, the pellet 3, and the lower lead frame 5 in predetermined positions, as well as a sealing resin that seals the lead frames except for their terminals. Below, the main parts of the semiconductor device 100 will be described in order.

[0016] The pellet 3 is a semiconductor substrate, for example, a chip with a built-in diode, that corresponds to the function of the semiconductor device 100. An oxide film 31 for insulating the semiconductor inside the pellet 3 is formed on the outer periphery of the upper surface of the pellet 3.

[0017] The upper lead frame 1 is a rigid body made of copper or the like for allowing current to flow, and is electrically connected to the upper surface of the pellet 3 via an upper solder layer 2 made of Sn-Cu solder or the like. The lower surface of this upper lead frame 1 is formed with recesses 11 and protrusions 12, the details of which will be described later.

[0018] The lower lead frame 5 is a rigid body made of copper or the like for allowing current to flow, and is electrically connected to the lower surface of the pellet 3 via a lower solder layer 4 made of Sn--Cu solder or the like.

[0019] The spherical filler 6 is an additive that is pre-mixed with the solder material (solder sheet, solder paste, etc.) that forms the upper solder layer 2 and the lower solder layer 4. Specifically, it is a metal sphere made of nickel or the like, which has a higher melting point than solder. The dimensions of the spherical filler 6 are set appropriately according to the minimum film thickness required for the upper solder layer 2 and the lower solder layer 4 to ensure the desired connection quality.

[0020] During the reflow process in the manufacturing process of the semiconductor device 100, when the solder material that forms the upper solder layer 2 and the lower solder layer 4 melts, the spacing between the upper lead frame 1 and the pellet 3, and the spacing between the pellet 3 and the lower lead frame 5, are basically maintained at the designed dimensions by the above-mentioned support portions. However, if the support portions are not accurate enough to properly maintain each spacing, the spherical fillers 6 will maintain each spacing at a dimension equivalent to the diameter of the spherical fillers 6. Therefore, when the upper solder layer 2 and the lower solder layer 4 solidify after the reflow process, the film thickness of each solder layer can be ensured to be at least equal to the diameter of the spherical fillers 6. In this way, the spherical fillers 6 function as spacers that guarantee the minimum film thickness of the upper solder layer 2 and the lower solder layer 4.

[0021] FIG. 2 is a bottom view of the upper lead frame 1. As shown here, recesses 11 and protrusions 12 are formed in a concentric rectangular shape on the bottom surface of the upper lead frame 1. As can be seen from FIG. 1, the protrusions 12 in this embodiment are designed to have dimensions that push the fluid spherical filler 6 to the side during the reflow process. Therefore, the spherical filler 6 collects in the space below the recesses 11, while being excluded from the space below the protrusions 12. As a result, the distribution of the spherical filler 6 below the upper lead frame 1 is as shown in FIG. 2. Note that FIG. 2 is a schematic diagram showing an example of the shape of the recesses 11 and protrusions 12. The number and shape of the recesses 11 and protrusions 12 may be different from those shown in FIG. 2, as long as the spherical filler 6 can be distributed evenly over the entire bottom surface of the upper lead frame 1.

[0022] 3 is an enlarged cross-sectional view illustrating the function of the recessed portions 11 and protruding portions 12 provided on the lower surface of the upper lead frame 1. The spherical fillers 6 are roughly uniform in size, but a certain degree of manufacturing error is allowed. Hereinafter, the largest spherical filler 6 within the allowable error is referred to as the maximum filler 6a, and the smallest spherical filler 6 is referred to as the minimum filler 6b. The diameter of the largest filler 6a is referred to as Da, and the diameter of the smallest filler 6b is referred to as Db. Here, an example of the diameters of the largest filler 6a and the smallest filler 6b is where the diameter Da is 60 μm and the diameter Db is 50 μm.

[0023] As shown in the figure, if the distance between the bottom surface of the recess 11 of the upper lead frame 1 and the top surface of the pellet 3 is La, then in order to accommodate the largest filler 6a in the space below the recess 11, the distance La must be larger than the diameter Da (La>Da). Also, if the distance between the bottom surface of the protrusion 12 of the upper lead frame 1 and the top surface of the pellet 3 is Lb, then in order to prevent the smallest filler 6b from slipping through the space below the protrusion 12, the distance Lb must be smaller than the diameter Db (Lb <Db)。

[0024] By designing the diameters Da, Db of the spherical fillers 6 and the spacing La, Lb of the semiconductor device 100 so as to satisfy this size relationship, the reflow process can be performed while suppressing the occurrence of uneven distribution of the spherical fillers 6 due to the flow of molten solder, and the upper solder layer 2 after the reflow process can be formed to a film thickness of a predetermined value or more.

[0025] 1 shows an example of a configuration in which the recessed portion 11 and the protruding portion 12 are formed on the upper lead frame 1, but recessed portion 51 and protruding portion 52 having functions equivalent to those of the recessed portion 11 and the protruding portion 12 may also be formed on the surface of the lower lead frame 5 facing the pellet 3 (i.e., the upper surface). This allows the lower solder layer 4 to be formed to a predetermined thickness or more after the reflow process.

[0026] As described above, the semiconductor device of this embodiment can fully ensure the quality of connection between the semiconductor substrate and the lead frame when a solder material containing spherical fillers is used to connect the two. [Example]

[0027] Second Embodiment Next, a semiconductor device 100 according to a second embodiment of the present invention will be described with reference to Figures 4 and 5. Note that a duplicated description of points common to the first embodiment will be omitted.

[0028] As described above, during the reflow process of the semiconductor device 100 of Example 1, the protrusions 12 of the upper lead frame 1 push the fluid spherical filler 6 to the side, so that the spherical filler 6 is not usually present in the space below the protrusions 12. However, sometimes the spherical filler 6 gets caught between the protrusions 12 and the pellets 3, and the spherical filler 6 lifts up the upper lead frame 1.

[0029] In particular, if the sandwiched spherical filler 6 is the largest filler 6a, a large gap equivalent to the diameter Da of the largest filler 6a is formed between the protrusion 12 and the pellet 3, allowing the majority of the spherical filler 6 to flow through this gap. As a result, if a flow of spherical filler 6 is formed from the upstream side to the downstream side of the molten solder as the molten solder flows, there is a possibility that the density of the spherical filler 6 will be low on the upstream side of the molten solder and high on the downstream side.

[0030] To suppress this uneven distribution of the spherical filler 6, the upper lead frame 1 of this embodiment has a groove 12a on the underside of the protrusion 12, which has an R-shaped structure that fits with the upper surface of the largest filler 6a, and whose upper end is at a height La from the pellet 3 and whose lower end is at a height Lb from the pellet 3, as shown in Figure 4. As a result, even if the largest filler 6a is sandwiched between the protrusion 12 and the pellet 3, the upper lead frame 1 is not lifted, and the function of the protrusion 12 to suppress the movement of the spherical filler 6 is not impaired. Note that, since the groove 12a in this embodiment has a shape that extends in the direction of the paper surface in Figure 4, the spherical filler 6 that fits in the groove 12a may move in the direction of the paper surface, but this does not cause any problems.

[0031] 5 is a cross-sectional view specifically illustrating the function of the groove 12a. As shown in the left diagram of FIG. 5, when the molten upper solder layer 2 flows leftward while the largest filler 6a is contained in the groove 12b of the protrusion 12 of the upper lead frame 1, a force acts to move the largest filler 6a and the smallest filler 6b leftward. However, even when such a force acts, the largest filler 6a held in the groove 12b does not move leftward. Furthermore, because the distance Lb between the bottom end of the protrusion 12 and the pellet 3 remains smaller than the diameter Db of the smallest filler 6b, the smallest filler 6b can remain on the right side of the protrusion 12, as shown in the right diagram of FIG. 5.

[0032] Therefore, according to the configuration of this embodiment, even if the largest filler 6a is located directly below the protrusion 12 of the upper lead frame 1, it is possible to suppress the occurrence of uneven distribution of the spherical filler 6 due to the flow of molten solder.

[0033] 4 and 5 show an example of a configuration in which grooves 12a are formed in the protrusions 12 of the upper lead frame 1, but grooves 52a having a function equivalent to that of the grooves 12a may also be formed in the protrusions 52 of the lower lead frame 5. This makes it possible to prevent uneven distribution of the spherical filler 6 in the lower solder layer 4 during the reflow process. [Explanation of symbols]

[0034] 100 Semiconductor device 1 Upper lead frame 11 Recess 12 Convex part 12a groove 2 Upper solder layer 3 pellets 31 Oxide film 4 Lower solder layer 5 Lower lead frame 51 Recess 52 Convex part 6 Spherical filler 6a Max Filler 6b Minimum Filler

Claims

1. A semiconductor device in which a lead frame and a pellet are connected by a solder material containing spherical fillers, the lead frame has a recess and a protrusion on a surface facing the pellet, The semiconductor device is characterized in that the spherical filler is disposed in the space between the recess and the pellet.

2. 2. The semiconductor device according to claim 1, the interval between the recess and the pellet is greater than the maximum interval between the spherical filler; The semiconductor device is characterized in that the distance between the protrusion and the pellet is smaller than the smallest distance between the spherical filler particles.

3. 3. The semiconductor device according to claim 2, The semiconductor device is characterized in that the recessed portion and the protruding portion are formed in a concentric rectangular shape over the entire opposing surface.

4. 4. The semiconductor device according to claim 1, the lead frame is an upper lead frame that is positioned above the pellet during a reflow process; The semiconductor device is characterized in that the recessed portion and the protruding portion are provided on the lower surface of the upper lead frame.

5. 4. The semiconductor device according to claim 1, the lead frame is a lower lead frame that is disposed below the pellet during a reflow process; The semiconductor device is characterized in that the recessed portion and the protruding portion are provided on the upper surface of the lower lead frame.

6. 4. The semiconductor device according to claim 1, The semiconductor device is characterized in that the convex portion has a groove formed therein that is shaped to fit the largest of the spherical fillers.

7. 4. The semiconductor device according to claim 1, The semiconductor device is characterized in that the spherical filler is a metal sphere having a melting point higher than that of the solder material.

8. 8. The semiconductor device according to claim 7, The semiconductor device is characterized in that the metal balls are nickel balls having a diameter of 50 to 60 μm.

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