Semiconductor device

Abstract

The purpose of the present disclosure is to provide a semiconductor device having a lead frame having a shape that relaxes stress and capable of reducing a force applied when forming the lead frame. A semiconductor device according to the present disclosure includes a substrate having an electrode pad, a semiconductor element mounted on the substrate and connected to the electrode pad, a plate-shaped lead frame having one end connected to the semiconductor element or the electrode pad of the substrate, and a sealing material sealing the semiconductor element, the substrate, and the lead frame. On the inner side of the sealing material, linear portions of the lead frame, which are adjacent to each other so as to form mountains and valleys in side view, are folded back at an angle of less than 180 degrees.

Description

Technical Field

[0001] The present disclosure relates to a semiconductor device. Background Art

[0002] It is known that a technology for increasing the area of semiconductor devices is achieved by using a plate-shaped lead frame as the wiring connecting the surface electrodes of semiconductor devices. Compared with conventional wires, this can improve the bonding strength with the semiconductor devices and also improve the heat dissipation, thereby extending the power cycle life of the semiconductor device.

[0003] However, due to the heat applied during manufacturing, a difference in thermal expansion and contraction occurs between components such as a substrate, a semiconductor element, a lead frame, and a sealing material, generating residual stress, which may cause warping in these components.

[0004] Patent Document 1 discloses a structure in which a lead frame is provided with a corrugated spring portion that is folded 180 degrees vertically to relieve stress. The expansion and contraction of the spring portion absorbs the thermal expansion difference between components, thereby suppressing the occurrence of warping.

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2017-174927

[0006] However, in the above method, the lead frame needs to be folded back 180 degrees to form the wave shape, and thus the processing requires labor. Summary of the Invention

[0007] In order to solve the above-mentioned problems, an object of the present disclosure is to provide a semiconductor device having a lead frame having a shape that relaxes stress and capable of reducing the force applied when forming the lead frame.

[0008] A first aspect of the present disclosure is preferably a semiconductor device, wherein:

[0009] have:

[0010] a substrate having electrode pads;

[0011] a semiconductor element mounted on the substrate and connected to the electrode pad;

[0012] a plate-shaped lead frame, one end of which is connected to the electrode pad of the semiconductor element or the substrate; and

[0013] a sealing material for sealing the semiconductor element, the substrate, and the lead frame;

[0014] On the inner side of the sealing material, adjacent straight line portions of the lead frame are folded back at an angle smaller than 180 degrees so as to form hills and valleys in a side view.

[0015] A second aspect of the present disclosure is preferably a semiconductor device, wherein:

[0016] have:

[0017] a substrate having electrode pads;

[0018] a semiconductor element mounted on the substrate and connected to the electrode pad;

[0019] a plate-shaped lead frame, one end of which is connected to the electrode pad of the semiconductor element or the substrate; and

[0020] a sealing material for sealing the semiconductor element, the substrate, and the lead frame;

[0021] The lead frame has a U-shaped annular portion on the inner side of the sealing material, or has a sawtooth shape or a stepped shape in a plan view.

[0022] According to the first aspect of the present disclosure, the lead frame has a sawtooth shape when viewed from the side, eliminating the need for folding 180 degrees. Furthermore, according to the second aspect, the lead frame does not need to be bent, thereby reducing the force applied during processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a side view of the semiconductor device according to the first embodiment of the present disclosure.

[0024] Figure 2 This is a side view of the lead frame according to the first embodiment.

[0025] Figure 3 This is a modification of the semiconductor device of the first embodiment.

[0026] Figure 4 This is a modification of the semiconductor device of the first embodiment.

[0027] Figure 5 It is a top view of a semiconductor device according to Embodiment 2 of the present disclosure.

[0028] Figure 6 It is a side view of a semiconductor device according to Embodiment 2 of the present disclosure.

[0029] Figure 7 It is a top view of a semiconductor device according to Embodiment 3 of the present disclosure.

[0030] Figure 8 It is a diagram showing the shape pattern of the lead frame according to the third embodiment.

[0031] Figure 9 It is a diagram showing the shape pattern of the lead frame according to the third embodiment.

[0032] Figure 10It is a diagram showing the shape pattern of the lead frame according to the third embodiment.

[0033] Figure 11 It is a diagram showing the shape pattern of the lead frame according to the third embodiment.

[0034] Figure 12 This is a top view of a semiconductor device in which Embodiments 1 to 3 are combined.

[0035] Description of Reference Numerals

[0036] 1…semiconductor element; 2…semiconductor element; 3…substrate; 4…lead frame; 5…bonding material; 6…bonding material; 7…bonding material; 8…bonding material; 9…sealing material; 31…electrode pad; 32…insulating layer; 33…substrate heat dissipation layer; 41…spring portion; 42…spring portion; 43…through hole; 100…semiconductor device; 312…electrode pad. DETAILED DESCRIPTION

[0037] The embodiments of the present disclosure will be described with reference to the accompanying drawings. Identical or corresponding components are denoted by the same reference numerals and overlapping descriptions may be omitted.

[0038] Implementation Method 1

[0039] Figure 1 1 is a side view of a semiconductor device 100 according to Embodiment 1 of the present disclosure. The semiconductor device 100 includes a semiconductor element 1, a substrate 3 on which the semiconductor element 1 is mounted, a plate-shaped lead frame 4, bonding materials 5 and 6, and a sealing material 9 for sealing these.

[0040] The substrate 3 includes an electrode pad 31, an insulating layer 32, and a substrate heat dissipation layer 33, and performs switching control of the semiconductor element 1. The electrode pad 31 is an electrode layer of the substrate 3. By using a metal material with high thermal conductivity as the electrode pad 31, heat dissipation can be improved.

[0041] Insulating layer 32 is positioned between electrode pad 31 and substrate heat dissipation layer 33, providing insulation between them. Using a highly deformable resin as insulating layer 32 can suppress cracking even when the component undergoes minor deformation due to power cycling, for example. The material for insulating layer 32 is not limited to resin; AlN, Al2O3, Si3N4, and other materials can also be used.

[0042] By using a material with high thermal conductivity for the substrate heat dissipation layer 33 , heat dissipation from the electrode pad 31 can be improved via the insulating layer 32 , thereby suppressing a temperature increase in the semiconductor device 100 .

[0043] The semiconductor element 1 is electrically connected to the electrode pad 31 via a bonding material 5. The semiconductor element 1 is, for example, a Si RC-IGBT (Reverse Conducting Insulated Gate Bipolar Transistor) or a SiC MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor).

[0044] Bonding material 5 is disposed between semiconductor element 1 and electrode pad 31. Furthermore, bonding material 6 is disposed between semiconductor element 1 and lead frame 4. Bonding materials 5 and 6 are preferably materials with high electrical and thermal conductivity, and solder and silver are used. Lead-free solder, in addition to the aforementioned properties, also acts as a stress-relieving buffer. Using lead-free solder can improve the reliability of semiconductor device 100. Alternatively, sintered silver can be used.

[0045] Sealing material 9 seals semiconductor element 1, substrate 3, lead frame 4, and the like. Sealing material 9 is preferably made of a material that can improve the reliability of semiconductor device 100, such as a thermosetting epoxy resin filled with SiO2 filler. Transfer molding is an example of a sealing method.

[0046] The lead frame 4 is a plate-shaped metal, and one end thereof is electrically connected to a control electrode such as a gate electrode, an emitter electrode, or a collector electrode of the semiconductor element 1 . Alternatively, one end thereof is electrically connected to the electrode pad 31 .

[0047] The other end of the lead frame 4 not connected to the semiconductor element 1 and the electrode pad 31 extends outside the sealing material 9. The lead frame 4 has a zigzag spring portion 41 inside the sealing material 9 to relieve stress.

[0048] More specifically, at the sawtooth-shaped spring portion 41, the lead frame 4 is folded back to form hills and valleys when viewed from the side, and the angle θ of the folded back adjacent straight portions forming hills or valleys is less than 180 degrees. From the perspective of reducing the folding force, as shown in this figure, the angle θ is more preferably 90 degrees or less.

[0049] The spring portion 41 is generally processed by bending a metal plate, but a press process using a die or the like may also be applied.

[0050] As mentioned above, the prior art spring portion is wavy, requiring the lead frame 4 to be folded 180 degrees, which requires considerable effort during processing. On the other hand, by providing the spring portion 41 with a sawtooth shape, as disclosed herein, the force applied during processing can be reduced. Furthermore, if the number of repetitions of the spring windings is the same, a sawtooth shape can further reduce the volume of the base metal than a wavy shape. This reduces the resistance of the lead frame and further reduces manufacturing costs.

[0051] Figure 2 This is a side view of the lead frame 4 of Embodiment 1. To increase the deflection of the spring, it is preferable to ensure that the height W1 of the mountain is greater than the plate thickness. In addition, as long as there is at least one mountain or valley, it can function as a spring.

[0052] Thus, the lead frame 4 of this embodiment has a sawtooth-shaped spring portion 41. The lead frame 4 is folded back at the spring portion 41 to form a hill and a valley when viewed from the side. The angle θ of the folded back adjacent straight portions forming a hill or valley is less than 180 degrees. This reduces the force applied during processing.

[0053] Furthermore, the semiconductor element 1 is not limited to being formed of silicon, but may also be formed of a wide bandgap semiconductor having a larger bandgap than silicon. Examples of wide bandgap semiconductors include silicon carbide, gallium nitride-based materials, or diamond. The semiconductor element 1 formed of such a wide bandgap semiconductor can be miniaturized due to its high voltage resistance and allowable current density. By using this miniaturized semiconductor element 1, the semiconductor device 100 incorporating the semiconductor element 1 can also be miniaturized and highly integrated. In addition, since the semiconductor element 1 has high heat resistance, the heat sink of the radiator can be miniaturized, and the water cooling part can be air-cooled, thereby enabling further miniaturization of the semiconductor device 100. In addition, since the semiconductor element 1 has low power loss and high efficiency, the semiconductor device 100 can be highly efficient. It is preferred that all semiconductor elements 1 be formed of wide bandgap semiconductors, but any one of them can be formed of a wide bandgap semiconductor, and the effects described in this embodiment can be obtained. This point is common to all the following embodiments.

[0054] <Variation 1>

[0055] Figure 3 This is a modified example of the semiconductor device 100 of the first embodiment. In the sealing material 9, the end of the lead frame 4 not connected to the semiconductor element 1 is connected to the other semiconductor element 2. As shown in the figure, the lead frame 4 connecting the two semiconductor elements 1 and 2 may also be provided with a zigzag-shaped spring portion 41. This achieves the same effects as the first embodiment.

[0056] <Variant 2>

[0057] Figure 4 This is a modified example of the semiconductor device 100 of the first embodiment. The end of the lead frame 4 not connected to the semiconductor element 1 is connected to another electrode pad 312 on the substrate 3 where no semiconductor element 1 is mounted. In this manner, the lead frame 4 connecting the semiconductor element 1 and the substrate 3 may also be provided with a zigzag-shaped spring portion 41. This achieves the same effects as the first embodiment.

[0058] Implementation Method 2

[0059] In this embodiment, a through hole 43 for flowing the bonding material 6 is provided at the end of the lead frame 4 connected to the semiconductor element 1. In addition, the following describes the changes from the first embodiment.

[0060] Figure 5 This is a top view of a semiconductor device 100 according to Embodiment 2 of the present disclosure. Leadframe 4 is provided with a through-hole 43 extending from the top surface to the surface connected to semiconductor element 1. During bonding, bonding material 6 flows through through-hole 43. Conventionally, bonding semiconductor element 1 and leadframe 4 is bonded by inserting solder foil between them and soldering while positioning them. By flowing bonding material 6 through through-hole 43 as in the present disclosure, the three components—semiconductor element 1, solder foil, and leadframe 4—are no longer required to be simultaneously positioned, making bonding easier.

[0061] Figure 6 This is a side view of a semiconductor device 100 according to a second embodiment of the present disclosure. The bonding material 6 between the lead frame 4 and the semiconductor element 1 passes through the through-hole 43 and protrudes from the upper surface of the lead frame 4. This increases the contact area between the bonding material 6 and the lead frame 4, allowing the semiconductor element 1 and the lead frame 4 to be more firmly fixed than with a conventional lead frame without through-holes 43.

[0062] Implementation 3

[0063] Figure 7 This is a top view of a semiconductor device 100 according to a third embodiment of the present disclosure. To alleviate stress, the lead frame 4 of this embodiment includes a spring portion 42 having a zigzag shape when viewed from above. Specifically, the spring portion 42 has repeated V-shaped peaks and valleys when viewed from above. Since the spring portion 42 of this embodiment does not need to be bent like the lead frame 4 of the first embodiment, it can be processed using a die stamping method, etc., reducing the force applied during processing.

[0064] The spring portion 42 of this embodiment has a larger area moment of inertia than that of Embodiment 1, and therefore has a smaller expansion and contraction effect. In order to increase the deflection of the spring, the deformation amount W2 is preferably sufficiently larger than the plate width W3.

[0065] Figures 8 to 11 1 is a diagram showing a shape pattern of a lead frame 4 according to a third embodiment, and is a plan view of the lead frame 4 . Figure 8 For Figure 7 The same sawtooth shape is omitted for description. The lead frame 4 can also be as Figure 9 In this way, it bends into a step shape when viewed from above. The number of repetitions of the steps is not limited.

[0066] Alternatively, the lead frame 4 may be Figure 10 In this way, the U-shaped ring portion is formed when viewed from above. Figure 8 Compared with the sawtooth shape, the stress concentrated on the corners can be relieved. Among them, the wavy spring portion 42 can also be formed by continuously arranging the ring.

[0067] Figure 11 and Figure 9 Similarly, the lead frame 4 is stepped when viewed from above, but the bent portion of the step is curved. That is, the bent portion of the step is rounded or chamfered. Figure 9 In comparison, the stress relaxation effect at the corners can be expected. Figure 8 In the sawtooth shape, the folded portion of the sawtooth may be formed into a curve.

[0068] Thus, in this embodiment, the spring portion 42 has a sawtooth shape, a stepped shape, or a U-shaped ring when viewed from above. This can alleviate stress in the same manner as in Embodiment 1. In addition, the force applied during processing of the spring portion 42 can be further reduced compared to Embodiment 1.

[0069] As described above, according to the present disclosure, it is possible to provide a semiconductor device having a lead frame having a shape that relaxes stress and capable of reducing the force applied when forming the lead frame.

[0070] In addition, the present disclosure is not limited to the above-mentioned embodiments, and various modifications can be made in the implementation stage without departing from the scope of the main purpose. In addition, each embodiment can also be implemented in combination as appropriate, in which case the combined effect can be obtained. For example, Figure 12 This is a top view of a semiconductor device 100 obtained by combining Embodiments 1 to 3. Thus, the effects of combining Embodiments 1 to 3 can be obtained.

[0071] Hereinafter, each aspect of the present disclosure will be collectively described as supplementary notes.

[0072] (Note 1)

[0073] A semiconductor device, wherein:

[0074] have:

[0075] a substrate having electrode pads;

[0076] a semiconductor element mounted on the substrate and connected to the electrode pad;

[0077] a plate-shaped lead frame, one end of which is connected to the electrode pad of the semiconductor element or the substrate; and

[0078] a sealing material for sealing the semiconductor element, the substrate, and the lead frame;

[0079] On the inner side of the sealing material, adjacent straight line portions of the lead frame are folded back at an angle smaller than 180 degrees so as to form hills and valleys in a side view.

[0080] (Note 2)

[0081] The semiconductor device according to Supplementary Note 1, wherein:

[0082] Adjacent straight line portions of the lead frame are folded back at an angle smaller than 90 degrees inside the sealing material.

[0083] (Note 3)

[0084] A semiconductor device, wherein:

[0085] have:

[0086] a substrate having electrode pads;

[0087] a semiconductor element mounted on the substrate and connected to the electrode pad;

[0088] a plate-shaped lead frame, one end of which is connected to the electrode pad of the semiconductor element or the substrate; and

[0089] a sealing material for sealing the semiconductor element, the substrate, and the lead frame;

[0090] The lead frame has a U-shaped annular portion on the inner side of the sealing material, or has a sawtooth shape or a stepped shape in a plan view.

[0091] (Note 4)

[0092] The semiconductor device according to any one of Supplementary Notes 1 to 3, wherein

[0093] The one end of the lead frame is connected to the semiconductor element.

[0094] The other end of the lead frame is connected to another semiconductor element or another electrode pad of the substrate in the sealing material, or extends outside the sealing material.

[0095] (Note 5)

[0096] The semiconductor device according to any one of Supplementary Notes 1 to 4, wherein

[0097] The one end of the lead frame is connected to the semiconductor element.

[0098] The one end of the lead frame has a through hole extending from the upper surface to the surface connected to the semiconductor element.

[0099] A bonding material bonding the one end of the lead frame to the semiconductor element passes through the through hole and rises on the upper surface.

[0100] (Note 6)

[0101] The semiconductor device according to any one of Supplementary Notes 1 to 5, wherein

[0102] The semiconductor element is formed of a wide-bandgap semiconductor.

[0103] (Note 7)

[0104] The semiconductor device according to any one of Supplementary Notes 3 to 6, wherein

[0105] The lead frame is in a step-like shape when viewed from above, and the bent portion of the step is a curve.

[0106] (Note 8)

[0107] The semiconductor device according to any one of Supplementary Notes 3 to 6, wherein

[0108] The lead frame has a sawtooth shape when viewed from above, and the folded portion of the sawtooth is a curve.

Claims

1. A semiconductor device, wherein: have: a substrate having electrode pads; a semiconductor element mounted on the substrate and connected to the electrode pad; a plate-shaped lead frame, one end of which is connected to the semiconductor element or the electrode pad of the substrate; as well as a sealing material that seals the semiconductor element, the substrate, and the lead frame, On the inner side of the sealing material, adjacent straight line portions of the lead frame are folded back at an angle smaller than 180 degrees so as to form hills and valleys in a side view.

2. The semiconductor device according to claim 1, wherein Adjacent straight line portions of the lead frame are folded back at an angle smaller than 90 degrees on the inner side of the sealing material.

3. A semiconductor device, wherein: have: a substrate having electrode pads; a semiconductor element mounted on the substrate and connected to the electrode pad; a plate-shaped lead frame, one end of which is connected to the semiconductor element or the electrode pad of the substrate; as well as a sealing material that seals the semiconductor element, the substrate, and the lead frame, The lead frame has a U-shaped annular portion on the inner side of the sealing material, or has a sawtooth shape or a stepped shape in a plan view.

4. The semiconductor device according to any one of claims 1 to 3, wherein The one end of the lead frame is connected to the semiconductor element, The other end of the lead frame is connected to another semiconductor element or another electrode pad of the substrate in the sealing material, or extends outside the sealing material.

5. The semiconductor device according to any one of claims 1 to 3, wherein The one end of the lead frame is connected to the semiconductor element, The one end of the lead frame has a through hole extending from the upper surface to the surface connected to the semiconductor element. A bonding material bonding the one end of the lead frame to the semiconductor element passes through the through hole and rises on the upper surface.

6. The semiconductor device according to any one of claims 1 to 3, wherein The semiconductor element is formed of a wide bandgap semiconductor.

7. The semiconductor device according to claim 3, wherein The lead frame is in a step shape when viewed from above, and the bent portion of the step is a curve.

8. The semiconductor device according to claim 3, wherein The lead frame is in a sawtooth shape when viewed from above, and the folded portion of the sawtooth is a curve.

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