Semiconductor device

Abstract

A semiconductor chip (2) is provided on the upper surface (1a) of a heat sink (1). Lead terminals (5, 6) are electrically connected to the semiconductor chip (2) and extend above the second side surface (1d) of the heat sink (1) instead of extending above the first side surface (1c) of the heat sink (1). A molding resin (10) covers the upper surface, the first side surface (1c), and the second side surface (1d) of the heat sink (1), the semiconductor chip (2), and a part of the lead terminals (5, 6). The lower surface (1b) of the heat sink (1) is exposed from the molding resin (10). An anchoring structure (11) is provided which is filled with the molding resin (10) due to a depression in the lower part of the first side surface (1c) of the heat sink (1). There is no anchoring structure (11) on the second side surface (1d) of the heat sink (1). The heat sink (1) does not protrude from the side surface (10a) of the molding resin (10).

Description

Technical Field

[0001] The present invention relates to a resin-molded encapsulated semiconductor device. Background Art

[0002] In a resin-molded encapsulated semiconductor device, a semiconductor chip is provided on a heat sink, the semiconductor chip is connected to a lead terminal by a wire, and they are covered with a molding resin. In such a semiconductor device, a heat sink having an anchoring structure in which the lower part of the side surface is recessed and filled with the molding resin is used. Thereby, the heat sink is prevented from coming off from the molding resin, and reliability can be ensured.

[0003] If there is an anchoring structure below the lead terminal, the inductance increases, and thus the impedance of the lead terminal cannot be reduced to a desired level. Therefore, it hinders high performance when the semiconductor device is used as a high-frequency amplifier or the like. To solve this problem, a semiconductor device has been proposed in which the impedance of the lead terminal is reduced by using a heat sink in which a part of the side surface protrudes from the molding resin below the lead terminal (see, for example, Patent Document 1).

[0004] Patent Document 1: Japanese Patent No. 6289792

[0005] In molding, two molding dies separated in the vertical direction with the lead terminal of the semiconductor device as a boundary are used. After injecting and filling the molding resin into the die from the injection port, the two dies are separated in the vertical direction. However, in the manufacture of an existing semiconductor device in which a part of the side surface of the heat sink protrudes from the molding resin, since a part of the protruding heat sink becomes a physical obstacle, a molding die having a shape more complicated than a normal molding die is required. Also, the process of separating the semiconductor device after filling with the molding resin from the molding die becomes complicated. Therefore, there are problems such as an increase in manufacturing cost, deterioration of productivity, and deterioration of product yield. Summary of the Invention

[0006] The present invention has been made to solve the above-described problems, and an object thereof is to obtain a semiconductor device that can ensure reliability, reduce the impedance of a lead terminal, reduce manufacturing costs, and improve productivity and product yield.

[0007] The semiconductor device according to the present invention is characterized in that it includes: a heat sink; a semiconductor chip disposed on the upper surface of the heat sink; lead terminals electrically connected to the semiconductor chip and extending above the second side surface of the heat sink instead of above the first side surface of the heat sink; and a molding resin covering the upper surface, the first side surface, the second side surface, the semiconductor chip, and a part of the lead terminals of the heat sink, with the lower surface of the heat sink exposed from the molding resin, and an anchoring structure filled with the molding resin due to a depression in the lower part of the first side surface of the heat sink, and the second side surface of the heat sink has no such anchoring structure, and the heat sink does not protrude from the side surface of the molding resin.

[0008] In the present invention, an anchoring structure is provided on the first side surface of the heat sink. Thereby, it is possible to prevent the heat sink from detaching from the molding resin, thus ensuring reliability. In addition, there is no anchoring structure on the second side surface of the heat sink where the lead terminals extend above. Thereby, the impedance of the lead terminals can be reduced. In addition, the heat sink does not protrude from the side surface of the molding resin. Thereby, ordinary molding can be applied, so that the manufacturing cost can be reduced, and the productivity and product yield can be improved. Description of the Drawings

[0009] Figure 1 It is a top view showing the semiconductor device according to Embodiment 1.

[0010] Figure 2 It is a cross-sectional view taken along Figure 1 I-II.

[0011] Figure 3 It is a cross-sectional view taken along Figure 1 III-IV.

[0012] Figure 4 It is a cross-sectional view showing a modified example of the semiconductor device according to Embodiment 1.

[0013] Figure 5 It is a cross-sectional view showing the state in which the semiconductor device according to Embodiment 1 is mounted.

[0014] Figure 6 It is a cross-sectional view Figure 5 obtained by magnifying a part of

[0015] Figure 7 It is a cross-sectional view showing the semiconductor device according to Comparative Example 1.

[0016] Figure 8 It is a cross-sectional view showing the semiconductor device according to Comparative Example 2.

[0017] Figure 9 This is a cross-sectional view of the semiconductor device according to Embodiment 2.

[0018] Figure 10 This is a cross-sectional view of the semiconductor device according to Embodiment 3. Detailed Embodiments

[0019] The semiconductor device according to the embodiment will be described with reference to the accompanying drawings. The same or corresponding components are denoted by the same reference numerals, and repeated descriptions may be omitted sometimes.

[0020] Embodiment 1

[0021] Figure 1 This is a top view of the semiconductor device according to Embodiment 1. Figure 2 It is a cross-sectional view taken along the I-II Figure 1 section. Figure 3 It is a cross-sectional view taken along the III-IV Figure 1 section. The heat sink 1 has an upper surface 1a as a mounting surface, a lower surface 1b as a heat dissipation surface, and a first side surface 1c and a second side surface 1d that are orthogonal to each other. In the drawing, the upper surface 1a and the lower surface 1b of the heat sink 1 face each other in the Z direction. The first side surface 1c is two side surfaces that face each other in the Y direction. The second side surface 1d is two side surfaces that face each other in the X direction.

[0022] The semiconductor chip 2 and the circuit board 3 are provided on the upper surface 1a of the heat sink 1 through a bonding member 4. The bonding member 4 is Ag paste resin, solder, sintered Ag, etc. The semiconductor chip 2 is a field effect transistor such as a Si-LDMOS chip, a GaAsFET chip, or a GaN HEMT suitable for high-frequency power amplifier applications.

[0023] The lead terminals 5 and 6 are arranged above the heat sink 1. The lead terminals 5 and 6 do not extend above the first side surface 1c of the heat sink 1, but extend above the second side surface 1d of the heat sink 1. The lead terminal 5 is electrically connected to the circuit board 3 through a bonding wire 7. The circuit board 3 is electrically connected to the gate electrode pad on the upper surface of the semiconductor chip 2 through a bonding wire 8. The lead terminal 6 is electrically connected to the drain electrode pad on the upper surface of the semiconductor chip 2 through a bonding wire 9. The bonding wires 7, 8, and 9 are made of a metal material such as Au, Ag, or Al.

[0024] The circuit board 3 is set to an optimum load impedance with respect to the semiconductor chip 2 so that the semiconductor device operates with high efficiency as a high-frequency power amplifier and outputs high high-frequency power. The circuit board 3 is provided on the gate side of the semiconductor chip 2, but is not limited thereto, and may also be provided between the drain electrode pad of the semiconductor chip 2 and the lead terminal 6, or may be provided on both the gate side and the drain side.

[0025] The heat sink 1 is electrically connected to the source electrode on the upper surface of the semiconductor chip 2 and also serves as a source electrode terminal. As a method of connecting the heat sink 1 to the source electrode, there are a method of connecting through a through-hole that penetrates from the upper surface to the lower surface of the semiconductor chip 2, and a method of connecting a pad connected to the source electrode to the heat sink 1 using a bonding wire.

[0026] The molding resin 10 covers the upper surface, the first side surface 1c, and the second side surface 1d of the heat sink 1, the semiconductor chip 2, and a part of the lead terminals 5 and 6. All side surfaces and the upper surface of the heat sink 1 are enclosed by the molding resin 10, and only the lower surface 1b, which serves as a heat dissipation surface, of the heat sink 1 is exposed from the molding resin 10. The heat sink 1 does not protrude from the side surface 10a of the molding resin 10.

[0027] The heat released from the semiconductor chip 2 and the circuit board 3 is conducted to the outside from the lower surface 1b of the heat sink 1. Therefore, it is preferable that the heat sink 1 has a thermal conductivity of 200 W / mK or more, and for example, it is made of Cu having a high thermal conductivity of 398 W / mK. The semiconductor device having such a structure is suitable for outputting high-frequency power with a frequency of 1 GHz or more and 1 W or more.

[0028] An anchoring structure 11 is provided in which the lower part of the first side surface 1c of the heat sink 1 is recessed and filled with the molding resin 10. The second side surface 1d of the heat sink 1 does not have the anchoring structure 11. Among them, in the usual manufacturing method of the heat sink, for example, a Cu material as a base material is formed into a heat sink with a desired size by compression processing using an upper mold and a lower mold. It is necessary to be able to separate the heat sink from the mold after compression processing, and the shape of the formed heat sink is restricted by this. The shape of the heat sink 1 of the present embodiment can be formed without complicating such a usual manufacturing method.

[0029] As a method of forming the outer shape of the semiconductor device, it is usually as follows: After injecting and filling the molding resin 10 from a predetermined injection port using two molding dies that are separated in the vertical direction with the lead terminals 5 and 6 as boundaries, the two molding dies are separated in the vertical direction (Z direction). In order to easily pull out the semiconductor device from the molding die, a taper is usually provided on both the upper molding die and the lower molding die. Therefore, the side surface 10a of the molding resin 10 is inclined in a conical shape. The usual conical angle is about 3° to 15°.

[0030] Figure 4 It is a cross-sectional view showing a modified example of the semiconductor device according to Embodiment 1. Figure 2In [the figure], below the lead terminals 5 and 6, the lower end of the second side surface 1d of the heat sink 1 is at the same position as the lower end of the side surface 10a of the molded resin 10. However, in reality, the heat sink 1 needs to be reliably incorporated into the lower mold for molding, and dimensional tolerances need to be considered. The dimensional tolerances that should be considered are mainly the dimensions of the heat sink 1, the dimensions of the lower mold for molding, etc.

[0031] In a normal manufacturing method, if the lower end of the second side surface 1d of the heat sink 1 is located at a position up to 0.2 mm inward from the lower end of the side surface 10a of the molded resin 10, the heat sink 1 can be reliably incorporated into the lower mold for molding. Therefore, the distance D between the lower end of the second side surface 1d of the heat sink 1 and the lower end of the side surface 10a of the molded resin 10 is set to 0.2 mm or less.

[0032] Next, the effects of the present embodiment will be compared with Comparative Examples 1 and 2 for explanation. Figure 5 It is a cross-sectional view showing the state of the semiconductor device according to Embodiment 1. Figure 6 It is Figure 5 An enlarged cross-sectional view of a part of [the figure]. The lower surface 1b of the heat sink 1 that is electrically connected to the source electrode of the semiconductor chip 2 is connected to the conductor 12. The lower surfaces of the lead terminals 5 and 6 of the semiconductor device are electrically connected to the substrate 13 for matching.

[0033] Figure 7 It is a cross-sectional view showing the semiconductor device according to Comparative Example 1. In Comparative Example 1, an anchoring structure 11 is also provided below the lead terminals 5 and 6. In Comparative Example 1, when the heat sink 1 is grounded, a parasitic inductance component on the heat sink 1 side is superimposed. Therefore, the impedance of the lead terminals 5 and 6 cannot be reduced to the desired level.

[0034] On the other hand, in the present embodiment, there is no anchoring structure 11 on the second side surface 1d of the heat sink 1 where the lead terminals 5 and 6 extend upward, and the lower end of the second side surface 1d of the heat sink 1 is at the same position as the lower end of the side surface 10a of the molded resin 10. Thereby, the influence of the parasitic inductance component on the heat sink 1 side can be reduced, and thus, the impedance of the lead terminals 5 and 6 can be reduced. In addition, an anchoring structure 11 is provided on the first side surface 1c of the heat sink 1. Thereby, the heat sink 1 can be prevented from falling off from the molded resin 10, and reliability can be ensured.

[0035] Figure 8FIG. 0 is a cross-sectional view showing the semiconductor device according to Comparative Example 2. In Comparative Example 2, the heat sink 1 protrudes from the side surface of the molded resin 10. Therefore, a molding die with a complex shape is required, and the process of separating the semiconductor device after the molded resin is filled becomes complicated. On the other hand, in the present embodiment, the heat sink 1 does not protrude from the side surface of the molded resin 10. Thus, ordinary molding can be applied, and therefore, the manufacturing cost can be reduced, and the productivity and product yield can be improved. Therefore, the present embodiment is suitable for application in a market field that requires a low price.

[0036] Next, a simulation was conducted to confirm the effect of the present embodiment. As the molded resin 10, ordinary epoxy resin was assumed, and the relative dielectric constant was set to 3.7. The tapered angle θ of the side surface portion of the molded resin 10 was set to 8°, the distance L from the lower surface 1b of the heat sink 1 to the lower surfaces of the lead terminals 5 and 6 was set to 1.6 mm, and the thickness t of the heat sink 1 was set to 1.0 mm. At this time, the distance X between the lower end portion of the substrate 13 and the lower end of the second side surface 1d of the heat sink 1 can be geometrically determined. In Embodiment 1, when D = 0, the distance X is 0.22 mm, and when D = 0.2 mm, the distance X is 0.42 mm. In Comparative Example 1, the distance D is 1.16 mm, and the distance X is 1.3 mm. In Comparative Example 2, the distance X is 0 mm.

[0037] Table 1 summarizes the results of calculating the impedance Z of the lead terminals of each semiconductor device.

[0038] Distance x Impedance Embodiment 1 (D = 0) 0.22 mm 18 Ω Embodiment 1 (D = 0.2 mm) 0.42 mm 20.5 Ω Comparative Example 1 1.30 mm 31 Ω Comparative Example 2 0.0 mm 14 Ω

[0039] The impedance Z of the lead terminals 5 and 6 in Comparative Example 1 is the highest, at 31 Ω, which is 2.21 times that of Comparative Example 2. When the impedance Z becomes high, the frequency band characteristics of the operating frequency, which are an important factor when the semiconductor device is used as a high-frequency power amplifier, deteriorate. The impedance Z of the lead terminals 5 and 6 in Comparative Example 2 is the lowest, at 14 Ω. However, as described above, Comparative Example 2 has problems such as extremely difficult manufacturing methods for semiconductor devices and inevitable cost increases.

[0040] On the other hand, in the present embodiment, when D = 0, the impedance Z is 18 Ω, which is 1.29 times that of Comparative Example 2, but it can be significantly reduced compared to Comparative Example 1. In addition, in the present embodiment, when D = 0.2 mm, the impedance Z of the lead terminals 5 and 6 is 20.5 Ω. The impedance Z becomes 1.14 times that in the case of D = 0, but a value sufficiently lower than that in Comparative Example 1 can be obtained. Therefore, even when D = 0.2 mm, deterioration of the frequency band characteristics of the operating frequency can be suppressed.

[0041] Among them, the distance X varies according to the taper angle θ of the side surface 10a of the molded resin 10 and the distance L from the lower surface of the heat sink 1 to the lower surfaces of the lead terminals 5 and 6. The smaller the taper angle θ and the smaller the distance L, the smaller the distance X. The smaller the distance X, the more the impedance Z of the lead terminals 5 and 6 can be reduced. However, the taper angle θ and the distance L are design parameters restricted by manufacturing methods and the like.

[0042] Embodiment 2

[0043] Figure 9 is a cross-sectional view showing the semiconductor device according to Embodiment 2. This cross-sectional view corresponds to that of Embodiment 1. Figure 2 In Embodiment 1, the lower surface of the heat sink 1 serving as the heat dissipation surface is flat. On the other hand, in the present embodiment, a recess 14 is provided on the lower surface of the heat sink 1. The recess 14 is filled with the molded resin 10. Thereby, the anchoring effect can be further improved. Other structures and effects are the same as those in Embodiment 1.

[0044] Embodiment 3

[0045] Figure 10 is a cross-sectional view showing the semiconductor device according to Embodiment 3. This cross-sectional view corresponds to that of Embodiment 1. Figure 2 In the present embodiment, protrusions 15 are provided on the second side surface 1d of the heat sink 1 below the lead terminals 5 and 6. When the heat sink 1 is disposed in the lower mold for molding, the self-aligning function is exerted by the protrusions 15. Therefore, the controllability of the distance D between the lower end of the second side surface 1d of the heat sink 1 and the lower end of the side surface 10a of the molded resin 10 is improved, and thus, the deviation of the impedance of the lead terminals 5 and 6 can be suppressed. Other structures and effects are the same as those in Embodiment 1.

[0046] Description of Reference Numerals

[0047] 1... Heat sink; 1a... Upper surface; 1b... Lower surface; 1c... First side surface; 1d... Second side surface; 2... Semiconductor chip; 5, 6... Lead terminals; 10... Molded resin; 11... Anchoring structure; 14... Recess; 15... Protrusion.

Claims

1. A semiconductor device, characterized in that, comprising: a heat sink; a semiconductor chip disposed on the upper surface of the heat sink; a lead terminal electrically connected to the semiconductor chip and extending above the second side surface of the heat sink instead of extending above the first side surface of the heat sink; and a molding resin covering the upper surface, the first side surface, the second side surface of the heat sink, the semiconductor chip and a part of the lead terminal, the lower surface of the heat sink is exposed from the molding resin, an anchoring structure is provided which is filled with the molding resin due to the depression of the lower part of the first side surface of the heat sink, the second side surface of the heat sink does not have the anchoring structure, the heat sink does not protrude from the side surface of the molding resin, the distance between the lower end of the second side surface of the heat sink and the lower end of the side surface of the molding resin is 0.2 mm or less, a protrusion is provided on the second side surface of the heat sink.

2. The semiconductor device according to claim 1, characterized in that, a recess is provided on the lower surface of the heat sink, the recess is filled with the molding resin.

3. The semiconductor device according to claim 1 or 2, characterized in that, the side surface of the molding resin is inclined in a conical shape.

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