Semiconductor device and method for manufacturing same

Abstract

A semiconductor chip (3) has an upper surface electrode (3b). A metal lead electrode (6) is disposed above the semiconductor chip (3) and is joined to the upper surface electrode (3b) by means of solder (7). A sealing material (12) seals the semiconductor chip (3), the solder (7), and the metal lead electrode (6). The metal lead electrode (6) has a through-hole (6a) at a position facing the upper surface electrode (3b). The solder (7) extends to the upper surface of the metal lead electrode (6) through the through-hole (6a) and wets and spreads around the through-hole (6a) on the upper surface of the metal lead electrode (6). A recess section (7a) is formed on the upper surface of the solder (7) above the through-hole (6a). The sealing material (12) enters the recess section (7a).

Description

Semiconductor device and manufacturing method thereof

[0001] The present disclosure relates to a semiconductor device and a manufacturing method thereof.

[0002] A semiconductor device has been proposed in which a metal lead electrode having a through hole is soldered to an upper electrode of a semiconductor chip and then sealed with a sealing material (see, for example, Patent Document 1). The solder extends through the through hole to the upper surface of the metal lead electrode, and then wets and spreads around the through hole on the upper surface of the metal lead electrode. This improves the bonding strength between the metal lead electrode and the upper electrode due to an anchor effect.

[0003] Japanese Patent Application Publication No. 2008-182074

[0004] However, the adhesion strength between the encapsulant and solder is weaker than that between the encapsulant and metal lead electrodes. Therefore, when the solder spreads over the top surface of the metal lead electrodes, the adhesion strength of the encapsulant decreases. As a result, peeling occurs at the interface between the encapsulant and metal lead electrodes due to stress from temperature cycles, etc., which reduces the reliability of the semiconductor device.

[0005] The present disclosure has been made to solve the above-mentioned problems, and its object is to provide a semiconductor device that can suppress peeling of a sealing material, and a method for manufacturing the same.

[0006] The semiconductor device according to the present disclosure comprises a semiconductor chip having an upper surface electrode, a metal lead electrode arranged above the semiconductor chip and joined to the upper surface electrode by solder, and a sealing material that seals the semiconductor chip, the solder, and the metal lead electrode, wherein the metal lead electrode has a through hole at a position opposite the upper surface electrode, the solder extends through the through hole onto the upper surface of the metal lead electrode and wets and spreads around the through hole on the upper surface of the metal lead electrode, and a recess is formed in the upper surface of the solder above the through hole, and the sealing material fills the recess.

[0007] a step of heating and melting the mounted solder to join the top electrode and the metal lead electrode with the solder; a step of cooling and solidifying the molten solder; and a step of sealing the semiconductor chip, the solder, and the metal lead electrode with a sealing material after solidifying the solder. The solidified solder extends to an upper surface of the metal lead electrode through the through hole, wetting and spreading around the through hole on the upper surface of the metal lead electrode, and a recess is formed in the upper surface of the solidified solder above the through hole, with the sealing material filling the recess.

[0008] In the present disclosure, a recess is formed on the upper surface of the solder above the through hole, and the sealing material is placed in the recess, which has an anchor effect that improves the adhesion of the sealing material, thereby preventing peeling of the sealing material.

[0009] Fig. 1 is a cross-sectional view showing a semiconductor device according to a first embodiment; Fig. 2 is a cross-sectional view showing an enlarged solder joint of the semiconductor device according to the first embodiment; Fig. 3 is a cross-sectional view showing a manufacturing method of the semiconductor device according to the first embodiment; Fig. 4 is a cross-sectional view showing a state in which solder joint has failed; Fig. 5 is a cross-sectional view showing an enlarged solder joint of the semiconductor device according to a second embodiment; Fig. 6 is a cross-sectional view showing an enlarged solder joint of the semiconductor device according to a third embodiment;

[0010] A semiconductor device and a manufacturing method thereof according to an embodiment will be described with reference to the drawings. The same or corresponding components are designated by the same reference numerals, and repeated description may be omitted.

[0011] First Embodiment. Figure 1 is a cross-sectional view showing a semiconductor device according to a first embodiment. Metal plate 1 is a block made of a material with excellent thermal and electrical conductivity, such as copper or an aluminum alloy. A composite insulating sheet 2 made of an insulating layer 2a and a protective metal layer 2b is fixed to the underside of metal plate 1. Note that metal plate 1 may also be a circuit pattern on an insulating substrate. The insulating substrate is made of an insulating layer made of ceramic or resin with excellent thermal conductivity, such as aluminum nitride or silicon nitride, on both sides of which circuit patterns are made of copper or an aluminum alloy.

[0012] Semiconductor chips 3 and 4 are mounted on the upper surface of the metal plate 1. The semiconductor chip 3 is an IGBT (Insulated Gate Bipolar Transistor), and the semiconductor chip 4 is a diode. A collector electrode 3a on the lower surface of the semiconductor chip 3 and a cathode electrode 4a on the lower surface of the semiconductor chip 4 are each bonded to the metal plate 1 with a bonding material 5. The semiconductor chips 3 and 4 may be reverse conducting IGBTs, MOSFETs, Schottky diodes, or the like. There is no limit to the number of semiconductor chips 3 and 4 mounted on the metal plate 1; the required number of metal plates 1 may be mounted depending on the application. The bonding material 5 is solder or soft solder, but may also be a sintered bonding material made of a paste of minute silver or copper particles.

[0013] A metal lead electrode 6 is joined by solder 7 to the emitter electrode 3b, which is an upper electrode of the semiconductor chip 3, and to the anode electrode 4b, which is an upper electrode of the semiconductor chip 4. A metal lead electrode 8 is connected to the gate electrode 3c of the semiconductor chip 3 by a wire 9 made of a material with excellent thermal and electrical conductivity, such as aluminum, copper, or gold. A metal lead electrode 10 is joined to the metal plate 1 by solder 11. A sealing material 12 seals the semiconductor chips 3 and 4, the wire 9, the solder 7, and the metal lead electrodes 6, 8, and 10.

[0014] The metal lead electrodes 6 are disposed above the semiconductor chips 3 and 4, with a distance between the metal lead electrodes 6 and the semiconductor chips 3 and 4 of, for example, 1 mm or less. The metal lead electrode 6 has a through-hole 6a facing the emitter electrode 3b and a through-hole 6b facing the anode electrode 4b. The diameters of the through-holes 6a and 6b are, for example, φ10 mm or less, which are smaller than the planar outer diameters of the emitter electrode 3b and the anode electrode 4b (15 mm × 15 mm). The metal lead electrodes 6, 8, and 10 are flat plates made of copper or a copper alloy with excellent electrical conductivity and a thickness of approximately 0.1 to 2 mm. The solder 7 is a solder alloy material primarily composed of Sn with various metal elements added. The sealing material 12 is silicone gel or epoxy resin, but is not limited thereto. Any sealing material having desired physical properties, such as elastic modulus, heat resistance, adhesiveness, and linear expansion coefficient, may be used.

[0015] 2 is an enlarged cross-sectional view of a solder joint of the semiconductor device according to the first embodiment. The solder 7 extends through the through hole 6a onto the upper surface of the metal lead electrode 6 and spreads around the through hole 6a on the upper surface of the metal lead electrode 6. This improves the bond strength between the metal lead electrode 6 and the emitter electrode 3b due to an anchor effect. However, the adhesion strength at the interface between the encapsulant 12 and the solder 7 is lower than the adhesion strength between the encapsulant 12 and the metal lead electrode 6. Therefore, if the solder 7 spreads onto the upper surface of the metal lead electrode 6, the adhesion strength of the encapsulant 12 decreases, making the encapsulant 12 more likely to peel off.

[0016] In contrast, in this embodiment, a recess 7a is formed on the upper surface of the solder 7 above the through hole 6a, and the sealing material 12 is inserted into the recess 7a. This improves the adhesion of the sealing material 12 due to the anchor effect, thereby preventing the sealing material 12 from peeling off. As a result, the reliability of the semiconductor device is improved, and a semiconductor device with a long life can be provided. The solder joint between the anode electrode 4b of the semiconductor chip 4 and the metal lead electrode 6 has a similar configuration, and the same effect can be obtained.

[0017] Next, a semiconductor device manufacturing method according to the present embodiment will be described. FIG. 3 is a cross-sectional view showing the semiconductor device manufacturing method according to the first embodiment. First, the collector electrode 3a of the semiconductor chip 3 is bonded to the metal plate 1 with a bonding material 5. The bonding material 5 may be plate solder or may be screen-printed solder paste. The bonding is performed by heating the bonding material 5 to a temperature higher than its melting point, causing the bonding material 5 to melt. The bonding material 5 may also be a sintered material formed by kneading minute silver or copper particles into a paste-like material with a thixotropic viscous material. However, if a sintered material is used, a process of heating and pressurizing the semiconductor chip 3 is required.

[0018] Next, the metal lead electrode 6 is disposed above the semiconductor chip 3 , and the through hole 6 a of the metal lead electrode 6 is aligned with the position facing the emitter electrode 3 b of the semiconductor chip 3 .

[0019] Next, solder 7 is prepared, which has a tip portion 7b with a diameter smaller than that of through hole 6a and a rear portion 7c with a diameter larger than that of through hole 6a. Solder 7 is an alloy primarily composed of Sn, and is formed by casting, pressure molding, or machining. Next, solder 7 is mounted so that tip portion 7b passes through through hole 6a and contacts emitter electrode 3b, and rear portion 7c is positioned above metal lead electrode 6. Note that the volume of solder 7 is designed to be smaller than the sum of the volume between semiconductor chip 3 and metal lead electrode 6 and the volume inside through hole 6a, so that recessed portion 7a can be formed later.

[0020] Next, the applied solder 7 is heated to a temperature higher than its melting point to melt it, and the emitter electrode 3b and the metal lead electrode 6 are joined by the solder 7. The rear portion 7c of the solder 7 wets and spreads around the through-hole 6a on the upper surface of the metal lead electrode 6. The molten solder 7 is cooled and solidified. A metal lead electrode 8, which is connected to a signal circuit that controls the semiconductor chip 3, is connected to the gate electrode 3c of the semiconductor chip 3 by ultrasonic bonding of a wire 9.

[0021] Next, the semiconductor chip 3, solder 7, metal lead electrodes 6, etc. are sealed with sealing material 12. The resin can be molded by pressurizing the molten resin in a mold, or by directly pouring the molten resin into the mold. The shape of the semiconductor device is completed by placing the molding material 12 in a curing oven or the like to harden it. Terminals can be formed or the sealing material 12 can be processed as needed. Thereafter, the electrical characteristics of the semiconductor device are inspected. The semiconductor device according to this embodiment is manufactured through the above steps.

[0022] As described above, in this embodiment, the solder 7 is formed to have a tip portion 7b having a diameter smaller than that of the through hole 6a and a rear portion 7c having a diameter larger than that of the through hole 6a. This suppresses uneven supply of the solder 7. Furthermore, a recess 7a can be stably formed on the upper surface of the solder 7 above the through hole 6a. Furthermore, by inserting the tip portion 7b, which has a diameter smaller than that of the through hole 6a, into the through hole 6a of the metal lead electrode 6, a joint between the solder 7 and the emitter electrode 3b can be stably formed. Furthermore, the rear portion 7c, which has a diameter larger than that of the through hole 6a, is positioned above the metal lead electrode 6. This allows the solder 7 to wet and spread around the through hole 6a on the upper surface of the metal lead electrode 6, thereby improving the joint strength between the metal lead electrode 6 and the emitter electrode 3b due to an anchor effect.

[0023] Furthermore, when the solder 7 melts, a rear portion 7c of the solder 7 melts onto the upper surface of the metal lead electrode 6 and spreads around the through-hole 6a. The solder 7 also wets and drips onto the emitter electrode 3b of the semiconductor chip 3, causing a depression in the solder 7 inside the through-hole 6a. The molten solder 7 is then cooled from the underside of the semiconductor chip 3. As a result, the solder 7 solidifies from the bottom, and the final solidification point of the solder 7 is near the metal lead electrode 6. The solder 7 shrinks in volume during solidification. However, because an intermetallic compound is formed at the interface between the metal lead electrode 6 and the solder 7, volume shrinkage sufficient to cause the bond to separate does not occur. Therefore, the volume shrinkage of the solder 7 is concentrated inside the through-hole 6a, allowing a deep depression 7a to be stably formed in the solder 7 above the through-hole 6a. The cooling method may involve spraying a low-temperature fluid such as air or nitrogen onto the underside of the metal plate 1, or a contact cooling method in which a low-temperature cooling plate is brought into contact with the underside of the metal plate 1 for cooling.

[0024] FIG. 4 is a cross-sectional view showing a failed solder joint. When the emitter electrode 3b of the semiconductor chip 3 and the solder 7 are not joined, the solder 7 remains wet only on the metal lead electrode 6, and the height of the solder 7 above the metal lead electrode 6 is significantly higher than in a good joint. Therefore, the quality of the joint can be determined by measuring the maximum height of the solder 7 above the metal lead electrode 6 after solidifying the solder 7. For example, if the maximum height exceeds a predetermined threshold, the joint is determined to be defective. This allows for detection of joint defects earlier than the final electrical characteristic test, thereby improving production efficiency. The maximum height of the solder 7 can be measured using a laser displacement meter, an image focusing method, or a moire method using interference fringes.

[0025] Furthermore, if the emitter electrode 3b of the semiconductor chip 3 and the solder 7 are not bonded, a large amount of the solder 7 remains on the metal lead electrode 6 as shown in Figure 4, and therefore a recess 7a of the solder 7 is not formed above the through hole 6a of the metal lead electrode 6. Therefore, after the solder 7 is solidified, the quality of the bonded state may be determined by visually checking whether or not there is a recess 7a of the solder 7 above the through hole 6a. This allows for detection of bond defects earlier than the electrical characteristic test in the final process, thereby improving production efficiency.

[0026] Second Embodiment. Figure 5 is an enlarged cross-sectional view of a solder joint of a semiconductor device according to a second embodiment. In this embodiment, the deepest part of the recess 7a is lower than the upper surface of the metal lead electrode 6. By allowing the encapsulant 12 to penetrate into this deep recess 7a, a stronger anchoring effect than in the first embodiment can be obtained, thereby further improving the adhesion of the encapsulant 12. Furthermore, even if a peeling point occurs at the interface between the bonding material 5 and the metal lead electrode 6, the peeling can be prevented from progressing horizontally. As a result, the reliability of the semiconductor device is improved compared to the first embodiment, and a semiconductor device with a longer life can be provided. The other configurations, manufacturing processes, and effects are the same as those of the first embodiment.

[0027] Third Embodiment. FIG. 6 is an enlarged cross-sectional view of a solder joint of a semiconductor device according to a third embodiment. In this embodiment, the metal lead electrode 6 has an embossed portion 6c, which protrudes toward the semiconductor chip 3 at a portion facing the semiconductor chip 3. The embossed portion 6c is formed by embossing the metal lead electrode 6 with a mold. A through-hole 6a is formed at the bottom of the embossed portion 6c. The step of the embossed portion 6c prevents the solder 7 from spreading on the upper surface of the metal lead electrode 6. This prevents the solder 7 from spreading more than necessary, improving the adhesion of the sealing material 12. As a result, the reliability of the semiconductor device is improved compared to the first embodiment, and a longer-life semiconductor device can be provided. The remaining configuration, manufacturing process, and effects are the same as those of the first and second embodiments.

[0028] The semiconductor chips 3 and 4 are not limited to those made of silicon, but may also be made of wide-bandgap semiconductors with a wider bandgap than silicon. Examples of wide-bandgap semiconductors include silicon carbide, gallium nitride-based materials, and diamond. Semiconductor chips made of such wide-bandgap semiconductors have high voltage resistance and allowable current density, allowing for miniaturization. By using these miniaturized semiconductor chips, semiconductor devices incorporating these semiconductor chips can also be miniaturized and highly integrated. Furthermore, because the semiconductor chips have high heat resistance, the heat dissipation fins of the heat sink can be miniaturized, and the water-cooled portion can be replaced with air-cooled, further miniaturizing the semiconductor device.

[0029] 3, 4 Semiconductor chip, 3b Emitter electrode (upper surface electrode), 4b Anode electrode (upper surface electrode), 6 Metal lead electrode, 6a Through hole, 6c Embossed portion, 7 Solder, 7a Recessed portion, 7b Tip portion, 7c Rear portion, 12 Sealing material

Claims

1. A semiconductor chip having an upper electrode, A metal lead electrode is positioned above the semiconductor chip and is joined to the upper electrode by solder, The semiconductor chip, the solder, and the sealing material for sealing the metal lead electrodes are provided. The metal lead electrode has a through hole at a position opposite to the upper electrode, The solder extends through the through hole to the upper surface of the metal lead electrode and wets and spreads around the through hole on the upper surface of the metal lead electrode. A recess is formed on the upper surface of the solder above the through hole. A semiconductor device characterized in that the sealing material is contained within the recessed portion.

2. The semiconductor device according to claim 1, characterized in that the deepest part of the recess is lower than the upper surface of the metal lead electrode.

3. The metal lead electrode has an embossed portion that protrudes in a direction toward the semiconductor chip in the portion facing the semiconductor chip, The semiconductor device according to claim 1 or 2, characterized in that the through hole is formed at the bottom of the embossed portion.

4. The semiconductor device according to claim 1 or 2, characterized in that the semiconductor chip is formed of a wide-bandgap semiconductor.

5. A step of arranging a metal lead electrode having a through hole above a semiconductor chip having an upper electrode, and aligning the through hole to a position opposite the upper electrode, A step of preparing solder that has a tip portion having a diameter smaller than the through hole and a rear portion having a diameter larger than the through hole, A step of mounting the solder such that the tip portion passes through the through hole and contacts the upper electrode, and the rear portion is positioned above the metal lead electrode, A step of heating and melting the solder that has been mounted to join the upper electrode and the metal lead electrode with the solder, A step of cooling and solidifying the molten solder, The process includes a step of solidifying the solder and then sealing the semiconductor chip, the solder, and the metal lead electrodes with a sealing material. The solidified solder extends through the through hole to the upper surface of the metal lead electrode, and wets and spreads around the through hole on the upper surface of the metal lead electrode. Above the through hole, a recess is formed on the upper surface of the solidified solder. A method for manufacturing a semiconductor device, characterized in that the sealing material is filled into the recessed portion.

6. The method for manufacturing a semiconductor device according to claim 5, characterized in that the molten solder is cooled from the lower surface side of the semiconductor chip when cooling it.

7. The method for manufacturing a semiconductor device according to claim 5 or 6, further comprising the step of determining the quality of the bonding state by measuring the maximum height of the solder above the metal lead electrode after the solder has been solidified.

8. The method for manufacturing a semiconductor device according to claim 5 or 6, further comprising the step of determining the quality of the bonding state by measuring the presence or absence of the recessed portion of the solder above the through hole after the solder has solidified.