Semiconductor device and manufacturing method for semiconductor device

Abstract

To provide a semiconductor device that realizes securing of thermal reliability at a solder joint portion and a manufacturing method for the semiconductor device.SOLUTION: A semiconductor device comprises a semiconductor element and a conductor plate joined to the semiconductor element by solder. The semiconductor element and the conductor plate are sealed by a resin member. The solder has Sn as a main component and has a Cu content of 4 wt% or more and 6 wt% or less. The conductor plate has an Ni coating formed on a surface thereof. In the Ni coating, the Ni coating in a region that is brought into close contact with the resin member is subjected to a roughening treatment, and a surface roughness of the Ni coating in the region of the Ni coating that is brought into close contact with the solder is smaller than a surface roughness of the Ni coating subjected to the roughening treatment.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device. [Background technology]

[0002] The RoHS and ELV directives restrict the use of lead in electronic control devices installed in automobiles, and as a result, the use of lead-free solder, primarily consisting of Sn-3Ag-0.5Cu (mass%), has been promoted. Also, power modules used in inverters are required to have higher power density by increasing the current flowing per chip in order to reduce their size.

[0003] On the other hand, as power semiconductor elements made of SiC, GaN, and the like, which can operate at higher temperatures than Si, are becoming more widespread, there is a risk that the heat generated by the semiconductor elements will increase and the solder joints will reach high temperatures. Therefore, in addition to heat dissipation measures, it is necessary to ensure reliability by taking measures to increase the guaranteed temperature of the power semiconductor joints. As an example of a measure to ensure the reliability of semiconductor devices, Patent Document 1 listed below discloses a configuration in which a roughened coating is formed on a conductor plate to improve adhesion between the conductor plate and the sealing resin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-303215 Summary of the Invention [Problem to be solved by the invention]

[0005] The technology described in Patent Document 1 prevents fatigue failure of solder joints by sealing them with a hard resin to suppress deformation. However, at high temperatures, the Sn contained in the solder joints reacts with the Ni-based electrodes of the semiconductor element, resulting in the unavoidable loss of the Ni coating. [Means for solving the problem]

[0006] A semiconductor device comprising a semiconductor element and a conductor plate joined to the semiconductor element by solder, the semiconductor element and the conductor plate being sealed with a resin member, the solder being mainly composed of Sn and having a Cu content of 4% by weight or more and 6% by weight or less, the conductor plate having a Ni coating formed on its surface, the Ni coating in an area that comes into close contact with the resin member being roughened, and the surface roughness of the Ni coating in the area that comes into close contact with the solder being smaller than the surface roughness of the roughened Ni coating. [Effects of the Invention]

[0007] It is possible to provide a semiconductor device and a method for manufacturing the semiconductor device that ensures thermal reliability at solder joints. [Brief explanation of the drawings]

[0008] [Figure 1] Schematic diagram of crack formation in a solder joint. [Figure 2] 2 is a schematic diagram of a solder joint according to one embodiment of the present invention. [Figure 3] 1 is a graph showing the relationship between the Cu content of Sn-based solder and the thickness of the Ni coating that has disappeared when held at 200°C for 1000 hours. [Figure 4] Schematic diagram of a solder joint using Sn-based solder with a Cu content greater than 6%. [Figure 5] 1 is a graph showing the relationship between the bonding time between a semiconductor element and a conductor plate at 285°C and the thickness of the Ni coating that has disappeared. [Figure 6] 1 is a graph showing the relationship between the holding time at 200° C. and the consumed thickness of the roughened Ni coating. [Figure 7] 1A and 1B are schematic diagrams illustrating a flat Ni coating and a roughened Ni coating according to an embodiment of the present invention. [Figure 8] First modified example of FIG. 7. [Figure 9] Second variant of FIG. 7. [Figure 10]1 shows the results of evaluation tests of an example and a comparative example using the configuration of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The following description and drawings are examples for explaining the present invention, and some omissions and simplifications have been made as appropriate for clarity of explanation. The present invention can be implemented in various other forms. Unless otherwise specified, each component may be singular or plural.

[0010] In order to facilitate understanding of the invention, the position, size, shape, range, etc. of each component shown in the drawings may not represent the actual position, size, shape, range, etc. Therefore, the present invention is not necessarily limited to the position, size, shape, range, etc. disclosed in the drawings.

[0011] (One embodiment and overall configuration) (Fig. 1, Fig. 2) FIG. 2(a) is a schematic diagram illustrating a semiconductor device 100, and FIG. 2(b) is an enlarged view of FIG. 2(a). The semiconductor device 100 has a semiconductor element 1 and a conductor plate 2. The semiconductor element 1 and the conductor plate 2 are joined together by solder and are mold-sealed with a resin member 9 (hard resin). The solder joint between the semiconductor element 1 and the conductor plate 2 is illustrated as a solder joint 3. The semiconductor element 1 is provided with a Ni-based electrode 6. The conductor plate 2 has a Ni coating 7 formed as a coating layer.

[0012] In the region of the Ni coating 7 that is in close contact with the resin member 9, a Ni coating 7a having fine needle-like irregularities formed thereon is formed by roughening treatment. The roughened Ni coating 7a is shown in detail in FIGS. 7 to 9.

[0013] By doing this, in the conventional method (Figure 1), when a semiconductor element 1 and a conductor plate 2 were soldered together, cracks 101 would occur in the solder joint 3 at high temperatures.However, with the configuration of the present invention, the adhesion between the Ni coating 7a of the conductor plate 2 and the resin member 9 is improved, and reactions at the interface of the solder joint 3 are suppressed even at high temperatures, preventing cracks 101 from occurring, thereby suppressing thermal fatigue failure of the solder joint 3.

[0014] Furthermore, the solder used to join the semiconductor element 1 and the conductive plate 2 is primarily composed of Sn and has a Cu content of 4% by weight to 6% by weight, which allows the solder joint 3 to maintain a good bond even if it is held at a temperature of up to 175°C for 1000 hours.

[0015] However, when the temperature of the solder joint 3 is 200°C, after 500 hours, the Ni coating 7 is completely removed due to a reaction at the interface of the solder joint 3, and a thick layer is formed due to reaction with the conductor plate 2. In the area of ​​the solder joint 3 where a thick layer is formed, defects such as voids occur due to volume change, and the solder joint 3 deteriorates. In other words, to ensure the high-temperature reliability of the solder joint, it is necessary not only to suppress the thermal fatigue resistance of the solder joint 3, but also to suppress the reaction of the solder joint 3 at a high temperature of 200°C.

[0016] Therefore, a flat Ni coating 7b is formed on the Ni coating 7 in the region that comes into close contact with the solder joint 3. The surface roughness of the flat Ni coating 7b is smaller than the surface roughness of the roughened Ni coating 7a. By forming the flat Ni coating 7b with a reduced surface area in the region that comes into close contact with the solder joint 3, fatigue failure of the solder joint 3 is suppressed and the reliability of the solder joint 3 can be ensured even at high temperatures.

[0017] With the above configuration, the solder joint 3 forms a layer of Cu-Sn compound 5 when heated in close contact with the Ni-based electrode 6 and the Ni coating 7. Note that not all of the solder joint 3 becomes a layer of Cu-Sn compound 5, but rather a portion of the solder joint 3 remains in the solder layer as the solder parent phase 4. By establishing such a state of the solder joint 3, thermal reliability can be ensured.

[0018] (Fig. 3, Fig. 4) FIG. 3 is a graph showing the relationship between the Cu content (wt%) in the solder and the thickness of the Ni coating 8 lost after the flat Ni coating 7b (FIG. 2) was maintained at 200°C for 1,000 hours. FIG. 3 reveals that the loss of the flat Ni coating 7b is significantly suppressed when the Cu content in the solder is 4 wt% or higher. On the other hand, when the Cu content in the solder is higher than 6 wt%, as shown in FIG. 4, excessive Cu-Sn compounds 5 are generated in the solder joint 3, which are not adjacent to the joint interface, which may adversely affect the joint reliability of the solder joint 3. Therefore, in the present invention, the reliability of the solder joint 3 can be ensured by using solder whose main component is Sn and whose Cu content is 4 wt% or higher and 6 wt% or lower.

[0019] (Figure 5) In the present invention, the solder used in the solder joint 3 is primarily composed of Sn and has a Cu content of 4% by weight to 6% by weight. Here, we compare this with the use of a general Sn-based solder in the solder joint 3. The solder used in the present invention is shown in the graph as Sn-5Cu. As shown in the figure, the solder used in the present invention can suppress the reaction between the solder and the Ni coating 7 more effectively than the use of a general Sn-based solder.

[0020] (Figure 6) Figure 6 is a graph showing the thickness loss of the roughened Ni coating 7a when held at 200°C for 1000 hours. Holding at 200°C for 1000 hours is a measure of reliability, and as shown in the figure, the thickness loss of the roughened Ni coating 7a is less than 5 μm even after holding for 1000 hours. Furthermore, the flat Ni coating 7b, which is the contact surface with the solder joint 3, uses the solder of the aforementioned configuration and is hardly lost, as shown in Figure 3. Therefore, the thickness loss is small even after holding at 200°C for 1000 hours.

[0021] Thus, if the thickness of the flat Ni coating 7b, which is the region of the Ni coating 7 that comes into close contact with the solder, is 5 μm or more, the reliability of the solder joint 3 can be ensured. Furthermore, as described above, the surface roughness of the flat Ni coating 7b is smaller than that of the Ni coating 7a, and therefore the reliability of the joint can be ensured even when held at a high temperature of 200°C.

[0022] Furthermore, the resin member 9 used in the semiconductor device 100 does not contain Sb in the portion that comes into contact with the Ni coating 7a. If a resin member 9 containing Sb is used, the interface between the resin member 9 and the Ni coating 7a can remain intact even after 1,000 hours of storage at temperatures up to 175°C. However, if the resin member 9 is stored at a high temperature of 200°C, the Sb contained in the resin member 9 reacts with the roughened Ni coating 7a. As a result, a reaction product with Sb is formed at the tip of the Ni coating 7a at the interface between the resin member 9 and the roughened Ni coating 7a after storage at 200°C for 500 hours. Furthermore, the Ni coating 7a itself is consumed by the reaction with Sb. Furthermore, if Sb reacts with the Ni coating 7a, since the Ni coating 7a is part of the Ni coating 7 and is connected to the flat Ni coating 7b, this reaction may also accelerate the consumption of the flat Ni coating 7b.

[0023] Therefore, by using a resin member 9 that does not contain Sb, it is possible to suppress the reaction at the interface between the resin member 9 and the Ni coating 7a even when held at 200° C. for 1000 hours, thereby ensuring reliability.

[0024] (Embodiment of the present invention, second modified example, third modified example) (Figures 7 to 9) As shown in FIG. 7, a portion of the roughened Ni coating 7b of the Ni coating 7 is processed by laser flattening, thereby forming a flat Ni coating 7b. This determines the bonding area between the conductor plate 2 and the solder joint 3. As a first modification of this configuration, as shown in FIG. 8, after forming a flat Ni plating 8 on the surface of the conductor plate 2, a roughened Ni coating 7a (roughened plating) may be provided on the portion that does not contact the solder joint 3. This contributes to cost reduction. Furthermore, as a second modification, as shown in FIG. 9, a portion of the flat Ni plating 8 may be roughened by blasting to form the Ni coating 7a (roughened plating).

[0025] (Verification of configuration examples of the present invention and comparative examples) (Figure 10) Figure 10(a) is a table of an example configuration in which Sn-based lead-free solder used in the present invention is supplied to the solder mounting position of a conductor plate 2 having a 5 μm thick Ni coating 7, and Figure 10(b) is a table of a comparative example not using the configuration used in the present invention.

[0026] The semiconductor device 100 of the present invention is manufactured by the following procedure. First, a Ni coating 7 is formed on the surface of the conductor plate 2. Next, the Ni coating 7 in the area that will be in close contact with the resin member 9 is roughened to form a Ni coating 7a. Furthermore, a flat Ni coating 7b is formed in the area that will be in close contact with the solder, so that the surface roughness of the Ni coating 7 in the area that will be in close contact with the solder is smaller than the surface roughness of the roughened Ni coating 7a. The semiconductor element 1 and the conductor plate 2 are then bonded together using solder that is primarily composed of Sn and has a Cu content of 4% by weight to 6% by weight, and the bonded semiconductor element 1 and conductor plate 2 are then sealed with the resin member 9 by transfer molding. This completes the semiconductor device 100 of the present invention. The cooling function of the semiconductor device 100 is ensured by adhering a cooling fin to the conductor plate 2 exposed from the resin member 9 via an insulating resin (not shown).

[0027] The high-temperature reliability of the configuration examples of the present invention and comparative examples was evaluated. First, as a first evaluation test, a temperature cycle test was conducted in which temperature changes from -40°C to 200°C were performed 1000 cycles to evaluate thermal fatigue failure. After the test, a bonding ratio of 80% or more was evaluated as ◯ (pass), and a bonding ratio of less than 80% was evaluated as × (fail). Next, as a second evaluation test, the sample was held at 200°C for 1000 hours, and the interfacial stability of the solder joint 3 was evaluated by checking whether the Ni coating 7 of the conductor plate 2 that was in close contact with the solder joint 3 was lost. If the Ni coating 7 was not lost, it was evaluated as ◯ (pass), and if it was lost, it was evaluated as × (fail).

[0028] For Example 1-9 of the present invention shown in Fig. 10(a), the above two types of evaluation tests were conducted and both passed, confirming that high-temperature reliability was obtained. On the other hand, for Comparative Example 1-12 shown in Fig. 10(b), at least one of the first and second evaluation tests failed, confirming that high-temperature reliability was not obtained.

[0029] In the first evaluation test, comparative examples 1, 4, 7, and 10 all failed because peeling occurred between the Ni coating 7 of the 5 μm-thick conductor plate 2 and the resin member 9, causing cracks to develop due to increased strain in the solder joint 3. Subsequently, in the second test, of comparative examples 1, 4, 7, and 10, comparative examples 1 and 4 passed because the Ni coating 7 of the conductor plate 2 remained, but comparative examples 7 and 10 also failed because the Ni coating 7 of the conductor plate 2 disappeared in the second test.

[0030] In the first evaluation test, Comparative Examples 2, 3, 5, 6, 8, 9, 11, and 12 all passed because no peeling occurred between the resin member 9 and the Ni coating 7 of the conductor plate 2, but all failed in the second evaluation test because the Ni coating 7 of the conductor plate 2 reacted with the solder and disappeared. In this way, it was verified that the configuration of the solder joint 3 of the present invention has a significant effect on thermal fatigue fracture and interface stability of the solder joint 3.

[0031] According to the embodiment of the present invention described above, the following advantageous effects are achieved.

[0032] (1) A semiconductor device 100 includes a semiconductor element 1 and a conductor plate 2 joined to the semiconductor element 1 by solder, the semiconductor element 1 and the conductor plate 2 being sealed with a resin member 9, the solder being mainly composed of Sn and having a Cu content of 4% by weight or more and 6% by weight or less, a Ni coating 7 formed on the surface of the conductor plate 2, the Ni coating 7 in the region that comes into close contact with the resin member 9 is roughened, and the surface roughness of the Ni coating 7 in the region that comes into close contact with the solder is smaller than the surface roughness of the roughened Ni coating 7. This ensures thermal reliability at the solder joint 3.

[0033] (2) A method for manufacturing a semiconductor device 100 is adopted in which a Ni coating 7 is formed on the surface of a conductor plate 2, a region of the Ni coating 7 that comes into close contact with a resin member 9 is roughened, and the surface roughness of the Ni coating 7 in the region that comes into close contact with solder is formed to be smaller than the surface roughness of the roughened Ni coating 7, the semiconductor element 1 and the conductor plate 2 are joined using solder that is mainly composed of Sn and has a Cu content of 4% by weight or more and 6% by weight or less, and the joined semiconductor element 1 and conductor plate 2 are sealed with a resin member 9. In this way, a semiconductor device 100 can be provided that ensures thermal reliability at the solder joints 3.

[0034] (3) The resin member 9 does not contain Sb in the portion that is in close contact with the Ni coating 7. This makes it possible to suppress reaction at the interface between the resin member 9 and the Ni coating 7a, thereby ensuring reliability.

[0035] (4) The thickness of the area of ​​the Ni coating 7 that is in close contact with the solder is 5 μm or more, which prevents the flat Ni coating 7b from disappearing.

[0036] The present invention is not limited to the above-described embodiments, and various modifications and combinations of other configurations are possible without departing from the spirit of the present invention. Furthermore, the present invention is not limited to those having all of the configurations described in the above-described embodiments, and includes those in which some of the configurations are omitted. [Explanation of symbols]

[0037] 1. Semiconductor element 2 Conductor plate 3 Solder joints 4 Solder mother phase 5 Cu-Sn compounds 6 Ni-based electrode 7 Ni coating 7a Roughened Ni coating 7b Flat Ni coating 9 Resin parts 100 Semiconductor device 101 Crack

Claims

1. A semiconductor element; a conductor plate joined to the semiconductor element by soldering, the semiconductor element and the conductor plate are sealed with a resin member, The solder is mainly composed of Sn and has a Cu content of 4% by weight or more and 6% by weight or less, The conductor plate has a Ni coating formed on its surface, The Ni coating is subjected to a roughening treatment in a region of the Ni coating that is in close contact with the resin member, The surface roughness of the Ni coating in the region that is in close contact with the solder is smaller than the surface roughness of the Ni coating that has been roughened. Semiconductor device.

2. A method for manufacturing a semiconductor device including a semiconductor element and a conductor plate, forming a Ni coating on the surface of the conductor plate; A region of the Ni coating that is in close contact with a resin member is subjected to a roughening treatment, and the surface roughness of the Ni coating in a region that is in close contact with a solder is formed so as to be smaller than the surface roughness of the roughened Ni coating; The semiconductor element and the conductor plate are joined using the solder containing Sn as a main component and having a Cu content of 4% by weight or more and 6% by weight or less; The joined semiconductor element and the conductive plate are sealed with the resin member. A method for manufacturing a semiconductor device.

3. The resin member does not contain Sb in the portion that comes into close contact with the Ni coating. The semiconductor device according to claim 1 .

4. The thickness of the Ni coating in the area that is in close contact with the solder is 5 μm or more. The semiconductor device according to claim 1 .

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