Clamping piece

Abstract

A clip for a semiconductor device is disclosed. At least a portion of the clip is formed of a metal foam.

Description

Technical Field

[0001] The present invention relates to a clip for a semiconductor device, a semiconductor device including the clip, and a method for manufacturing the semiconductor device. Background Art

[0002] Semiconductor assemblies, such as transistors, are manufactured as layered assemblies that include components such as a die pad, a die, a clip, and a housing. The housing provides a protective function and at least partially surrounds the die and other components that form part of the semiconductor assembly.

[0003] Semiconductor assemblies are susceptible to temperature fluctuations during use. These temperature fluctuations cause the components of the clip to expand and contract. The coefficient of thermal expansion of each component is different, and therefore each component expands and contracts by a different amount due to temperature changes. This causes internal stresses to accumulate within the components of the clip. Internal stresses are undesirable because they can cause delamination of the components of the clip. There are other reasons for delamination of the components of the clip.

[0004] There is a need to overcome the disadvantages associated with existing semiconductor assemblies and clips for semiconductor assemblies, whether or not mentioned in this document. Summary of the invention

[0005] In a first aspect of the present invention, a clip for a semiconductor device is provided, wherein at least a portion of the clip is formed of a metal foam.

[0006] In use, semiconductor devices are susceptible to temperature fluctuations, and in some applications, the temperature may exceed a range of 200°C or more. Therefore, semiconductors are generally designed to withstand temperatures as low as -65°C (or lower) and as high as 150°C (or higher). These fluctuations cause the size of the components of the device to change due to thermal expansion. The clip is generally made of a different material than the die it fixes and the solder used to fix the clip to the die. For example, the clip may be made of copper, while the die may be made of silicon and the solder may be made of an aluminum alloy. Each of these materials has a different coefficient of thermal expansion, and therefore each of the components expands and contracts at a different rate as the temperature changes. This causes stress accumulation within the component, which may cause the component to delaminate and ultimately cause the semiconductor device to fail. Conventional clips are generally made of solid copper and are therefore rigid. This reduces the ability of the clip to absorb stress in use. Because at least a portion of the clip is formed of metal foam, the clip is better able to absorb the stress it is subjected to in use. This reduces the possibility of delamination of the components of the semiconductor device of which the clip forms a part.

[0007] The semiconductor device includes a spacer covering and adhering to a clip. The clip formed of foam improves adhesion between the clip and the spacer because the spacer enters the holes defined by the foam, which provides a larger contact area between the spacer and the clip. This advantageously reduces the likelihood of separation of the spacer from the clip.

[0008] The pore size of the foam may be at least 10 μm. The pore size of the foam may be up to 100 μm.

[0009] The pore size may be up to 50 μm. The pore size may be at least 10 μm and / or up to 30 μm. The pore size may be 20 μm.

[0010] The conductivity of the clip is inversely proportional to the pore size. The flexibility of the clip is directly proportional to the pore size. With a pore size of at least 10 μm and up to 100 μm in the foam, the balance of the conductivity of the clip and the flexibility of the clip is advantageously optimized. This allows the clip to operate efficiently while reducing the likelihood of delamination.

[0011] One or more portions of the clip formed from the metal foam may have a porosity of at least 30% and / or up to 80%.

[0012] The electrical conductivity of the clip is inversely proportional to the porosity. The elasticity of the clip is directly proportional to the porosity. With a porosity of at least 30% and / or up to 80% of the clip, the balance of the electrical conductivity of the clip and the flexibility of the clip is advantageously optimized. This allows the clip to operate efficiently while reducing the likelihood of delamination.

[0013] The metal foam may be formed from copper.

[0014] The metal foam may be an open cell foam.

[0015] The foam may be a reticulated foam.

[0016] The term "net-like" may be understood to mean that the material of the clip forms a network of interconnected branches. That is, one may move from one point of the clip to any other point while maintaining contact with the clip material.

[0017] Where the foam is an open-cell foam, the clip is better able to absorb internal stresses to which the clip may be subjected in use.

[0018] The entire clip may be formed from metal foam.

[0019] In a second aspect of the present invention, a semiconductor device is provided. The semiconductor device comprises: a lead frame including a die attaching portion and a lead portion; a semiconductor die mounted on the attaching portion; and a clip according to the first aspect of the present invention. At least a portion of the clip is fixed to the semiconductor die. At least a portion of the clip is fixed to the lead portion.

[0020] The advantages discussed above in relation to the first aspect of the invention apply mutatis mutandis to this aspect.

[0021] In a third aspect of the present invention, a method for manufacturing a semiconductor device is provided. The method includes providing a lead frame. The lead frame includes a die attaching portion and a lead portion. The method also includes: attaching a semiconductor die to the die attaching portion of the lead frame; providing a first metal layer to the semiconductor die and providing a second metal layer to the lead portion; providing a clip according to the first aspect of the present invention so that a first portion of the clip contacts the first metal layer and a second portion of the clip contacts the second metal layer; and heating the clip, the first metal layer, and the second metal layer so that the first metal layer and the second metal layer melt.

[0022] The advantages discussed above in relation to the first aspect of the invention apply mutatis mutandis to this aspect.

[0023] The method may further comprise providing a cover.The cover may be provided such that it encloses the leadframe, preferably excluding the leadframe, the semiconductor die and at least a portion of any leads of the clip.

[0024] The melting of the first metal layer and the second metal layer may cause the first metal layer and the second metal layer to migrate into the clip to form the first joint and the second joint, respectively.

[0025] The first metal layer and the second metal layer may migrate into the clip by capillary action.

[0026] The first contact may include a portion disposed in the region of the first portion of the clip and a portion disposed in the region of the first metal layer. The second contact may include a portion disposed in the region of the second portion of the clip and a portion disposed in the region of the second metal layer.

[0027] The first joint and the second joint may be formed as the assembly cools.

[0028] The melting temperature of the first joint and the second joint may be at least 400°C.

[0029] In the case where the melting temperature of the first joint and the second joint is at least 400°C, the possibility of the first joint and the second joint melting while the semiconductor device is fixed to the external circuit is reduced. When the semiconductor device is fixed to the external circuit, the melting of the first joint and / or the second joint is undesirable because it may cause the strength of the joint to be reduced. Therefore, reducing the possibility of the first joint and the second joint melting reduces the possibility of short circuits and current leakage in use. Therefore, in the case where the melting temperature of the first joint and the second joint is at least 400°C, the semiconductor device obtained by this method is advantageously more reliable.

[0030] Prior to being heated, the first metal layer and the second metal layer may be formed of tin, and the clip may be formed of copper. The first joint and the second joint may be formed of a copper-tin intermetallic compound.

[0031] The first metal layer and the second metal layer may be formed of pure tin.

[0032] In the case where the metal layer is formed of tin and the clip is formed of copper, there is no need to use solder to fix the clip to the tube core and the lead frame. In addition, compared with using traditional welding materials to connect the clip to the lead frame and the tube core, the possibility of melting the first joint and / or the second joint during the assembly of the semiconductor device into an external circuit is reduced. The melting of traditional welding materials during assembly may increase the possibility of short circuits and / or current leakage during use. The remelting of traditional solder reduces the maximum peak forward surge current of the semiconductor device. Therefore, by reducing the possibility of melting the first joint and / or the second joint during the assembly of the semiconductor device into the external circuit, the maximum peak forward surge current is improved. Therefore, in the case where the metal layer is formed of tin and the clip is formed of copper, the semiconductor device obtained by this method is advantageously more reliable.

[0033] Neither the first metal layer nor the second metal layer may be formed of lead.

[0034] Lead waste may pollute the environment. In the case where both the first metal layer and the second metal layer are not formed of lead, the method is more environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

[0036] Figure 1 shows a perspective view of a semiconductor device;

[0037] Figure 2 A perspective view showing a semiconductor device according to a second embodiment of the present invention; and

[0038] Figures 3 to 5 Shows Figure 1 A side view of the assembly and manufacturing steps of a semiconductor device. DETAILED DESCRIPTION

[0039] Figure 1 The semiconductor device 2 is shown. The semiconductor device 2 includes a lead frame 4. The lead frame 4 may also be referred to as a die holder. The semiconductor device 2 includes a die 6. The semiconductor device 2 includes a clip 8. The semiconductor device 2 includes a cover (for clarity, Figure 1 not shown).

[0040] The lead frame 4 serves as a substrate for the semiconductor device 2, to which other components of the device are attached. The lead frame 4 includes a die attaching portion 3. A die 6 is fixed to the die attaching portion 3. The lead frame 4 includes a lead portion 5. The lead portion 5 includes a plurality of leads 7 ( Figure 1 1 and 1 ). The plurality of leads allow the semiconductor device 2 to be connected to an external circuit (not shown). Each portion of the lead frame 4 is generally rectangular. However, in other embodiments, the portion of the lead frame may be any suitable shape. The lead frame 4 is made of a conductive material such as copper (including copper alloys). The lead portion 5 is formed separately from the die attach portion 3. However, in some embodiments, the lead portion 5 and the die attach portion may be formed integrally.

[0041] The tube core 6 is fixed to the lead frame 4. The tube core 6 is fixed to the lead frame 4 by the first solder layer 10. Specifically, the tube core 6 is fixed to the tube core bonding part 3 of the lead frame 4 by the first solder layer 10. The tube core 6 can be a single component or can include multiple components. The tube core 6 is made of semiconductor material. The tube core 6 has a functional circuit made thereon. The tube core 6 is generally rectangular, but it can also be any other suitable shape. The tube core 6 is a plate-like shape.

[0042] The cover encapsulates the components of the semiconductor device 2 (i.e., the lead frame 4, the die 6, and the clip 8). The leads 7 of the clip 8 extend through the cover. This allows the leads 7 to be connected to an external circuit (not shown). The cover can be made of any suitable electrically insulating material (such as epoxy). The cover can also be referred to as an insulator, a housing, or an enclosure.

[0043] Clip 8 includes a first portion 9, a second portion 13, and an intermediate portion 15. Second portion 13 includes a first arm 17 and a second arm 19. However, in some embodiments, second portion 13 may include only a single arm. Intermediate portion 15 is adjacent to and disposed between first portion 9 and second portion 13. Clip 8 is fixed to die 6. Specifically, first portion 9 of clip 8 is fixed to die 6. Clip 8 is fixed to lead portion 5 of lead frame 4. Specifically, second portion 13 of clip 8 is fixed to lead portion 5 of lead frame 4. Therefore, clip 8 electrically connects die 6 and lead portion 5 of lead frame 4. Clip 8 may also be referred to as a connector.

[0044] The clip 8 is formed of metal foam. The clip 8 can be made of copper foam. In some embodiments, the clip can be formed of nickel or silver foam. However, copper is preferred for its thermal and electrical conductivity, availability, and cost. The entire clip 8 can be formed of metal foam. The foam can be open-cell or closed-cell. The foam forming the clip 8 can have a pore size of at least 10 μm and / or up to 100 μm. In some embodiments, the pore size can be up to 50 μm. In some embodiments, the pore size can be at least 10 μm and / or up to 30 μm. In some embodiments, the pore size can be 20 μm. The pore size can be selected based on the desired flexibility of the clip 8. The porosity of the clip 8 can be at least 30% and / or up to 80%. The porosity of the clip 8 can be selected based on the desired flexibility of the clip 8. Compared with the clip 8 being formed of a continuous or solid material, the clip 8 formed of foam increases the flexibility of the clip 8. This advantageously allows the clip 8 to absorb internal stresses generated due to temperature fluctuations of the semiconductor device 2 during use. The clip 8 formed of foam also better secures the cover to the clip 8. This is because the cover at least partially enters the hole of the clip 8, which increases the contact area between the clip 8 and the cover compared to when the clip 8 is made of solid material. The clip 8 is better able to absorb internal stresses, and the cover is better secured to the clip 8, which advantageously reduces the possibility of component delamination of the semiconductor device 2 in use.

[0045] exist Figure 2 In the illustrated embodiment, only the first portion 9 and the second portion 13 are formed of metal foam. Specifically, the distal regions 25, 27 of the first and second arms 17, 19 of the first and second portions 9, 13 may be formed of metal foam.

[0046] Now refer to Figures 3 to 5 Let's discuss the method of fixing the clip 8 to the lead frame 4 and the tube die 6. This method is applicable to Figure 1 The clip 8 shown and Figure 2 The clips 8 shown are both. First, refer to Figure 3, a first metal layer 20 is applied to the tube core 6. The first metal layer 20 can be applied using electroplating or sputtering. These application methods are advantageously more efficient than conventional soldering methods. This is because the electroplating or sputtering of the first metal layer 20 can occur during the assembly of other components onto the tube core 6 using the same method. The first metal layer 20 can be at least 2 μm and / or up to 10 μm thick. The thickness of the first metal layer 20 can be selected based on, for example, the desired contact area between the tube core 6 and the clip 8, the size of the clip 8 and the semiconductor device 2. A second metal layer 22 is applied to the lead portion 5 of the lead frame 4. The second metal layer 22 can be applied using electroplating. The second metal layer 22 can be at least 2 μm and / or up to 10 μm thick. The thickness of the second metal layer 22 can be selected based on, for example, the size of the clip 2 and the semiconductor device 2. The first metal layer 20 and the second metal layer 22 can be formed of tin (preferably pure tin). In some embodiments, the first metal layer 20 and / or the second metal layer 22 can be formed of indium. The materials of first metal layer 20 and second metal layer 22 may be selected based on the material from which clip 8 is made. In some embodiments, first metal layer 20 and second metal layer 22 are both lead-free.

[0047] The clip 8 is then positioned so that the first portion 9 of the clip 8 contacts the first metal layer 20 and the second portion 13 of the clip 8 contacts the second metal layer 22. The resulting assembly 24 is Figure 4 . The assembly 24 is then heated. The temperature to which the assembly 24 is heated is determined by the materials from which the first metal layer 20 and the second metal layer 22 are made. Specifically, the assembly 24 is heated to at least the melting temperature of the first metal layer 20 and the second metal layer 22. In the case where the first metal layer 20 and the second metal layer 22 are formed of tin (preferably pure tin), the temperature to which the assembly 24 is heated may be at least 232°C.

[0048] The melting of the first metal layer 20 and the second metal layer 22 causes the first metal layer 20 and the second metal layer 22 to migrate into the clip 8. The first metal layer 20 and the second metal layer 22 migrate into the clip 8 by capillary action. The first metal layer 20 and the second metal layer 22 migrate into the clip 8 in the region of the first portion 9 and the second portion 13 of the clip 8, respectively. However, it should be understood that some of the first metal layer 20 and some of the second metal layer 22 may migrate outside the first portion 9 and the second portion 13. Once the first metal layer 20 and the second metal layer 22 are melted, the assembly 24 is cooled.

[0049] Figure 5The assembly 24 after cooling is shown. The melting and cooling of the first metal layer 20 form a first joint 23. A portion of the first joint 23 is disposed in the region of the first portion 9 of the clip 8, and a portion is disposed in the region of the first metal layer 20. The first joint 23 fixes the first portion 9 of the clip 8 to the tube core 6. The first joint 23 is formed by an intermetallic compound. The intermetallic compound of the first joint 23 includes the material from which the clip 8 (before heating) is made and the material from which the first metal layer 20 (before heating) is made. The intermetallic compound of the first joint 23 is a copper-tin compound. In some embodiments, the intermetallic compound of the first joint 23 may be a nickel-tin compound, a silver-tin compound, or a copper-indium compound.

[0050] The melting and cooling of the second metal layer 22 form a second joint 26. A portion of the second joint 26 is disposed in the region of the second portion 13 of the clip 8, and a portion is disposed in the region of the second metal layer 22. The second joint 26 fixes the second portion 13 of the clip 8 to the lead portion 5 of the lead frame 4. The second joint 26 is formed by an intermetallic compound. The intermetallic compound of the second joint 26 includes the material of the manufacturing clip 8 (before heating) and the material of the manufacturing second metal layer 22 (before heating). The intermetallic compound of the second joint 26 is a copper-tin compound. In some embodiments, the intermetallic compound of the second joint 26 may be a nickel-tin compound, a silver-tin compound, or a copper-indium compound. The intermetallic compound of the second joint 26 may be the same as the intermetallic compound of the first joint 23. The intermetallic compound of the first joint 23 and the intermetallic compound of the second joint 26 may not be formed by lead or contain lead. This advantageously meets the regulations requiring lead-free semiconductor devices.

[0051] The cover 18 is then provided in a conventional manner.

[0052] Although specific embodiments of the present invention have been described above, it should be understood that the present invention may be practiced in a manner other than that described. The above description is intended to be illustrative rather than limiting. Therefore, it will be apparent to those skilled in the art that the described invention may be modified without departing from the scope of the claims set forth below.

Claims

1. A clip for a semiconductor device, at least a portion of the clip being formed from a metal foam.

2. The clip of claim 1, wherein the pore size of the foam is at least 10 μm and up to 100 μm.

3. A clip according to claim 1 or claim 2, wherein one or more portions of the clip formed from metal foam have a porosity of at least 30% and / or up to 80%.

4. A clip according to any preceding claim, wherein the metal foam is formed from copper.

5. A clip according to any preceding claim, wherein the metal foam is an open cell foam.

6. A clip according to any preceding claim, wherein the entire clip is formed from metal foam.

7. A semiconductor device comprising: A lead frame, the lead frame comprising a die attach portion and a lead portion; a semiconductor die mounted on the die attach portion; A clip as claimed in any preceding claim, at least a portion of the clip being secured to the semiconductor die and at least a portion of the clip being secured to the lead portion.

8. A method for manufacturing a semiconductor device, comprising: providing a lead frame, the lead frame comprising a die attach portion and a lead portion; attaching a semiconductor die to the die attach portion of the lead frame; providing the semiconductor die with a first metal layer and providing the lead portion with a second metal layer; Providing a clip according to any one of claims 1 to 6 such that a first portion of the clip contacts the first metal layer and a second portion of the clip contacts the second metal layer; as well as The clip, the first metal layer, and the second metal layer are heated to melt the first metal layer and the second metal layer.

9. The method of claim 8, wherein the melting of the first metal layer and the second metal layer causes the first metal layer and the second metal layer to migrate into the clip to form a first joint and a second joint, respectively.

10. The method of claim 9, wherein the melting temperature of the first joint and the second joint is at least 400°C.

11. A method according to claim 9 or claim 10, wherein before being heated, the first and second metal layers are formed of tin and the clip is formed of copper, and wherein the first and second joints are formed of a copper-tin intermetallic compound.

12. The method according to any one of claims 8 to 11, wherein neither the first metal layer nor the second metal layer is formed of lead.

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