JP6033011B2 - Power semiconductor device and method for manufacturing power semiconductor device - Google Patents

Description

  The present invention relates to a power semiconductor device, and more particularly to a configuration of a power semiconductor device in which an electrode terminal is bonded to an electrode of a power semiconductor element by ultrasonic bonding and a manufacturing method thereof.

  In a power semiconductor device, an aluminum wire bond connecting an electrode on the surface of a power semiconductor element and an electrode terminal has been used in order to pass a current through the power semiconductor element. However, since the wire diameter is limited, it is necessary to increase the number of wires in accordance with the current. However, as the power semiconductor element becomes smaller and larger in capacity, the number of wires necessary to energize the electrodes is wired. It has become difficult to do. For this reason, it is conceivable to solder the electrode terminal to the electrode. However, there is a problem that the electrode surface needs to be treated in order to cope with the solder or that the bonding reliability decreases as the operating temperature increases. there were.

  As a method for solving these problems, a method in which an electrode terminal is directly ultrasonically bonded to an electrode of a power semiconductor element can be considered. Thereby, the surface treatment of an electrode is unnecessary and it can respond also to high temperature.

  However, ultrasonic bonding is performed by ultrasonically vibrating the material to be bonded with an ultrasonic horn to remove the oxide film formed on the bonding interface and adhering dirt and bringing the new surfaces into close contact with each other. This is a technique for forming a bonding layer. For this reason, if the types of materials to be joined are different, the material having the lower hardness is unilaterally plastically deformed, so that it is possible that the necessary joining strength cannot be obtained. On the other hand, materials having different hardnesses such as aluminum are used for the surface electrode of the power semiconductor element used in a general power semiconductor device and copper is used for the electrode terminal. Therefore, a technique (for example, see Patent Document 1 or 2) for increasing the bonding strength of materials having different hardnesses by coating the surface of a material having a high hardness with a material having a lower hardness than that material for bonding electrode terminals. It can be applied.

JP-A-60-206054 (Page 273, upper left column to page 273, lower left column) JP-A-8-252679 (paragraphs 0014 to 0016, FIGS. 1 to 2)

  However, the above-described technique is a technique corresponding to a case where the difference in hardness between the materials to be bonded is too large, or a case where the hardness of the member that comes into contact with the ultrasonic horn when the aluminum wire is bonded to a hard material is low. . Therefore, the material having high hardness is coated with a material having a hardness higher than that of the material having low hardness, and damage to the member on the lower hardness side is not considered. Therefore, if the above-described technique is applied as it is to the junction between the electrode of the power semiconductor element and the electrode terminal, the transistor formed on the electrode side of the power semiconductor element on the base side or the power semiconductor element itself may be destroyed. It is difficult to obtain a power semiconductor device with high reliability.

  The present invention has been made to solve the above-described problems, and an object thereof is to obtain a highly reliable power semiconductor device that can handle a large current.

A power semiconductor device according to the present invention includes a circuit board having a circuit surface formed on one surface, a power semiconductor element having a back surface bonded to the circuit surface side of the circuit board, and an electrode formed on the surface, The power semiconductor element is made of a material having a higher proof strength than the main constituent material of the electrode, and a joint surface facing the electrode of the power semiconductor element is formed at one end, and the joint surface is interposed through a buffer member. An electrode terminal that is ultrasonically bonded to the electrode of the power semiconductor element, and the buffer member has at least a portion of the material in contact with the electrode of the power semiconductor element of the electrode of the power semiconductor element. It has a proof strength equal to or less than that of the main constituent material, and the bonding surface and the electrode of the power semiconductor element are spaced apart from each other between the bonding surface and the electrode of the front power semiconductor element via the buffer member. To it It is characterized by having a bonding layer.
A method for manufacturing a power semiconductor device according to the present invention includes a step of fixing a circuit board having a back surface of a power semiconductor element bonded to a circuit surface to an ultrasonic bonding apparatus, and an electrode of the power semiconductor element. The material of the portion in contact with the electrode of the semiconductor element for power use has a higher strength than the main constituent material of the electrode of the power semiconductor element and the buffer member having a proof strength equal to or less than the main constituent material of the electrode of the power semiconductor element A step of sequentially stacking electrode terminals made of a material, a horn of the ultrasonic bonding apparatus from the opposite side of the bonding surface of the electrode terminals, and the buffer of the electrode of the power semiconductor element and the electrode terminal It includes a step of ultrasonic bonding through the member, wherein the thickness of the buffer member before the step of bonding ultrasound is performed is thicker than the electrode of the power semiconductor device, the thin from the electrode terminal In the ultrasonic bonding step, the bonding surface and the electrode of the power semiconductor element are bonded to each other between the bonding surface and the electrode of the power semiconductor element via the buffer member in a state where the bonding surface and the electrode of the power semiconductor element are separated from each other. A layer is formed .
Further, at least one electrode of the power semiconductor element is formed on at least one surface of the bonding surface of the electrode terminal composed of a material having higher proof strength than the main constituent material of the electrode of the power semiconductor element and the electrode of the power semiconductor element. Forming a buffer member having a proof strength equal to or less than that of the main component material of the electrode of the power semiconductor element, and a circuit board in which the back surface of the power semiconductor element is bonded to the circuit surface. A step of fixing to the ultrasonic bonding apparatus; a step of overlapping the electrode terminal on the electrode of the power semiconductor element; and a horn of the ultrasonic bonding apparatus from the opposite side of the bonding surface of the electrode terminal, Ultrasonically bonding the electrode of the element and the electrode terminal via the buffer member, and the thickness of the buffer member before the ultrasonic bonding step is performed Thicker than the electrode of the semiconductor element, the electrode rather thin from the terminal, the step of joining ultrasound, electrodes of the joining surface and the power semiconductor element, in a spaced apart condition, the bonding surface via the cushioning member And a bonding layer formed between each of the electrodes of the power semiconductor element .

  According to the present invention, since the electrode terminal can be firmly joined to the power semiconductor element without damaging the power semiconductor element, a highly reliable power semiconductor device corresponding to a large current can be obtained. .

It is a fragmentary sectional view for demonstrating the structure of the power semiconductor device concerning Embodiment 1 of this invention. It is sectional drawing in each process of the junction part of the power semiconductor element and electrode terminal for demonstrating the manufacturing method of the power semiconductor device concerning Embodiment 1 of this invention. It is a fragmentary sectional view for demonstrating the structure of the power semiconductor device of a comparative example. It is sectional drawing in each process of the junction part of the power semiconductor element and electrode terminal for demonstrating the manufacturing method of the power semiconductor device of a comparative example. It is a fragmentary sectional view for demonstrating the structure of the power semiconductor device concerning Embodiment 2 of this invention. It is sectional drawing in each process of the junction part of the power semiconductor element and electrode terminal for demonstrating the manufacturing method of the power semiconductor device concerning Embodiment 2 of this invention.

Embodiment 1 FIG.
1 and 2 are diagrams for explaining the configuration of the power semiconductor device according to the first embodiment of the present invention. 1 is a partial cross-sectional view of a power semiconductor device, FIG. 2 is a partial cross-sectional view in each step of a joint portion between a power semiconductor element and an electrode terminal, and FIG. 2A is an electrode to be joined to the power semiconductor element. FIG. 2B shows a state in which the terminal is placed, FIG. 2B shows a state in the middle of joining using an ultrasonic horn, and FIG. 2C shows a state when the ultrasonic joining is completed. FIGS. 3 and 4 are for explaining the configuration of the power semiconductor device of the comparative example, and correspond to FIGS. 1 and 2 used for explaining the power semiconductor device according to the first embodiment, respectively.

  Note that in the drawings used in this embodiment and other embodiments, the same or similar components are denoted by the same reference numerals. In each of the drawings, the size and scale of each corresponding component are independent. For example, in the cross-sectional view in which a part of the configuration is changed, in the illustration of the same component that is not changed, the size of the same component And the scale may be different. In addition, although the configuration of the power semiconductor device actually includes a plurality of members, only the portions necessary for the description are shown and the other portions are omitted for the sake of simplicity. For example, other wiring members or cases).

  As shown in FIG. 1, in the power semiconductor device 100 according to the first embodiment of the present invention, the circuit board 5 on which the circuit patterns 52a and 52b are formed on both sides of the insulating base 51 has a heat radiation surface side (circuit The heat dissipating member 6 is joined to the pattern 52b side) by the solder 8, and the back surface of an IGBT 1 (Insulated Gate Bipolar Transistor), which is a power semiconductor element, is joined to the circuit surface side (circuit pattern 52a side) by the solder 7. . The electrode terminal 3 is ultrasonically bonded to the surface electrode 2 formed on the surface of the IGBT 1 via the buffer member 4. Details will be described below.

  A plurality of transistors 11 are formed under the surface electrode 2 of the IGBT 1. The IGBT 1 is a vertical semiconductor element, and an electrode (back surface electrode 12) is formed not only on the front surface side but also on the back surface side. However, since the problem to be solved by the present invention is to suppress damage on the front electrode 2 side, the structure on the back electrode 12 side is simplified, and the circuit pattern 52a of the circuit board 5 is joined to the circuit pattern 52a by the solder 7 in the figure. It expresses only that

  The IGBT 1 is a power semiconductor element that constitutes an inverter, a converter, and the like. The power semiconductor device 100 according to the present embodiment only needs to be configured by at least one power semiconductor element, but an IGBT or a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is connected in reverse parallel to the diode. It is preferable. The material of the IGBT 1 is silicon (Si), silicon carbide (SiC), gallium nitride (GaN) -based material, etc., but wide band gap semiconductor materials such as SiC, GaN-based material, and diamond compared to Si The area using the surface electrode 2 with respect to the rated current is smaller in the element using the material called. Therefore, a power semiconductor element using a wide band gap semiconductor material is required to have a higher-density wiring technique than Si.

  Therefore, in the power semiconductor device 100 using, for example, SiC as a wide band gap semiconductor material, the advantages of the present invention in which a large area is bonded at a time by ultrasonically bonding the electrode terminal 3 to the surface electrode 2 are more advantageous. Prominently appear. On the other hand, even when general Si is used as the material of the IGBT 1, one element is required compared to the wire bond when the rated current is 100 A or more or when the element size is 10 mm × 10 mm or more. It is preferable because the tact time can be shortened and the merit of the present invention becomes more effective. In addition, as the thickness of the element increases, the chip itself is less likely to break due to pressurization and ultrasonic vibration during ultrasonic bonding. Therefore, the thickness of the IGBT 1 is preferably 0.1 mm or more.

  The surface electrode 2 is a metal film for electrode wiring formed on the surface of the IGBT 1. Generally, aluminum (Al) is used as the material of the surface electrode 2, but the hardness of the surface electrode 2 is higher than that of Al if Al alloy such as AlSi or AlCu, Cu, Cu alloy or the like is used. It becomes difficult to be deformed during ultrasonic bonding. In that case, even if the same aluminum as the main constituent material of the surface electrode 2 is used for the buffer member 4, the buffer member 4 is deformed preferentially over the surface electrode 2 as will be described later. The effect of can be demonstrated.

  In addition, the surface electrode 2 may have a metal coating layer such as Ti, Mo, Ni, Au, or the like formed on, for example, an aluminum layer serving as a base layer. Even in this case, when the thickness of these coating layers is smaller than the thickness of the underlayer, the overcoat layer is displaced to the surroundings during ultrasonic bonding in conjunction with the movement of the underlayer. Therefore, when the thickness of these coating layers is less than 50% of the thickness of the foundation layer, the surface electrode 2 behaves according to the hardness of the foundation layer (aluminum) regardless of the hardness of the coating layer. Will show.

  If the deformation of the surface electrode 2 during ultrasonic bonding is large, the transistor 11 formed under the surface electrode 2 may be affected. Therefore, in order to suppress damage (destruction) of the transistor 11 at the time of bonding, the thickness of the surface electrode 2 is preferably as thick as possible, and is preferably 0.07 mm or more.

  The electrode terminal 3 is a wiring member for electrically connecting the surface electrode 2 of the IGBT 1 and an external circuit. The material of the electrode terminal 3 is preferably a metal having a low electrical resistance, and generally a material obtained by pressing a plate material such as Cu or Al is used. A joining surface 3j with the surface electrode 2 is formed at one end, and the other end side. Are electrically connected to other circuit members and external circuits. Therefore, a material having rigidity is used so that the shape itself can be maintained, and a material harder than the surface electrode 2 is often used even if it is the same aluminum-based material. In order to increase the current that can be energized, it is preferable that the electrode terminal 3 has a large cross-sectional area, but the power applied during ultrasonic bonding is applied to the object to be bonded (in this embodiment, the buffer member 4 and the surface electrode 2). In order to be easily transmitted, it is preferable that the thickness is small. Therefore, it is preferable that the plate material constituting the electrode terminal 3 or at least the joining surface 3j portion facing the surface electrode 2 has a thickness of about 0.1 mm to 1.0 mm and a width of about 1.0 mm to 5.0 mm.

  The buffer member 4 is deformed preferentially over the surface electrode 2 and the electrode terminal 3 during ultrasonic bonding, and is ultrasonically bonded to each of the surface electrode 2 and the electrode terminal 3. The buffer member 4 may be any material that can be energized, but must be preferentially deformed over the surface electrode 2 and the electrode terminal 3 by pressure and vibration applied during ultrasonic bonding. Therefore, it is necessary that the material to be joined (surface electrode 2 and electrode terminal 3) has a hardness equal to or lower than that of the material having low hardness (surface electrode 2). In general, the difference in hardness is often specified by the difference in Vickers hardness, etc., but whether or not deformation is easy during ultrasonic bonding is determined by whether or not plastic strain is likely to occur, that is, by yield strength. It is better to do. In addition, as described above, the behavior of the surface electrode 2 during ultrasonic bonding reflects the state of the base occupying more than half of the thickness than the state of the outermost coating layer. Therefore, the characteristic of the buffer member 4 is defined as that the main constituent material has a yield strength (0.2% yield strength) equal to or less than that of the surface electrode 2. Thereby, plastic strain (deformation) can be generated in the buffer member 4 before the surface electrode 2 and the electrode terminal 3.

  Note that the proof stress referred to here is used to define the yield strength of a material having no clear yield point in a material test, and is a stress (0) that causes an influence strain of 0.2%. .2% yield strength).

  For example, when pure Al (proof strength: 30 to 150 MPa, Hv: 10 to 50) is used for the surface electrode 2 and oxygen-free copper (proof strength: 200 to 355 MPa, Hv: 50 to 120) is used for the electrode terminal 3, the buffer member 4 is used. As the material, a material having a proof strength of pure Al (proof strength: 30 to 150 MPa, Hv: 10 to 50) or less is selected.

  In addition, the buffer member 4 is thinly deformed by pressurization and vibration applied during ultrasonic bonding, but the buffer member 4 is too thick so as not to be deformed and discharged from between the surface electrode 2 and the electrode terminal 3. It is necessary to set to an appropriate value in consideration of the amount of deformation by sonic bonding. Specifically, it is preferable to make it thicker than the thickness of the surface electrode 2. On the other hand, if the thickness of the buffer member 4 is too thick, the power applied at the time of ultrasonic bonding is not transmitted to the contact surface between the surface electrode 2 and the buffer member 4, and a sufficient bonding area may not be obtained. . Therefore, the thickness of the buffer member 4 is preferably in the range of about 0.05 mm to 0.5 mm and thinner than the thickness of the electrode terminal 3.

  Further, the buffer member 4 may be integrated with the electrode terminal 3 before the bonding step by ultrasonic bonding to the electrode terminal 3 in advance by bimetal. Here, since the buffer member 4 can obtain the same effect even with the same material (equivalent or less proof stress) as the surface electrode 2 and the electrode terminal 3, for example, the material of the electrode terminal 3 of the first embodiment is Al. However, the same effect can be obtained. When the proof stress differs depending on the surface, such as bimetal, the proof strength of at least the portion facing the surface electrode 2 is, for example, aluminum on the surface electrode 2 (Al) side and copper material on the electrode terminal 3 (Cu) side. What is necessary is just to comprise so that it may become below the yield strength of the surface electrode 2. FIG.

  Next, the effect and the manufacturing method of the power semiconductor device 100 configured as described above will be described with reference to a cross-sectional view in the vicinity of a joint portion for each step of FIG.

  First, as shown in FIG. 2A, the buffer member 4 and the electrode terminal 3 are placed on the surface electrode 2 of the IGBT 1. At this time, the entire circuit board 5 on which the IGBT 1 is mounted is fixed to the ultrasonic bonding apparatus, but only the IGBT 1 and the electrode terminal 3 are shown in the figure. Then, the ultrasonic horn 50 is lowered (z direction) so that the tip contacts a predetermined position on the upper surface 3z of the electrode terminal 3.

  Next, as shown in FIG. 2B, the ultrasonic horn 50 is pressurized against the electrode terminal 3 and further ultrasonically vibrated in the direction of the arrow (in the xy plane). The frequency at this time is, for example, several tens KHz, and the ultrasonic horn 50 is lowered while being vibrated. As a result, the contact surfaces of the surface electrode 2 and the buffer member 4 and the electrode terminals 3 and the buffer member 4 are slid to remove a film or the like that inhibits bonding, such as an oxide film covering the contact surface. . The protruding portion of the ultrasonic horn 50 bites into the upper surface 3z portion of the electrode terminal 3. The buffer member 4 is stretched mainly in the vibration direction (xy) by the pressurization and ultrasonic vibration by the ultrasonic horn 50, and in particular, the portion below the protrusion of the ultrasonic horn 50 is thinly deformed.

Finally, as shown in FIG. 2 (c), the surface electrode 2 and the buffer member 4, and the electrode terminal 3 and the buffer member 4 are bonded to each other by ultrasonic vibration so that the strong bonding layer J _2-4 , J _3-4 are formed. At this time, the buffer member 4 is further deformed and thinly stretched, but since the surface electrode 2 is not deformed, the transistor 11 is not destroyed.

  When the power semiconductor device 100 configured as described above is operated, a current flows through the IGBT 1 to generate heat. At this time, the surface electrode 2 and the electrode terminal 3 of the IGBT 1 are firmly joined via the buffer member 4, and the transistor 11 formed below the surface electrode 2 operates normally without being damaged. can do. Therefore, the IGBT 1 operates efficiently, and there is no extra power loss due to wiring members or poor bonding. As a result, heat generation due to power loss is small and stable operation is possible.

Here, a power semiconductor device according to a comparative example in which the buffer member is joined without being inserted between the surface electrode and the electrode terminal will be described with reference to FIGS. 3 and 4.
In the power semiconductor device 100 </ b> C according to the comparative example, as illustrated in FIG. 3, the surface electrode 2 and the electrode terminal 3 of the IGBT 1 are directly joined without the buffer member 4 interposed therebetween. Other configurations are the same as those of the power semiconductor device 100 according to the first embodiment.

  In this case, as shown in FIG. 4A, the electrode terminal 3 is placed on the surface electrode 2 without inserting the buffer member 4, and ultrasonic bonding is started. And it joins as shown in FIG.4 (b) on joining conditions (pressing force, deformation amount, etc.) required in order to obtain sufficient joining area at the time of ultrasonic joining. Then, since the proof stress of the surface electrode 2 is smaller than that of the electrode terminal 3, the surface electrode 2 is unilaterally deformed by pressurization and ultrasonic vibration by the ultrasonic horn 50. At this time, since the actual thickness of the surface electrode 2 is too thin compared to the amount of deformation of the surface electrode 2, a part of the surface electrode 2 is discarded, and even the transistor 11 formed thereunder is destroyed. Is done.

  When the bonding further proceeds, the electrode terminal 3 comes into contact with the base material of the IGBT 1 as shown in FIG. 4C, and in some cases, the crack K1 is generated and the IGBT 1 itself may be destroyed.

  On the other hand, in the power semiconductor device 100 according to the first embodiment of the present invention described above, the buffer member 4 is inserted between the surface electrode 2 and the electrode terminal 3. Therefore, since the buffer member 4 is selectively deformed during ultrasonic bonding, it is not necessary to consider the difference in hardness between the surface electrode 2 and the electrode terminal 3. Therefore, the range of selection of the material used for the surface electrode 2 and the electrode terminal 3 can be expanded.

  Further, no matter how large the difference in the proof stress between the electrode terminal 3 and the surface electrode 2, the surface electrode 2 and the electrode terminal 3 can be joined without destroying the IGBT 1 or the transistor 11 immediately below the surface electrode 2, and a buffer member Since the transistors 4 are selectively deformed and bonded along the unevenness in which the transistor 11 is formed, a larger bonding area than the conventional bonding can be obtained. Furthermore, since the buffer member 4 may be inserted as a separate member between the surface electrode 2 and the electrode terminal 3, it is not necessary to use vapor deposition or plating, and can be easily adjusted to a required thickness. Therefore, by adjusting the thickness of the buffer member 4, power can be efficiently applied during ultrasonic bonding, and a sufficient bonding area can be obtained to pass a target current.

  Further, with respect to the thermal stress caused by the operation of the IGBT 1, since the buffer member 4 is preferentially deformed, the destruction of the IGBT 1 and the transistor 11 due to the thermal stress can be prevented.

  The buffer member 4 may have any shape as long as it satisfies the above functions. However, the width (cross-sectional area) varies along the thickness direction, for example, a wire or a sphere having a circular cross section. The shape is preferred. By adopting such a shape, the narrow portion is deformed so as to be crushed and expanded during ultrasonic bonding, and a film that inhibits bonding such as an oxide film is gradually discharged to the surroundings. The bonded area can be increased. Similarly, by adopting a shape in which the protrusion is arranged at a desired position of the buffer member 4, in addition to the above effects, preferential deformation is possible with a lower load and damage to the surface electrode 2 is achieved. Can be reduced.

  Further, by preliminarily bonding the buffer member 4 to the surface electrode 2 or the electrode terminal 3, positioning when placing each member can be facilitated. For example, an Al wire is previously bonded to the surface electrode 2 of the IGBT 1 as the buffer member 4, and the electrode terminal 3 is placed thereon to perform ultrasonic bonding so that positioning can be performed easily. Furthermore, since the cross section of the wire changes along the thickness direction, the Al wire is deformed in stages, so that the bonding area can be increased as compared with the case where a flat plate is used.

  As described above, according to the power semiconductor device 100 of the first embodiment of the present invention, the circuit board 5 having the circuit surface formed on one surface and the back surface is bonded to the circuit surface side of the circuit substrate 5. IGBT1, which is a power semiconductor element having an electrode (surface electrode 2) formed on the surface, and a higher yield strength than the main constituent material (for example, Al) of the electrode (surface electrode 2) of the power semiconductor element (IGBT1) A joint surface 3j that is made of a material (for example, Cu) and that faces the electrode (surface electrode 2) of the power semiconductor element (IGBT1) is formed at one end, and the joint surface 3j is connected to the power via the buffer member 4. The electrode (surface electrode 2) of the semiconductor element (IGBT1) and the electrode terminal 3 ultrasonically bonded are provided, and the buffer member 4 contacts at least the electrode (surface electrode 2) of the power semiconductor element (IGBT1). Partial Fee, since it is configured to have a main component material and equal to or less than the yield strength of the electrode (surface electrode 2) of the power semiconductor element (IGBT 1), the buffer member 4 is selectively plastically deformed during ultrasonic welding. As a result, the surface electrode 2 can be joined without unilateral plastic deformation, so that the transistor 11 formed on the surface side of the power semiconductor element (IGBT1) and the element itself are prevented from being destroyed during ultrasonic joining, A highly reliable power semiconductor device 100 that can handle a large current can be obtained. Furthermore, sufficient joining area can be obtained by joining the surface electrode 2 and the buffer member 4 and joining the electrode terminal 3 and the buffer member 4 well.

Embodiment 2. FIG.
In the power semiconductor device according to the second embodiment, a protrusion is formed on the bonding surface of the electrode terminal as compared with the first embodiment. 5 and 6 are diagrams for explaining the configuration of the power semiconductor device according to the second embodiment of the present invention. 5 is a partial cross-sectional view of the power semiconductor device, FIG. 6 is a partial cross-sectional view in each step of the power semiconductor element and the electrode terminal portion, and FIG. 6A shows the electrode terminal to be bonded to the power semiconductor element. 6B is a state in the middle of joining by applying an ultrasonic horn, and FIG. 6C is a state when the ultrasonic joining is completed. This corresponds to FIGS. 1 and 2 used in the description of the power semiconductor device. Although the shape of the buffer member may be adjusted in accordance with the protrusion, the other configuration is basically the same as that described in the first embodiment, and the description thereof is omitted.

  As shown in FIG. 5, in the power semiconductor device 200 according to the second embodiment, the protrusion 3p is formed on a part of the joint surface 3j of the electrode terminal 3, and the buffer member 4 exists around the protrusion 3p. In addition to the bonding layer between the surface electrode 2 and the buffer member 4 and the electrode terminal 3 and the buffer member 4, the bonding layer between the surface of the protrusion 3 p of the electrode terminal 3 and the surface electrode 2 is provided.

  The number and shape of the protrusions 3p formed on the electrode terminal 3 are determined in consideration of the required bonding area between the electrode terminal 3 and the surface electrode 2. The height of the protrusion 3p may be equal to or less than the thickness of the buffer member 4, but it is desirable that the height of the projection 3p be further reduced in view of the fact that the thickness of the buffer member 4 becomes thinner due to deformation during joining. When the height of the protrusion 3p is equal to the thickness of the buffer member 4, the protrusion 3p comes into contact with the surface electrode 2 before the ultrasonic bonding, and the protrusion 3p deforms the surface electrode 2 as the bonding proceeds. This is because there is a possibility that the transistor 11 is destroyed. Therefore, it is preferable that the height of the protrusion 3p is lower than the thickness of the buffer member 4 (outer edge portion thereof) to the extent that the buffer member 4 is rejected from the tip of the protrusion 3p at the time of joining.

  Further, the arrangement of the protrusion 3p in the bonding surface 3j is such that the bonding layer of the surface electrode 2 and the buffer member 4 and the electrode terminal 3 and the buffer member 4 surrounds the protrusion 3p in consideration of mechanical bonding strength. It is desirable to make it. Therefore, the area of the protrusion 3p is preferably about 30 to 70% of the smaller area of the surface electrode 2 or the electrode terminal 3 (joint surface 3j thereof) or the entire area of the buffer member 4. In the second embodiment, one protrusion is formed at the center of the joint surface of the electrode terminal 3 as the protrusion 3p. However, the shape of the protrusion 3p is not limited to the cylindrical shape, and may be a prism or the like. It doesn't matter. Similarly, a plurality of the projections 3p may be formed, but the projection 3p is preferably arranged so that the opposing surface can be supported so that the electrode terminal 3 does not tilt when pressed by the ultrasonic horn 50.

  Next, the effect and the manufacturing method of the power semiconductor device 200 according to the second embodiment will be described with reference to the cross-sectional view in the vicinity of the joining portion for each step in FIG.

  First, as shown in FIG. 6A, the buffer member 4 and the electrode terminal 3 are placed on the surface electrode 2 of the IGBT 1, and ultrasonic waves are applied so that the tip contacts a predetermined position on the upper surface 3z of the electrode terminal 3. The horn 50 is lowered (z direction). Here, in the buffer member 4 according to the second embodiment, the concave portion 4c is formed so as to correspond to the shape of the projection 3p and the portion corresponding to the projection 3p is thinner than the peripheral portion. The shape of the buffer member 4 is not necessarily matched with the shape corresponding to the protrusion 3p. However, for example, if the protrusion 3p has a cylindrical shape and the buffer member 4 has a ring shape corresponding to the protrusion 3p, the surface electrode 2 and the protrusion 3p are surely brought into direct contact with each other by accommodating the protrusion 3p in the ring. Can do.

  Thus, when the buffer member 4 is made into a ring shape, the buffer member 4 surrounds the protrusion 3p in the extending direction (xy plane) of the joint surface. Then, a strong bonding layer using the buffer member 4 can be formed on the outer peripheral portion (peripheral portion) where deformation is large and thermal stress is generated. Furthermore, since the buffer member 4 can be handled from the outer peripheral side, positioning of the buffer member 4 is facilitated. Therefore, it is preferable that the buffer member 4 has a shape surrounding the protrusion 3p like a ring.

  If the protrusion 3p is in contact with the surface electrode 2 in the stage before ultrasonic bonding in FIG. 6A, the electrode terminal 3 (protrusion 3p) at the time of bonding as in the comparative example of the first embodiment. However, the surface electrode 2 may be deformed and the transistor 11 may be destroyed. Therefore, it is preferable that the protrusion 3p is not in contact with the surface electrode 2 in the stage of FIG. For that purpose, it is necessary to adjust the relationship between the thickness of the buffer member 4 and the height of the protrusion 3p, but in order to suppress damage by adjusting only the height, it is necessary to increase the accuracy of the deformation amount at the time of joining. There is. Therefore, in the second embodiment, after adjusting the height relationship, the concave portion 4c is left with a thickness that can be easily eliminated by the peripheral edge as the joining progresses.

  And as shown in FIG.6 (b), the ultrasonic horn 50 is pressurized with respect to the electrode terminal 3, and ultrasonically vibrates in the direction of an arrow (in xy plane). As a result, the contact surfaces of the surface electrode 2 and the buffer member 4 and the electrode terminals 3 and the buffer member 4 are slid to remove a film or the like that inhibits bonding, such as an oxide film covering the contact surface. . The buffer member 4 is stretched mainly in the vibration direction (xy) by the pressurization and ultrasonic vibration by the ultrasonic horn 50, and in particular, the portion below the protrusion of the ultrasonic horn 50 is thinly deformed. At this time, the buffer member 4 between the protrusion 3p and the surface electrode 2 is deformed and rejected by pressurization and ultrasonic vibration by the ultrasonic horn 50, and the protrusion from which the oxide film, the film inhibiting the bonding, and the like are removed. The tip surface of 3p and the surface electrode 2 are in direct contact.

Finally, as shown in FIG. 6 (c), the contact surfaces of the surface electrode 2 and the buffer member 4 and the electrode terminal 3 and the buffer member 4 are joined to each other by ultrasonic vibration at the peripheral portion, so that they are strong. The bonding layers J _2-4 and J _3-4 are formed. In addition, a bonding layer _J2-3 is formed by ultrasonic vibration by the surface electrode 2 and the tip surface of the protrusion 3p. Since the adjustment is made so that the bonding is completed when the protrusion 3p and the surface electrode 2 are in contact with each other, the surface electrode 2 is not deformed and the transistor 11 is not destroyed.

Thereby, the electrode terminal 3 and the surface electrode 2 are mechanically firmly joined by the joining layers J _2-4 and J _3-4 through the buffer member 4. On the other hand, the protrusion 3p portion, by direct bonding layer J _2-3 between the electrode terminals 3 and the surface electrode 2 is electrically firmly bonded. In other words, energization of the IGBT1 will be able to perform through the bonding layer _{J 2-3} of the surface electrode 2 and the protrusion 3p. Therefore, since the buffer member 4 can be selected regardless of the electrical resistivity of the material, it can be selected from more materials.

  As described above, in the power semiconductor device 200 according to the second embodiment, the protrusion 3p protruding toward the electrode (surface electrode 2) of the power semiconductor element (IGBT1) is formed on the bonding surface 3j of the electrode terminal 3. Since the surface electrode 2 and the electrode terminal 3 are directly joined to each other, it is possible to efficiently energize. Furthermore, the material choice of the buffer member 4 is expanded.

  Moreover, according to the manufacturing method of the power semiconductor devices 100 and 200 according to each of the above embodiments, the step of fixing the circuit board 5 to which the power semiconductor element (IGBT1) is bonded to the ultrasonic bonding apparatus, The step of sequentially stacking the buffer member 4 and the electrode terminal 3 on the electrode (surface electrode 2) of the semiconductor element (IGBT1), and the horn of the ultrasonic bonding apparatus from the upper surface 3z opposite to the bonding surface 3j of the electrode terminal 3 ( The ultrasonic horn 50) is applied and the electrode (surface electrode 2) of the power semiconductor element (IGBT1) and the electrode terminal 3 are ultrasonically bonded via the buffer member 4, so that the above-mentioned is included. The obtained power semiconductor devices 100 and 200 can be easily obtained.

  Moreover, according to another manufacturing method of the power semiconductor devices 100 and 200 according to the above embodiments, the electrode (surface electrode 2) of the power semiconductor element (IGBT1) is formed by, for example, wire bonding, vapor deposition, plating, or the like. And a step of forming the buffer member 4 on at least one surface of the bonding surface 3j of the electrode terminal 3, a step of fixing the circuit board 5 to which the power semiconductor element (IGBT1) is bonded to the ultrasonic bonding apparatus, The step of superimposing the electrode terminal 3 on the electrode (surface electrode 2) of the semiconductor element (IGBT1), and the horn (ultrasonic horn 50) of the ultrasonic bonding apparatus from the upper surface 3z opposite to the bonding surface 3j of the electrode terminal 3 And the step of ultrasonically bonding the electrode (surface electrode 2) and the electrode terminal 3 of the power semiconductor element (IGBT1) via the buffer member 4, so that the power described above is included. It is possible to obtain a semiconductor device 100, 200 with ease.

  In particular, the buffer member 4 is formed of a wire whose cross-sectional area changes along the thickness direction, for example, a wire, before the ultrasonic bonding process is performed. As a result, stronger bonding is possible. Further, if the buffer member 4 is formed by bonding (bonding) the wire to the surface electrode 2 or the electrode terminal 3 in advance, positioning is facilitated.

  In particular, since the thickness before the ultrasonic bonding step of the buffer member 4 is performed is configured to be thicker than the electrode (surface electrode 2) of the power semiconductor element (IGBT1), the deformability of the buffer member 4 is improved. It can be joined with higher power.

1: IGBT (power semiconductor element),
2: Surface electrode
3: Electrode terminal,
3j: bonding surface, 3p: protrusion
4: Buffer member,
5: Circuit board,
6: heat dissipation member,
50: Ultrasonic horn,
100, 200: Power semiconductor device.

Claims (6)

A circuit board having a circuit surface formed on one surface;
A power semiconductor element in which a back surface is bonded to the circuit surface side of the circuit board and an electrode is formed on the surface;
The power semiconductor element is made of a material having a higher proof strength than the main constituent material of the electrode, and a joint surface facing the electrode of the power semiconductor element is formed at one end, and the joint surface is interposed through a buffer member. An electrode terminal ultrasonically bonded to the electrode of the power semiconductor element,
The buffer member has at least a proof stress equal to or less than that of a main constituent material of the electrode of the power semiconductor element, at least a material of a portion in contact with the electrode of the power semiconductor element.
The bonding surface and the electrode of the power semiconductor element each have a bonding layer between the bonding surface and the electrode of the power semiconductor element via the buffer member in a state of being separated from each other. Semiconductor device.   2. The power semiconductor device according to claim 1, wherein a protrusion projecting toward an electrode of the power semiconductor element is formed on a bonding surface of the electrode terminal.   The power semiconductor device according to claim 1, wherein the buffer member is formed between the joint surface and an electrode of the power semiconductor element. Fixing the circuit board having the back surface of the power semiconductor element bonded to the circuit surface to the ultrasonic bonding apparatus;
A buffer member having a proof strength equal to or less than that of a main constituent material of the electrode of the power semiconductor element, at least a portion of a material contacting the electrode of the power semiconductor element, and an electrode of the power semiconductor element of the power semiconductor element A step of sequentially laminating electrode terminals made of a material having higher proof strength than the main constituent material of the electrode;
Applying the horn of the ultrasonic bonding device from the opposite side of the bonding surface of the electrode terminal, and ultrasonically bonding the electrode of the power semiconductor element and the electrode terminal via the buffer member;
Including
When the thickness of the buffer member before the step of bonding ultrasound is performed it is thicker than the electrode of the semiconductor element for electric power, rather thin from the electrode terminal,
The ultrasonic bonding step includes bonding layers between the bonding surface and the electrode of the power semiconductor element via the buffer member, with the bonding surface and the electrode of the power semiconductor element being separated from each other. Forming a power semiconductor device. Contact with at least one of the electrodes of the power semiconductor element and at least one surface of the joint surface of the electrode terminal composed of a material having higher proof strength than the main constituent material of the electrode of the power semiconductor element and the electrode of the power semiconductor element Forming a buffer member having a yield strength equal to or less than that of the main constituent material of the electrode of the power semiconductor element;
Fixing a circuit board having a back surface of the power semiconductor element bonded to a circuit surface to an ultrasonic bonding apparatus;
Superimposing the electrode terminal on the electrode of the power semiconductor element;
Applying the horn of the ultrasonic bonding device from the opposite side of the bonding surface of the electrode terminal, and ultrasonically bonding the electrode of the power semiconductor element and the electrode terminal via the buffer member;
Including
When the thickness of the buffer member before the step of bonding ultrasound is performed it is thicker than the electrode of the semiconductor element for electric power, rather thin from the electrode terminal,
The ultrasonic bonding step includes bonding layers between the bonding surface and the electrode of the power semiconductor element via the buffer member, with the bonding surface and the electrode of the power semiconductor element being separated from each other. Forming a power semiconductor device. When the thickness of the buffer member before the step of bonding ultrasound is performed, method of manufacturing the power semiconductor device according to claim 4 or 5, characterized in that in the range of 0.05 mm to 0.5 mm.

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