JP4976688B2 - Joining method between heat spreader and metal plate - Google Patents

Description

  The present invention relates to a method of joining a heat spreader and a metal plate when fixing a heat spreader fixed on a semiconductor chip for heat dissipation and a metal plate as an external lead-out conductor.

  In recent years, power converters have been reduced in size and density. In order to reduce the size and increase the density of the power converter, it is necessary to improve the wiring inside the package, the package structure, the heat dissipation method, and the like. In particular, semiconductor chips such as IGBTs (Insulated Gate Bipolar Transistors), FWDs (Free Wheeling Diodes), power MOSFETs, and power bipolar transistors, which are power devices, may be used at a high current density with an increase in current and size. It is getting more.

  The problem here is an increase in heat generation density as the current density increases. For example, a semiconductor chip that has been used at a rating of 50A has been increasingly used to pass a current exceeding the rating, for example, a current of 75A, as the performance of the semiconductor chip increases. Conversely, if the same current is supplied, the area of the chip can be reduced by improving the performance of the semiconductor chip. For example, if 100 semiconductor chips of 10 mm □ can be taken out from a single wafer, the same wafer is assumed if the area is 30% smaller (about 8.4 mm □) as the performance of the semiconductor chip increases. The number of semiconductor chips that can be taken out from the wafer is about 142, and the number of semiconductor chips that can be taken per wafer is increased. In this way, if a larger amount of current can flow with a smaller semiconductor chip, the number of semiconductor chips per wafer increases, leading to cost reduction.

  Further, downsizing of a semiconductor chip has an advantage that the size of a semiconductor package configured by combining a plurality of these semiconductor chips can be reduced. For these reasons, even with the same rated current, there is a strong tendency to prefer smaller chips, and as a result, there is a current situation in which higher heat generation density is being advanced.

In power semiconductor elements such as IGBT and FWD, the upper limit of the operating temperature is often set to 125 ° C. However, the heat generation density increases with the miniaturization and high current density of the chip, and it is impossible to suppress the temperature rise of the chip surface with the conventional wiring using the aluminum wire.
This is because the aluminum wire is a thin wire having a diameter of, for example, 300 μm or 400 μm, and not only the heat generated by the chip cannot be transferred, but also the aluminum wire itself generates heat due to Joule heat generation, and sometimes melts. There is a point.

  In a semiconductor package that employs a single-sided cooling system, heat generated from a semiconductor chip can be radiated only from the lower surface of the semiconductor chip. The semiconductor package is filled with a silicone-based sealing resin for insulation protection, and the upper surface of the semiconductor chip is covered with this sealing resin. The thermal conductivity of the silicone-based sealing resin is about 0.1 to 0.2 W / mK, and heat dissipation from the upper surface of the semiconductor chip cannot be expected with this configuration.

  As a method for efficiently escaping heat from the upper surface of the semiconductor chip, a metal heat spreader is applied to the upper surface of the semiconductor chip, here the IGBT chip, by using a heat conductive resin or a solder material as shown in FIG. There has been devised a method for lowering the maximum temperature by bonding and diffusing the heat at the center of the chip, which is the highest temperature, to the periphery of the chip (for example, see Patent Document 1).

  FIG. 7 is a cross-sectional view of a main part of a conventional IGBT module. A conductive pattern lunar insulating substrate 50 having a back surface copper foil 52 fixed to the back surface of the ceramics 51 and an emitter conductor pattern 53, a collector conductor pattern 54, and a gate conductor pattern 55 fixed to the surface, and the collector conductor pattern 54 An IGBT chip 56 is fixed to the top of the IGBT chip 56 by solder 60, a heat spreader 62 is fixed to the upper surface of the IGBT chip 56 by solder 59, the heat spreader 62 and the emitter conductor pattern 53 are connected by an aluminum wire 63, and a gate on the IGBT chip 56 is connected. An aluminum wire 61 connects between the pad 58 and the gate conductor pattern 55.

  In addition, in order to perform the inverter operation, a diode is necessary in addition to this, but it is omitted in the description in this patent for the sake of simplicity. Further, the structure shown in FIG. 7 is housed in a resin case such as PPS (polyphenylene sulfide) or PBT (polybutylene terephthalate), and further filled with silicone resin as element protection. The

  FIG. 8 shows a cross-sectional view of a main part of another conventional IGBT module. The aluminum wire 61 on the heat spreader 62 is a metal plate 64 such as copper or aluminum. By using the aluminum wire 61 as the metal plate 64, the wiring resistance can be reduced, the Joule heat generation of the wiring can be reduced, and the heat generated from the semiconductor chip can be transferred.

  As a method of joining the heat spreader 62 and the metal plate 64, joining using a conductive adhesive, joining using a solder material, direct joining using ultrasonic waves, or the like can be considered.

  Patent Document 2 describes that a heat spreader (a metal plate having good conductivity) is joined on a semiconductor chip by ultrasonic welding.

  Patent Document 3 describes that a heat spreader thermally connected to a semiconductor element is welded to a printed wiring board by laser welding, and Ni plating is applied to the heat spreader.

  Patent Document 4 describes welding a copper alloy heat sink to a lead frame with a YAG laser.

  Patent Document 5 describes that a copper wire and a tungsten probe are joined by laser welding via a metal material.

Patent Document 6 describes that a low-melting-point material made of copper or aluminum and a joining clad plate made of a high-melting-point material, laser welding of the joining clad plate, and a heat spreader that is frequently used as a joint clad material. ing.
JP 2000-307058 A JP 2004-96135 A JP 2001-168244 A ([Summary] [0027]) JP 11-191607 A ([Summary] [Claim 1]) JP 2000-187043 A ([Claim 6]) Japanese Patent Laying-Open No. 3272787 ([Claim 1] [0021] [0003])

  However, in FIG. 8, the conductive adhesive is not preferable because it has a larger electric resistance than solder bonding or ultrasonic bonding. In the case of solder bonding, the heat generated from the IGBT chip 56 is conducted through the heat spreader 62, so that the solder bonding is thermally deteriorated and it is difficult to ensure the bonding reliability. In ultrasonic bonding, a copper plate 64 is placed on the heat spreader 62, and a load and vibration are applied, so that cracks may occur in the solder 59 that bonds the heat spreader 62 and the IGBT chip 56.

  In order to solve this, there is a method using laser welding, which will be described.

  9 and 10 are views showing a state in which a copper heat spreader and a copper plate are laser-welded. This shows part C of FIG. The YAG laser (wavelength 1064 nm) is irradiated from the laser emission unit 65, the copper plate 64 and the copper heat spreader 62a are melted, and the copper plate 64 and the copper heat spreader 62a are fixed.

  By irradiating the YAG laser, melting starts from the surface of the copper plate 64 first. Then, the melting part 67 gradually advances in the depth direction, and reaches the copper heat spreader 62a installed on the lower side of the copper plate 64 so that the interface between the copper plate 64 and the copper heat spreader 64 is joined.

  When the laser power and energy are too low, the melted portion 67 cannot reach the copper heat spreader 62a as shown in FIG. When the laser power and energy are too high, the copper plate 64 and the copper heat spreader 62a are penetrated as shown in FIG.

  On the other hand, due to the difference between the thermal expansion coefficient of the semiconductor chip and the thermal expansion coefficient of the heat spreader made of a high thermal conductivity material such as copper, there is a problem that a repeated stress acts on the solder and a crack occurs in the solder part in a cold and hot environment. is there.

  FIG. 11 is a diagram showing the expansion and contraction behavior of the IGBT chip and the heat spreader in the heat-repeating environment in the heat spreader joining structure, where FIG. 11 (a) is a schematic diagram at high temperature, and FIG. 11 (b) is a schematic diagram at low temperature. It is. In FIG. 5A, the thermal expansion coefficient of the copper heat spreader 62a is larger than that of the IGBT chip 56, and therefore the copper heat spreader 62a is pulled left and right. In FIG. 5B, the copper heat spreader 62a is pulled to the center. In the reliability test of the IGBT module, repeated tests of several hundred cycles are performed under the temperature condition of 125 ° C. on the high temperature side and −40 ° C. on the low temperature side. The solder 59 deteriorates due to this repeated stress, and a crack is generated from a location where the stress is the largest.

Specifically, the thermal expansion coefficient of silicon is about 3 × 10 ⁻⁶ / ° C., and the thermal expansion coefficient of copper is 16.5 × 10 ⁻⁶ / ° C. Due to the difference in thermal expansion coefficient, stress is applied to the solder 59 for fixing the IGBT chip 56 and the copper heat spreader 62a.

  When the crack generated by this stress progresses, the current path from the IGBT chip 56 is narrowed, resulting in an inconvenience that the wiring resistance increases and conduction failure occurs.

Therefore, as a material of the heat spreader 62, molybdenum having a thermal expansion coefficient close to that of silicon (thermal expansion coefficient is 5.1 × 10 ⁻⁶ / ° C.), tungsten (4.5 × 10 ⁻⁶ / ° C.), Alternatively, a metal or sintered body having a low thermal expansion coefficient, such as a copper-molybdenum sintered body (7 to 14 × 10 ⁻⁶ / ° C.) or a copper-tungsten sintered body (6 to 12 × 10 ⁻⁶ / ° C.). By using it, it is possible to reduce the thermal stress applied to the solder 56 between the IGBT chip 56 and the copper heat spreader 62a.

  Next, a case where a copper-molybdenum sintered body is used as the heat spreader material in order to reduce the difference in thermal expansion coefficient between the heat spreader 62 and the IGBT chip 56 will be described.

  12 and 13 are cross-sectional views of a main part in which a copper plate and a copper-molybdenum sintered body are welded with a YAG laser. The copper plate 64 begins to melt on the surface of the copper plate 64 by the energy of the YAG laser 66 irradiated from the laser emitting unit 65, and the melting portion 67 approaches the surface of the copper-molybdenum sintered body 62b with the irradiation time. However, as shown in FIG. 12, the melting portion 67 stops at the surface of the copper-molybdenum sintered body 62 b or only enters a slightly intruded state. This is because there is a large difference between the melting points of the copper and the copper-molybdenum sintered body 62b. That is, although the melting point of copper is 1083 ° C., the melting point of molybdenum is 2620 ° C. Therefore, even if the melting part 67 reaches the surface of the copper-molybdenum sintered body 62b, the temperature is 2620 ° C., which is the melting point of molybdenum. Otherwise, it stops at the interface between the copper plate 64 and the copper-molybdenum sintered body 62b. Alternatively, only the copper component in the copper-molybdenum sintered body 62b is melted, and the melted portion 67 only enters the copper-molybdenum sintered body 62b.

  In such a state, desired bonding strength between the copper plate 64 and the copper-molybdenum sintered body 62b cannot be obtained. Therefore, when the laser power and energy are increased and the molten part 67 is to be deeply inserted into the copper-molybdenum sintered body 62b, a part of the molten part 67 disappears as spatter as shown in FIG. As a result, there is a problem that the disappearing portion 68 occurs. When such a loss | disappearance part 68 generate | occur | produces, the fall of joining strength and the increase in electrical / thermal resistance will be caused, and it cannot be used.

  As shown in FIG. 14 and FIG. 15, the same thing occurs when the tungsten sintered body 62c is used. That is, since the melting point of tungsten is 3410 ° C., there is too much difference compared to the melting point of copper 1083 ° C., and the bonding becomes more difficult than in the case of bonding the copper-molybdenum sintered body 62b and the copper plate 64.

  The object of the present invention is to solve the above-mentioned problems and laser-weld the heat spreader and a metal plate which is an external lead-out conductor so that the solder under the heat spreader is not damaged and has high strength and high reliability. A bonding method is provided.

In order to achieve the above object, in a joining method of a heat spreader and a metal plate, wherein the heat spreader and the metal plate are made of copper, overlaid on a heat spreader fixed on a semiconductor chip via a fixing material, and joining the metal plate. A heat spreader having a thickness of 1.5 mm or less and a thickness of the metal plate of 0.5 mm or less; irradiating the metal plate with a YAG laser to weld the heat spreader and the metal plate; A bonding method in which the density is greater than 0.4 MW / cm ² and less than 1.5 MW / cm ² , and the laser energy is greater than 50 J and less than 150 J.

Moreover, in the joining method of a heat spreader and a metal plate, which is superposed on a heat spreader fixed on a semiconductor chip via a fixing material, and joining the metal plate, the heat spreader is a laminate of copper and a copper-molybdenum sintered body. A clad material or a clad material that is a laminate of copper and a copper-tungsten sintered body, wherein the metal plate is made of copper, the thickness of the heat spreader is 1.5 mm or less, and the thickness of the metal plate is 0.5 mm. The metal plate is irradiated with a YAG laser to weld the metal plate and the copper clad material, and the laser power density exceeds 0.4 MW / cm ² and 1.5 MW / cm ^The joining method is less than ² and the laser energy is more than 50J and less than 150J .

Further, in a joining method of a heat spreader and a metal plate, which is superposed on a heat spreader fixed on a semiconductor chip via a fixing material, and joining the metal plate, the heat spreader is a clad material or copper which is a laminate of copper and molybdenum. A clad material that is a laminate of tungsten, the metal plate is formed of copper, the heat spreader has a thickness of 1.5 mm or less, the metal plate has a thickness of 0.5 mm or less, and the metal plate has a YAG laser the irradiated by welding the copper clad material which is the laminate with the metal plate, the laser power density exceeds 0.4 mW / cm ^2, less than 1.5 MW / cm ^2, the laser energy is a 50J It is set as the joining method which is more than 150J .

Moreover, in the joining method of a heat spreader and a metal plate which overlaps a heat spreader fixed on a semiconductor chip via a fixing material and joins the metal plate, the heat spreader is a sintered body of molybdenum, tungsten or copper-molybdenum. , A copper-tungsten sintered body, a Ni plating film is formed on at least a joint surface of the heat spreader with the metal plate, the metal plate is copper, and the thickness of the heat spreader is 1.5 mm or less. The thickness of the metal plate is 0.5 mm or less, the metal plate is disposed on the Ni plating film of the heat spreader, and the metal plate and the heat spreader are welded by irradiating the metal plate with a YAG laser. , the laser power density exceeds 0.4 mW / cm ^2, less than 1.5 MW / cm ^2, the laser energy is 50 , Greater and joining method is less than 150 J.

  Further, a Ni plating film may be formed on the copper surface.

  Moreover, it is good to use aluminum instead of copper for the said metal plate.

  According to the present invention, since the welding of the copper heat spreader and the copper plate is laser-welded and the welding condition is set to a predetermined condition, pressure and vibration are not applied unlike ultrasonic bonding. High bonding reliability can be ensured without damaging the underlying solder and semiconductor chip.

  Also, the clad material, which is a copper-molybdenum and copper-tungsten laminate, is used as a heat spreader, the copper plate and the copper side of the heat spreader are laser welded, and the welding conditions are set to predetermined conditions, so that ultrasonic bonding is performed. Since no pressure or vibration is applied to the solder, the solder and the semiconductor chip under the heat spreader are not damaged, and high bonding reliability can be ensured.

  Furthermore, the heat spreader that joins the semiconductor chip is molybdenum or tungsten with a low coefficient of thermal expansion, so even when the semiconductor chip is in actual operation, the thermal stress applied to the solder that fixes the heat spreader and the semiconductor chip can be reduced, and cracks can be generated. Can be suppressed.

  1A and 1B are configuration diagrams of a semiconductor device to which the present invention is applied. FIG. 1A is a cross-sectional view of an essential part, and FIG. 1B is an enlarged view of a portion A of FIG. This figure is a cross-sectional view of the main part of the IGBT module.

A conductive pattern lunar insulating substrate 10 having a backside copper foil 12 fixed to the back surface of the ceramics 11 and an emitter conductor pattern 13, a collector conductor pattern 14 and a gate conductor pattern 15 fixed to the surface, and the collector conductor pattern 14 The IGBT chip 6 is fixed to the upper surface of the IGBT chip 6 with the solder 16, and the copper heat spreader 1 is fixed to the upper surface of the IGBT chip 6 with the solder 7. The YAG laser 19 (see the description of FIG. 2) is irradiated from the laser emitting unit 18 and melted and fixed at the melted portion 20. An aluminum wire 17 connects the gate pad 9 on the IGBT chip 6 and the gate conductor pattern 15.

  In addition, in order to perform the inverter operation, a diode is necessary in addition to this, but it is omitted in the description in this patent for the sake of simplicity. The structure shown in FIG. 1 is housed in a resin case such as PPS (polyphenylene sulfide) or PBT (polybutylene terephthalate), and further filled with a silicone resin as element protection. The

  FIG. 2 is a process diagram showing a method of joining a heat spreader and a metal plate according to the first embodiment of the present invention, and FIG. 2 (a) to FIG. . This figure is a portion B of FIG.

A copper plate 5 serving as an external lead-out conductor is disposed on the copper heat spreader 1 ((a) in the figure).
Next, the aim of the laser emitting unit 18 is adjusted to the planned melting point 21 ((b) in the figure).
Next, the YAG laser 19 is irradiated by the laser emitting unit 18, and the copper plate 6 and the copper heat spreader 1 are melted and fixed at the melting portion 20 (FIG. 3C).

According to the experiment, when the thickness of the copper plate 5 is 0.5 mm and the thickness of the copper heat spreader 1 is 1.0 mm, the fiber core diameter is 0.4 mm, the laser power density is 1.0 MW / cm ² , and the energy is 100 J. Laser bonding is possible. Further, when the laser power density is 1.5 MW / cm ² kW and the energy is 100 J, the molten portion 20 penetrates to the back surface of the copper heat spreader 1, and the molten copper disappears as spatter. Therefore, joining was impossible.

Furthermore, when the laser power density was set to 0.4 MW / cm ² , the melted portion 20 could not reach the surface of the copper heat spreader 1 and could not be joined. When the laser power density was 1.0 MW / cm ² and the energy was lowered to 50 J, the melting of the molten portion 20 into the copper heat spreader 1 side was so shallow that the desired bonding strength could not be obtained. Further, when the laser power density was 1.0 MW / cm ² and the energy was increased to 150 J, the melting portion 20 was deeply melted into the heat spreader 1 side, and a desired bonding strength could not be obtained.

Therefore, the thickness of the copper plate 5 is 0.5 mm or less, the thickness of the copper heat spreader 1 is 1.5 mm or less, the laser power density is more than 0.4 Mw / cm ² and less than 1.5 MW / cm ² , and the energy is 50 J By selecting an appropriate laser power and energy that is more than and less than 150 J, a desired welding state can be obtained.

  In the above-mentioned joining example, the case where copper is used as the material of the metal plate which is the external lead-out conductor has been described. However, since the absorption rate of copper and copper alloy YAG laser (wavelength 1064 nm) is only about 10%, about 90% of the emitted laser is wasted. Therefore, as shown in FIG. 3, a Ni plating film 22 having a high YAG laser absorption rate was formed on the surface of the copper plate 5 (copper and copper alloy). The Ni plating 22 may be formed at least in a portion directly irradiated with laser light, but the entire surface of the metal plate (copper plate 5) may be more simply plated. The absorption rate of the YAG laser in Ni is about 25%, which is 2.5 times that of copper and copper alloys. Thereby, it becomes possible to obtain a desired welding state with a laser power and energy lower than those in the case of irradiating the YAG laser without forming the Ni plating film 22 on the copper and copper alloy surfaces.

  Further, unlike ultrasonic bonding, no pressurization or vibration is applied, so that cracks are not generated in the solder 7 and the IGBT chip 6 under the heat spreader 1.

  The formation of the Ni plating film 22 in this case does not necessarily have to be formed on the entire surface because the purpose can be achieved if it is formed on at least the laser irradiation surface.

  However, in the copper heat spreader 1, as described above, when a thermal stress such as a temperature cycle or a heat cycle is applied, a crack is generated in the solder 7 that is a joint portion with the IGBT chip 6. A method for preventing this will be described in the next embodiment.

  FIG. 4 is a process diagram showing a method of joining a heat spreader and a metal plate according to a second embodiment of the present invention, and FIG. 4 (a) to FIG. . This figure shows a wiring structure in which a copper plate 5 on a heat spreader 2 of a clad material formed of a laminate of copper 2a and a copper-molybdenum sintered body 2b is fixed. This laminate is called a clad material.

A copper plate 5 as an external lead-out conductor is disposed on the copper 2a side of the heat spreader 2 of the clad material formed of a laminate of the copper 2a and the copper-molybdenum sintered body 2b ((a) in the figure).
Next, the aim of the laser emitting unit 18 is adjusted to the planned melting point 21 ((b) in the figure).
Next, the YAG laser 19 is irradiated by the laser emitting unit 18 to melt the copper plate 5 and the copper 2a of the clad material heat spreader 2 and fix them at the melting part 20 (FIG. 2C).

  The clad heat spreader 2 has a structure in which a copper 2a is disposed on the upper side and a copper-molybdenum sintered body 2b is disposed on the lower side. The lower side may be a copper-tungsten sintered body.

  As shown in FIG. 4 (c), in the copper plate 5 and the heat spreader 2 made of a clad material, a deep molten portion 20 reaching the copper-molybdenum sintered body 2b can be obtained. A weld structure with excellent resistance can be realized. If the ratio of the thickness of the copper plate 5 and the copper-molybdenum sintered body 2b (or copper-tungsten sintered body) in the heat spreader 2 of this clad material is appropriately determined depending on the required thermal expansion coefficient and the depth of the copper melted part. Good.

  Also in this case, a Ni plating film may be formed on the surface of the copper plate 5 as in the first embodiment.

  FIG. 5 is a process diagram showing a method of joining a heat spreader and a metal plate according to a third embodiment of the present invention, and FIG. 5 (a) to FIG. . This figure shows a wiring structure on a heat spreader 3 of a clad material in which copper 3a and molybdenum 3b are laminated. In this laminated body, this molybdenum called a clad material may be tungsten.

A copper plate 5 serving as an external lead-out conductor is disposed on the copper 5 of the heat spreader 3 made of a clad material formed of a laminate of copper 3a and molybdenum 3b (FIG. 1A).
Next, the aim of the laser emitting unit 18 is adjusted to the planned melting point 21 ((b) in the figure).
Next, the YAG laser 19 is irradiated by the laser emitting unit 18 to melt the copper plate 3a and the copper 3a of the clad material heat spreader 3 and fix them at the melting part 20 (FIG. 2C).

  FIG. 5 (c) shows a case where the clad material is composed of copper 3a on the upper side and molybdenum 3b (or tungsten) on the lower side, and a molten portion 20 similar to that described in FIG. 4 (c) can be obtained. it can.

  FIG. 6 is a process diagram showing a method of joining a heat spreader and a metal plate according to a fourth embodiment of the present invention, and FIGS. . 4 is a heat spreader of molybdenum. At least a Ni plating film 22 is formed on the joint surface of the molybdenum heat spreader 4 with the copper plate 5.

  . First, a copper plate 5 serving as an external lead-out conductor is disposed on a molybdenum heat spreader 4 (FIG. 1A).

  Next, the aim of the laser emitting unit 18 is aligned with the planned melting point 21 ((b) in the figure).

  Next, the YAG laser 19 is irradiated by the laser emitting unit 18 to melt the copper plate 5 and the Ni plating film 22 on the surface of the heat spreader 4 and fix them at the melting part 20 ((c) in the figure).

  When the heat spreader 4 is formed of molybdenum, the Ni plating film is provided on the joint surface side of the heat spreader with the metal plate (copper plate 5) for the following reason.

  That is, the metal plate (copper plate) and molybdenum are greatly different in melting point and YAG laser absorption. First, when a YAG laser is irradiated with a power capable of melting molybdenum having a high melting point, the copper subjected to the YAG laser greatly exceeds the melting point, and when the boiling point is reached, the copper disappears and a sufficient bonding cannot be obtained. In addition, since molybdenum has a higher laser absorptivity, when the irradiated laser reaches molybdenum, the power is absorbed at a stretch and the molybdenum may be penetrated. Therefore, it is difficult to laser weld copper and molybdenum, and the laser power must be set to such an extent that copper can be melted.

  Ni does not have a higher laser absorptivity and melting point than molybdenum, so a Ni plating film is provided on the surface of molybdenum, and the laser is irradiated with power that reaches the Ni plating film, so that copper and Ni melt. Thus, a bonding layer can be formed.

  In the above, the heat spreader of molybdenum has been described as an example, but molybdenum may be any of tungsten, a copper-molybdenum sintered body, and a copper-tungsten sintered body, and the reason for providing the Ni plating film is also the same. .

  4 to 6, as described in FIG. 3, it is possible to increase the absorption rate of the YAG laser by forming a Ni plating film on the surface of the copper plate 5.

  In addition, although the metal plate which is an external lead-out conductor was demonstrated with the copper plate in the said 1st Example-4th Example, you may replace this with an aluminum plate. At that time, the laser welding conditions need to be optimized. However, since aluminum has a higher laser absorption rate than copper, it is not necessary to form a Ni plating film on the laser irradiation surface. Further, although the case where the laser is a YAG laser has been described, it may be a semiconductor laser.

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram of the semiconductor device to which this invention is applied, (a) is principal part sectional drawing, (b) is the A section enlarged view of the same figure (a). It is process drawing which shows the joining method of the heat spreader and metal plate of 1st Example of this invention, (a) to (c) is principal part process sectional drawing shown in process order Cross-sectional view of the main part of a heat spreader in which a Ni plating film 22 is formed on the copper surface It is process drawing which shows the joining method of the heat spreader and metal plate of 2nd Example of this invention, (a) to (c) is principal part process sectional drawing shown in process order It is process drawing which shows the joining method of the heat spreader and metal plate of 3rd Example of this invention, (a) to (c) is principal part process sectional drawing shown in process order It is process drawing which shows the joining method of the heat spreader and metal plate of 4th Example of this invention, (a) to (c) is principal part process sectional drawing shown in process order Sectional view of the main part of a conventional IGBT module Sectional drawing of the principal part of another conventional IGBT module The figure which shows a mode that a copper heat spreader and a copper plate are laser-welded The figure which shows a mode that a copper heat spreader and a copper plate are laser-welded It is a figure which shows the expansion-contraction behavior of the IGBT chip | tip and a heat spreader in a cold-heat repetition environment in the joining structure of a heat spreader, (a) is a schematic diagram at the time of high temperature, (b) is a schematic diagram at the time of a low temperature. Cross-sectional view of the principal part where a copper plate and copper-molybdenum sintered body are welded with a YAG laser Cross-sectional view of the principal part where a copper plate and copper-molybdenum sintered body are welded with a YAG laser Cross-sectional view of the main part where a copper plate and tungsten sintered body are welded with a YAG laser Cross-sectional view of the main part where a copper plate and tungsten sintered body are welded with a YAG laser

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Copper heat spreader 2 Clad heat spreader 2a Copper 2b Copper-molybdenum sintered body 3 Clad heat spreader / molybdenum 3a Copper 3b Molybdenum 4 Heat spreader 5 Copper plate 6 IGBT chip 7 Solder 8 Emitter electrode 9 Gate pad 10 Insulating substrate with conductive pattern DESCRIPTION OF SYMBOLS 11 Ceramics 12 Back surface copper foil 13 Conductor pattern for emitter 14 Conductor pattern for collector 15 Conductive pattern for gate 16 Solder 17 Aluminum wire 18 Laser emission unit 19 YAG laser 20 Melting part 21 Planned melting point 22 Ni plating film

Claims (3)

In a joining method of a heat spreader and a metal plate, which is superposed on a heat spreader fixed on a semiconductor chip via a fixing material and joining a metal plate, the heat spreader and the metal plate are made of copper, and the thickness of the heat spreader is 1 0.5 mm or less, and the thickness of the metal plate is 0.5 mm or less. The metal plate is irradiated with a YAG laser to weld the heat spreader and the metal plate, and the laser power density is 0.4 MW / cm ² . A method for joining a heat spreader and a metal plate, characterized in that the heat energy is less than 1.5 MW / cm ² and the laser energy is more than 50 J and less than 150 J. In a method of joining a heat spreader and a metal plate, which is superposed on a heat spreader fixed on a semiconductor chip via a fixing material, and joining the metal plate, the heat spreader is a clad material which is a laminate of copper and a copper-molybdenum sintered body. Or it is a clad material which is a laminated body of copper and a copper-tungsten sintered body, the metal plate is formed of copper, the thickness of the heat spreader is 1.5 mm or less, and the thickness of the metal plate is 0.5 mm or less. There is irradiated with YAG laser welding and copper clad material which is the laminate with the metal plate to the metal plate, the laser power density exceeds 0.4 mW / cm ^2, less than 1.5 MW / cm ² A method for joining a heat spreader and a metal plate, wherein the laser energy is more than 50 J and less than 150 J. In a joining method of a heat spreader and a metal plate, which is superposed on a heat spreader fixed on a semiconductor chip via a fixing material, and joining the metal plate, the heat spreader is a clad material or a copper-tungsten which is a laminate of copper and molybdenum. The clad material is a laminate, the metal plate is made of copper, the heat spreader has a thickness of 1.5 mm or less, the metal plate has a thickness of 0.5 mm or less, and the metal plate is irradiated with a YAG laser. and then welding the copper clad material which is the laminate with the metal plate, the laser power density exceeds 0.4 mW / cm ^2, less than 1.5 MW / cm ^2, the laser energy exceeds 50 J, A joining method of a heat spreader and a metal plate, characterized by being less than 150 J.

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