JP2012004468A - Method for manufacturing semiconductor module unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor device which uses a thermally-conductive grease capable of suppressing generation of bleeding and vaporization, and not causing rise in heat-resistance due to heat expansion at high temperature caused by warpage of a package and a base material.SOLUTION: The method for manufacturing a semiconductor module unit in which an external housing for the semiconductor module is mounted on a radiator comprises (a) a step for applying a thermally-conductive grease 14 having viscosity of 130 Pas or less at 20°C and the shear rate of 5/sec, on a mounting surface of the semiconductor module or the radiator; (b) a step for mounting the semiconductor module on the radiator via a grease coated surface; and (c) a step for thickening the grease so that the yield value of viscosity at 20°C is 40 Pa or more, and 300 Pa or less, after the step (b).

Description

  The present invention relates to a method for manufacturing a semiconductor module unit in which an outer casing of a semiconductor module is mounted on a radiator.

  Between the semiconductor module and the heat sink on which it is mounted, a highly thermally conductive grease layer is provided as a thermally conductive layer that improves heat transfer. However, for example, a thermal conductive grease having a thermal conductivity of 2 W / mK or more has a difficulty in the mounting process because of its high viscosity and difficult application. On the other hand, when the molecular weight of the base oil is lowered in order to reduce the viscosity, there is a problem that bleeding and volatilization are likely to occur, and reliability is lacking.

  In order to prevent oil bleed in the grease layer, a gel is used instead of the grease layer (for example, Patent Document 1). If a material that gels by a heating reaction after coating is used, coating is easy, and bleeding does not occur after coating.

Japanese Patent Laid-Open No. 10-284659

  When a gel sheet as shown in Patent Document 1 is used as a heat conductive layer, the gel sheet cured by a heating reaction after coating has a problem that it cannot follow the case where the warpage of the package or the substrate is large, and lacks reliability. . Furthermore, since it thermally expands at a high temperature, there is a problem that the thermal resistance increases.

  In view of the above-described problems, an object of the present invention is to provide a method for mounting a semiconductor module using a thermally conductive grease that has good coatability and reliability, and also has good followability to warpage of a substrate.

  A first method for manufacturing a semiconductor module unit of the present invention is a method for manufacturing a semiconductor module unit in which an outer casing of a semiconductor module is mounted on a radiator, and (a) on the mounting surface of the semiconductor module or the radiator. Applying a thermally conductive grease having a viscosity of 130 Pa · s or less at 20 ° C. and a shear rate of 5 / sec; and (b) mounting a semiconductor module on a radiator via a grease application surface; ) After the step (b), the grease is thickened so that the yield value of the viscosity at 20 ° C. is 40 Pa or more and 300 Pa or less.

  In the second method for producing a semiconductor module unit of the present invention, (a) a thermally conductive grease having a viscosity of 130 Pa · s or less at 20 ° C. and a shear rate of 5 / sec is applied to the mounting surface of the semiconductor module or radiator. A step of applying, a step of (b) increasing the viscosity of the thermally conductive grease so that the yield value of the viscosity at 20 ° C. is 40 Pa or more and 300 Pa or less, and (c) after step (b), the semiconductor module is made a radiator. And a process of mounting via a thermally conductive grease application surface.

  According to the first method of manufacturing a semiconductor module unit of the present invention, (a) a thermally conductive grease having a viscosity of 130 Pa · s or less at 20 ° C. and a shear rate of 5 / sec is applied to a mounting surface of a semiconductor module or a radiator. And (b) a step of mounting the semiconductor module on the radiator via the grease application surface, and (c) after step (b), the yield value of the viscosity of the grease at 20 ° C. is 40 Pa or more and 300 Pa or less. And a step of increasing the viscosity. By reducing the viscosity of the heat conductive grease at the time of application, it can be applied without rubbing, and by increasing the viscosity after mounting the semiconductor module on the radiator, pumping out is prevented and a reliable grease is obtained. Furthermore, it is possible to follow the warpage of the semiconductor module by setting the yield value of the viscosity at 20 ° C. to 300 Pa or less. In addition, unlike the gel sheet and the adhesive, the grease easily changes its shape, and thus has an advantage that the thermal resistance does not increase due to thermal expansion at a high temperature.

  A second method for manufacturing a semiconductor module unit of the present invention is a method for manufacturing a semiconductor module unit in which an outer casing of a semiconductor module is mounted on a radiator, and (a) mounting of the semiconductor module or the radiator. Applying a thermally conductive grease having a viscosity of 130 Pa · s or less at 20 ° C. and a shear rate of 5 / sec to the surface; and (b) a yield value of the viscosity at 20 ° C. of the thermal conductive grease being 40 Pa or more and 300 Pa or less. And (c) after the step (b), a step of mounting the semiconductor module on the radiator via a thermally conductive grease application surface. By reducing the viscosity of the thermal conductive grease at the time of application, it can be applied without rubbing, and after thickening the thermal conductive grease, the semiconductor module is mounted on the radiator to prevent pumping out and improve reliability. It becomes a certain grease. Furthermore, it is possible to follow the warpage of the semiconductor module by setting the yield value of the viscosity at 20 ° C. to 300 Pa or less. In addition, since the shape of a grease is easily changed unlike a gel sheet or an adhesive, an increase in thermal resistance due to thermal expansion at a high temperature does not occur.

It is sectional drawing of a mold type inverter module. It is sectional drawing of a case type inverter module. It is sectional drawing which shows the mounting process of a mold type inverter module. It is sectional drawing which shows the mounting structure of a mold type inverter module. It is a figure which shows the characteristic of the material used for a heat conductive layer. It is a figure which shows the evaluation result of a commercially available heat conductive grease. It is a figure which shows the relationship between the shear rate of a heat conductive grease, and a shear stress. 5 is a cross-sectional view showing a mounting process of the molded inverter module according to Embodiment 1. FIG. FIG. 3 is a diagram illustrating a printing pattern of the thickening grease according to the first embodiment. It is a figure which shows the viscosity change of a reactive grease. FIG. 10 is a cross-sectional view showing a mounting process of the molded inverter module according to the second embodiment.

<Semiconductor module>
FIG. 1 shows a cross-sectional structure of a molded inverter module which is an example of the semiconductor module of the present embodiment. The mold-type inverter module includes a lead frame 1, a power element 4 mounted on the lead frame 1 through a highly thermally conductive conductive die bond 5, and a wire bond 3 that conducts between the plurality of lead frames 1. Further, the mold type inverter module includes an inner heat spreader 6 provided on the back surface of the lead frame 1 and having a heat dissipation function, a heat conductive insulating sheet 7 provided on the back surface of the inner heat spreader 6, and a heat conductive insulating sheet 7 The copper foil 8 provided on the back surface of the copper foil 8 and the sealing resin 2 that exposes a part of the copper foil 8 and the lead frame 1 and seals the other components described above are provided. The heat of the power element 4 is radiated through the inner heat spreader 6, the heat conductive insulating sheet 7 and the copper foil 8.

  FIG. 2 shows a cross-sectional structure of a case type inverter module which is another example of the semiconductor module of the present embodiment. The case type inverter module includes a metal base plate 13, a plurality of DBC (Direct Bonding Copper) ceramic substrates 12 formed on the metal base plate 13 via a highly thermally conductive conductive die bond 5, and a DBC ceramic substrate 12. Each of the power elements 4 to be mounted and a wire bond 3 that conducts between the power elements 4 are provided. Further, the case-type inverter module is provided for electrically connecting the resin case frame 10 provided so as to surround the region where the power element 4 is mounted on the metal base plate 13 and the wire bond 3 to the outside of the resin case frame 10. Embedded with the embedded bus bar 9 embedded in the resin case frame 10 and the silicone gel 11 for sealing the inside of the resin case frame 10. The heat of the power element 4 is dissipated through the metal base plate 13.

  The inverter module shown in FIG. 1 is mounted on a heat sink 15 via a heat conductive layer 14 on a surface on the copper foil 8 side as shown in the procedure of FIGS. 3A, 3B, and 3C. It becomes a module unit. When mounted on the heat sink 15, as shown in FIG. 4, the inverter module is pressurized using a disc spring 17 and a disc spring support 18 so as to be fixed to the heat sink 15.

<Heat conduction layer>
For the heat conductive layer 14 provided between the inverter module and the heat sink 15, conventionally, a gel sheet, a rubber sheet, a curable adhesive, or the like is used in addition to the heat conductive grease.

  FIG. 5 shows the advantages and disadvantages of each of the materials used for the heat conductive layer. The most commonly used is a thermally conductive grease in which a filler is added to oil. However, if the amount of filler is increased so that the electrical conductivity is 2.0 W / m · K or more, the viscosity increases and the coating is hindered. In order to reduce the viscosity, it is effective to reduce the molecular weight of the oil component, but since it tends to volatilize, the heat resistance is reduced. In addition, if the viscosity is low, coating is easy, but pumping out occurs due to the heat cycle accompanying the operation of the element after mounting, and the grease gradually moves outside between the semiconductor module and the heat sink 15, so that the thermal resistance Increases and lacks reliability. As described above, when using the thermally conductive grease, a trade-off occurs between the applicability and the reliability, so that a product satisfying both of them cannot be obtained.

  Since pumping out is derived from oily physical properties such as grease, this problem can be solved if the semiconductor module and the heat sink 15 are solid. Gel-like or rubber-like high thermal conductive sheets are commercially available, and these are simply put on a heat sink and sandwiched by a semiconductor module, so that the mounting process is easy and no special equipment is required. Moreover, since it can be easily removed, it has excellent repairability. However, unlike grease, these do not have a property of spreading thinly, so that the film thickness increases and the thermal resistance increases. Further, at a high temperature, the sheet is thermally expanded and the thermal resistance is increased. In addition, there is a drawback that the thermal resistance at the interface in contact with the semiconductor module or the heat sink is large.

  Also, when an adhesive obtained by adding a filler to a thermosetting or moisture curable resin is applied to the module or the heat sink 15 and bonded together, the occurrence of pumping out can be eliminated. Since these adhesives are cured after application, the components do not volatilize. Therefore, a low molecular weight component can be used to reduce the viscosity at the time of application, and it can be easily applied. Further, since the semiconductor module and the heat sink 15 are firmly bonded to the interface, the interface thermal resistance is relatively low. However, there is a drawback in that the module cannot follow the warp of the module due to cold, and once the crack or peeling occurs, the thermal resistance greatly increases and cannot be restored. Further, as in the case of gel sheets and rubber sheets, the adhesive expands thermally at high temperatures, increasing the thermal resistance.

  By the way, the gap between the semiconductor module and the heat sink 15 increases due to the warp of the module caused by the heat generated during the operation of the module. For example, in the case of a mold type inverter module, the gap that was 0.05 mm at room temperature reaches 0.2 mm at 125 ° C. The heat conductive layer 14 sandwiched between the semiconductor module and the heat sink 15 must follow a module warp and flow between the semiconductor module and the heat sink 15, so that it must be liquid. Therefore, the inventors use thickening grease as the heat conductive layer 14 filled between the module and the heat sink 15 in consideration of application properties, pumping-out resistance, warpage followability, and heat resistance. Was found to be optimal. The thickening grease of the present invention has an optimum viscosity for application in an uninitialized state, and changes to an optimum viscosity from the viewpoint of reliability after reaction. Thickening is manifested by heating, light, radiation, moisture, or solvent drying.

<Thickening grease>
The viscosity before thickening of the thickening grease to be used, the viscosity after thickening, the actual applicability, and the reliability evaluation results were repeatedly investigated. The examination result of the viscosity and the screen printing finish result is shown in FIG. Seven types of commercially available greases (Grease 1 to Grease 7) were printed on a 0.5 mm thick SUS stencil plate using a screen printer. A 50 mm square pattern was printed in a 3 × 5 array, a squeegee angle of 75 ° using a urethane flat squeegee, and a coating speed of 5 mm / sec. At this time, the viscosity (Pa · s) measured at a shear rate of 5 (1 / sec) and a shear rate of 1 (1 / sec) at room temperature (20 ° C.), a yield value (Pa), and the presence or absence of rubbing are shown. ing.

  From this result, it was found that when the printability (applicability) is evaluated, it is preferable to measure the viscosity of the grease at a shear rate of 5 (1 / sec). If the speed is higher than this, in the case of grease with high viscosity, the grease cannot follow the rotational speed, and slipping occurs between the rotating plate and the grease dilution type, making it difficult to obtain reproducible data. As a result of examining the correlation with the actual coating property, when the viscosity at 20 ° C. and 5 (1 / sec) is 150 Pa · s or more, the coating accuracy on the screen printing machine is remarkably lowered, and rubbing easily occurs. I understood that. If it is 130 Pa · s or less, rubbing does not occur and coating properties are good.

  Next, pumping out was evaluated (FIG. 6). On the center of a 2 mm thick aluminum plate of 50 mm x 35 mm, a 10 mm diameter round pattern is printed by screen printing at a thickness of 110 microns, covered with a glass plate of the same shape from above via a 100 micron spacer, and both ends are clipped It was. It was confirmed that the grease was in contact with both the glass plate and the aluminum plate.

  The resulting sample was placed in a heat cycle test apparatus with the longitudinal direction standing at a right angle downward, taken out after 500 cycles at −40 ° C./120° C., and the position of the grease dripping from the initial position was measured. The length was used as an index of ease of pumping out. This result is also shown in FIG. From the relationship between the sagging length and the viscosity, it can be seen that it is most appropriate to evaluate the yield value.

  The yield value shown in FIG. 6 is derived from the Casson equation shown in equation (1).

Here, τ shear stress, η∞ shear viscosity (infinite viscosity) and D shear rate when the shear rate is infinite, and τ ₀ is the yield value. Therefore, the yield value is obtained from the y-axis intercept of a straight line drawn when the shear power 1/2 power and the shear speed 1/2 power are plotted as shown in FIG.

  From the results of thermal resistance measurement after the heat cycle test (−50 ° C./125° C., 500 cycles, module vertical installation), it was found that the yield value is preferably 40 Pa or more. Further, when the transfer mold type inverter module CT300DAB060 (manufactured by Mitsubishi Electric Corporation) was heated to 125 ° C. and the warpage was measured, it was about 0.1 mm. After applying grease to this inverter module and mounting it on a heat sink, heat was generated and the thermal resistance was measured. In the case of grease with a yield value of 300 Pa or higher at 20 ° C, the grease does not follow the warp. An increase in thermal resistance, which is thought to have voids, was observed.

  From the above examination results, the thickening grease used for the heat conductive layer 14 of the present invention has a viscosity of not more than 130 Pa · s at 20 ° C. and a shear rate of 5 (1 / sec) before thickening, and after thickening. It was found that the yield value at 20 ° C. is preferably 40 Pa or more and 300 Pa or less. However, none of the greases 1 to 7 shown in FIG. Examples of greases that satisfy both requirements include reactive greases and solvent-diluted greases that thicken by volatilization of the solvent after application. Even if these greases are applied to either the package side or the substrate / heat sink side, good thermal resistance can be obtained.

(Embodiment 1)
In the manufacturing method of the semiconductor module unit of the first embodiment, reactive grease is used as the thickening grease. FIG. 8 shows a process of mounting the CT300DAB060 (manufactured by Mitsubishi Electric Corp.), which is the transfer mold type semiconductor module shown in FIG. 1, on the metal base plate 19 to form a semiconductor module unit. In FIG. 8, the same components as those shown in FIGS. 3 and 4 are denoted by the same reference numerals.

  As shown in FIG. 8, the outer surface of the semiconductor module (the outer surface of the sealing resin 2 and the copper foil 8) of the semiconductor module in FIG. Reactive grease 14a is screen-printed on the surface using a stencil plate having a thickness of 50 μm (FIG. 8B). The reactive grease 14a has a thermosetting property by adding 7g of a commercially available addition-type silicone coating material having a viscosity of 0.1 Pa · s to 100g of a commercially available silicone grease (Grease 3 in FIG. 6) and further stirring. Use a mixture of reactive grease. The viscosity after mixing is 120 Pa · s at 20 ° C. and a shear rate of 5 (1 / sec). The print pattern is a square pattern of 9 mm square arranged at a 1 mm pitch in a 59 × 39 mm print range (FIG. 9). The grease thickness is about 50 μm. The reactive grease 14a may be screen-printed on the copper base plate 19 (heat radiator) instead of the semiconductor module.

  Next, the semiconductor module is mounted on a 3 mm-thick nickel-plated copper base plate 19 with the printing surface (grease application surface) facing down, and the lead frame 1 is screwed to the bus bar 20 at three locations. Further, the disk module 17 and the disk spring support 18 are used to fix the semiconductor module and the metal base plate 19 so that they do not move, and a load of about 400 N is applied from above. In this state, the reactive grease 14a is thickened by heating at 150 ° C. for 1 hour to obtain a semiconductor module unit in which the semiconductor module is mounted on the copper base plate 19 (FIG. 8C). When the reactive grease 14a was heated to 150 ° C. for 1 hour and then cooled to room temperature, the yield value was 190 Pa. The reactive grease 14a that has undergone the above steps satisfies the conditions of the viscosity yield value of 40 Pa or more and 300 Pa or less, and has desirable characteristics that follow the warpage of the module without causing pumping out. The relationship between the viscosity before and after the reaction and the shear rate is shown in FIG.

  In the above description, the reactive grease 14a is thickened after the semiconductor module is mounted on the metal base plate 19. However, when reactive grease is used, a thickening process may be performed before mounting. Further, the thickening method is not limited to heating, but may be light irradiation, irradiation radiation, water supply, or the like depending on the grease material.

<Effect>
According to the manufacturing method of the semiconductor module unit of the present embodiment, the following effects are obtained. That is, the manufacturing method of the semiconductor module unit according to the first embodiment is a manufacturing method of a semiconductor module unit in which an outer casing of a semiconductor module is mounted on a radiator (metal base plate 19), and (a) a semiconductor module Alternatively, a step of applying a reactive grease 14a having a viscosity of 130 Pa · s or less at 20 ° C. and a shear rate of 5 / sec to the mounting surface of the metal base plate 19; and (b) applying a grease on the metal base plate 19 to the semiconductor module. And (c) after step (b), the reactive grease 14a is thickened so that the yield value of the viscosity at 20 ° C. is 40 Pa or more and 300 Pa or less. By reducing the viscosity of the reactive grease 14a at the time of application, the reactive grease 14a can be applied without rubbing, and by increasing the viscosity after mounting the semiconductor module on the metal base plate 19, pumping out is prevented and a reliable grease is obtained. . Furthermore, it is possible to follow the warpage of the semiconductor module by setting the yield value of the viscosity at 20 ° C. to 300 Pa or less. In addition, the reactive grease 14a does not increase in thermal resistance due to thermal expansion at high temperatures unlike gel sheets and adhesives.

  Moreover, in the said process (c), it is possible to make it the grease which implement | achieves both applicability | paintability and reliability by thickening the grease 14 by heating, light or radiation irradiation, or a water supply.

  Further, when the reactive grease 14a containing the thermosetting grease is applied in the step (a), the reactive grease 14a is heated to increase the viscosity in the step (c), thereby providing applicability and reliability. It is possible to make a grease that achieves both.

(Embodiment 2)
In the method for manufacturing the semiconductor module unit of the second embodiment, solvent diluted grease is used as the thickening grease. FIG. 11 shows a process of mounting the CT300DAB060 (manufactured by Mitsubishi Electric Corp.), which is the transfer mold type semiconductor module shown in FIG. 1, on the metal base plate 19 to form a semiconductor module unit. In FIG. 11, the same components as those shown in FIG. 8 are denoted by the same reference numerals.

  As shown in FIG. 11, the outer surface of the semiconductor module of FIG. 11A (the outer surface of the sealing resin 2 and the copper foil 8) on which the copper foil 8 is formed (heat radiation side) On the surface, solvent-diluted grease 14b is screen-printed using a stencil plate having a thickness of 50 μm (FIG. 11B). As the solvent dilution grease 14b, one obtained by adding 5 g of toluene as a volatile solvent to 100 g of a commercially available silicone grease (grease 3 in FIG. 6) is used. The viscosity after mixing is 120 Pa · s at 20 ° C. and a shear rate of 5 (1 / sec). The printing pattern is 59 × 39 mm and is a rectangular pattern. The grease thickness is about 55 μm. The solvent dilution grease 14b may be screen-printed on the copper base plate 19 (heat radiator) instead of the semiconductor module.

  Next, the semiconductor module on which the solvent-diluted grease 14b is printed is heated at 70 ° C. for 30 minutes and further at 150 ° C. for 1 hour without touching the grease application surface, and the toluene in the grease is volatilized to increase the viscosity. Let As described above, when the solvent diluted grease 14b is used, the solvent needs to be volatilized, so that the thickening step is performed before the mounting step. The yield value of the grease after toluene volatilization was 52 Pa which was almost the same as the yield value before addition of toluene. However, the film thickness slightly decreased to 50 μm.

  After that, the printed surface (grease-applied surface) is mounted on a nickel-plated copper base plate 19 having a thickness of 3 mm, and a pressure of about 1000 N is applied for 20 seconds to crush the solvent-diluted grease 14b from above (see FIG. 11 (c)), and then the pressure was loosened, and the lead frame 1 was screwed to the bus bar 20 at three locations. Further, by applying a load of about 400 N from above using the disc spring 17 and the disc spring support 18, a semiconductor module unit in which the semiconductor module is mounted on the copper base plate 19 is obtained (FIG. 11D).

  In the above description, the solvent-diluted grease 14b is thickened by heating. However, the thickening method is not limited to heating, and depending on the material of the grease, light irradiation, radiation irradiation, water supply, etc. good.

<Effect>
According to the manufacturing method of the semiconductor module unit of the present embodiment, the following effects are obtained. In other words, the method for manufacturing a semiconductor module unit according to the second embodiment is a method for manufacturing a semiconductor module unit in which an outer casing of a semiconductor module is mounted on a radiator (metal base plate 19), and (a) a semiconductor module Or a step of applying a solvent diluted grease 14b having a viscosity of 130 Pa · s or less at 20 ° C. and a shear rate of 5 / sec to the mounting surface of the metal base plate 19, and (b) yielding the viscosity of the solvent diluted grease 14b at 20 ° C. And (c) a step of mounting the semiconductor module on the metal base plate 19 via a grease application surface. The step of increasing the viscosity so that the value is 40 Pa or more and 300 Pa or less. By lowering the viscosity of the solvent diluted grease 14b at the time of application, it can be applied without rubbing, and after thickening the solvent diluted grease 14b, the semiconductor module is mounted on the metal base plate 19 to prevent pumping out and to be reliable. It becomes a characteristic grease. Furthermore, it is possible to follow the warpage of the semiconductor module by setting the yield value of the viscosity at 20 ° C. to 300 Pa or less. In addition, the solvent-diluted grease 14b does not increase in thermal resistance due to thermal expansion at high temperatures unlike gel sheets and adhesives.

  Moreover, in the said process (b), it is possible to make it the grease which implement | achieves both applicability | paintability and reliability by making the solvent dilution grease 14b thicken by heating or solvent drying at room temperature.

  Furthermore, in the case where the solvent diluted grease 14b containing a volatile solvent is applied in the step (a), the grease is thickened by volatilizing the solvent in the step (b), so that both applicability and reliability are achieved. It is possible to obtain a grease that realizes

  DESCRIPTION OF SYMBOLS 1 Lead frame, 2 Sealing resin, 3 Wire bond, 4 Power element, 5 Die bond, 6 Heat spreader, 7 Thermal conductive insulating sheet, 8 Copper foil, 9 Embedded bus bar, 10 Resin case frame, 11 Silicone gel, 12 DBC ceramic Substrate, 13 Metal base plate, 14 Thermal conductive layer 14a Reactive grease, 14b Solvent dilution grease, 15 Heat sink, 17 Belleville spring, 18 Belleville spring support, 19 Metal base plate, 20 Busbar.

Claims (6)

A method for manufacturing a semiconductor module unit comprising an outer casing of a semiconductor module mounted on a radiator,
(A) applying a thermally conductive grease having a viscosity of 130 Pa · s or less at 20 ° C. and a shear rate of 5 / sec to the mounting surface of the semiconductor module or the radiator;
(B) mounting the semiconductor module on the radiator via the grease application surface;
(C) After the said process (b), the process of making the said grease thicken so that the yield value of the viscosity in 20 degreeC may be 40 Pa or more and 300 Pa or less, The manufacturing method of a semiconductor module unit.   The method of manufacturing a semiconductor module unit according to claim 1, wherein the step (c) is a step of thickening the thermally conductive grease by any one of heating, light or radiation irradiation, and water supply.   The method of manufacturing a semiconductor module unit according to claim 2, wherein the step (a) is a step of applying the thermally conductive grease including a thermosetting grease. A method for manufacturing a semiconductor module unit comprising an outer casing of a semiconductor module mounted on a radiator,
(A) applying a thermally conductive grease having a viscosity of 130 Pa · s or less at 20 ° C. and a shear rate of 5 / sec to the mounting surface of the semiconductor module or the radiator;
(B) increasing the viscosity of the thermally conductive grease so that the viscosity yield value at 20 ° C. is 40 Pa or more and 300 Pa or less;
(C) After the step (b), a step of mounting the semiconductor module on the radiator via the thermally conductive grease application surface.   The method of manufacturing a semiconductor module unit according to claim 4, wherein the step (b) is a step of thickening the thermally conductive grease by any one of heating, light or radiation irradiation, and water supply.   The method of manufacturing a semiconductor module unit according to claim 5, wherein the step (a) is a step of applying the thermally conductive grease containing a volatile solvent.

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