JP5664028B2 - Manufacturing method of electronic device - Google Patents

Description

  The present invention relates to a method for manufacturing an electronic device, for example, a method for manufacturing an electronic device that joins a first base and a second base.

  It is known to use solder as a method for bonding the substrates (for example, bonding a semiconductor chip to a substrate). Solder is excellent as a bonding material, but its thermal conductivity is not high. Solder also deteriorates in a temperature cycle test. It is known that substrates are bonded to each other by using a paste on a metal obtained by adding an organic adhesive material to metal particles such as silver. Silver is the metal with the highest thermal conductivity, but with this method the thermal conductivity of the silver paste is low. Therefore, in order to obtain high thermal conductivity, it is known to form bumps by sintering metal particles without interposing an organic material (for example, Patent Document 1).

JP 2007-19144 A

  However, when oxides are formed on the surfaces of the metal particles, it is difficult to join the metal particles together. For this reason, the bonding between the substrates is weakened. On the other hand, if, for example, gold is used as the metal that is difficult to oxidize as the metal particles, the cost cannot be reduced.

  An object of the manufacturing method of the electronic device is to form a strong bond between the substrates.

For example, an aggregate of the metal particles is formed by bonding the first substrate and the second substrate via a metal paste containing metal particles and an organic solvent, and removing the organic solvent of the metal paste. After the step, the step of reducing the surface of the metal particles constituting the aggregate using a reducing gas, and the step of reducing the surface of the metal particles constituting the aggregate, the first base and the second Pressing the substrate, and joining the first substrate and the second substrate through the aggregate while maintaining the state of the aggregate including the interface and gap between the metal particles. An electronic device manufacturing method characterized by this can be used.

  According to the method for manufacturing the electronic device, it is possible to form a strong bond between the substrates.

FIG. 1A to FIG. 1D are cross-sectional views illustrating a method for manufacturing an electronic device according to the first embodiment. FIG. 2 is a cross-sectional view (part 1) illustrating the method of manufacturing the electronic device according to the second embodiment. FIG. 3 is a sectional view (No. 2) illustrating the method for manufacturing the electronic device according to the second embodiment. FIG. 4 is a sectional view (No. 3) illustrating the method for manufacturing the electronic device according to the second embodiment. FIG. 5 is a sectional view (No. 4) illustrating the method for manufacturing the electronic device according to the second embodiment. FIG. 6 is a sectional view (No. 5) illustrating the method for manufacturing the electronic device according to the second embodiment. FIG. 7 is a sectional view (No. 6) illustrating the method for manufacturing the electronic device according to the second embodiment. FIG. 8 is a diagram showing the temperature of the metal paste or aggregate in each step. 9A is a schematic diagram of an SEM image of the aggregate before the aggregate is crushed, and FIG. 9B is a schematic diagram of the SEM image of the aggregate after the aggregate is crushed. FIG. 10 is an example of a module including the electronic device according to the second embodiment. FIG. 11A is a cross-sectional view of the electronic device according to the third embodiment, and FIG. 11B is an enlarged view of the bump in FIG.

  Embodiments will be described below with reference to the drawings.

  FIG. 1A to FIG. 1D are cross-sectional views illustrating a method for manufacturing an electronic device according to the first embodiment. As shown in FIG. 1A, the first base 10a and the second base 20a are bonded via a metal paste 30 containing metal particles 32 and an organic solvent 34. As shown in FIG. 1B, the aggregate 36 of the metal particles 32 is formed by removing the organic solvent 34 of the metal paste 30. As shown in FIG. 1C, the surface of the metal particles 32 constituting the aggregate 36 is reduced using a reducing gas. As shown in FIG. 1D, the first base 10a and the second base 20a are pressed as shown by an arrow 45 to join the first base 10a and the second base 20a using the aggregate 36. According to the first embodiment, as shown in FIG. 1D, the aggregate 36 includes the metal particles 32 and has a gap, so that the aggregate 36 is more easily displaced than an integral metal without a gap and can suppress deterioration due to a temperature cycle. . Moreover, after removing the oxide on the surface of the metal particles 36, the metal particles 32 can be joined together. Therefore, the bonding between the first base 10a and the second base 20a can be strengthened.

  Example 2 is an example of a semiconductor element in which the first base is a DCB (Direct Copper Bonding) substrate and the second base is provided with an IGBT (Insulated Gate Bipolar Transistor). 2 to 7 are cross-sectional views illustrating the method for manufacturing the electronic device according to the second embodiment. As shown in FIG. 2, the metal paste 30 is disposed on the surface of the DCB substrate 10. The DCB substrate 10 includes, for example, a metal layer 12, an insulating layer 14, and a wiring layer 16. The metal layer 12 and the wiring layer 16 are, for example, a metal mainly containing copper. The insulating layer 14 is made of ceramic, for example, and mainly contains aluminum oxide, for example. The metal paste 30 includes metal particles 32 and an organic solvent 34. The metal particles 32 mainly contain silver or copper, for example. As the organic solvent 32, for example, ester alcohol, terpineol, pine oil, butyl carbitol acetate, butyl carbitol, carbitol can be used. These organic solvents can be dried at relatively low temperatures. Further, the metal paste 30 may contain at least one of an acrylic resin, a cellulose resin, and an alkyd resin for preventing aggregation of the metal particles 32. For example, methyl methacrylate polymer can be used as the acrylic resin, ethyl cellulose can be used as the cellulose resin, and phthalic anhydride resin can be used as the alkyd resin. As a method for arranging the metal paste 30, for example, a printing method or a dispensing method can be used. The thickness of the metal paste 30 is, for example, 30 μm.

  As shown in FIG. 3, the DCB substrate 10 and the semiconductor element 20 are bonded through a metal paste 30. The semiconductor element 20 includes, for example, a back electrode 22, a semiconductor substrate 24, and a surface electrode 26. The back electrode 22 includes, for example, titanium, nickel, or gold. The surface electrode 26 mainly contains aluminum, for example. The semiconductor substrate 24 mainly contains silicon. An IGBT is formed on the semiconductor substrate 24, and the front electrode 26 and the back electrode 22 are electrically connected to the IGBT. When bonding the DCB substrate 10 and the semiconductor element 20 via the metal paste 30, it is preferable to press the DCB substrate 10 and the semiconductor element 20 using a pressure corresponding to the viscosity of the metal paste 30. For example, the DCB substrate 10 and the semiconductor element 20 can be pressed with a pressure of several MPa.

  As shown in FIG. 4, the organic solvent 34 of the metal paste 30 is removed to form an aggregate 36 of the metal particles 32. As a method for removing the organic solvent 34, the organic solvent 34 is volatilized and separated by, for example, heating the metal paste 30. For example, it can be heated at a temperature of 200 ° C. for 10 minutes. The organic solvent 34 can be further volatilized by heating the metal paste 30 under reduced pressure, for example. Further, by performing heating of the metal paste 30 in an atmosphere not containing oxygen, further oxidation of the surface of the metal particles 32 can be suppressed. In the aggregate 36, the metal particles 32 are bonded together by, for example, van der Waals force. As described above, the metal particles 32 are in contact with each other and temporarily sintered. In the aggregate 36, for example, a gap of several tens of percent is formed with respect to the entire volume.

  As shown in FIG. 5, the DCB substrate 10 and the semiconductor element 20 bonded by the aggregate 36 are introduced into the container 42. The surface of the metal particles 32 constituting the aggregate 36 is reduced using a reducing gas 44. The reducing gas 44 reaches the gaps between the metal particles 32 of the aggregate 36 and reduces the oxide formed on the metal particles 32. In order for the reducing gas 44 to easily reach the gaps between the aggregates 36, the inside of the container 42 can be decompressed (for example, 10 Pa), and the reducing gas 44 can be introduced. If the decompression in the container 42 and the introduction of the reducing gas 44 are repeated a plurality of times, the surface of the metal particles 32 can be further reduced. Furthermore, the surface of the metal particles 32 can be further reduced by heating the surface of the aggregate 36 using the heater 40. The temperature of the aggregate 36 can be set to 150 ° C. to 200 ° C., for example. For example, it can be 175 degreeC. As the reducing gas 44, for example, a gas containing formic acid can be used. For example, a gas obtained by adding a formic acid gas to an inert gas such as nitrogen can be used as the reducing gas 44. The concentration of formic acid gas can be, for example, 10 ppm to 10%. Since formic acid gas has a reducing property at 130 ° C. or higher, the temperature of the aggregate 36 is preferably 130 ° C. or higher. The reducing gas may be a gas containing plasma hydrogen or radical hydrogen in addition to formic acid gas.

  As shown in FIG. 6, the DCB substrate 10 and the semiconductor element 20 are pressed using, for example, a load application jig 46. The metal particles 32 of the aggregate 36 are combined to collapse the aggregate 36. As a result, the DCB substrate 10 and the semiconductor element 20 are bonded using the aggregate 36. For example, the gap between the metal particles 32 of the aggregate 36 is less than half before pressing the DCB substrate 10 and the semiconductor element 20. Since gaps are formed between the metal particles 32, the aggregate 36 can be crushed even if the pressure applied to the aggregate 36 is equal to or lower than the yield stress of the material of the metal particles 32. Since the pressing pressure may be small, the load applying jig 46 can be downsized. For example, when the metal particles 32 are silver, the pressing pressure can be about 10 MPa. When pressing the DCB substrate 10 and the semiconductor element 20, it is preferable to heat the aggregate 36 using the heater 40. Thereby, the metal particle 32 can be joined more firmly. When the metal particles 32 are silver, the temperature of the aggregate 36 can be set to 250 ° C., for example. Moreover, the time of a press can be made into 10 to 30 minutes, for example.

  The bonding strength with the DCB substrate 10 was measured using a semiconductor element of a 5 mm × 5 mm substrate using silver as the metal particles 32. When the process of FIG. 6 is performed in a nitrogen atmosphere, the bonding strength between the DCB substrate 10 and the semiconductor element 20 is about 200N. On the other hand, when the process of FIG. 6 is performed at a reduced pressure of about 10 Pa, the bonding strength between the DCB substrate 10 and the semiconductor element 20 is about 400N. Thus, when the DCB substrate 10 and the semiconductor element 20 are pressed, the inside of the container 42 is preferably decompressed (for example, vacuum). When pressing is performed at an atmospheric pressure such as a nitrogen atmosphere, a gas such as nitrogen gas is trapped in the gap between the metal particles 32 of the aggregate 36. Thereby, metal joining between the metal particles 32 is inhibited. Therefore, it is considered that the bonding strength between the DCB substrate 10 and the semiconductor element 20 decreases.

  As shown in FIG. 7, the metal particles 32 of the aggregate 36 are crushed, and the metals of the metal particles 32 are diffused to each other, thereby joining the metal particles 32 together. Thereby, the DCB substrate 10 and the semiconductor element 20 can be joined via the aggregate 36.

  FIG. 8 is a diagram showing the temperature of the metal paste or aggregate in each step. As shown in FIG. 8, the temporary bonding process between the DCB substrate 10 and the semiconductor element 20 in FIG. 4 is performed under the condition that the load between the DCB substrate 10 and the semiconductor element 20 is, for example, 1 MPa, the temperature is 200 ° C., and the time is 2 minutes. Do. The reduction process of the surface of the metal particle 32 in FIG. The joining process of the DCB substrate 10 and the semiconductor element 20 in FIG. 6 is performed under the conditions that the load between the DCB substrate 10 and the semiconductor element 20 is, for example, 10 MPa, the temperature is 250 ° C., and the time is 10 to 30 minutes. Thus, each temperature can be a different temperature. For example, in the temporary bonding process, the load in the temporary bonding process is preferably smaller than the load in the bonding process so that the metal particles 32 are not crushed. Moreover, it is preferable that the temperature of a temporary bonding process is lower than the temperature of a joining process.

  9A is a schematic diagram of an SEM (scanning electron microscope) image of the aggregate 36 before the aggregate 36 is crushed, and FIG. 9B is a schematic diagram of the aggregate 36 after the aggregate 36 is crushed. As shown in FIG. 9A, before crushing the aggregate 36, the metal particles 32 are accumulated and a gap 38 is formed between the metal particles 32. As shown in FIG. 9B, after the aggregate 36 is crushed, the metal particles 32 are joined and the volume of the gap 38 is reduced.

  According to Example 2, as shown in FIG. 5, the surface of the metal particles 32 constituting the aggregate 36 is reduced using the reducing gas 44. Thereafter, the DCB substrate 10 and the semiconductor element 20 are pressed to join the DCB substrate 10 and the semiconductor element 20 using the aggregate 36. Thereby, similarly to Example 1, the junction between the DCB substrate 10 and the semiconductor element 20 can be strengthened.

  In FIG. 5, when reducing the surface of the metal particles 32 constituting the aggregate 36, the step of exposing the surface of the metal particles 32 constituting the aggregate 36 to the reducing gas 44, and the reducing gas 44 The step of sucking is alternately performed. Thereby, the oxide of the metal particle 32 surface can be removed more.

  The metal particles 32 preferably contain at least one of silver, copper and tin. For example, the metal particles 32 can be silver, copper and tin, or alloys thereof. When the metal particles 32 are gold, for example, it is difficult for oxides to be formed on the surfaces of the metal particles 32. However, gold is expensive. According to Example 1, silver, copper, or tin that is inexpensive but easily oxidized can be used as the metal particles 32. Thereby, an electronic device can be provided at low cost.

  When the diameter of the metal particles 32 is small, it becomes difficult to sufficiently penetrate the reducing gas between the metal particles 32 in the reduction process. On the other hand, when the diameter of the metal particles 32 is large, the strength of the aggregate 36 cannot be increased. Therefore, the diameter of the metal particles 32 is preferably 0.1 μm or more and 1 μm or less, and more preferably 0.2 μm or more and 0.8 μm or less.

  FIG. 10 is an example of a module including the electronic device according to the second embodiment. A resin case 50 is provided on the outer periphery of the DCB substrate 10. An external connection terminal 54 is provided in the resin case 50. The external connection terminal 54 is electrically connected to the surface electrode 26 of the semiconductor element 20 using a bonding wire 51. The semiconductor element 20 and the bonding wire 51 are sealed with a sealing gel 52. The metal layer 12 of the DCB substrate 10 and the copper base 58 are joined by an aggregate 56. The aggregate 56 is formed by the same method as the aggregate 36. A heat radiating fin 60 is connected to the copper base 58 via a thermal grease 59. As shown in FIG. 10, the first base may be the copper base 58 and the second base may be the DCB substrate 10.

  The IGBT is used for a voltage conversion semiconductor element such as an inverter. A module mounted with an IGBT is required to be downsized. In a module including an IGBT as shown in FIG. 10, a DCB substrate 10 having excellent heat dissipation is used. In addition, an insulating layer 14 is provided on the DCB substrate 10 to float the back electrode 12 of the IGBT chip. Joining with a solder material causes slip failure at the grain boundaries of the solder. When the IGBT chip is joined to the DCB substrate 10 using solder, the solder deteriorates due to the heat generation cycle of the IGBT chip. When the solder deteriorates, the heat dissipation becomes worse, the temperature of the IGBT chip rises, and the solder deteriorates at an accelerated rate.

  On the other hand, when a die attach material using an organic metal paste or nano-sized metal particles instead of solder is used, the organic material remains, resulting in poor thermal conductivity. For example, while the thermal conductivity of tin-based solder is 60 W / m · K, the thermal conductivity of a die attach material using an organic material metal paste or nano-sized metal particles is about 5 W / m · K. .

  According to the second embodiment, the metal particles 32 can be bonded to each other after the oxide on the surface of the metal particles 36 is removed. Therefore, the thermal conductivity of the aggregate 36 can be increased. For example, the thermal conductivity of the aggregate using silver particles is as high as about 300 W / m · K, and a heat release of 5 times that of solder joints can be expected. Moreover, since the aggregate 36 has a gap, deterioration due to the temperature cycle can be suppressed.

  In the second embodiment, the example of the DCB substrate 10 as the first substrate and the example of the semiconductor element 20 in which the IGBT is formed as the second substrate have been described. Devices other than IGBTs may be formed in the semiconductor element 20. The first substrate and the second substrate can be a mounting substrate or a semiconductor element. For example, both the first base and the second base can be used as mounting boards. Further, both the first substrate and the second substrate can be semiconductor elements.

  Example 3 is an example in which an aggregate is used as a bump. FIG. 11A is a cross-sectional view of the electronic device according to the second embodiment, and FIG. 11B is an enlarged view of the bump in FIG. 11A. As shown in FIGS. 11A and 11B, the mounting substrate 70 has an electrode 74 formed on the surface of an insulating substrate 72. In the semiconductor element 80, a pad 86 is formed on the surface of the semiconductor substrate 82, and an electrode 88 is formed on the pad 86 (below in FIG. 11A and FIG. 11B). An insulating protective film 84 is formed on the surface of the semiconductor element 80. The semiconductor element 80 is flip-chip mounted on the mounting substrate 70 using the aggregate 90 as a bump. The aggregate 90 includes metal particles 92 and is formed in the same manner as the aggregate 30 of the first embodiment. As in Example 3, the aggregate 90 can be used as a bump.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

The following additional remarks are disclosed regarding the embodiment including Examples 1 to 3.
Appendix 1: Adhering the first base and the second base via a metal paste containing metal particles and an organic solvent, and removing the organic solvent of the metal paste to form an aggregate of the metal particles After the step of reducing the surface of the metal particles constituting the aggregate using a reducing gas and the step of reducing the surface of the metal particles constituting the aggregate, the first base and the second A method of manufacturing an electronic device, the method comprising: joining the first base and the second base using the aggregate by pressing the base.
Appendix 2: The step of reducing the surface of the metal particles constituting the aggregate includes the step of exposing the surface of the metal particles constituting the aggregate to the reducing gas and the step of sucking the reducing gas. The method of manufacturing an electronic device according to appendix 1, wherein the method is performed alternately.
Appendix 3: The method of manufacturing an electronic device according to Appendix 1 or 2, wherein the step of joining using the aggregate is performed under reduced pressure.
APPENDIX 4: The step of joining using the agglomerate applies a pressure equal to or less than a yield stress of the material of the metal particles to the agglomerate. The electronic device according to any one of appendices 1 to 3, Production method.
Supplementary Note 5: The method for manufacturing an electronic device according to any one of Supplementary notes 1 to 4, wherein the diameter of the metal particles is 0.1 μm or more and 1 μm or less.
Appendix 6: The method for manufacturing an electronic device according to any one of Appendixes 1 to 5, wherein the reducing gas includes formic acid.
Appendix 7: The method of manufacturing an electronic device according to any one of Appendixes 1 to 6, wherein the metal particles include at least one of silver, copper, and tin.

DESCRIPTION OF SYMBOLS 10 DCB board | substrate 10a 1st base | substrate 20 Semiconductor element 20a 2nd base | substrate 30 Metal paste 32 Metal particle 34 Organic solvent 36 Aggregate 44 Reducing gas

Claims (4)

Adhering the first base and the second base via a metal paste containing metal particles and an organic solvent;
Removing the organic solvent of the metal paste to form an aggregate of the metal particles;
Reducing the surface of the metal particles constituting the aggregate using a reducing gas;
After the step of reducing the surface of the metal particles constituting the aggregate, the first base and the second base are pressed, and the first base and the second base are brought into contact with the interface between the metal particles and Joining via the aggregates while maintaining the state of the aggregates including gaps;
A method for manufacturing an electronic device, comprising:   The step of reducing the surface of the metal particles constituting the aggregate is alternately performed by exposing the surface of the metal particles constituting the aggregate to the reducing gas and sucking the reducing gas. The method of manufacturing an electronic device according to claim 1.   3. The method of manufacturing an electronic device according to claim 1, wherein the step of bonding using the aggregate is performed under reduced pressure.   4. The method of manufacturing an electronic device according to claim 1, wherein in the step of bonding using the aggregate, a pressure equal to or lower than a yield stress of the material of the metal particles is applied to the aggregate. 5. .

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