JP2015115535A - PASTE FOR FORMING Ag BASE LAYER - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a paste for forming an Ag base layer enabling an Ag base layer having excellent joining strength, conductivity and thermal conductivity to be formed on the surface of a copper layer made of cupper or copper alloy joined to a body to be joined out of a metal member having the copper layer.SOLUTION: The paste for forming an Ag base layer is provided which is used when the Ag base layer is formed on the surface of a copper layer made of copper or copper alloy joined to a body to be joined out of a metal member having the copper layer. The paste contains: Ag powder 11; powder 12 of Sn or Sn alloy; and acrylic resin 13 whose decomposition temperature in Natmosphere is 400°C or less.

Description

  The present invention relates to a paste for forming an Ag foundation layer used when forming an Ag foundation layer on the surface of the copper layer to be joined to a body to be joined among metal members having a copper layer made of copper or a copper alloy. It is.

A semiconductor device such as an LED or a power module has a structure in which a semiconductor element is bonded on a circuit layer made of a conductive material.
In power semiconductor elements for large power control used to control wind power generation, electric vehicles, hybrid vehicles, etc., the amount of heat generated is large. Therefore, for example, AlN (aluminum nitride), Al _An insulating circuit board comprising an insulating layer made of a ceramic substrate such as ₂ O ₃ (alumina) and a circuit layer formed by disposing a metal having excellent conductivity on one surface of the insulating layer has been conventionally used. Widely used. In addition, as an insulating circuit board, a board provided with a metal layer formed by disposing a metal having excellent thermal conductivity on the other surface of the insulating layer is also provided.

  For example, Patent Document 1 proposes an insulated circuit board in which a first metal plate and a second metal plate constituting a circuit layer and a metal layer are copper plates, and this copper plate is directly bonded to a ceramic substrate by a DBC method. Yes. In this DBC method, by utilizing a eutectic reaction between copper and copper oxide, a liquid phase is generated at the interface between the copper plate and the ceramic substrate, and the copper plate and the ceramic substrate are joined.

In the insulated circuit board described in Patent Document 1, an electronic component such as a semiconductor element is mounted on the surface of a circuit layer, and a heat sink base is soldered on the surface of a metal layer. Then, heat generated in an electronic component such as a semiconductor element is transmitted to the insulating circuit board side and dissipated to the outside through a heat sink base.
Recently, from the viewpoint of environmental protection, as a solder material used when joining an electronic component such as a semiconductor element and a circuit layer, or a heat sink base and a metal layer, for example, Sn-Ag, Sn-In, or Sn- Lead-free solders such as Ag-Cu are the mainstream.

Here, when directly soldering to a circuit layer or a metal layer made of copper or a copper alloy, the molten solder material reacts with copper, and the components of the solder material penetrate into the circuit layer or the metal layer, The characteristics of the circuit layer and the metal layer may be deteriorated. For this reason, conventionally, a Ni plating film is formed on the surface of a circuit layer or a metal layer, and solder bonding is performed.
Also, recently, compound semiconductor elements such as SiC or GaN are expected to be put into practical use from silicon semiconductors, and since the heat resistance of the semiconductor elements themselves is expected to be improved, there is a need for a bonding material that has better heat resistance than solder materials. It has been.

Therefore, as an alternative to the solder material, for example, Patent Document 2 proposes a technique for joining an electronic component such as a semiconductor element or a heat sink base using a metal paste having metal particles and an organic substance.
Patent Documents 3 and 4 propose a technique for joining an electronic component such as a semiconductor element or a heat sink base using an oxide paste containing metal oxide particles and an organic reducing agent.

  However, as disclosed in Patent Documents 2-4, when an electronic component such as a semiconductor element is joined using a metal paste or an oxide paste without using a solder material, it is made of a fired body of these pastes. Since the bonding layer is formed to be thinner than the solder material, the stress at the time of thermal cycle load tends to act on the electronic component such as a semiconductor element, and the electronic component such as the semiconductor element itself may be damaged. It was. Similarly, when the bonding layer formed between the metal layer and the heat sink becomes thin, thermal strain caused by the difference in thermal expansion coefficient between the insulating circuit board and the heat sink acts on the insulating circuit board, and the insulating layer is cracked. There was a fear.

Therefore, in Patent Documents 5 and 6, after forming an Ag underlayer on a circuit layer made of copper or a copper alloy using a glass-containing Ag paste, the circuit layer and the semiconductor element are bonded via a solder material or an Ag paste. Techniques to do this have been proposed. In this technique, a glass-containing Ag paste is applied to the surface of a circuit layer made of copper or a copper alloy and baked to remove the oxide film formed on the surface of the circuit layer by reacting with glass to remove the Ag underlayer. The semiconductor element is bonded to the circuit layer on which the Ag underlayer is formed by a solder material or an Ag paste.
Here, the Ag underlayer includes a glass layer formed by reacting glass with an oxide film of a circuit layer, and an Ag layer formed on the glass layer. Conductive particles are dispersed in the glass layer, and conduction of the glass layer is ensured by the conductive particles.

Japanese Patent Laid-Open No. 04-162756 JP 2006-202938 A JP 2008-208442 A JP 2009-267374 A JP 2012-109315 A JP 2013-012706 A

By the way, in the case where an Ag underlayer is formed on the surface of a circuit layer made of copper or a copper alloy using the glass-containing paste of Patent Documents 5 and 6, and the circuit layer and an electronic component such as a semiconductor element are joined, the Ag underlayer However, if the glass layer is formed thick, the electrical resistance value increases, so that there is a possibility that the electrical conductivity between the circuit layer and the electronic component such as a semiconductor element cannot be secured.
Further, when an Ag underlayer is formed on the surface of a metal layer made of copper or a copper alloy using the glass-containing pastes of Patent Documents 5 and 6, and the metal layer and the heat sink are joined, heat conduction is increased when the electrical resistance value increases. As a result, the heat transfer from the metal layer to the heat sink is also hindered, and heat may not be efficiently dissipated.

  The present invention has been made in view of the above-described circumstances, and has a bonding strength, conductivity on the surface of the copper layer to be bonded to the object to be bonded among metal members having a copper layer made of copper or a copper alloy. And an Ag underlayer-forming paste capable of forming an Ag underlayer excellent in thermal conductivity.

In order to solve such a problem and achieve the above-mentioned object, the Ag underlayer forming paste of the present invention is bonded to an object to be joined among metal members having a copper layer made of copper or a copper alloy. An Ag underlayer forming paste used for forming an Ag underlayer on the surface of a copper layer, an Ag powder, Sn or Sn alloy powder, and an acrylic having a decomposition temperature of 400 ° C. or lower in an N ₂ atmosphere And a series resin.

Since the Ag underlayer forming paste having this configuration has Sn or Sn alloy powder, the Ag underlayer forming paste is applied to the surface of the copper layer of the metal member to form the Sn or Sn alloy. By heating above the solidus temperature of the powder, the Sn or Sn alloy powder melts and a molten layer is formed. Here, Sn and copper of the circuit layer are diffused and alloyed with each other, and Ag powder is surrounded by the molten layer, and Ag powder and Sn are diffused and alloyed with each other.
Then, the interdiffusion of the molten layer and Ag and Cu further progresses, and the molten layer becomes an intermetallic compound containing Ag and Sn having a high melting point, and by solidifying, the plurality of Ag particles are intermetallic compounds containing Ag and Sn. Thus, an Ag underlayer having a structure bonded to each other is formed. The intermetallic compound containing Ag and Sn includes an intermetallic compound of Ag and Cu and an intermetallic compound of Cu and Sn in addition to the intermetallic compound of Ag and Sn. Further, when an Sn alloy is used as Sn or Sn alloy powder, an intermetallic compound of an element contained in the Sn alloy and Ag, Cu, or Sn is included. For example, when an Sn—Sb alloy is used as Sn or Sn alloy powder, the intermetallic compound containing Ag and Sn includes intermetallic compounds such as Ag and Sb, Cu and Sb, and Sn and Sb.
Thus, since the Ag particles excellent in conductivity and thermal conductivity are bonded to the copper layer with an intermetallic compound containing Ag and Sn, the Ag underlayer excellent in bonding strength, conductivity and thermal conductivity. Can be formed.
Moreover, since the decomposition temperature in the N ₂ atmosphere contains an acrylic resin having a temperature of 400 ° C. or lower, the acrylic resin is decomposed by setting the heating temperature after applying the Ag underlayer forming paste to 400 ° C. or higher. It can be removed, and the acrylic resin can be prevented from remaining in the Ag underlayer.

Here, in the paste for forming an Ag underlayer of the present invention, the average particle diameter of the Ag powder is preferably in the range of 0.1 μm or more and 10 μm or less.
In this case, since the average particle diameter of the Ag powder is 0.1 μm or more, the Ag powder can be uniformly dispersed in the Ag underlayer paste, and the Ag underlayer can be reliably formed. Become. On the other hand, since the average particle diameter of the Ag powder is 10 μm or less, the Ag particles are relatively densely arranged in the Ag underlayer, and the Ag underlayer having excellent conductivity and thermal conductivity. Can be formed.

In the Ag underlayer forming paste of the present invention, the average particle diameter of the Sn or Sn alloy powder is preferably in the range of 0.5 μm to 15 μm.
In this case, since the average particle diameter of the Sn or Sn alloy powder is 0.5 μm or more, the Sn or Sn alloy powder can be uniformly dispersed in the Ag underlayer paste. It becomes possible to form reliably. On the other hand, since the average particle diameter of the Sn or Sn alloy powder is 15 μm or less, the Ag powder and the Sn or Sn alloy powder can be uniformly mixed, and the intermetallic compound containing Ag and Sn can be mixed. Ag particles can be reliably bonded to each other.

Furthermore, in the paste for forming an Ag underlayer of the present invention, the content of the Ag powder is preferably in the range of 50 mass% to 80 mass%.
In this case, since the content of the Ag powder is 50 mass% or more, the Ag particles can be sufficiently disposed in the Ag underlayer, and the conductivity, thermal conductivity, and bondability with silver or silver oxide are sufficient. It is possible to form an Ag underlayer excellent in the thickness. On the other hand, since the content of the Ag powder is 80 mass% or less, the content of Sn or Sn alloy powder and acrylic resin is ensured, and the Ag particles are formed by the intermetallic compound containing Ag and Sn. Can be reliably bonded, and paste applicability and shape retention after application can be ensured.

Furthermore, in the paste for forming an Ag underlayer of the present invention, the content of the Sn or Sn alloy powder is preferably in the range of 15 mass% or more and 35 mass% or less.
In this case, since the content of the Sn or Sn alloy powder is 15 mass% or more, a molten layer can be sufficiently formed, and an Ag underlayer excellent in bonding strength with the copper layer is formed. Is possible. On the other hand, since the content of the Sn or Sn alloy powder is 35 mass% or less, the content of the Ag particles and the acrylic resin is ensured, and a relatively large number of Ag particles are combined to conduct electricity. And heat conductivity can be ensured, and paste applicability and shape retention after application can be ensured.

  According to the present invention, an Ag underlayer excellent in bonding strength, conductivity, and thermal conductivity is formed on the surface of the copper layer to be bonded to the object to be bonded among metal members having a copper layer made of copper or a copper alloy. A paste for forming an Ag underlayer that can be formed can be provided.

It is explanatory drawing of the paste for Ag foundation layer formation which is embodiment of this invention, and Ag foundation layer. It is a flowchart of the manufacturing method of the paste for Ag base layer formation which is embodiment of this invention. It is explanatory drawing which shows an example of the conjugate | zygote (semiconductor device) which formed Ag base layer using the paste for Ag base layer formation which is this embodiment. It is a flowchart which shows the manufacturing method of the conjugate | zygote (semiconductor device) shown in FIG. It is explanatory drawing which shows the manufacturing method of the conjugate | zygote (semiconductor device) shown in FIG. It is explanatory drawing which shows the other example of the joined body (semiconductor device) which formed Ag base layer using the paste for Ag base layer formation which is this embodiment. In an Example, it is upper surface explanatory drawing which shows the measuring method of the electrical resistance value of the thickness direction of Ag base layer. In an Example, it is side explanatory drawing which shows the measuring method of the electrical resistance value of the thickness direction of Ag base layer.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a schematic view of an Ag underlayer forming paste 10 according to the present embodiment and an Ag underlayer 20 formed using the Ag underlayer forming paste 10.
As shown in FIG. 1, this Ag underlayer forming paste 10 includes Ag powder 11, Sn or Sn alloy powder 12, and acrylic resin 13 having a decomposition temperature of 400 ° C. or lower in an N ₂ atmosphere. doing. In addition, you may add a solvent and a dispersing agent as needed.

The average particle diameter of Ag powder 11 (center particle diameter d50 measured by microtrack method) is 0.1 μm or more and 10 μm or less, and the average particle diameter of Sn or Sn alloy powder 12 (center particle diameter measured by microtrack method) d50) is 0.5 μm or more and 15 μm or less.
Further, the content of the Ag powder 11 is set to 50 mass% to 80 mass%, and the content of the Sn or Sn alloy powder 12 is set to 15 mass% or more and 35 mass% or less.

Here, as the powder 12 of Sn or Sn alloy, Sn—Ag alloy, Sn—Cu alloy, Sn—Zn—Al alloy, Sn—Sb alloy and the like can be used in addition to Sn.
Further, Ni, Co, Ge, P, Si, In, Bi, or the like may be added to the Ag underlayer forming paste 50 in an amount of 0.2 mass% or less based on the powder weight of Sn or Sn alloy. Addition of Ni, Co, Ge, P, Si, In, Bi, etc. improves the wettability when the Sn or Sn alloy powder is melted, facilitates the reaction with the circuit layer, and improves the bonding reliability. improves. In addition, when adding Ni, Co, Ge, P, Si, In, Bi, etc., it adds as an alloy (for example, Sn-Ni alloy or Sn-Sb-Ni alloy) of these elements and Sn or Sn alloy. It is desirable.

The N ₂ Acrylic resin 13 decomposition temperature of 400 ° C. or less in the atmosphere, for example, methyl methacrylate, n- butyl, i- butyl methacrylate, butyl t- methacrylate, 2-ethylhexyl methacrylate, methacrylic acid Lauryl, alkyl methacrylate, tridecyl methacrylate, stearyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, isobornyl methacrylate, glycidyl methacrylate, tetrahydrofurfuryl methacrylate, allyl methacrylate, 2-hydroxyethyl methacrylate , 2-methoxyethyl methacrylate, 2-ethoxyethyl methacrylate, dimethylaminoethyl methacrylate, ethylene glycol dimethacrylate, 1,3-butylene dimethacrylate A polymer such as glycol can be used.
In addition, it is preferable that content of the acrylic resin 13 shall be in the range of 0.1 mass% or more and 2 mass% or less.
Moreover, as an organic solvent, what can melt | dissolve acrylic resin can be used, for example, (alpha)-terpineol, a butyl carbitol acetate, diethylene crycol dibutyl ether etc. can be used. As the amount of the organic solvent, an organic solvent 7 to 24 times the organic solvent weight 1 can be used.
Furthermore, a dispersing agent can be added as needed. In the case of adding a dispersant, it is soluble in the organic solvent, preferably a carboxylic acid type or an amine type, and the amount of the dispersant is 0.05 to It is desirable to use in the range of 0.50.

Next, a method for producing the Ag underlayer forming paste 10 according to the present embodiment will be described with reference to the flowchart shown in FIG.
First, the above-mentioned Ag powder 11 and Sn or Sn alloy powder 12 are mixed to produce a mixed powder (powder mixing step S1). Moreover, the acrylic resin 13, the dispersant, and the solvent are mixed to produce an organic mixture (organic matter mixing step S2).

Then, the mixed powder obtained in the powder mixing step S1 and the organic mixture obtained in the organic matter mixing step S2 are premixed by a mixer (preliminary mixing step S3).
Next, the preliminary mixture is mixed while kneading using a roll mill having a plurality of rolls (kneading step S4).
The kneaded material obtained by kneading process S4 is filtered with a paste filter (filtration process S5).
In this way, the Ag underlayer forming paste 10 according to the present embodiment is produced.

Next, a process of forming the Ag underlayer 20 on the surface of the copper layer 18 made of copper or copper alloy using the Ag underlayer forming paste 10 according to the present embodiment will be described with reference to FIG.
First, the Ag underlayer forming paste 10 according to the present embodiment is applied to the surface of the copper layer 18 made of copper or a copper alloy.
Next, this Ag underlayer forming paste 10 is heat-treated. The heat treatment conditions are preferably a temperature of 400 ° C. to 600 ° C. and a holding time of 30 minutes to 2 hours in a nitrogen atmosphere, for example. Thereby, as shown in FIG. 1B, the acrylic resin in the Ag underlayer forming paste 10 is decomposed and removed, and the Sn or Sn alloy powder 12 is melted to form a molten layer 12a. Is done. At this time, Sn in the molten layer 12a and copper in the copper layer 18 are diffused and alloyed, and the Ag powder 11 is surrounded by the molten layer 12a, so that the Ag powder 11 and the molten layer 12a diffuse to each other. To alloy.
Then, as shown in FIG. 1C, the interdiffusion between the molten layer 12a and Ag and Cu further progresses, and the molten layer 12a becomes an intermetallic compound containing Ag and Sn having a high melting point, and solidifies by being solidified. Thus, an Ag underlayer 20 having a structure in which the Ag particles 21 are bonded with an intermetallic compound 22 containing Ag and Sn is formed. The intermetallic compound 22 containing Ag and Sn includes an intermetallic compound of Ag and Cu and an intermetallic compound of Cu and Sn in addition to the intermetallic compound of Ag and Sn. Further, when an Sn alloy is used as the Sn or Sn alloy powder 12, an intermetallic compound of Ag, Cu, and Sn with an element contained in the Sn alloy is included. For example, when an Sn—Sb alloy is used as the Sn or Sn alloy powder 12, the intermetallic compound 22 containing Ag and Sn includes an intermetallic compound such as Ag and Sb, Cu and Sb, or Sn and Sb. .

Here, FIG. 3 shows an example of a joined body (semiconductor device 51) in which the Ag underlayer 20 is formed using the Ag underlayer forming paste 10 according to the present embodiment.
The semiconductor device 51 includes an insulating circuit substrate 60 and a semiconductor element 53 bonded to one surface (upper surface in FIG. 3) of the insulating circuit substrate 60 via a bonding layer 52.

The insulating circuit board 60 includes a ceramic substrate 61 serving as an insulating layer, and a circuit layer 62 disposed on one surface (the upper surface in FIG. 3) of the ceramic substrate 61.
The ceramic substrate 61 is made of highly insulating AlN (aluminum nitride), Si ₃ N ₄ (silicon nitride), Al ₂ O ₃ (alumina), or the like. In this embodiment, it is comprised with AlN (aluminum nitride) excellent in heat dissipation. Further, the thickness of the ceramic substrate 61 is set in a range of 0.2 to 1.5 mm, and in this embodiment, is set to 0.635 mm.

  As shown in FIG. 5, the circuit layer 62 is formed by bonding a copper plate 72 made of copper or a copper alloy to one surface of the ceramic substrate 61. In the present embodiment, an oxygen-free copper rolled plate is used as the copper plate 72 constituting the circuit layer 62. A circuit pattern is formed on the circuit layer 62, and one surface (the upper surface in FIG. 3) is a mounting surface on which the semiconductor element 3 is mounted. Here, the thickness of the circuit layer 62 (thickness of the copper plate 72) is set within a range of 0.1 mm or more and 1.0 mm or less, and is set to 0.3 mm in the present embodiment. In the semiconductor device 51 (insulated circuit board 60), the circuit layer 62 corresponds to the copper layer 18 in FIG.

The above-described Ag underlayer 20 is formed on one surface of the circuit layer 62. As shown in FIG. 1C, the Ag underlayer 20 includes Ag particles 21 and an intermetallic compound 22 containing Ag and Sn, and a plurality of Ag particles 21 is a metal containing Ag and Sn. It is a structure bonded by the intermetallic compound 22.
In the present embodiment, the thickness of the Ag underlayer 20 is in the range of 1 μm to 15 μm.

  Here, the bonding layer 52 interposed between the Ag underlayer 20 and the semiconductor element 53 is a sintered body of a bonding material containing at least one or both of Ag particles and silver oxide particles and an organic material. In the form, a sintered body of a silver oxide paste containing silver oxide particles and a reducing agent made of an organic substance is used. In other words, the bonding layer 52 is an Ag fired body obtained by reducing silver oxide. Here, since the particles produced by reducing silver oxide are very fine, for example, with a particle size of 10 nm to 1 μm, a dense Ag fired layer is formed.

This silver oxide paste contains silver oxide powder (silver oxide particles), a reducing agent, a resin, and a solvent, and in this embodiment, in addition to these, contains an organometallic compound powder. .
The content of the silver oxide powder is 60 mass% or more and 92 mass% or less of the entire silver oxide paste, the content of the reducing agent is 5 mass% or more and 20 mass% or less of the entire silver oxide paste, and the content of the organometallic compound powder is oxidized. It is set as 0 mass% or more and 10 mass% or less of the whole silver paste, and the remainder is made into the solvent. In this silver oxide paste, a dispersant and a resin are not added in order to prevent unreacted organic matter from remaining in the bonding layer 52 obtained by sintering.

The reducing agent is an organic substance having reducibility, and for example, alcohol and organic acid can be used.
The organometallic compound has an action of promoting the reduction reaction of silver oxide and the decomposition reaction of organic substances by the organic acid generated by thermal decomposition, for example, formic acid Ag, acetic acid Ag, propionic acid Ag, benzoic acid Ag, oxalic acid. A carboxylic acid metal salt such as Ag is applied.
The silver oxide paste has a viscosity adjusted to 10 Pa · s to 500 Pa · s, more preferably 50 Pa · s to 300 Pa · s.

Next, a method for manufacturing the semiconductor device 51 shown in FIG. 3 will be described with reference to FIGS.
First, a copper plate 72 is bonded to one surface of the ceramic substrate 61 using a copper member bonding paste containing Ag and a nitride forming element to form a circuit layer 62 (circuit layer forming step S01).
Here, the copper member bonding paste contains a powder component containing Ag and a nitride-forming element, a resin, a solvent, a dispersant, a plasticizer, and a reducing agent. In addition to Ag and nitride forming elements, one or more additive elements selected from In, Sn, Al, Mn and Zn are included. In the present embodiment, Ti is used as the nitride forming element.

  Specifically, as shown in FIG. 5, Ag and nitride-forming element layer 74 is formed by applying a copper member bonding paste to one surface of ceramic substrate 61 by screen printing and drying. The thickness of the Ag and nitride forming element layer 74 is set to 60 μm or more and 300 μm or less after drying. Next, the copper plate 72 is laminated on one surface side of the ceramic substrate 61. That is, the Ag and nitride forming element layer 74 is interposed between the ceramic substrate 61 and the copper plate 72.

The circuit board 62 is formed on one surface of the ceramic substrate 61 by inserting and heating the copper plate 72 and the ceramic substrate 61 in a vacuum heating furnace in a state of being pressurized in the stacking direction (pressure 1 to 35 kgf / cm ² ). Form. During this heating, Ag and Ag in the nitride-forming element layer 74 diffuse toward the copper plate 72. At this time, a part of the copper plate 72 is melted by the reaction between Cu and Ag, and a molten metal region is formed at the interface between the copper plate 72 and the ceramic substrate 61. Then, when the molten metal region is solidified, the ceramic substrate 61 and the copper plate 72 are joined, and the circuit layer 62 is formed.

Here, in this embodiment, the pressure in the vacuum heating furnace is set in a range of 10 ⁻⁶ Pa to 10 ⁻³ Pa, and the heating temperature is set in a range of 790 ° C. to 850 ° C.
Note that after the solidification is completed, Ag and the Ag of the nitride forming element layer 74 are sufficiently diffused, and the Ag and nitride forming element layer 74 remains at the bonding interface between the ceramic substrate 61 and the copper plate 72. Absent.

Next, the Ag base layer 20 is formed on one surface of the circuit layer 62 (Ag base layer forming step S02).
In this Ag underlayer forming step S02, the Ag underlayer forming paste 10 according to the present embodiment is applied to one surface of the circuit layer 62 and heat-treated, as shown in FIG. 20 is formed.
Thus, the insulated circuit board 60 which is this embodiment in which the Ag underlayer 20 is formed on the surface of the circuit layer 62 made of copper or a copper alloy is manufactured.

Next, a silver oxide paste to be the bonding layer 52 is applied to the surface of the Ag underlayer 20 (silver oxide paste application step S03).
In addition, when apply | coating a silver oxide paste, various means, such as a screen printing method, an offset printing method, and a photosensitive process, are employable. In this embodiment, the silver oxide paste was printed by the screen printing method.

Next, after drying with the silver oxide paste applied (for example, stored at room temperature in an air atmosphere for 24 hours), the semiconductor element 53 is stacked on the silver oxide paste of the insulating circuit substrate 60 (semiconductor element stacking step S04). ).
Then, the semiconductor element 53 and the insulating circuit substrate 60 are stacked and placed in a heating furnace, and the silver oxide paste is baked (baking step S05). At this time, the semiconductor element 53 and the insulating circuit substrate 60 can be bonded more reliably by heating in a state where the semiconductor element 53 and the insulating circuit substrate 60 are pressurized in the stacking direction. In this case, the pressurizing pressure is desirably 0.5 to 10 MPa.
In this way, the bonding layer 52 is formed on the Ag base layer 20, and the semiconductor element 53 and the circuit layer 62 are bonded. Thereby, the semiconductor device 51 which is this embodiment is manufactured.

According to the Ag underlayer forming paste 10 according to the present embodiment having the above-described configuration, the Ag underlayer forming paste 10 includes the Sn or Sn alloy powder 12. By applying to the surface of the (circuit layer 62) and heating to above the solidus temperature of the Sn or Sn alloy powder 12, the Sn or Sn alloy powder 12 is melted and a molten layer 12a is formed. The molten layer 12a is diffused and alloyed with the copper layer 18 (circuit layer 62), and is present between the plurality of Ag powders 11 in the Ag underlayer forming paste 10. They diffuse into each other and form an alloy. Then, the interdiffusion of the molten layer 12a with Ag and Cu further progresses, and the molten layer 12a becomes an intermetallic compound containing Ag and Sn having a high melting point, and by solidifying, the plurality of Ag particles 21 convert Ag and Sn. An Ag underlayer 20 having a structure bonded with the intermetallic compound 22 is formed. Therefore, it is possible to form the Ag underlayer 20 having excellent bonding strength, conductivity, and thermal conductivity.
Further, since the decomposition temperature in the N ₂ atmosphere containing an acrylic resin 13 of 400 ° C. or less, the heating temperature after the application of the Ag base layer forming paste 10 With 400 ° C. or higher, the acrylic resin 13 can be decomposed and removed, and the acrylic resin 13 can be prevented from remaining in the Ag underlayer 20.

  Further, in the Ag underlayer forming paste 10 according to this embodiment, the average particle diameter (center particle diameter d50 measured by the microtrack method) of the Ag powder 11 is in the range of 0.1 μm or more and 10 μm or less. Therefore, the Ag powder 11 can be uniformly dispersed in the Ag underlayer forming paste 10, and the Ag underlayer 20 can be reliably formed. Furthermore, the Ag particles 21 are arranged relatively densely in the Ag underlayer 20, and it is possible to form the Ag underlayer 20 having excellent conductivity, thermal conductivity, and bonding properties.

  Further, in the Ag underlayer forming paste 10 according to the present embodiment, the average particle diameter (center particle diameter d50 measured by the microtrack method) of the Sn or Sn alloy powder 12 is in the range of 0.5 μm or more and 15 μm or less. Therefore, the Sn or Sn alloy powder 12 can be uniformly dispersed in the Ag underlayer forming paste 10, and the Ag underlayer 20 can be reliably formed. Furthermore, the Ag powder 11 and the Sn or Sn alloy powder 12 can be uniformly mixed, and the Ag particles 21 can be reliably bonded together by the intermetallic compound 22 containing Ag and Sn.

  Further, in the Ag underlayer forming paste 10 according to the present embodiment, the content of the Ag powder 11 is 50 mass% or more, so that the Ag particles 21 can be sufficiently disposed in the Ag underlayer 20. It is possible to form the Ag underlayer 20 excellent in conductivity, thermal conductivity, and bondability. On the other hand, since the content of the Ag powder 11 is 85 mass% or less, the content of the low-melting-point metal powder 12 and the acrylic resin 13 is secured, and the intermetallic compound 22 containing Ag and Sn is used. The Ag particles 21 can be securely bonded, and paste applicability and shape retention after application can be ensured.

  Further, in the Ag underlayer forming paste 10 according to the present embodiment, the content of the Sn or Sn alloy powder 12 is 15 mass% or more, so that the molten layer 12a can be sufficiently formed, It is possible to form the Ag underlayer 20 having excellent bonding strength with the layer 18 (circuit layer 62). On the other hand, since the content of Sn or Sn alloy powder 12 is 35 mass% or less, the content of Ag powder 11 and acrylic resin 13 is ensured, and a relatively large number of Ag particles 21 are bonded. Thus, conductivity and thermal conductivity can be ensured, and paste applicability and shape retention after application can be ensured.

  Furthermore, since Sn, Sn—Ag alloy, Sn—Cu alloy, Sn—Zn—Al alloy, Sn—Sb alloy or the like is used as the Sn or Sn alloy powder 12 in this embodiment, the Ag underlayer is formed. In step S02, heat treatment is performed at a temperature of 400 ° C. or higher and 600 ° C. or lower, so that the Sn or Sn alloy powder 12 can be melted to reliably form the intermetallic compound 22 containing Ag and Sn. .

  In the semiconductor device 51 shown in FIG. 3, as described above, the Ag underlayer 20 having a structure in which a plurality of Ag particles 21 are bonded to the surface of the circuit layer 62 by the intermetallic compound 22 containing Ag and Sn. Since it is formed, the circuit layer 62 and the intermetallic compound 22 containing Ag and Sn are firmly bonded, and the bonding strength between the circuit layer 62 and the Ag underlayer 20 can be sufficiently increased. And since the circuit layer 62 in which this Ag foundation layer 20 was formed, and the semiconductor element 53 are joined via the joining layer 52 which consists of a baking body of a silver oxide paste, Ag foundation layer 20, the joining layer 52, Becomes the bonding between the same kind of metals (Ag), the bonding strength between the Ag underlayer 20 and the bonding layer 52 is improved, and the bonding reliability between the insulating circuit substrate 60 and the semiconductor element 53 can be improved. Further, the electrical resistance of the Ag base layer 20 is kept low, and the conductivity between the insulating circuit substrate 60 and the semiconductor element 53 can be ensured. Furthermore, since heat conductivity is also ensured, the heat generated in the semiconductor element 53 can be efficiently dissipated to the insulating circuit board 60 side.

  Furthermore, in this embodiment, since the bonding layer 52 is a fired body of silver oxide paste containing silver oxide powder and a reducing agent, the silver oxide is reduced by the reducing agent when the silver oxide paste is fired. Thus, the Ag layer becomes fine and the bonding layer 52 can have a dense structure. Further, since the reducing agent is decomposed when the silver oxide is reduced, it is difficult to remain in the bonding layer 52 and the conductivity and strength in the bonding layer 52 can be ensured. Furthermore, since the silver oxide paste can be fired at a relatively low temperature condition such as 300 ° C., for example, the bonding temperature of the semiconductor element 53 can be kept low, and the thermal load on the semiconductor element 53 can be reduced. it can.

As mentioned above, although embodiment of this invention was described, this invention is not limited to this, It can change suitably in the range which does not deviate from the technical idea of the invention.
In the above embodiment, as an example of the metal member for forming the Ag underlayer, a circuit layer made of a copper plate has been described as an example. However, the present invention is not limited to this. For example, as shown in FIG. The Ag underlayer 120 may be formed on the surface of the copper layer 162b of the circuit layer 162 (metal member) formed by solid phase diffusion bonding of 162b and the aluminum layer 162a.

  A confirmation experiment conducted to confirm the effectiveness of the present invention will be described.

(Invention Example 1-9, Comparative Example)
First, the present invention example 1 was obtained by the method described in the embodiment using Ag powder, Sn or Sn alloy powder, acrylic resin, and the balance as a solvent (α-terpineol) shown in Table 1. 9 and comparative example Ag underlayer forming pastes were prepared.

(Invention example 11-19, comparative example)
A copper plate to be a circuit layer is joined to one surface of a ceramic substrate by an active metal brazing method, and an aluminum plate to be a metal layer is joined to the other surface of the ceramic substrate by a brazing method to produce an insulated circuit board. did. Here, the ceramic substrate was AlN, and the size was 27 mm × 17 mm × 0.6 mm. The copper plate used as the circuit layer was made of oxygen-free copper, and the size was 25 mm × 15 mm × 0.3 mm. The aluminum plate used as the metal layer was 4N aluminum having a purity of 99.99 mass% or more, and the size was 25 mm × 15 mm × 1.6 mm.

  On the surface of the circuit layer, an Ag underlayer was formed by applying and heat-treating an Ag underlayer forming paste having the composition shown in Table 1.

  Next, as a silver oxide paste, commercially available silver oxide powder (manufactured by Wako Pure Chemical Industries, Ltd.), myristyl alcohol as a reducing agent, and 2,2,4-trimethyl-1,3-pentanediol mono (2 -Methyl propanoate), silver oxide powder; 80% by mass, reducing agent (myristyl alcohol); 10% by mass, solvent (2,2,4-trimethyl-1,3-pentanediol mono (2) -Methylpropanoate)); the mixture in the ratio of the remainder was prepared.

Then, the above silver oxide paste is applied on the Ag underlayer (application thickness: 10 μm), a semiconductor element having an Au film formed on the bonding surface is disposed, and the silver oxide paste is baked to form a bonding layer. Thus, semiconductor devices of Inventive Examples 11-19 and Comparative Examples were produced.
Here, the firing conditions of the silver oxide paste were a vacuum atmosphere, a firing temperature of 300 ° C., a firing time of 10 minutes, and a pressing pressure of 5 MPa.

(Conventional example)
On the surface of the circuit layer made of a copper plate, an Ag underlayer was formed using a glass-containing Ag paste, and the circuit layer and the semiconductor element were bonded by a bonding layer obtained by baking a silver oxide paste, thereby manufacturing a comparative semiconductor device. . The other conditions were the same as in Invention Example 11-19.
After applying the glass-containing Ag paste on the circuit layer, it was placed in a heating furnace and baked at 600 ° C. to form an Ag underlayer on the circuit layer. The glass-containing Ag paste used here was a glass-based Ag paste containing cellulose resin, Bi ₂ O ₃ —ZnO—B ₂ O ₃ lead-free glass frit, α-terpineol and Ag as solvents.

  About the obtained various semiconductor devices, shear strength, thermal resistance, and electrical resistance were evaluated. The evaluation results are shown in Table 1.

(Share strength)
The shear strength was measured using a shear strength evaluation tester for a semiconductor device in which 2.5 mm × 2.5 mm × 0.200 mm semiconductor elements were joined. In the measurement, the circuit layer of the semiconductor device was fixed horizontally, the position 50 μm above the surface of the circuit layer was pushed horizontally from the side with a shear tool, and the strength when the semiconductor element was broken was measured. The moving speed of the share tool was set to 0.1 mm / sec. The strength test was performed three times for one condition, and the arithmetic average value was taken as the measured value. As a shear strength evaluation tester, a bonding tester (Model: PTR-1101) manufactured by Reska Co., Ltd. was used.

(Thermal resistance)
Semiconductor devices were fabricated using heater chips (13 mm × 10 mm × 0.25 mm) as semiconductor elements, and these semiconductor devices were brazed and joined to a cooler. Next, the heater chip was heated with a power of 100 W, and the temperature of the heater chip was measured using a thermocouple. Further, the temperature of the cooling medium (ethylene glycol: water = 9: 1) flowing through the cooler was measured. And the value which divided the temperature difference of a heater chip | tip and the temperature of a cooling medium with electric power was made into thermal resistance. In addition, the conventional example which formed Ag base layer using the glass containing Ag paste was set to 1 on the basis, and it evaluated by the ratio with this conventional example.

(Electrical resistance)
With respect to the insulated circuit board on which the Ag underlayer was formed, the electrical resistance value in the thickness direction of the Ag underlayer was measured using a tester (manufactured by KEITHLEY: 2010 MULTITIMER) by the method described in FIGS. The electrical resistance is measured on a circuit layer that is separated from the Ag base layer edge by H when the upper surface center point of the Ag base layer is a distance H from the top center point of the Ag base layer to the Ag base layer edge. And went between.

In the conventional example in which the Ag underlayer was formed with the glass-containing Ag paste on the surface of the circuit layer, the electric resistance was higher than that in the inventive example.
In a comparative example using an acrylic resin having a decomposition temperature exceeding 400 ° C., the thermal resistance and the electrical resistance were higher than those of the present invention example.
On the other hand, in Example 11-19 of the present invention in which the Ag underlayer was formed on the surface of the circuit layer using the Ag underlayer forming paste of the present invention, the thermal resistance and electrical resistance were low.

10 Ag base layer forming paste 11 Ag powder 12 Sn or Sn alloy powder 13 Acrylic resin 20 Ag base layer 21 Ag particles 22 Intermetallic compound containing Ag and Sn

Claims (5)

A paste for forming an Ag foundation layer used when forming an Ag foundation layer on the surface of the copper layer to be joined to a body to be joined among metal members having a copper layer made of copper or a copper alloy,
A paste for forming an Ag underlayer comprising Ag powder, Sn or Sn alloy powder, and an acrylic resin having a decomposition temperature of 400 ° C. or lower in an N ₂ atmosphere.   2. The paste for forming an Ag underlayer according to claim 1, wherein an average particle diameter of the Ag powder is in a range of 0.1 [mu] m to 10 [mu] m.   3. The Ag underlayer forming paste according to claim 1, wherein an average particle diameter of the Sn or Sn alloy powder is in a range of 0.5 μm to 15 μm.   The Ag base layer forming paste according to any one of claims 1 to 3, wherein a content of the Ag powder is in a range of 50 mass% or more and 80 mass% or less.   The content of the powder of the Sn or Sn alloy is in a range of 15 mass% or more and 35 mass% or less, for forming an Ag underlayer according to any one of claims 1 to 4. paste.

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