Joining sheet with preform layer, method of manufacturing joined body, and joined member with preform layer

Abstract

To provide a preform-layered joining sheet highly strong in a sheet itself and a method of making a joined body having a high joining strength.SOLUTION: A joining sheet, for joining a base material and an electronic component together, includes a copper sheet and a porous preform layer consisting of a copper particle on one or both surfaces of the copper sheet, in which the copper particle is coated at a surface with a copper nano-particle smaller than an average particle size of the copper particle, an average particle size calculated from a BET value of the copper nano-particle is 9.59 nm or greater and 850 nm or smaller, and the preform layer has an average porosity of 11% or higher and 78% or lower. A joined body is made by laminating a base material and an electronic component through the joining sheet to obtain a laminate and then heating the laminate with pressurization in a direction of lamination.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a bonding sheet having a porous preform layer for bonding a substrate and an electronic component in the assembly or mounting of the electronic component, a method for manufacturing a bonded body using this preform layer, and a bonded member having a porous preform layer. [Background technology]

[0002] Traditionally, solder materials made of lead, tin, or their alloys have been widely used to join dissimilar metals, but lead-free solder materials are now being used to avoid the harmful effects of lead on the human body and the environment. Particularly for power devices used in high-temperature ranges, there is an increasing demand for materials that ensure high reliability even at high temperatures by utilizing the sintering phenomenon of copper or silver.

[0003] Against this background, a method using a bonding material is known for joining two or more components in assembling electronic components such as power semiconductor chips and LEDs. A method for manufacturing a bonded body using a paste containing micrometer-sized metal particles such as silver, gold, or copper, a binder, and a solvent has been disclosed (see, for example, Patent Documents 1 and 2).

[0004] On the other hand, a preform sheet, which is a clad material that utilizes the bonding of an intermetallic compound formed by laminating two or more different metals into a ribbon or sheet shape, has been disclosed as a bonding material (see, for example, Patent Documents 3 and 4). In Patent Documents 3 and 4, a preform material for semiconductor encapsulation containing an intermetallic compound of Cu and Sn is produced.

[0005] Also disclosed is a preform material that combines a hard metal made of Cu, Au, or Ag, or an alloy thereof, with a soft metal made of Sn (see, for example, Patent Document 5). Patent Document 5 also utilizes bonding of intermetallic compounds. Furthermore, a dealloying method has been disclosed in which an alloy made of two or more metal elements is left with one metal or alloy and the other components are dissolved using acid, alkali, or electrochemically to obtain a nanoporous metal with a high surface area. This method involves polishing an Au-65 at% Ag alloy with 2000-grit abrasive paper and then immersing it in 60% HNO3 kept at 25°C for 1 hour to produce an Au nanoporous sheet (see Non-Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-167616 [Patent Document 2] Japanese Patent Application Publication No. 2019-220641 [Patent Document 3] Japanese Patent Application Publication No. 2018-001238 [Patent Document 4] Japanese Patent Application Publication No. 2018-121012 [Patent Document 5] Japanese Patent Application Publication No. 2019-036603 [Non-patent literature]

[0007] [Non-Patent Document 1] K. Matsunaga et al., "High temperature reliability of joints using a Au nanoporous sheet," pp. 147-150, Proceedings of the 25th Microelectronics Symposium, September 2015 Summary of the Invention [Problem to be solved by the invention]

[0008] The methods for manufacturing a bonded body using pastes shown in Patent Documents 1 and 2 improve bonding performance, but require the introduction of printing technology, dispensing equipment, etc., and require a large number of application steps, resulting in relatively high manufacturing costs. Another issue is the concern that voids caused by organic substances derived from the contained binder, flux, and solvent may reduce bonding reliability.

[0009] Furthermore, in the joining of intermetallic compounds shown in Patent Documents 3 to 5, although intermetallic compounds such as Cu6Sn5 have the advantage of being hard, they have low strength and there is a concern that they may not pass strict reliability tests. Also, the preform materials shown in Patent Documents 3 and 4 are made by rolling metal powder, but the strength of the preform material itself is low and there is a problem that the shape of the preform material is easily distorted depending on how it is handled.

[0010] Furthermore, the Au nanoporous sheet shown in Non-Patent Document 1 is produced by etching Ag from an AuAg alloy. A similar dealloying method is envisioned: an alloy foil is produced from an alloy of Cu and a metal less noble than Cu, and the metal less noble than Cu is then etched to produce a Cu porous sheet. However, with the above method, both the Au nanoporous sheet and the Cu porous sheet become porous, and Ag and metals less noble than Cu remain in the core sheet, which poses a problem of the porous sheet's shape being easily distorted. For this reason, there is a need for a structure in which a preform material is firmly formed around a core sheet, or a structure in which a preform material is formed directly on an arbitrary substrate.

[0011] An object of the present invention is to provide a bonding sheet with a preform layer that has high strength itself. Another object of the present invention is to provide a method for producing a bonded body with high bonding strength. Yet another object of the present invention is to provide bonded members with a preform layer for obtaining a bonded body with high bonding strength.

[0012] A first aspect of the present invention is a bonding sheet for bonding a substrate and an electronic component, comprising a copper sheet and a porous preform layer made of copper particles on one or both sides of the copper sheet, wherein the surfaces of the copper particles are coated with copper nanoparticles smaller than the average particle size of the copper particles, and the average particle size calculated from the BET value of the copper nanoparticles is 9.59 nm or more and 850 nm or less, and the average porosity of the preform layer is 11% or more and 78% or less, and the average porosity of the preform layer is calculated by image analysis of the cross section of the bonding sheet using a scanning electron microscope. Based on the total area (S1) of the preform layer and the area (S2) of the pores in the preform layer, this is an arithmetic average of the porosity (P) calculated by the following formula (1): A bonding sheet with a preform layer. P(%) = (S2 / S1) × 100 (1)

[0013] A second aspect of the present invention is a method for producing a bonded body by laminating a substrate and an electronic component via the bonding sheet with the preform layer of the first aspect to obtain a laminate, and then pressurizing and heating the laminate in the lamination direction.

[0014] A third aspect of the present invention is a method for producing a bonded body, comprising the steps of: forming a porous preform layer according to the first aspect on a substrate and / or an electronic component having a copper surface or a nickel surface; laminating the substrate and the electronic component with the preform layer interposed therebetween to obtain a laminate; and pressurizing and heating the laminate in the lamination direction.

[0015] A fourth aspect of the present invention is a bonded member with a preform layer, which is a bonded member for bonding an electronic component or a substrate to the substrate or the electronic component, characterized in that the substrate and / or the electronic component has a copper surface or a nickel surface, and the copper surface or the nickel surface has the porous preform layer according to the first aspect. [Effects of the Invention]

[0016] The bonding sheet of the first aspect of the present invention has a porous preform layer provided on one or both sides of a copper sheet core sheet, which provides high strength and prevents deformation during handling. Furthermore, the surfaces of the copper particles are coated with copper nanoparticles smaller than the average particle size of the copper particles, and the average particle size of the copper nanoparticles calculated from the BET value is 9.59 nm to 850 nm. Therefore, when the bonding sheet is placed between a substrate and an electronic component and pressurized and heated, the porous preform layer having a predetermined average porosity is densified, some of the copper particles are sintered, and the copper nanoparticles are easily sintered, forming a bonding layer that bonds the copper particles together and firmly bonds the substrate and the electronic component.

[0017] In the method for producing a bonded body according to the second aspect of the present invention, when a laminate consisting of a substrate, a bonding sheet with a preform layer according to the first aspect, and an electronic component is pressurized and heated in the stacking direction, the porous preform layer becomes densified, and some of the copper particles are sintered, resulting in a bonded body in which the copper particles are bonded together and form a bonding layer that firmly bonds the substrate and the electronic component.

[0018] In a method for producing a bonded body according to a third aspect of the present invention, when a laminate in which a substrate and an electronic component are laminated via the preform layer according to the first aspect is pressurized and heated in the stacking direction, the porous preform layer is densified, and some of the copper particles are sintered, resulting in a bonded body in which the copper particles are bonded to each other and form a bonding layer that firmly bonds the substrate and the electronic component.

[0019] The bonded member with a preform layer according to the fourth aspect of the present invention has the porous preform layer according to the first aspect on the copper surface of a substrate and / or an electronic component, and when this bonded member is pressed against the electronic component or substrate and heated, the porous preform layer becomes densified, and the bonded member can be firmly bonded to the electronic component or substrate. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a structural view of a bonding sheet, schematically showing a porous preform layer according to a first embodiment of the present invention. [Figure 2]FIG. 1 is a diagram showing a state in which preform layers are formed on both sides of a copper sheet by the electrolytic copper alloy plating method of the first embodiment of the present invention. [Figure 3] FIG. 1 is a diagram showing a state in which a preform layer is formed on one side of a copper sheet by the electrolytic copper alloy plating method of the first embodiment of the present invention. [Figure 4] 4A and 4B are diagrams showing a method for manufacturing a bonded body according to a first embodiment of the present invention, in which Fig. 4A shows a bonding sheet being placed on a base material, Fig. 4B shows an electronic component being placed on the bonding sheet, followed by application of pressure and heat, and Fig. 4C shows a bonding body being produced after application of pressure and heat. [Figure 5] 5(a) to 5(d) are views showing a method for manufacturing a bonded body according to a second embodiment of the present invention, in which a preform layer is formed on a part of a substrate by electrolytic copper alloy plating, and FIGS. 5(e) to 5(h) are views showing a method for manufacturing a bonded body by placing an electronic component on the preform layer and then applying pressure and heat. [Figure 6] FIG. 2 is a scanning electron microscope photograph of the surface of the preform layer of Example 1 manufactured by the method of the first embodiment of the present invention. [Figure 7] 7A and 7B are scanning electron microscope photographs of a longitudinal section of a preform layer of Example 13 manufactured by the method of the second embodiment of the present invention, in which Fig. 7A is a longitudinal section photograph of a copper substrate and a preform layer formed on the substrate, and Fig. 7B is an enlarged longitudinal section photograph of the preform layer portion. DETAILED DESCRIPTION OF THE INVENTION

[0021] Next, an embodiment of the present invention will be described with reference to the drawings.

[0022] First Embodiment [Joint sheet] As shown in Fig. 1, a bonding sheet 10 of the first embodiment has a copper sheet 11 and porous preform layers 13 made of copper particles 12 on both sides of the copper sheet. As shown in Figs. 4(a) to 4(c), the bonding sheet 10 is interposed between a base material 16, typically a substrate, and an electronic component 17, typically a semiconductor chip element, to form a bonding layer 15 that bonds the electronic component 17 to the base material 16. As shown in Fig. 3, a bonding sheet 20 may be used in which a porous preform layer 13 made of copper particles 12 is formed on one side of the copper sheet 11. The bonding sheets 10 and 20 of the present embodiment have the copper sheet 11, and therefore have the characteristics of high strength and resistance to deformation, unlike the preform materials shown in Patent Documents 3 and 4.

[0023] (Copper sheet: copper foil) The thickness of the copper sheet 11 is preferably 10 μm to 90 μm, and more preferably 15 μm to 50 μm. If the thickness is less than the lower limit of 10 μm, the copper sheet becomes difficult to handle during manufacturing of the bonding sheet. If the thickness exceeds the upper limit of 90 μm, the flexibility of the copper sheet decreases, and its ability to conform to the irregularities on the bonding layer surface deteriorates, which may affect the reliability of the bonding. The thickness of the copper sheet 11 is determined by the following method. First, the copper foil sheet 11 is completely encapsulated with epoxy resin and then cut perpendicular to the foil surface direction of the copper foil, and the cut surface is polished with an argon ion beam. Next, the polished surface is observed with an SEM (scanning electron microscope), and the thickness of the copper foil at 100 or more random locations is measured, and the average value is taken as the thickness of the copper foil (copper sheet 11). When the copper sheet is a copper foil, the thickness of the copper sheet can also be measured with a digital caliper.

[0024] Pure copper or a copper alloy can be used as the copper foil constituting the copper sheet 11. For example, oxygen-free copper, tough pitch copper, phosphorus-deoxidized copper, etc. can be used. The copper foil can be a rolled copper foil obtained by rolling such a copper material, or an electrolytic copper foil produced by electroplating.

[0025] To produce electrolytic copper foil, any copper plating solution containing appropriate additives is used. An example of a manufacturing method involves using a cylindrical drum cathode, rotating the drum cathode, electroplating copper foil, and then winding it up. On the other hand, rolled copper foil is produced by casting a Cu ingot, and then processed to the desired thickness through hot rolling, cold rolling, and annealing. Generally, rolled copper foil has a smoother surface than electrolytic copper foil, but considering the adhesion of the plating on the porous body described below, it is preferable to perform a surface treatment such as a roughening treatment on both copper foils. Both rolled copper foil and electrolytic copper foil can be degreased, washed with water and acid-washed before the next preform layer is formed on the foil surface.

[0026] (preform layer) As shown in FIGS. 1 to 3, the porous preform layer 13 is formed in the form of an aggregate of copper particles, in which copper particles 13 are stacked on both sides or one side of a copper sheet 11. The aggregate of copper particles 12 has an average porosity of 11% or more and 78% or less. If the average porosity is less than 11%, there are few copper particles that contribute to sintering the porous preform layer, and the sinterability of the copper particles decreases. If the average porosity exceeds 78%, the porosity within the porous preform layer becomes too high, making the preform layer 13 brittle and reducing the sinterability of the copper particles. Therefore, when the bonding layer 15 shown in FIG. 4 is formed, it is not possible to bond the substrate 16 and the electronic component 17 with high bonding strength. The preferred average porosity is 15% or more and 67% or less.

[0027] As shown in the enlarged view of Figure 1, the copper particles 12 are preferably coated on their surfaces with copper nanoparticles having an average particle size smaller than that of the copper particles 12, because this facilitates sintering of the copper particles together to form a robust bonding layer 15 when the porous preform layer 13 is pressurized, as shown in Figure 4. Here, the average particle size of the copper nanoparticles is difficult to calculate from a microscope image because the copper particles are composed of fine copper particles and nanoparticles even finer than the copper particles, so the average particle size is calculated from BET measurements. Thus, the average particle size of the copper nanoparticles calculated from BET measurements is preferably 9.59 nm or more and 850 nm or less.

[0028] The thickness of the porous preform layer 13 is preferably 15 μm to 50 μm. If the thickness of the preform layer is less than 15 μm, the strength of the preform layer itself decreases, making it difficult to handle. If the thickness of the preform layer exceeds 50 μm, the preform layer will have difficulty conforming to the irregularities on the surfaces of the members to be joined during joining, which may result in a decrease in joining strength.

[0029] The average porosity of the preform layer 13 described above is calculated by image analysis of the cross section of the bonding sheet 10 using a scanning electron microscope. The arithmetic mean of the porosities (P) calculated by the following formula (1) is defined as the average porosity. Specifically, the measurement is performed by taking photographs three times in different fields of view, and the average value of the calculated porosities is defined as the average porosity. P(%) = (S2 / S1) × 100 (1) In the formula (1), P is the porosity of the preform layer, S1 is the total area of ​​the preform layer, and S2 is the area of ​​the pores in the preform layer.

[0030] The average particle size of the copper nanoparticles described above is measured by the BET method using the porous preform layer. BET measurements are performed using a Macsorb HM-model-1201. The copper sheet with the preform layer is cut into 2 mm squares, filled into a measurement cell, and measured using the BET single-point method. The mass of the copper sheet is subtracted from the measured value, and the value is converted to the mass of the preform layer itself. The particle size of the copper nanoparticles is calculated from the calculated BET measurement value using the following equation (2). Note that the coefficient 335.95 in the following equation (2) is a value calculated from the theoretical values ​​of the copper density, the surface area of ​​the copper nanoparticles, and the volume of the copper nanoparticles. The average particle size (d) of the copper nanoparticles is the average value of three measurements performed using the BET method. d(nm)=335.95 / (BET measurement value (m 2 / g)) (2)

[0031] [Method for manufacturing bonding sheet] One example of a method for forming the porous preform layer 13 on one or both sides of the copper sheet 11 is to form a copper alloy plating film by co-depositing copper and a metal species that is electrochemically less noble than copper on the surface of the copper sheet by electroplating, and then dealloying the less noble metal species in the copper alloy plating film to form a porous preform layer made of copper particles.

[0032] In this method, by controlling the deposition ratio and deposition form of copper and metal species less noble than copper, a porous preform layer having a desired porosity and shape can be easily formed. In addition, when forming a porous preform layer on the surface of a long copper sheet, the copper sheet can be produced by unwinding the copper sheet wound around a roll, electrolytically plating it with a copper alloy while winding it around another roll, and then undergoing a dealloying process.

[0033] Next, the copper alloy plating and dealloying methods will be described in detail. Copper alloy plating is performed by forming a copper-zinc alloy plating film on one or both sides of a copper sheet using a copper-zinc alloy plating solution containing, for example, copper salt, zinc salt, and additives and solvents that control the deposition of copper and zinc. This copper alloy plating must contain copper, but can be performed by electroless plating or electrolytic plating. Metal species that are electrochemically less noble than copper (e.g., Fe, Mn, etc.) can also be selected as alloy species. The copper ion concentration of the copper-zinc alloy plating solution is preferably 0.0025 mol / L to 0.1 mol / L, and the zinc ion concentration is preferably 0.1 mol / L to 0.8 mol / L. The zinc ion concentration is higher than the copper ion concentration because copper deposits preferentially over zinc due to the difference in standard oxidation-reduction potential. The pH of the plating solution is preferably 6.1 or higher to adjust the deposition balance between copper and zinc. Furthermore, the cathode current density is preferably 0.3 A / dm 2 ~0.8A / dm 2 Set to the range.

[0034] The copper and zinc ion sources for copper alloy plating can be copper salts and zinc salts known as metal ion sources for plating systems. Examples include sulfates, pyrophosphates, acetates, chlorides, and sulfamates. Trisodium citrate and potassium pyrophosphate are used as conductive and supporting salts as additives for controlling the deposition of copper and zinc to form a copper-zinc alloy plating film with a smooth surface. Brighteners can include surfactants such as amino acids, compounds selected from their salts, and alkanolamines. An example of a surfactant is (ethylenedinitrilo)tetrakis(2-propanol). Amino acids that are water-soluble and do not precipitate with copper salts (copper ions) or zinc salts (zinc ions) at any concentration can be used. Examples include glycine, serine, alanine, tyrosine, aspartic acid, glutamic acid, histidine, and the like, or their salts. It is preferable to select appropriate additives to achieve a structure in which the surfaces of copper particles are coated with copper nanoparticles smaller than the average particle size of the copper particles during dealloying.

[0035] The dealloying of the formed copper-zinc alloy plating film can be achieved by, for example, an etching reaction using a chemical solution or an electrochemical anodic reaction. In this embodiment, acid dealloying is performed by immersing and stirring the copper alloy film in a solution containing hydrochloric acid at a concentration of 0.002 mol / L to 0.5 mol / L at a temperature of 20°C to 35°C for 30 minutes or longer (depending on the thickness of the plating film). This results in a porous preform layer 13 made of copper particles on one or both sides of the copper sheet 11. It is preferable to dealloy the preform layer 13 after dealloying so that the zinc concentration measured by energy dispersive X-ray analysis (EDX) is 0.6 at% or less.

[0036] Next, the copper sheet 11 having the porous preform layer 13 formed on one or both sides thereof is washed with a cleaning solvent such as ethanol, water, or acetone, and dried using dry air in the atmosphere. This results in a bonding sheet 10 or 20 having a porous preform layer 13 made of copper particle aggregates and having an average porosity of 11% to 78% formed on one or both sides of the copper sheet 11. The resulting bonding sheet is preferably immersed for a predetermined period of time in a rust inhibitor mainly composed of benzotriazole and a surfactant to prevent surface oxidation.

[0037] The total thickness of the bonding sheets 10, 20 is at least 15 μm. That is, it is 15 μm or more. The preferred total thickness is 20 μm to 50 μm. If the total thickness is less than the lower limit of 15 μm, the strength of the bonding sheet itself may be reduced. If the total thickness exceeds 50 μm, when the base material is a substrate, if the substrate to which the electronic component is bonded has warpage, the warpage may not be absorbed. The total thickness of the copper bonding sheet is measured in the same way as the thickness of the copper sheet 11.

[0038] [Method for joining a substrate and an electronic component using a joining sheet] As shown in Fig. 4, a method for bonding a substrate 16 and an electronic component 17 using a bonding sheet 10 will be described. Examples of the substrate 16 include an oxygen-free copper plate, various heat dissipation substrates, FR4 (Flame Retardant Type 4) substrates, Kovar substrates, etc. Also, a substrate having nickel (Ni) formed on the bonding surface may be used. Examples of the electronic component 17 include electronic components such as silicon chip elements and LED chip elements.

[0039] As shown in FIG. 4(a), first, the bonding sheet 10 is placed at a predetermined position on the substrate 16, and then, as shown in FIG. 4(b), electronic components 17 are mounted on the bonding sheet 10. In this state, the bonding sheet 10 is heated in a nitrogen atmosphere in a heating furnace at a temperature of 250°C to 350°C for 1 minute to 30 minutes. In some cases, the substrate 16 and the electronic components 17 may be bonded while applying a pressure of 1 MPa to 20 MPa. As a result, as shown in FIG. 4(c), the bonding sheet 10 becomes a bonding layer 15, which bonds the substrate 16 and the electronic components 17 to form a bonded body 18, and the substrate 16 and the electronic components 17 are bonded together.

[0040] <Second embodiment> [Joined members with porous preform layer formed thereon] As shown in FIGS. 5(d) and 5(e), the second embodiment is a bonded member 40 to which an electronic component is bonded, which includes a substrate 46 and a porous preform layer 13 formed on the substrate 46, with the porous preform layer 13 having an average porosity of 11% to 78%. The substrate 46 (FIG. 5) in the second embodiment corresponds to the copper sheet 11 (FIG. 1) in the first embodiment. The porous preform layer 13 is the same as the porous preform layer 13 in the first embodiment. The substrate 46 has a copper surface, and is, for example, an oxygen-free copper plate or a substrate with a copper-metallized bonding surface. Alternatively, a substrate 16 having a Ni surface can be used as the substrate 46. One example is an oxygen-free copper plate with a Ni surface formed by Ni plating.

[0041] The second embodiment of the bonded member 40 having a porous preform layer formed thereon can be manufactured by the following method. As shown in FIG. 5(a), in this method, a substrate 46 is prepared. As shown in FIG. 5(b), the substrate 46 is masked with a resist film 41 except for the bonding surface 46a. In this state, the substrate 46 is immersed in a copper alloy plating solution. As shown in FIG. 5(c), a porous preform layer 13 is formed on the bonding surface 46a. Then, as shown in FIG. 5(d), the resist film 41 is removed to obtain the bonded member 40. Although not shown, a copper alloy plating film is formed on the bonding surface 46a using the copper alloy plating solution. The porous preform layer 13 is then formed by dealloying the copper alloy plating film. The copper alloy plating and dealloying can be performed in the same manner as in the first embodiment. In the above description, the preform layer 13 is formed only on the bonding surface 46a. However, the preform layer 13 may be formed on the entire surface of the substrate 46 without providing the resist film 41.

[0042] [Method for joining a member to be joined and an electronic component] As shown in FIG. 5( e), to bond an electronic component 47 such as a silicon chip element or an LED chip element onto a bonded member 40, the bonded member 40 having the porous preform layer 13 formed thereon is placed on a pressure plate 42. As shown in FIG. 5( f), the electronic component 47 is placed on the preform layer 13 to obtain a laminate. Then, as shown in FIG. 5( g), the laminate consisting of the bonded member 40 and the electronic component 47 is pressed in the stacking direction by pressure plates 42 and 43. The pressure conditions are the same as those for the substrate 16 and the electronic component 17 shown in FIG. 4( a). As a result, as shown in FIG. 5( h), the preform layer 13 serves as a bonding layer 45, bonding the bonded member 40 and the electronic component 47 together, obtaining a bonded body 44.

[0043] Although not shown, the substrate may be an oxygen-free copper plate without a preform layer formed on its surface, or a substrate with a copper-metallized bonding surface, and the electronic component may have a preform layer formed on its bonding surface. Furthermore, although not shown, a preform layer may be formed on the substrate, and then a preform layer may be formed on the bonding surface of the electronic component. By forming preform layers on both surfaces, the bonding strength between the substrate and the electronic component can be further increased, which is preferable. [Example]

[0044] Next, examples of the present invention will be described in detail together with comparative examples. In the following examples 1 to 12 and comparative examples 1 to 6, bonding sheets were produced by the method of the first embodiment. In addition, in examples 13 to 20 and comparative examples 7 and 8, a porous preform layer was formed on an oxygen-free copper plate by the method of the second embodiment.

[0045] Example 1 (Example of manufacturing a bonding sheet by the method of the first embodiment) First, a 15 μm-thick rolled copper foil made of oxygen-free copper was used as the copper sheet. Prior to copper plating, the copper sheet was immersed in a degreasing solution containing sodium hydroxide as the main component. The copper sheet was then removed from the degreasing solution, washed with water, and then washed with an ethanol solution. It was then immersed in a 10% by mass sulfuric acid aqueous solution and acid-washed. The acid-washed copper sheet was then plated with copper zinc on both sides using the plating apparatus 30 shown in FIG. 2.

[0046] A copper-zinc alloy plating bath was prepared according to the following composition. The plating conditions are also shown. Table 1 below shows the composition of the plating bath and the plating conditions of Example 1, with particular attention paid to the plating bath composition and plating conditions.

[0047] [composition] Copper sulfate pentahydrate (Cu 2+ as): 0.01 mol / L Zinc sulfate heptahydrate (Zn 2+ as): 0.15 mol / L Potassium pyrophosphate: 0.3 mol / L (Ethylenedinitrilo)tetrakis(2-propanol): 0.01 mol / L Serine, an amino acid: 0.001 mol / L Ion-exchanged water: Remaining [Plating conditions] Bath temperature: 30℃ Bath pH: 8.6 Cathode current density: 0.5A / dm 2

[0048] [Table 1]

[0049] The copper-zinc plating film was immersed in a 27°C solution containing 0.05 mol / L hydrochloric acid and stirred for 60 minutes to remove zinc from the copper-zinc alloy plating film and dealloy it. To prevent surface oxidation, the dealloyed sheet was subjected to a rust prevention treatment by immersing it for 30 seconds in a rust inhibitor mainly composed of benzotriazole and a surfactant. This resulted in a bonding sheet in which a porous preform layer composed of copper particles was formed on both sides of the copper sheet. Figure 6 shows a scanning electron microscope photograph of the surface of the preform layer of Example 1.

[0050] <Examples 2 to 12 and Comparative Examples 1 to 6> In Examples 2 to 12 and Comparative Examples 1 to 6, the thickness of the copper sheet made of rolled oxygen-free copper foil was the same as or different from that in Example 1, the concentration of copper sulfate pentahydrate was the same as or different from that in Example 1, the concentration of zinc sulfate heptahydrate was the same as or different from that in Example 1, the concentration of potassium pyrophosphate or trisodium citrate was the same as or different from that in Example 1, the concentration of (ethylenedinitrilo)tetrakis(2-propanol) was the same as or different from that in Example 1, and the concentration of the amino acid was the same as or different from that in Example 1. The pH of the plating bath was the same as or different from that in Example 1, and the cathode current density during plating was the same as or different from that in Example 1. Otherwise, copper-zinc plating films were formed in the same manner as in Example 1. Characteristic items among the plating bath compositions and plating conditions for Examples 2 to 12 and Comparative Examples 1 to 6 are shown in Table 1 above. The copper zinc plating film was subjected to zinc dealloying and anti-rust treatment in the same manner as in Example 1 to obtain a bonding sheet in which a porous preform layer made of copper particles was formed on both sides of the copper sheet.

[0051] <Comparative Evaluation Part 1> <Average porosity of porous preform layer and average particle size of copper nanoparticles> The average porosity of the porous preform layer of the 18 types of bonding sheets obtained in Examples 1 to 12 and Comparative Examples 1 to 6 and the average particle size of the copper nanoparticles covering the copper particles constituting this preform layer were determined using the method described above.

[0052] <Manufacturing of the joint body> The 18 types of bonding sheets obtained in Examples 1 to 12 and Comparative Examples 1 to 6 were placed between a substrate 16 and a chip 17, which is an electronic component, as shown in Figures 4(a) and 4(b), and then pressed and heated to obtain a bonded body 18. The substrate 16 is made of a 33 mm square oxygen-free copper plate (thickness: 2 mm) or an oxygen-free copper plate with a Ni-plated surface (Ni plating thickness: 3 μm, total thickness: 2 mm). The chip 17 is made of a 2.5 mm square Si wafer (thickness: 200 μm) with copper metallization on the outermost surface. Next, the bonding sheet 10 was sandwiched between the chip 17 and the substrate 16 to produce a laminate. Furthermore, this laminate was held for 15 minutes in a nitrogen atmosphere at a temperature of 320°C and a pressure of 8 MPa using a pressure and heat bonding device (manufactured by Alpha Design; HTB-MM), to bond the substrate 16 and the chip 17 via the bonding layer 15. The shear strength of the 18 types of bonded bodies 18 was measured as follows.

[0053] <Method for measuring the shear strength of a bonded body> The shear strength of the bonded structures was measured using a shear strength evaluation tester (Bond Tester; Dage Series 4000, manufactured by Nordson Advanced Technologies, Inc.). Specifically, the shear strength was measured by fixing the substrate (oxygen-free copper plate) of the bonded structure horizontally and pressing the chip-attached Si wafer horizontally from the side at a position 50 μm above the surface (top surface) of the bonding layer. The strength was measured when the chip broke. The shear tool movement speed was 0.1 mm / s. Three strength tests were performed per condition, and the arithmetic mean of the strength values ​​was used as the measured bond strength. The shear strengths of the 18 bonded structures are shown in Table 2 below. A bond strength of 15 MPa or greater was rated "excellent," a bond strength of 1.7 MPa or greater but less than 15 MPa was rated "good," and a bond strength of less than 1.7 MPa was rated "poor." Note that a "-" in the bond strength table in Table 2 indicates that the chip and substrate were not bonded despite attempts to bond them, or that the chip delaminated before the bond strength was measured.

[0054] [Table 2]

[0055] As is clear from Table 2, in Comparative Examples 1 and 2, the average porosity was 9% and 9%, which is smaller than the aforementioned lower limit of 11%, and the average particle size of the copper nanoparticles calculated from the BET value was 871.0 nm and 885.0 nm, which is larger than the aforementioned upper limit of 850 nm. Therefore, the bonding sheets of Comparative Examples 1 and 2 were no longer optimal porous bodies for bonding. Even when the substrate and chip were bonded via the bonding sheets of Comparative Examples 1 and 2, the substrate and chip were bonded, but the bonding strength was only 10.1 MPa to 12.1 MPa, and the bonding evaluation was "good."

[0056] In Comparative Examples 3 and 4, the average porosity was 83% and 83%, respectively, exceeding the aforementioned upper limit of 78%, and the average particle size of the copper nanoparticles calculated from the BET value was 8.4 nm and 9.2 nm, respectively, which was smaller than the aforementioned lower limit of 9.59 nm. As a result, the strength of the porous preform layers on both sides of the copper sheet became weak, and it was not possible to use it as a bonded sheet. Even when the substrate and chip were bonded via the bonding sheets of Comparative Examples 3 and 4, the substrate and chip were not bonded, and the bonding evaluation was "poor."

[0057] In Comparative Example 5, the average porosity was 25% within the aforementioned range, which was satisfactory in terms of porosity, but the average particle size calculated by BET was 950.1 nm, which exceeded the aforementioned upper limit of 850 nm. Therefore, the bonding sheet of Comparative Example 5 did not have sufficient sinterability, and the bonding strength was only 3.9 MPa. In Comparative Example 6, the average particle size was 671.3 nm, within the aforementioned range, but the average porosity was 9%, below the aforementioned lower limit of 11%. Therefore, although the average particle size was sufficiently small, the bonding sheet of Comparative Example 6 lacked the porosity required for sintering, resulting in a bonding strength of only 4.1 MPa. As a result, even when the substrate and chip were bonded via the bonding sheets of Comparative Examples 5 and 6, the bonding evaluation was "good."

[0058] In contrast to these, in Examples 1 to 12, the average porosity of the preform layer and the average particle size calculated from the BET value were appropriately controlled, and the average porosity of the preform layer was within the aforementioned range of 11% to 78% and the average particle size of the copper nanoparticles calculated from the BET value was also within the aforementioned range of 9.59 nm to 850 nm. A porous preform layer was formed on both sides of the copper sheet, and when the substrate and chip were bonded via the bonding sheets of Examples 1 to 12, the substrate and chip were firmly bonded, and all bonding evaluations were "excellent."

[0059] Example 13 (Example of manufacturing of joined members by the method of the second embodiment) As shown in FIG. 5(a), a 33 mm square oxygen-free copper plate (thickness: 2 mm) was used as the substrate 46, which corresponds to the copper sheet of Example 1. This substrate 46 was treated before copper plating in the same manner as in Example 1. As shown in FIG. 5(b), a resist film 41 was formed on the substrate 46 except for a bonding surface 46a (14 mm square) to which a chip 47, an electronic component, was bonded. In this state, a copper-zinc plating film was formed on one side of the substrate 46 using the plating apparatus 30 shown in FIG. 3. Characteristic items among the plating bath composition and plating conditions of Example 25 are shown in Table 3 below.

[0060] [composition] Copper sulfate pentahydrate (Cu 2+ as): 0.01 mol / L Zinc sulfate heptahydrate (Zn 2+ as): 0.15 mol / L Potassium pyrophosphate: 0.3 mol / L (Ethylenedinitrilo)tetrakis(2-propanol): 0.01 mol / L Serine, an amino acid: 0.001 mol / L Ion-exchanged water: Remaining [Plating conditions] Bath temperature: 30℃ Bath pH: 8.6 Cathode current density: 0.5A / dm 2

[0061] [Table 3]

[0062] The copper-zinc plating film was immersed in a 27°C solution containing 0.05 mol / L hydrochloric acid and stirred for 60 minutes to remove zinc from the copper-zinc alloy plating film and dealloy it. The dealloyed substrate was then subjected to a rust prevention treatment by immersing it for 30 seconds in a rust inhibitor primarily composed of benzotriazole and a surfactant to prevent surface oxidation. This resulted in a bonded member 40 (see FIG. 5(d)), in which a porous preform layer 13 composed of copper particles was formed on the bonding surface 46a of the substrate 46. FIG. 7(a) shows a scanning electron microscope photograph of the longitudinal section of the preform layer and substrate (oxygen-free copper plate) of Example 13, and FIG. 7(b) shows an enlarged longitudinal cross-sectional photograph of the preform layer portion.

[0063] <Examples 14 to 20 and Comparative Examples 7 to 10> In Examples 14 to 20 and Comparative Examples 7 and 8, the type of substrate was the same as or different from that in Example 13, the concentration of copper sulfate pentahydrate was the same as or different from that in Example 13, the concentration of zinc sulfate heptahydrate was the same as or different from that in Example 13, the concentration of potassium pyrophosphate or trisodium citrate was the same as or different from that in Example 13, the concentration of (ethylenedinitrilo)tetrakis(2-propanol) was the same as or different from that in Example 13, and the concentration of amino acid was the same as or different from that in Example 13. The pH of the plating bath was the same as or different from that in Example 13, and the cathode current density during plating was the same as or different from that in Example 13. Otherwise, copper-zinc plating films were formed in the same manner as in Example 13. Characteristic aspects of the plating bath compositions and plating conditions for Examples 14 to 20 and Comparative Examples 7 to 10 are shown in Table 3 above.

[0064] <Comparative Evaluation No. 2> <BET specific surface area of ​​copper particles that make up the porous preform layer> The average porosity of the porous preform layers on the 12 types of substrates obtained in Examples 13 to 20 and Comparative Examples 7 to 10 and the average particle size of the copper nanoparticles covering the copper particles that make up these preform layers were measured using the same method as described in Comparative Evaluation Part 1. The results are shown in Table 4.

[0065] <Manufacturing of the joint body> As shown in Figures 5(e) to (h), a chip 17 made of a 2.5 mm square or 10 mm square Si wafer (thickness: 200 µm) with copper metallization on the outermost surface was placed on a porous preform layer 13 on the surface of a substrate made of 12 types of base material 16 obtained in Examples 13 to 20 and Comparative Examples 7 to 10, and the base material 16 and electronic component 17 were pressurized and heated to obtain a bonded body 18. This bonding was performed in the same manner as described in Comparative Evaluation 1. The shear strength of these 12 types of bonded bodies 44 was measured in the same manner as described in Comparative Evaluation 1. The shear strengths of the 12 types of bonded bodies are shown in Table 4 below. The bonding evaluation was the same as that described in Comparative Evaluation 1.

[0066] [Table 4]

[0067] As is clear from Table 4, in Comparative Examples 7 and 8, both the average porosity and the average particle size were outside the aforementioned ranges. In Comparative Example 7, the average porosity was smaller than the aforementioned range, and the bonding sheet of Comparative Example 7 lacked the porosity required for sintering. Also, since the average particle size was larger than the aforementioned range, sintering of the copper particles did not progress, and the degree of porosity of the reforming layer was insufficient. In Comparative Example 8, the average porosity was greater than the aforementioned range, and the average particle size was also less than the aforementioned range, so the preform layer of the bonding sheet in Comparative Example 8 was weak and brittle. Therefore, in Comparative Examples 7 and 8, although the substrate and the chip were joined, the bonding strength in Comparative Example 7 was only 12.5 MPa, and the bonding evaluation was "good," while in Comparative Example 8, the bonding strength was only 0.8 MPa, and the bonding evaluation was "poor."

[0068] In Comparative Example 9, the average porosity was within the aforementioned range, and the porosity was satisfactory, but the average particle size calculated from BET exceeded 850 nm, and the bonding sheet of Comparative Example 9 did not have sufficient sinterability, and the bonding strength was only 5.8 MPa. In addition, in Comparative Example 10, the average particle size was within the aforementioned range, but the average porosity was outside the aforementioned range. Therefore, although the average particle size was sufficiently small, the bonding sheet of Comparative Example 10 lacked the porosity that contributes to sintering, so the bonding strength was only 6.7 MPa and the bonding evaluation was "good."

[0069] In contrast, in Examples 13 to 20, zinc was dealloyed on one side of the substrate, and the average porosity of the formed preform layer was within the aforementioned range of 11% to 78%. Furthermore, a porous preform layer was formed, consisting of copper particles whose average particle size, calculated from the BET value, was also within the aforementioned range of 9.59 nm to 850 nm. When a chip, which is an electronic component, was placed on the bonded member on which the preform layer was formed on the substrate of Examples 13 to 20 and the bonded member and chip were bonded, the bonded member and chip were firmly bonded, and all bonding evaluations were "excellent." [Industrial Applicability]

[0070] The bonding sheet of the present invention can be used to bond an electronic component to a substrate by being interposed between the electronic component and the substrate. [Explanation of symbols]

[0071] 10, 20 Joining sheet 11 Copper Sheet 12 Copper particles 12a Copper nanoparticles 13 Preform layer 15, 45 bonding layer 16, 46 Base material 17, 47 Electronic Components 18, 44 zygote 40 Parts to be joined

Claims

1. A bonding sheet for bonding a substrate and an electronic component, comprising a copper sheet and a porous preform layer made of copper particles on one or both sides of the copper sheet, The surfaces of the copper particles are coated with copper nanoparticles smaller than the average particle size of the copper particles, and the average particle size calculated from the BET value of the copper nanoparticles is 9.59 nm or more and 850 nm or less, The average porosity of the preform layer is 11% or more and 78% or less, A bonding sheet with a preform layer, characterized in that the average porosity of the preform layer is the arithmetic mean of the porosity (P) calculated by the following formula (1) based on the total area (S1) of the preform layer calculated by image analysis of the cross section of the bonding sheet using a scanning electron microscope and the area (S2) of the pore portion in the preform layer. P (%) = (S2 / S1) x 100 (1)

2. A bonding sheet with a preform layer as described in claim 1, characterized in that the average porosity of the preform layer is 53% or more and 78% or less.

3. A method for producing a bonded body by laminating a substrate and an electronic component via the bonding sheet with the preform layer according to claim 1 or 2 to obtain a laminate, and then pressurizing and heating the laminate in the lamination direction.

4. A method for producing a bonded body, comprising: forming a porous preform layer according to claim 1 or 2 on a substrate and / or an electronic component having a copper surface or a nickel surface; laminating the substrate and the electronic component with the preform layer interposed therebetween to obtain a laminate; and pressurizing and heating the laminate in the lamination direction.

5. A bonded member to which an electronic component or a substrate is bonded to the substrate or the electronic component, A bonded member with a preform layer, characterized in that the substrate and / or the electronic component has a copper surface or a nickel surface, and the copper surface or the nickel surface has the porous preform layer according to claim 1 or 2 on it.

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