JP2020155461A - Bonding sheet and method for bonding electronic component to substrate using bonding sheet - Google Patents

Abstract

To provide a bonding sheet having a high bonding strength when an electronic component is bonded to a substrate, and a method for bonding an electronic component to a substrate using the bonding sheet.SOLUTION: There is provided a bonding sheet in which Ag fine particles having an average particle size of 10-500 nm are coated and fixed at an average coverage rate of 70% or more, on both sides of a core sheet that is made of a Cu foil. The surface roughness Ra of the Cu foil is preferably 1.0 μm or less, and the average crystallite diameter of Cu constituting the Cu foil is preferably 10 μm or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a bonding sheet used for bonding electronic components such as a semiconductor chip element and an LED chip element, and a method of bonding electronic components to a substrate using the bonding sheet. More specifically, the present invention relates to a joining sheet used for joining an electronic component to a substrate by interposing it between the electronic component and the substrate, and a method of joining the electronic component to the substrate using the joining sheet.

In recent years, in order to improve the functionality of electronic devices, miniaturization and high density of electronic devices have been required, and the operational stability of semiconductor devices is also ensured for bonding sheets for joining electronic components to substrates. Therefore, the bonding sheet is also required to have high heat dissipation characteristics and high bonding strength.

Conventionally, as this kind of bonding sheet, it is a self-supporting film formed of porous silver, which is a porous body of silver, and has a density of 40 to 72% by volume, and the average crystal grain size of silver crystals of porous silver. Is 1.7 to 2.6 μm, the flexural modulus obtained from the three-point bending test at 25 ° C. is 16 to 24 GPa, the maximum bending strength is 100 MPa or more, and the breaking bending strain is 1.3% or more. The sheet is disclosed (see, for example, Patent Document 1 (claim 1, paragraph [0017], paragraph [0034])). This porous silver sheet is obtained by molding a paste-like composition into a sheet, drying and heating to sinter the silver particles, or after sintering, exposing the mixture to 200 ° C. to 450 ° C. for 1 minute or more. Obtained by doing.

Further, as another bonding sheet, a bonding member having a metal fine particle layer in which metal fine particles having a particle diameter of 1 to 100 nm having a surface coated with an organic protective film are fixed on at least one surface of the metal foil is disclosed. (See, for example, Patent Document 2 (Claim 1, Claim 5, paragraph [0039])). The metal fine particles are produced by mixing the metal vapor and the steam of the organic protective film material under a reduced pressure inert gas atmosphere to produce a fine particle composition containing the metal fine particles whose surface portion is coated with the organic protective film. After that, it is produced by precipitating a fine particle composition containing metal fine particles whose surface is coated with an organic protective film on the surface of a metal foil. An organic protective film made of an amine compound is formed on the surface of the metal fine particles.

As yet another bonding sheet, a first bonding layer containing metal nanoparticles, a metal foil layer made of Ag, Au or an alloy thereof, and a second bonding layer containing metal nanoparticles are formed in this order. A metal bonding material in which the total amount of metal nanoparticles composed of one or more of Ag, Au, Cu, and Ni among the metal components contained in the first bonding layer and the second bonding layer containing metal nanoparticles is 10% by mass or more. Is disclosed (see, for example, Patent Document 3 (claim 7, claim 9, paragraph [0041])). In Patent Document 3, when forming a layer containing metal nanoparticles on a surface to be bonded or on a metal foil, a paste containing metal nanoparticles is prepared, and the metal nanoparticles paste is applied onto the surface to be bonded. As a metal nanoparticle paste, metal nanoparticles covered with an organic shell are prepared, and the metal nanoparticles are dispersed in a predetermined solvent to form a slurry, a paste, a grease, or the like. Alternatively, it is described that the composition is waxy or the like.

Japanese Unexamined Patent Publication No. 2016-169411 Japanese Unexamined Patent Publication No. 2006-073550 Japanese Unexamined Patent Publication No. 2015-093295

The porous silver sheet described in Patent Document 1 is obtained by forming a paste-like composition containing silver particles into a sheet, then drying and heating to sinter the silver particles, and heat-annealing the silver particles. Can be obtained. However, in the porous silver sheet described in Patent Document 1, the average crystal grain size of silver crystals is relatively large, 1.7 to 2.6 μm. Therefore, for example, when heated at a low temperature of 200 ° C., silver particles are formed. In some cases, it is difficult to sinter, and it is difficult to form a dense and high bonding layer.

Further, in the bonding member described in Patent Document 2, metal fine particles are coated with an organic protective film made of an amine compound. Further, in the metal bonding material described in Patent Document 3, a paste containing metal nanoparticles covered with an organic shell is prepared, and the metal nanoparticle paste is applied onto the surface to be bonded to be formed on the surface to be bonded or. A layer containing metal nanoparticles is formed on the metal foil. For this reason, when an electronic component and a substrate are bonded using the bonding member or metal bonding material described in Patent Document 2 or Patent Document 3, gas due to an organic substance is likely to be generated at the time of bonding, and voids are generated in the bonding layer. There is a problem that it is easy to perform and it is difficult to obtain high bonding strength.

An object of the present invention is to solve the above problems and to provide a bonding sheet having high bonding strength when an electronic component is bonded to a substrate and a method for bonding an electronic component to a substrate using the bonding sheet. ..

In the bonding sheet according to the first aspect of the present invention, Ag fine particles having an average particle size of 10 nm to 500 nm are coated and fixed on both sides of a core sheet made of Cu foil at an average coverage rate of 70% or more.

The bonding sheet according to the second aspect of the present invention is an invention based on the first aspect, wherein the surface roughness Ra of the Cu foil is 1.0 μm or less, and the average crystal of Cu constituting the Cu foil is formed. The child diameter is 10 μm or less.

A third aspect of the present invention is a method of joining electronic components to a substrate using the joining sheet of the first or second aspect.

The bonding sheet according to the first aspect of the present invention is an organic component because Ag fine particles having an average particle size of 10 nm to 500 nm are coated and fixed on both sides of a core sheet made of Cu foil at an average coverage rate of 70% or more. Does not include. Therefore, when the electronic component and the substrate are bonded, high bonding strength can be obtained without generating gas due to organic substances at the time of bonding and without generating voids in the bonding layer.

In the bonding sheet according to the second aspect of the present invention, the surface roughness Ra of the Cu foil is 1.0 μm or less, and the average crystallite diameter of Cu constituting the Cu foil is 10 μm or less. It firmly adheres to the surface of the core sheet.

In the method of the third aspect of the present invention, since the electronic component is bonded to the substrate by using the bonding sheet of the first or second aspect, the electronic component and the substrate can be bonded with high strength.

It is a block diagram of the bonding sheet of embodiment of this invention. It is a figure which shows the state which bonded the semiconductor chip element of embodiment of this invention to a substrate. It is a figure which shows the situation which Ag fine particles are coated on both sides of the core sheet of a copper foil by the contact plating method of embodiment of this invention.

Next, a mode for carrying out the present invention will be described with reference to the drawings.

[Joining sheet]
As shown in FIG. 1, the bonding sheet 10 of the present embodiment is configured by coating both sides of a core sheet 11 made of Cu foil with Ag fine particles 12. As shown in FIG. 2, the bonding sheet 10 is interposed between the semiconductor chip element 16 which is an electronic component and the substrate 17, and is used to bond an electronic component such as the semiconductor chip element 16 to the substrate 17. .. The core sheet 11 shown in FIG. 1 preferably has a thickness of 50 μm to 200 μm, and more preferably 100 μm to 150 μm. If the thickness is less than the lower limit of 50 μm, the core sheet is difficult to handle when manufacturing the joining sheet, and if the thickness exceeds the upper limit of 200 μm, the thermal resistance of the core sheet increases. Therefore, the joining of the present embodiment is performed. The heat dissipation of the electronic component obtained by using the sheet 10 is lowered, which may shorten the life of the electronic component. The thickness of the core sheet 11 is determined by the following method. First, the core sheet 11 which is a Cu foil is completely covered with an epoxy resin, then cut perpendicular to the foil surface direction of the Cu foil, and the cut surface is polished by an argon ion beam. Next, the polished surface is observed with an SEM (scanning electron microscope), the thickness of 100 or more copper foils is randomly measured, and the average value is taken as the thickness of the Cu foil (core sheet 11). ..

It is preferable that the Cu foil constituting the core sheet 11 is a rolled foil because Ag fine particles are likely to adhere to the rolled streaks. The surface roughness Ra of the Cu foil is preferably 1.0 μm or less. If the surface roughness Ra exceeds 1.0 μm, the Ag fine particles 12 may not be uniformly adhered to the surface of the core sheet 11. The preferable surface roughness Ra is 0.5 μm or less. The average crystallite diameter of Cu constituting the Cu foil is preferably 10 μm or less, and more preferably 5 μm or less. .. The surface roughness Ra of the Cu foil is measured using a laser microscope, and the average crystallite diameter of the Cu foil is measured by an X-ray diffraction method.

Pure copper or a copper alloy can be used as the Cu foil constituting the core sheet 11. For example, oxygen-free copper, tough pitch copper, phosphorus deoxidized copper and the like can be used.

The average particle size of the Ag fine particles 12 coated on both sides of the bonding sheet 10 is 10 nm to 500 nm. If the average particle size is less than 10 nm, the stability of the Ag fine particles is lowered, so that high bonding strength cannot be obtained. If it exceeds 500 nm, the sinterability of Ag fine particles is lowered, so that high bonding strength cannot be obtained. The average particle size of the preferred Ag fine particles is 50 nm to 300 nm. The average coverage of the Ag fine particles 12 is 70% or more. If the average coverage is less than 70%, high bonding strength cannot be obtained when Ag fine particles are sintered during bonding. As shown in FIG. 1, the Ag fine particles 12 are preferably coated so that the Ag fine particles uniformly form a single Ag fine particle layer 13. The preferable average coverage is 80% or more. The average particle size of the Ag fine particles 12 is measured by SEM observation. Specifically, the diameter of Ag coated on the surface of the bonding sheet 10 is randomly measured at 100 or more points, and the average value thereof is taken as the average particle size. The average coverage is calculated by SEM observation. Specifically, the SEM image (10 mm × 10 mm) on the surface of the joining sheet 10 randomly selected is multiplied by the number of Ag fine particles and the area obtained by converting the average particle size of the Ag fine particles into a perfect circle. It is defined as the coverage, and the average value measured at 10 or more points at random is defined as the average coverage. The Ag particles existing on the boundary are calculated as Ag particles inside the boundary.

The total thickness of the bonding sheet is at least 50 μm. That is, it is 50 μm or more. The preferred total thickness is 100 μm to 150 μm. If the total thickness is less than the lower limit of 50 μm, if the substrate to which the electronic components are bonded has a warp, the warp may not be absorbed. If the total thickness exceeds 200 μm, the thermal resistance of the core sheet 11 increases, which may shorten the life of the module manufactured by using the bonding sheet 10. The total thickness of the joining sheet is measured by the same method as the thickness of the core sheet 11.

[Manufacturing method of joining sheet]
Subsequently, a method for manufacturing the joining sheet of the present embodiment will be described. This manufacturing method includes a contact plating method, an Ag plating solution dipping method, and a coating heating method.

(Contact plating method)
As shown in FIG. 3, in this contact plating method, an Ag plating solution 21 is placed in a container 20, and a conductive sheet 22 made of Ag foil and a core sheet 11 made of Cu foil are arranged in the solution at intervals. As shown in FIG. 1, Ag fine particles are formed on both sides of the core sheet 11 by electrically connecting the conductive sheet 22 and the core sheet 11 with a lead wire 23 and reducing Ag ions in the Ag plating solution. 12 is a method of coating. In catalytic plating, Ag ions are reduced by electrons generated when the Ag salt described below is dissolved into Ag ions in a solution, and Ag is precipitated as fine particles on both surfaces of the core sheet 11. The Ag fine particles 12 not only stick to the core sheet 11, but the portion of the Ag fine particles 12 in contact with the core sheet 11 diffuses into the core sheet 11, and the Ag fine particles 12 adhere to the core sheet 11.

The conductive sheet 22 is preferably an Ag foil in order to supplement Ag ions in the Ag plating solution, which decreases as the core sheet 11 adheres to the surface.

The Ag plating solution 21 contains an Ag salt, a complexing agent and a solvent. Examples of the Ag salt include silver nitrate, silver oxide, silver sulfate, silver carbonate and the like, in addition to fatty acid silver such as silver acetate, silver citrate and silver oleate. The complexing agent forms a complex with Ag ions, and typical examples thereof include aliphatic amines such as aminodecane, ethylenediamine, ethylenediaminetetraacetic acid, ethylenediamine, glycine, hydantine, pyrrolidone, and succinateimide, and citric acid. , Citric acid, carboxylates such as nitrilotriacetic acid, hydroxyethylidenediphosphonic acid, aminotrimethylenephosphonic acid, mercaptopropionic acid, thioglycol, thiosemicarbazide and the like can be used. Examples of the solvent include butyl carbitol acetate (BCA), butyl carbitol (BC), ethylene glycol, diethylene glycol, triethylene glycol, glycerin, terpineol and the like. In the Ag plating solution 21, in order to more uniformly coat the core sheet 11 with the Ag fine particles 12, a surfactant, a brightener, a crystal regulator, a pH adjuster, a precipitation inhibitor, a stabilizer and the like are added as necessary. It may be added.

The Ag ion concentration in the Ag plating solution 21 is preferably 0.1 mol / L to 2 mol / L. If it is less than 0.1 mol / L, the average particle size of the precipitated Ag fine particles tends to be less than 10 nm. On the other hand, if it exceeds 2 mol / L, among the precipitated Ag fine particles, abnormal precipitation in which a significantly large primary particle size is mixed is likely to occur, and there is a possibility that the desired average particle size Ag fine particles cannot be obtained. The preferred Ag ion concentration is 0.5 mol / L to 1.5 mol / L. The concentration of the complexing agent in the Ag plating solution 21 is preferably 10 g / L to 1000 g / L.

As shown in FIG. 3, the Ag plating solution is placed in the container 20 and heated by a hot plate or the like. The Ag plating solution 21 is preferably maintained at a temperature of 30 ° C. to 70 ° C. and the solution is stirred. In this state, the core sheet 11 made of Cu foil and the conductive sheet 22 made of Ag foil are immersed in the liquid. After that, both sheets 11 and 22 are electrically connected by a lead wire 23 or the like. If the temperature of the Ag plating solution is less than 30 ° C., the amount of Ag ions deposited on the core sheet 11 is not sufficient, and it tends to be difficult to obtain Ag fine particles 12 having a desired average particle size with a desired average coverage. .. If the temperature exceeds 70 ° C., among the precipitated Ag fine particles, abnormal precipitation in which a significantly large primary particle size is mixed is likely to occur, and there is a possibility that Ag fine particles having a desired average particle size cannot be obtained. A particularly preferable temperature of the Ag plating solution is 40 ° C to 60 ° C. Further, the time for immersing the core sheet 11 and the conductive sheet 22 in the Ag plating solution is preferably 1 hour to 4 hours. If the immersion time is less than 1 hour, the amount of Ag ions deposited on the core sheet 11 is not sufficient, and it tends to be difficult to obtain Ag fine particles 12 having a desired average particle size with a desired average coverage. If it exceeds 4 hours, the amount of the Ag fine particles 12 deposited becomes too large, and the Ag fine particles grow into secondary particles, which makes it difficult to sinter at the time of bonding. The preferred immersion time of the Ag plating solution is 2 hours to 3 hours.

After immersing the core sheet 11 and the conductive sheet 22 in the Ag plating solution for the predetermined time, the lead wires 23 are removed from the sheets 11 and 22 and the core sheet 11 is pulled up from the Ag plating solution 21, and ethanol, water, acetone, etc. Wash with the cleaning solvent of No. 1 and dry in the air at a temperature of 20 ° C. to 50 ° C. As a result, a bonding sheet 10 is obtained in which Ag fine particles 12 having an average particle size of 10 nm to 500 nm are coated and fixed on both sides of a core sheet 11 made of Cu foil at an average coverage rate of 70% or more.

(Ag plating solution immersion method)
Although not shown, the Ag plating solution dipping method is a method of immersing the same sheet as the core sheet 11 made of Cu foil used in the contact plating method in the Ag plating solution used in the contact plating method. In this method, when the core sheet 11 made of Cu foil is placed in the heated Ag plating solution, a part of the Ag fine particles 12 reduced and precipitated by the Ag plating solution is formed by the intermolecular force of the core sheet 11 made of Cu foil. It adheres to both sides in the form of Ag fine particles. Similar to the contact plating method, the Ag fine particles 12 not only stick to the core sheet 11, but also the portion of the Ag fine particles 12 in contact with the core sheet 11 diffuses into the core sheet, and the Ag fine particles 12 adhere to the core sheet 11. ..

The Ag plating solution is preferably maintained at a temperature of 70 ° C. to 150 ° C. and the solution is stirred. In this state, the core sheet 11 made of Cu foil is immersed in the liquid. If the temperature of the Ag plating solution 21 is less than 70 ° C., the amount of Ag ions deposited on the core sheet 11 is not sufficient, and it becomes difficult to obtain Ag fine particles 12 having a desired average particle size with a desired average coverage. easy. If the temperature exceeds 150 ° C., among the precipitated Ag fine particles, abnormal precipitation in which a significantly large primary particle size is mixed is likely to occur, and there is a possibility that Ag fine particles having a desired average particle size cannot be obtained. The preferred temperature of the Ag plating solution is 90 ° C to 120 ° C. The time for immersing the core sheet in the Ag plating solution is preferably 1 hour to 8 hours. If the immersion time is less than 1 hour, the amount of Ag ions deposited on the core sheet 11 is not sufficient, and it tends to be difficult to obtain Ag fine particles 12 having a desired average particle size with a desired average coverage. If it exceeds 8 hours, the amount of the Ag fine particles precipitated becomes too large, and the Ag fine particles grow into secondary particles, which makes it difficult to sinter at the time of bonding. The preferred immersion time of the Ag plating solution is 4 to 6 hours.

After immersing the core sheet 11 in the Ag plating solution for the above predetermined time, the core sheet 11 is pulled up from the Ag plating solution, washed with a cleaning solvent such as ethanol or acetone, and 20 in the air, as in the catalytic plating method. Dry at ° C to 50 ° C. As a result, a bonding sheet is obtained in which Ag fine particles 12 having an average particle size of 10 nm to 500 nm are coated and fixed on both sides of the core sheet 11 made of Cu foil at an average coverage rate of 70% or more.

(Applying heating method)
The coating heating method is a method in which the Ag plating solution 21 described above is applied to the surface of the core sheet 11 and then dried to precipitate Ag fine particles 12.
Specifically, the core sheet 11 is immersed in, for example, the Ag plating solution 21, or the Ag plating solution 21 is applied to the core sheet 11 with a brush or the like and dried in an air atmosphere in the range of 150 ° C. to 200 ° C. Ag is reduced and precipitated, and Ag fine particles 12 are precipitated on the surface of the core sheet, washed with a cleaning solvent such as ethanol, water, and acetone, and dried in the air at 20 ° C. to 50 ° C. to form a Cu foil. A bonding sheet 10 is obtained in which Ag fine particles 12 having an average particle size of 10 nm to 500 nm are coated and fixed on both sides of a core sheet 11 made of the same material at an average coverage rate of 70% or more.
Further, as in the contact plating method, the Ag fine particles 12 not only stick to the core sheet 11, but the portion of the Ag fine particles 12 in contact with the core sheet 11 diffuses into the core sheet 11, and the Ag fine particles 12 are the core sheet 11. Stick to.

[How to join electronic components and substrates using a joining sheet]
To join electronic components such as silicon chip elements and LED chip elements to various heat dissipation substrates, FR4 (Flame Retardant Type 4) substrates, Koval and other substrates using the bonding sheet manufactured by the above method, on the substrate A bonding sheet is arranged at a predetermined position, and an electronic component, for example, a chip element is mounted on the sheet. In this state, the bonding sheet is heated by holding it in a heating furnace at a temperature of 250 ° C. to 350 ° C. for 5 minutes to 20 minutes in a nitrogen atmosphere. In some cases, the chip and the substrate may be joined while applying a pressure of 1 MPa to 20 MPa. As a result, as shown in FIG. 2, the bonding sheet 10 (FIG. 1) becomes a bonding layer 15, and the chip element 16 and the substrate 17 are bonded to form a bonded body 18, which is an electronic component. The element 16 is joined to the substrate 17.

Next, examples of the present invention will be described in detail together with comparative examples. In Examples 1 to 7 and Comparative Examples 1 to 4 shown below, a bonding sheet was produced by a catalytic plating method. Further, in Examples 8 and 9 and Comparative Examples 5 and 6, a bonding sheet was produced by the Ag plating solution immersion method. Further, in Examples 10 and 11 and Comparative Examples 7 and 8, a bonding sheet was produced by a coating heating method.

<Example 1>
(Example of manufacturing a bonding sheet by contact plating)
First, when silver acetate (silver fatty acid), aminodecane (aliphatic amine) and butyl carbitol acetate (solvent) are prepared as Ag salts, and the total amount of silver fatty acid, aliphatic amine and solvent is 100% by mass, 22% by mass of silver acetate (silver fatty acid), 41.3% by mass of aminodecane (aliphatic amine), and 36.7% by mass of butyl carbitol acetate (solvent), which are separated by a glass beaker together with a stirrer of Stirrer. Placed in a cell container. Then, the container was placed on a hot plate heated to 50 ° C., and the stirrer was stirred for 1 hour while rotating at a rotation speed of 300 rpm to prepare a mixed solution. Then, the container in which the mixed solution was stored was removed from the hot plate to lower the temperature of the mixed solution to room temperature. As a result, an Ag plating solution was prepared. The Ag ion concentration of this Ag plating solution was 1.4 g / L.

Next, a core sheet made of a square Cu foil having a thickness of 100 μm, a width of 10 mm and a length of 10 mm and a conductive sheet made of a square Ag foil having a thickness of 100 μm, a width of 10 mm and a length of 10 mm were prepared. The surface roughness Ra of the core sheet was 0.5 μm, and the average crystallite diameter of Cu constituting the Cu foil was 5 μm. As shown in FIG. 2, the prepared Ag plating solution 21 is placed in a container 20, heated to a temperature of 50 ° C. by a hot plate, and stirred at a rotation speed of 100 rpm from the core sheet 11 made of Cu foil and the Ag foil. The conductive sheet 22 was immersed in a liquid, and both sheets 11 and 22 were electrically connected by a lead wire 23. Three hours after the start of the electrical connection, the lead wire 23 was removed from the sheets 11 and 22, the core sheet 11 was pulled up from the Ag plating solution 21, washed with ethanol, and dried in the air at a temperature of 50 ° C. As a result, a bonding sheet was prepared in which Ag fine particles were coated and fixed on both sides of the core sheet 11 made of Cu foil. The average particle size of the Ag fine particles of the bonding sheet measured by the above method was 100 nm, and the average coverage of the Ag fine particles was 70%.

The results are shown in Table 1 below together with the manufacturing conditions of the bonding sheet. Table 1 also shows the production conditions of Examples 2 to 11 and Comparative Examples 1 to 8 described below, the average particle size of the Ag fine particles of the bonding sheet, and the average coverage of the Ag fine particles.

<Examples 2 to 7 and Comparative Examples 1 to 4>
(Example of manufacturing a bonding sheet by contact plating)
The same Ag plating solution as the Ag plating solution prepared in Example 1 was prepared. For joining Examples 2 to 7 and Comparative Examples 1 to 4 by the same contact plating method as in Example 1 except that the characteristics of the core sheet made of Cu foil and the manufacturing conditions of the joining sheet were changed to the contents shown in Table 1. A sheet was prepared.

<Example 8>
(Example of manufacturing a bonding sheet by the Ag plating solution immersion method)
The same Ag plating solution as the Ag plating solution prepared in Example 1 was prepared. The Ag plating solution was heated and held at a temperature of 100 ° C., and the core sheet made of the same Cu foil as in Example 1 was immersed in the solution while stirring. After soaking for 5 hours, the core sheet was pulled out of the liquid in the same manner as in Example 1, washed with ethanol, and dried in the air at a temperature of 50 ° C. As a result, the bonding sheet of Example 8 was prepared in which Ag fine particles were coated and fixed on both sides of the core sheet made of Cu foil.

<Example 9 and Comparative Examples 5 and 6>
(Example of manufacturing a bonding sheet by the Ag plating solution immersion method)
The same Ag plating solution as the Ag plating solution prepared in Example 1 was prepared. The bonding sheets of Example 9 and Comparative Examples 5 and 6 were prepared in the same manner as in Example 8 except that the temperature of the Ag plating solution and the immersion time of the core sheet were changed as shown in Table 1.

<Example 10>
(Example of manufacturing a bonding sheet by the coating heating method)
The same Ag plating solution as the Ag plating solution prepared in Example 1 was prepared. The Ag plating solution was heated and held at a temperature of 50 ° C., and the core sheet made of the same Cu foil as in Example 1 was immersed in the solution while stirring. After immersion for 1 hour, the core sheet was taken out to apply the Ag plating solution on both sides of the core sheet. The core sheet was held in the air at a temperature of 170 ° C. for 1 hour. As a result, a bonding sheet of Example 10 was prepared in which Ag fine particles were coated and fixed on both sides of a core sheet made of Cu foil.

<Example 11 and Comparative Examples 7 and 8>
(Example of manufacturing a bonding sheet by the coating heating method)
The same Ag plating solution as the Ag plating solution prepared in Example 1 was prepared. Joining Examples 11 and Comparative Examples 7 and 8 in the same manner as in Example 10 except that the temperature of the Ag plating solution, the immersion time of the core sheet, and the heating time of the core sheet after immersion were changed as shown in Table 1. Sheet was prepared.

<Comparative evaluation>
The shear strength of the bonding layer formed by using the 19 types of bonding sheets obtained in Examples 1 to 11 and Comparative Examples 1 to 8 was evaluated by the following procedure. First, the bonded body 20 shown in FIG. 2 was produced. Specifically, a 2.5 mm square Si wafer (thickness: 200 μm) having a gold-plated outermost surface was prepared as the first member instead of the electronic component. Further, as a second member instead of the substrate, a 20 mm square Cu plate (thickness: 1 mm) having a silver plating on the outermost surface was prepared. Next, the bonding sheet was sandwiched between the first member and the second member to prepare a laminated body. Further, by firing this laminate with a pressurized die bonder, that is, by holding the laminate at a temperature (heating temperature) of 250 ° C. (heating temperature) for 15 minutes (heating time) with a load of 10 MPa applied, the first member And the second member were joined via the joining layer 15. The shear strength of 19 types of joints was measured as follows.

<Measurement method of shear strength of joint>
The shear strength of the joint was measured using a shear strength evaluation tester. Specifically, the shear strength is measured by fixing the first member (Cu plate) of the bonded body horizontally and using the shear tool at a position 50 μm above the surface (upper surface) of the bonded layer to measure the second member (Si wafer). ) Was pushed from the side to the horizontal direction, and the strength when the second member was broken was measured. The moving speed of the share tool was 0.1 mm / sec. The strength test was performed three times under one condition, and the arithmetic mean value was used as the measured value of the joint strength. The share strengths of the 19 types of bonded bodies are shown in Table 1 described above.

Comparing Examples 1 to 11 and Comparative Examples 1 to 8 from Table 1, the following was found. In Comparative Examples 1 to 8, the shear strength (bonding strength) was less than 20 MPa, and the Si wafer as the second member could not be bonded with sufficient strength. The reasons for this are as follows.
In Comparative Example 1, since the average particle size of the Ag fine particles was less than the lower limit, the stability of the Ag fine particles was lowered, and it is considered that the bondability became unstable.
In Comparative Example 2, Comparative Example 6 and Comparative Example 8, since the average particle size of the Ag fine particles exceeded the upper limit, the sinterability of the Ag fine particles became insufficient, and the strength inside the bonding layer and at the interface with the member was insufficient. It is believed that it was sufficient.
In Comparative Example 3, Comparative Example 4, Comparative Example 5, and Comparative Example 7, since the average coverage of Ag fine particles was below the lower limit, a sufficient bonding area could not be secured for the Si wafer as the second member. It is considered that the bondability was reduced.

On the other hand, in Examples 1 to 11, in order to satisfy the requirements of the first aspect of the present invention, the shear strength (bonding strength) was in the range of 20 MPa to 40 MPa, and all were "good".

The bonding sheet of the present invention can be used to bond an electronic component to a substrate by interposing it between the electronic component and the substrate.

10 Bonding sheet 11 Core sheet made of Cu foil 12 Ag fine particles 13 Ag fine particle layer 15 Bonding layer 16 Chip element 17 Substrate 18 Bonded body

Claims (3)

A bonding sheet in which Ag fine particles having an average particle size of 10 nm to 500 nm are coated and fixed on both sides of a core sheet made of Cu foil at an average coverage rate of 70% or more. The bonding sheet according to claim 1, wherein the surface roughness Ra of the Cu foil is 1.0 μm or less, and the average crystallite diameter of Cu constituting the Cu foil is 10 μm or less. A method of joining an electronic component to a substrate using the joining sheet according to claim 1 or 2.

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