JP7721964B2 - Method for manufacturing a circuit member with a copper pillar and method for manufacturing a bonded body - Google Patents

Description

The present invention relates to a method for manufacturing a circuit component with a copper pillar and a method for manufacturing a bonded assembly.

As a technology for forming connection terminals made of sintered copper pillars on circuit boards such as semiconductor wafers and lead frames, a method has been developed in which copper pillar precursors are formed by printing copper paste on the circuit board and then sintered to form sintered copper pillars. The copper pillar precursors are printed, for example, using a screen printing method using a metal mask.

Japanese Patent Application Laid-Open No. 2020-045514

In recent years, with the miniaturization of electronic components such as semiconductor devices, there has been a growing demand for smaller diameters and larger aspect ratios (ratio of height to diameter) of sintered copper pillars. However, as a result of research by the inventors, it has been found that when forming sintered copper pillars by printing copper paste using a screen printing method, for example, as the openings in the metal mask become smaller, problems such as the copper pillar precursor remaining in the openings of the metal mask after removal without adhering to the circuit components are more likely to occur.

The present invention therefore aims to provide an efficient method for manufacturing circuit components with fine sintered copper pillars, and a method for manufacturing a bonded assembly using this method.

In one aspect, the present invention provides a method for manufacturing a circuit member with a copper pillar, comprising: step (a) of preparing a laminate including a circuit member and a heat-fusible mask layer having openings disposed on the circuit member; step (b) of filling the openings in the mask layer with a copper paste containing copper particles and an organic dispersion medium to form a copper pillar precursor; step (c) of melting and removing the mask layer by heat; and step (d) of sintering the copper pillar precursor to form a sintered copper pillar.

The above method uses a heat-fusible mask layer, making it possible to efficiently produce circuit components with fine sintered copper pillars (circuit components with copper pillars).

In step c, the mask layer may be melted and removed by heating to 40 to 150°C. A mask layer that can be melted and removed by heating to 40 to 150°C can be easily removed by heating while maintaining its predetermined shape at room temperature. When such a mask layer is used, it is less likely that residue of the mask layer will be left behind.

In step d, the copper pillar precursor may be sintered by heating to 150 to 300°C to form a sintered copper pillar. If the copper pillar precursor is sintered by heating to 150 to 300°C to form a sintered copper pillar, sintering can proceed sufficiently while reducing thermal damage to the circuit components.

The mask layer may be formed from wax. In this case, the mask layer has excellent adhesion to the circuit board, making it less likely for the copper paste to bleed at the interface between the mask layer and the circuit board. Furthermore, the mask layer can be easily removed without leaving any residue after being melted by heating.

The diameter of the opening may be 200 μm or less.

The ratio of the depth of the opening to the diameter of the opening may be 0.5 or greater.

In another aspect, the present invention provides a method for manufacturing a joined body comprising a first circuit member, a second circuit member joined to the first circuit member, and a sintered copper pillar positioned between the first circuit member and the second circuit member, the method comprising the step of forming the sintered copper pillar on the first circuit member by the method described above.

In the method for manufacturing the side bonded assembly, after step c, the second circuit member may be mounted on the first circuit member, and then step d may be performed to form the sintered copper pillar and bond the first circuit member and the second circuit member together using the sintered copper pillar.

In the method for manufacturing the side bonded body, after step d, a bonding material may be placed on the bonding surface of the sintered copper pillar and/or the bonding surface of the second circuit member, and then the second circuit member may be mounted on the first circuit member, and the first circuit member and the second circuit member may be bonded together by the bonding material.

The present invention provides an efficient method for manufacturing circuit components having fine sintered copper pillars, and a method for manufacturing a bonded assembly using this method.

FIG. 1 is a schematic cross-sectional view showing a method for manufacturing a circuit member with a copper pillar according to one embodiment. FIG. 2 is a schematic cross-sectional view showing the bonded body of the first embodiment. FIG. 3 is a schematic cross-sectional view showing a method for manufacturing a bonded body according to the first embodiment. FIG. 4 is a schematic cross-sectional view showing a bonded body according to the second embodiment. FIG. 5 is a schematic cross-sectional view showing a method for manufacturing a bonded body according to the second embodiment.

In this specification, numerical ranges indicated using "to" indicate ranges that include the numerical values before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range may be replaced with the upper or lower limit of a numerical range in another stage. Furthermore, in numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with a value shown in the examples. Furthermore, upper and lower limits described individually can be combined in any way.

Embodiments of the present invention will be described in detail below, with reference to the drawings where appropriate. However, the present invention is not limited to the following embodiments.

<Circuit component with copper pillar>
The method for manufacturing a circuit member 10 with a copper pillar shown in FIG. 1 includes the steps of: step a) preparing a laminate 3 including a circuit member 1 and a heat-fusible mask layer 2 having an opening 2 a provided on the circuit member 1; step b) filling a copper paste 4 containing copper particles and an organic dispersion medium into the opening 2 a of the mask layer 2 to form a copper pillar precursor 5; step c) melting and removing the mask layer 2 by heat; and step d) sintering the copper pillar precursor 5 to form a sintered copper pillar 6.

In the above method, sintered copper pillars are formed using a heat-fusible mask layer, which reduces the risk of problems associated with mask removal and allows for the efficient production of circuit components with fine sintered copper pillars. Each step is described in detail below.

(Step a)
In step a, a laminate 3 shown in Fig. 1A is prepared. In step a, for example, a mask layer 2 is formed on a circuit member 1 to fabricate the laminate 3.

Examples of circuit components 1 include active or passive electronic devices, wiring boards on which electronic devices are mounted, and packages having electronic devices and rewiring layers disposed on the electronic devices. Examples of electronic devices include coils, capacitors, SAW filters, power ICs, logic chips, memory chips, sensors, piezoelectric elements, transistors, and diodes. Examples of wiring boards include mounting substrates, lead frames such as copper lead frames, ceramic substrates, resin molded products with printed metal wiring such as MIDs (molded interconnect devices), and packages with rewiring layers.

The mask layer 2 serves as a mold for forming the sintered copper pillar and is solid at room temperature (e.g., 25°C) and has a predetermined shape. Specifically, the mask layer 2 has an opening (through hole) 2a that is approximately the same shape as the desired sintered copper pillar. Because the copper paste shrinks slightly upon drying and sintering, the depth of the opening 2a in the mask layer 2 (the shortest distance between both ends in the thickness direction of the mask layer 2) is preferably slightly (e.g., 1.0 to 1.2 times) larger than the desired height H of the sintered copper pillar, and the diameter of the opening 2a in the mask layer 2 (the smallest diameter in a cross section perpendicular to the thickness direction of the mask layer 2) is preferably slightly (e.g., 1.0 to 1.2 times) larger than the desired diameter W of the sintered copper pillar.

The depth of the opening 2a may be, for example, 10 μm or more, and may be 20 μm or more, 30 μm or more, or 50 μm or more. The depth of the opening 2a may be, for example, 200 μm or less, 150 μm or less, or 100 μm or less. Therefore, the depth of the opening 2a may be, for example, 10 to 200 μm.

The diameter of the opening 2a is, for example, 200 μm or less, and may be 100 μm or less, 80 μm or less, or 60 μm or less. The diameter of the opening 2a is, for example, 20 μm or more, 30 μm or more, or 50 μm or more. Therefore, the diameter of the opening 2a may be, for example, 20 to 200 μm.

The ratio of the depth of the opening 2a to the diameter of the opening 2a (depth/diameter) is, for example, 0.5 or greater, and may be 0.7 or greater, or 1.0 or greater. The ratio of the depth of the opening 2a to the diameter of the opening 2a is, for example, 2.0 or less, and may be 1.7 or less, or 1.5 or less. Thus, the ratio of the depth of the opening 2a to the diameter of the opening 2a may be, for example, 0.5 to 2.0.

The openings 2a may be arranged in a grid pattern. The pitch may be 1 μm or more and 500 μm or less.

The mask layer 2 has thermal melting properties. From the viewpoint of excellent shape stability at room temperature, the melting initiation temperature of the mask layer 2 is, for example, 40°C or higher, and may be 50°C or higher, or 60°C or higher. From the viewpoint of easy removal after melting, the melting initiation temperature of the mask layer 2 is, for example, 150°C or lower, and may be 100°C or lower, or 80°C or lower. Therefore, the melting initiation temperature of the mask layer 2 may be, for example, 40 to 150°C, 40 to 100°C, or 40 to 80°C. If the melting initiation temperature of the mask layer 2 is 40 to 80°C, the mask layer 2 can be easily removed in step c by heating it to 40 to 150°C. The melting initiation temperature of the mask layer 2 can be confirmed by differential thermal analysis.

Mask layer 2 is formed, for example, from a heat-fusible material. Mask layer 2 is preferably formed from wax, as this allows for easy formation into a desired shape, excellent adhesion to the circuit board, and ease of removal upon heat melting. By closely adhering mask layer 2 to the circuit board, the phenomenon of copper paste bleeding at the interface between the mask layer and the circuit board, which is observed when copper paste is filled into openings in printing using a metal mask, etc., is less likely to occur.

The wax may be natural or synthetic. Examples of natural waxes include animal waxes, plant waxes, mineral waxes, and petroleum waxes. Examples of animal waxes include beeswax. Examples of plant waxes include palm wax and soy wax. Examples of petroleum waxes include paraffin wax.

The wax may be composed of a single component or a composition composed of multiple components. The wax may also contain additional components such as alkene polymers and branched polymers.

It is preferable that the wax does not dissolve in the copper paste. The amount of wax that dissolves in the organic dispersion medium used in the copper paste is, for example, 5 g or less per 100 g of organic dispersion medium, and may be 1 g or less or 0.1 g or less.

The mask layer 2 can be formed, for example, by using a 3D printer to draw the area other than the opening 2a with the material (e.g., wax) used to form the mask layer 2; by using a laser to burn off part of a film made of the material (e.g., wax) used to form the mask layer 2 and create the opening 2a; or by using photoresist to create resist posts in the areas of the mask layer 2 that will become the openings 2a, and then forming a film made of the material (e.g., wax) used to form the mask layer 2 so that it fills in the areas around the resist posts, and then removing the resist posts.

(Step b)
In step b, first, the openings 2a of the mask layer 2 are filled with copper paste 4 (see FIG. 1B). The copper paste 4 can be filled using, for example, a squeegee. The squeegee angle may be 10° or more and 90° or less, or 45° or more and 70° or less. The copper paste 4 will be described in detail later.

Next, the copper paste 4 is dried to form the copper pillar precursor 5 (see (c) in Figure 1). Drying the copper paste 4 can prevent flow and voids from occurring during sintering. However, drying the copper paste 4 is not essential. The copper paste 4 may be dried by heating in step c, or the undried copper paste 4 (copper pillar precursor made of copper paste) may be sintered in step d.

The drying temperature and time can be adjusted appropriately depending on the type and amount of organic dispersion medium used in the copper paste 4 and the type and amount of any optional flexibility-imparting components. The drying temperature may be below the melting point of the mask layer 2. The drying temperature may be, for example, 30 to 150°C. The drying time may be, for example, 5 to 60 minutes. The gas atmosphere during drying may be air, an oxygen-free atmosphere such as nitrogen or a rare gas, or a reducing atmosphere such as hydrogen or formic acid. The drying method may be drying at room temperature, heating, or drying under reduced pressure. For heating or reduced pressure drying, for example, a hot plate, warm air dryer, warm air oven, nitrogen oven, infrared dryer, infrared oven, far-infrared oven, microwave oven, laser oven, electromagnetic oven, heater, steam oven, or hot plate press may be used.

(Step c)
In step c, the mask layer 2 is melted and removed by heat (see (d) of FIG. 1). The heating temperature (maximum temperature reached during heating) may be equal to or higher than the melting start temperature of the mask layer 2. The heating temperature can be varied as appropriate depending on the material forming the mask layer 2, and may be, for example, 40 to 150°C, 40 to 120°C, or 40 to 100°C. The heating time (retention time at the maximum temperature reached) may be, for example, 5 to 60 minutes. The gas atmosphere during heating may be air, an oxygen-free atmosphere such as nitrogen or a rare gas, or a reducing atmosphere such as hydrogen or formic acid. For heating, for example, a hot plate, a warm air dryer, a warm air heating furnace, a nitrogen dryer, an infrared dryer, an infrared heating furnace, a far-infrared heating furnace, a microwave heating device, a laser heating device, an electromagnetic heating device, a heater heating device, a steam heating furnace, or the like may be used.

In Figure 1, step c is performed before step d, but step c may be performed after step d or simultaneously with step d. For example, in Figure 1, step d is performed after mask layer 2 is completely removed and circuit member 7 with copper pillar precursor is obtained, but mask layer 2 may be removed after forming sintered copper pillars in step d. Depending on the type of mask layer 2, heating to remove mask layer 2 may sinter part or all of copper pillar precursor 5. When step d is performed by continuous heating after step c, sintering of the copper pillar precursor proceeds immediately after mask removal, allowing for efficient formation of sintered copper pillars.

In step c, in order to thoroughly remove the mask layer 2, the circuit component 1 may be washed after the mask layer 2 has been heated and melted. The washing can be performed using, for example, benzene, chloroform, diethyl ether, carbon disulfide, petroleum benzine, etc.

(Step d)
In step d, the copper pillar precursor 5 is sintered to form a sintered copper pillar 6 (see (e) of FIG. 1). For the heat treatment to sinter the copper pillar precursor 5, for example, a hot plate, a warm air dryer, a warm air heating furnace, a nitrogen dryer, an infrared dryer, an infrared heating furnace, a far-infrared heating furnace, a microwave heating device, a laser heating device, an electromagnetic heating device, a heater heating device, a steam heating furnace, or the like can be used.

The gas atmosphere during sintering may be a reducing gas atmosphere from the viewpoint of removing surface oxides from the copper particles contained in the copper pillar precursor 5. Examples of reducing gas atmospheres include a pure hydrogen gas atmosphere, a mixed gas atmosphere of hydrogen and nitrogen such as forming gas, a nitrogen atmosphere containing formic acid gas, a mixed gas atmosphere of hydrogen and a rare gas, and a rare gas atmosphere containing formic acid gas.

When the diameter of the copper pillar precursor 5 is small (especially when it is 100 μm or less), the formic acid penetrates deep into the copper pillar precursor 5, making it easier to reduce the copper particles, and the copper particles can be sufficiently sintered in a reducing gas atmosphere containing formic acid gas. In this case, it is possible to sinter using a formic acid reflow furnace, which allows for efficient improvement of the degree of sintering.

The temperature of the heat treatment (maximum temperature reached during heating) can be varied as appropriate depending on the material constituting the copper pillar precursor 5, but from the viewpoint of reducing thermal damage to the circuit components while sufficiently promoting sintering, it may be, for example, 150 to 300°C, 200 to 260°C, or 200 to 250°C. If the heating in step d is performed at 150 to 300°C, the heating in step c may be performed at 40 to 150°C, from the viewpoint of efficiently removing the mask layer and sintering the copper pillar precursor by continuous temperature increase.

The heating time (the holding time at the maximum temperature) may be 5 to 120 minutes, or may be 5 to 60 minutes, 10 to 60 minutes, or 15 to 60 minutes, from the viewpoint of being able to sufficiently remove the organic dispersion medium and any optional flexibility-imparting components, and to sufficiently advance sintering.

The manufacturing method described above makes it possible to efficiently manufacture circuit components having fine sintered copper pillars 6 (circuit components 10 with copper pillars).

According to the above manufacturing method, the height H of the sintered copper pillar 6 (the shortest distance between both ends in the pillar extension direction) can be, for example, 20 μm or more, or 30 μm or more, or 50 μm or more. The height H of the sintered copper pillar 6 can be, for example, 200 μm or less, or 150 μm or less, or 100 μm or less.

According to the above manufacturing method, the diameter W of the sintered copper pillar 6 (the smallest diameter in a cross section perpendicular to the pillar extension direction) can be, for example, 100 μm or less, or can be 80 μm or less, or 60 μm or less. The diameter W of the sintered copper pillar 6 can be, for example, 20 μm or more, or can be 30 μm or more, or 50 μm or more.

According to the above manufacturing method, the ratio of the height H of the sintered copper pillar 6 to the diameter W of the sintered copper pillar 6 (aspect ratio, height H/diameter W) can be, for example, 0.5 or more, and can also be 0.7 or more, or 1.0 or more. The ratio of the height H of the sintered copper pillar 6 to the diameter W of the sintered copper pillar 6 can be, for example, 2.0 or less, and can also be 1.7 or less, or 1.5 or less.

<Jointed body and its manufacturing method>
By using the method for manufacturing a circuit member with a copper pillar according to the above embodiment, a bonded body including a circuit member with a copper pillar can be manufactured.

A bonded body comprising a circuit member with a copper pillar is, for example, an electronic component device such as a semiconductor device. The bonded body comprises, for example, a first circuit member, a second circuit member bonded to the first circuit member, and a sintered copper pillar located between the first and second circuit members. The sintered copper pillar is formed on the first circuit member. The second circuit member may be bonded to the first circuit member by the sintered copper pillar, or may be bonded via a bonding layer provided between the sintered copper pillar and the second circuit member. Here, the bonding layer is a layer formed from a bonding material, and examples include a sintered copper layer and a solder layer.

Below, we will explain, in two separate embodiments, the method for manufacturing a bonded assembly using the method for manufacturing a circuit member with copper pillars described above.

(First embodiment)
2 is a bonded body (first bonded body) 20 of the first embodiment of the present invention, which is a bonded body of a circuit member 1 (hereinafter referred to as the "first circuit member 1") and a second circuit member 12, and includes the first circuit member 1, a sintered copper pillar 6 provided on the first circuit member 1, and the second circuit member 12. In the first bonded body 20, the first circuit member 1 and the sintered copper pillar 6 constitute a copper pillar-equipped circuit member 10. In the first bonded body 20, the second circuit member 12 is bonded to the first circuit member 1 via the sintered copper pillar 6.

Figure 3 is a schematic cross-sectional view showing a method for manufacturing the first bonded body 20. In the method for manufacturing the first bonded body 20, a step of mounting a second circuit member 12 on the first circuit member 1 (on the surface on which the copper pillar precursor 5 is formed) is carried out between steps c and d in the method for manufacturing the circuit member 10 with a copper pillar described above.

Specifically, first, a circuit member 7 with copper pillar precursors is prepared (see FIG. 3(a)). The circuit member 7 with copper pillar precursors is obtained by performing steps a, b, and c in the above-described method for manufacturing a circuit member 10 with copper pillars. Next, a second circuit member 12 is mounted on the first circuit member 1 (see FIG. 3(b)). After that, step d is performed to form sintered copper pillars 6, and the first circuit member 1 and the second circuit member 12 are joined by the sintered copper pillars 6 (see FIG. 3(c)). This results in a first joined body 20.

Examples of circuit members that can be used as the second circuit member 12 are the same as the first circuit member 1 (the circuit member 1 used in the manufacturing method of the above-mentioned circuit member 10 with copper pillars). The second circuit member 12 may be the same as or different from the first circuit member 1. One of the first circuit member 1 and the second circuit member 12 may be an active or passive electronic device, and the other may be a wiring board on which the electronic device is mounted. In this case, highly reliable electronic device mounting is possible. Both the first circuit member 1 and the second circuit member 12 may be packages having an electronic device and a redistribution layer provided on the electronic device. In this case, highly reliable package-on-package mounting is possible.

The bonding surface of the second circuit member 12 (the surface bonded to the sintered copper pillar 6) may contain one or more metals selected from the group consisting of copper, nickel, silver, platinum, gold, and palladium. When the bonding surface contains these metals, the oxide film on the surface can be reduced and removed at a sintering temperature of 300°C or less in a reducing gas atmosphere such as hydrogen or formic acid. Therefore, the first bonding body 20 can have high bonding strength due to the metallic bond between the exposed bonding surface (metal surface) of the circuit member and the sintered copper pillar.

The method for mounting the second circuit member 12 is not particularly limited, but for example, if the first circuit member 1 and the second circuit member 12 are a microdevice and a substrate, a method using a chip mounter, a flip-chip bonder, or a carbon or ceramic positioning jig may be used.

The indentation depth (height of copper pillar precursor - height of sintered copper pillar) when the second circuit member 12 is mounted may be 500 μm or less, 100 μm or less, or 50 μm or less from the top of the copper pillar precursor.

Details of step d are as described above. Sintering of the copper pillar precursor 5 in step d may be carried out without pressure.

Second Embodiment
4 is a bonded body (second bonded body) 30 of the second embodiment shown in Figure 4, which is a bonded body of a first circuit member 1 and a second circuit member 12, and includes the first circuit member 1, a sintered copper pillar 6 provided on the first circuit member 1, a second circuit member 12, and a bonding layer 21 provided between a bonding surface 6a (a surface to be bonded to the second circuit member 12) of the sintered copper pillar 6 and a bonding surface 12a of the second circuit member 12. In the second bonded body 30, the first circuit member 1 and the sintered copper pillar 6 constitute a copper pillar-equipped circuit member 10. In the second bonded body 30, the second circuit member 12 is bonded to the first circuit member 1 via the bonding layer 21 and the sintered copper pillar 6.

Figure 5 is a schematic cross-sectional view showing a method for manufacturing a second bonded body 30. After step d in the method for manufacturing the copper pillar-equipped circuit member 10, the second bonded body 30 is manufactured by placing a bonding material 22 on the bonding surface 6a of the sintered copper pillar 6 and/or the bonding surface 12a of the second circuit member 12, mounting the second circuit member 12 on the first circuit member 1 (on the surface on which the sintered copper pillar 6 is formed), and bonding the first circuit member 1 and the second circuit member 12 with the bonding material 22.

Specifically, first, a circuit member 10 with copper pillars is prepared (see Figure 5(a)). The circuit member 10 with copper pillars is obtained by performing steps a, b, c, and d in the manufacturing method for the circuit member 10 with copper pillars described above.

Next, a bonding material 22 is placed on the bonding surface 6a of the sintered copper pillar 6 and/or the bonding surface 12a of the second circuit member 12 (see FIG. 5(b)). The bonding material 22 can be, for example, copper paste or solder paste. While the bonding material 22 shown in FIG. 5 is a paste-like material, the bonding material is not limited to this; for example, solder (e.g., solder plating) can also be used. For example, when the bonding material 22 is in paste form (e.g., when copper paste or solder paste is used), the bonding material 22 can be applied to the bonding surface 6a and/or the bonding surface 12a, or by transferring the bonding material 22 that has been applied to a flat plate or the like to the bonding surface 6a and/or the bonding surface 12a. When the bonding material is solder, the bonding material can be applied to the bonding surface 6a and/or the bonding surface 12a by plating, for example.

Next, after the second circuit member 12 is mounted on the first circuit member 1 (see FIG. 5(c)), the first circuit member 1 and the second circuit member 12 are bonded together using the bonding material 22 (see FIG. 5(d)). If the bonding material 22 is a copper paste, for example, the bonding material 22 is heated to sinter the copper particles, thereby bonding the first circuit member 1 and the second circuit member 12. If the bonding material 22 is a solder or solder paste, the bonding material is heated to melt and solidify the solder, thereby bonding the first circuit member 1 and the second circuit member 12. This results in a second bonded body 30. If the bonding material 22 is a paste containing a solvent such as an organic solvent (e.g., when using copper paste or solder paste), the bonding material 22 may be dried before or after the second circuit member 12 is mounted. In this case, the dried bonding material 22 is heated to form a bonding layer 21 and bond the first circuit member 1 and the second circuit member 12 together.

The bonding conditions (drying conditions and heating conditions for the bonding material 22) may be changed as appropriate depending on the type of material used for the bonding material 22. For example, if the bonding material 22 is copper paste, the heating (sintering) of the copper paste can be performed in the same manner as in step d in the manufacturing method of the circuit member 10 with a copper pillar described above. The sintering of the copper paste may be performed without applying pressure. If the copper paste is dried, the drying can be performed in the same manner as in step d in the manufacturing method of the circuit member 10 with a copper pillar described above.

<Copper paste>
The copper paste used in the above-described manufacturing method of a circuit member with a copper pillar and manufacturing method of a bonded body contains copper particles and an organic dispersion medium. Note that the copper paste used to form the sintered copper pillar and the copper paste used to form the bonding layer may be the same or different.

Examples of copper particles include submicro copper particles and micro copper particles. Submicro copper particles refer to copper particles with a particle size of 0.01 μm or more and less than 0.8 μm. Micro copper particles refer to copper particles with a particle size of 0.8 μm or more and less than 50 μm.

The copper paste preferably contains submicron copper particles, as this makes it easier to ensure bonding strength and connection reliability. If necessary, the copper paste may further contain micron copper particles and/or metal particles other than copper particles.

(Submicron copper particles)
The submicron copper particles may be copper particles that are sinterable in a temperature range of 150° C. to 300° C. Examples of the submicron copper particles include copper particles having a particle size of 0.01 μm or more and less than 0.8 μm, and for example, copper particles having a volume average particle size of 0.01 μm or more and less than 0.8 μm may be used.

In this specification, the term "volume average particle size" refers to the 50% volume average particle size. The volume average particle size of copper particles can be determined by, for example, dispersing raw copper particles or dried copper particles obtained by removing volatile components from copper paste in a dispersion medium using a dispersant, and measuring the resulting dispersion medium with a light scattering particle size distribution analyzer (for example, a Shimadzu nanoparticle size distribution analyzer (SALD-7500nano, manufactured by Shimadzu Corporation)). When using a light scattering particle size distribution analyzer, hexane, toluene, α-terpineol, 4-methyl-1,3-dioxolan-2-one, etc. can be used as the dispersion medium.

The shape of submicron copper particles may be, for example, spherical, blocky, needle-like, columnar, flake-like, nearly spherical, or an aggregate of these. From the viewpoint of dispersibility and packing ability, the shape of submicron copper particles may be spherical, nearly spherical, or flake-like. From the viewpoint of combustibility, dispersibility, mixability with flake-like microparticles, etc., the shape may be spherical or nearly spherical. In this specification, "flake-like" includes flat shapes such as plate-like and scale-like.

From the viewpoints of dispersibility, packing ability, and mixability with flake microparticles, the aspect ratio of submicron copper particles may be 5 or less, or may be 3 or less. In this specification, "aspect ratio of a particle" refers to the long side/thickness of a particle. The long side and thickness of a particle can be measured, for example, from an SEM image of the particle.

The submicron copper particles may be treated with a specific surface treatment agent. Examples of specific surface treatment agents include organic acids having 2 to 18 carbon atoms (e.g., organic acids having an alkyl group having 1 to 17 carbon atoms). Examples of organic acids having 2 to 18 carbon atoms include acetic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, caprylic acid, methylheptanoic acid, ethylhexanoic acid, propylpentanoic acid, pelargonic acid, methyloctanoic acid, ethylheptanoic acid, propylhexanoic acid, capric acid, methylnonanoic acid, ethyloctanoic acid, propylheptanoic acid, butylhexanoic acid, undecanoic acid, methyldecanoic acid, ethylnonanoic acid, propyloctanoic acid, butylheptanoic acid, lauric acid, methylundecanoic acid, ethyldecanoic acid, propylnonanoic acid, propylhex ... carboxylic acid, butyl octanoic acid, pentyl heptanoic acid, tridecanoic acid, methyl dodecanoic acid, ethyl undecanoic acid, propyl decanoic acid, butyl nonanoic acid, pentyl octanoic acid, myristic acid, methyl tridecanoic acid, ethyl dodecanoic acid, propyl undecanoic acid, butyl decanoic acid, pentyl nonanoic acid, hexyl octanoic acid, pentadecanoic acid, methyl tetradecanoic acid, ethyl tridecanoic acid, propyl dodecanoic acid, butyl undecanoic acid, pentyl decanoic acid, hexyl nonanoic acid, palmitic acid, methyl pentadecanoic acid, ethyl tetradecanoic acid, propanediol saturated fatty acids such as propyltridecanoic acid, butyldodecanoic acid, pentylundecanoic acid, hexyldecanoic acid, heptylnonanoic acid, heptadecanoic acid, octadecanoic acid, methylcyclohexanecarboxylic acid, ethylcyclohexanecarboxylic acid, propylcyclohexanecarboxylic acid, butylcyclohexanecarboxylic acid, pentylcyclohexanecarboxylic acid, hexylcyclohexanecarboxylic acid, heptylcyclohexanecarboxylic acid, octylcyclohexanecarboxylic acid, and nonylcyclohexanecarboxylic acid; octenoic acid, nonenoic acid, methylnonanoic acid, Examples of organic acids include unsaturated fatty acids such as decenoic acid, undecenoic acid, dodecenoic acid, tridecenoic acid, tetradecenoic acid, myristoleic acid, pentadecenoic acid, hexadecenoic acid, palmitoleic acid, sapienic acid, oleic acid, vaccenic acid, linoleic acid, linolenic acid, and linolenic acid; and aromatic carboxylic acids such as terephthalic acid, pyromellitic acid, o-phenoxybenzoic acid, methylbenzoic acid, ethylbenzoic acid, propylbenzoic acid, butylbenzoic acid, pentylbenzoic acid, hexylbenzoic acid, heptylbenzoic acid, octylbenzoic acid, and nonylbenzoic acid. These organic acids may be used alone or in combination of two or more. Combining such organic acids with the submicron copper particles tends to achieve both the dispersibility of the submicron copper particles and the release of the organic acid during sintering.

The amount of surface treatment agent may be 0.07% by mass or more and 2.1% by mass or less, 0.10% by mass or more and 1.6% by mass or less, or 0.2% by mass or more and 1.1% by mass or less.

Commercially available submicron copper particles can be used. Examples of commercially available submicron copper particles include CH-0200 (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 0.36 μm), HT-14 (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 0.41 μm), CT-500 (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 0.72 μm), Tn-Cu100 (manufactured by Taiyo Nippon Sanso Corporation, volume average particle size 0.12 μm), and Cu-C-40 (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle size 0.2 μm).

The content of submicron copper particles may be 20% by mass or more and 95% by mass or less, 30% by mass or more and 85% by mass or less, or 40% by mass or more and 75% by mass or less, based on the total amount of copper paste, from the viewpoints of promoting sintering and exhibiting low-temperature sintering properties.

(micro copper particles)
As the micro copper particles, copper particles having a particle size of 0.8 μm or more and 50 μm or less can be used, for example, copper particles having a volume average particle size of 0.8 μm or more and 50 μm or less can be used.

It is preferable to combine micro copper particles with submicro copper particles. In this case, volume shrinkage and void generation when sintering the copper pillar precursor formed from the copper paste can be reduced, making it easier to ensure the bonding strength of the bonded body obtained by sintering the copper pillar precursor. When the component of the bonded body is a micro device, the micro device tends to exhibit good die shear strength and connection reliability.

The shape of the micro copper particles is not particularly limited. Examples of the shape of the micro copper particles include spherical, blocky, needle-like, flake-like, approximately spherical, and aggregates thereof.

In this embodiment, flake-shaped micro copper particles can be blended in combination with submicro copper particles. In this case, the micro copper particles in the copper pillar precursor are oriented approximately parallel to the joining surface, thereby suppressing volumetric shrinkage in the joining surface direction when the copper pillar precursor is sintered, making it easier to ensure the joining strength of the joined body obtained by sintering the copper pillar precursor. From the perspective of further achieving the above effect, the aspect ratio of the flake-shaped micro copper particles is preferably 3 or more, more preferably 4 or more, and even more preferably 6 or more.

There are no particular limitations on whether or not the microcopper particles are treated with a surface treatment agent. From the perspective of dispersion stability and oxidation resistance, the microcopper particles may be treated with a surface treatment agent. The surface treatment agent may be removed during bonding. Examples of such surface treatment agents include aliphatic carboxylic acids such as dodecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, arachidic acid, linoleic acid, linolenic acid, and oleic acid; aromatic carboxylic acids such as terephthalic acid, pyromellitic acid, and o-phenoxybenzoic acid; aliphatic alcohols such as cetyl alcohol, stearyl alcohol, isobornylcyclohexanol, and tetraethylene glycol; aromatic alcohols such as p-phenylphenol; alkylamines such as octylamine, dodecylamine, and stearylamine; aliphatic nitriles such as stearonitrile and decanenitrile; silane coupling agents such as alkylalkoxysilanes; and polymer treatment agents such as polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, and silicone oligomers. Surface treatment agents may be used alone or in combination.

Commercially available micro copper particles can be used. Examples of commercially available flake-shaped micro copper particles include MA-C025KFD (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 7.5 μm), 4L3N (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle size 3.0 μm), 3L3N (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle size 5.7 μm), 3L3 (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle size 8.0 μm), and 2L3N (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle diameter 9.9 μm), 1110F (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle diameter 3.8 μm), 1050YP (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle diameter 0.94 μm), 1100YP (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle diameter 1.2 μm), 1200YP (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle diameter 3.4 μm), and 1400YP (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle diameter 5.2 μm). Examples of spherical or approximately spherical micro copper particles include 1050Y (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 0.81 μm), 1100Y (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 1.1 μm), 1200Y (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 2.1 μm), 1300Y (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 4.6 μm), 1400Y (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 5.5 μm), 1200YM (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 1.9 μm), 1300YM (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 3.4 μm), 1400YM (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 4.2 μm), Cu-HWQ 1.5 μm (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle size 1.5 μm), and Cu-HWQ Examples include Cu-HWQ 1.5 μm (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle size 1.4 μm), Cu-HWQ 3.0 μm (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle size 3.0 μm), Cu-HWQ 5.0 μm (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle size 4.1 μm), and Cu-HWQ 10 μm (manufactured by Fukuda Metal Foil & Powder Co., Ltd., volume average particle size 9.4 μm).

The content of micro copper particles is preferably 0% by mass or more and 70% by mass or less, more preferably 5% by mass or more and 50% by mass or less, and even more preferably 10% by mass or more and 40% by mass or less, based on the total mass of the copper particles.

The copper paste of this embodiment may contain copper nanoparticles to the extent that the effects of the microcopper particles and submicrocopper particles described above are not impaired, but it is preferable that it does not contain copper nanoparticles.

(Organic dispersion medium)
The organic dispersion medium includes a solvent having a boiling point below 300°C and/or a solvent having a boiling point of 300°C or higher.

Solvents with a boiling point below 300°C include α-terpineol, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, 4-methyl-1,3-dioxolan-2-one, and diethylene glycol monobutyl ether. Solvents with a boiling point below 300°C can be easily removed during the drying process or temperature increase process before sintering the copper pillar precursor. Solvents with a boiling point below 300°C can be used alone or in combination.

From the perspective of promoting sintering of the copper particles, the content of the solvent having a boiling point of less than 300°C may be 0 to 50 mass%, 10 to 40 mass%, or 20 to 30 mass%, based on the total mass of the organic dispersion medium.

To improve the dispersibility of copper particles, it is preferable to select a solvent with a boiling point of 300°C or higher that has a structure with high affinity for the copper particle surface. If the copper particles have been surface-treated with a surface treatment agent containing an alkyl group, it is preferable to select a solvent that has an alkyl group. Examples of such solvents having a boiling point of 300°C or higher include isobornylcyclohexanol (MTPH, manufactured by Nippon Terpene Co., Ltd.), butyl stearate, Exepar BS (manufactured by Kao Corporation), stearyl stearate, Exepar SS (manufactured by Kao Corporation), 2-ethylhexyl stearate, Exepar EH-S (manufactured by Kao Corporation), isotridecyl stearate, Exepar TD-S (manufactured by Kao Corporation), isooctadecanol, Fine Oxocol 180 (manufactured by Nissan Chemical Industries, Ltd.), Fine Oxocol 180T (manufactured by Nissan Chemical Industries, Ltd.), 2-hexyldecanol, Fine Oxocol 1600 (manufactured by Nissan Chemical Industries, Ltd.), tributyrin, tetraethylene glycol, heptadecane, octadecane, nonadecane, eicosane, heneicosane, docosane, methylheptadecane, tridecyl Examples of suitable solvents include cyclohexane, tetradecylcyclohexane, pentadecylcyclohexane, hexadecylcyclohexane, undecylbenzene, dodecylbenzene, tetradecylbenzene, tridecylbenzene, pentadecylbenzene, hexadecylbenzene, heptadecylbenzene, nonylnaphthalene, diphenylpropane, octyl octanoate, methyl myristate, ethyl myristate, methyl linoleate, methyl stearate, triethylene glycol bis(2-ethylhexanoate), tributyl citrate, pentylphenol, dibutyl sebacate, oleyl alcohol, cetyl alcohol, methoxyphenethyl alcohol, benzylphenol, hexadecanenitrile, heptadecanenitrile, benzyl benzoate, and cinmethylin. Solvents having a boiling point of 300°C or higher can be used alone or in combination.

The content of the solvent with a boiling point of 300°C or higher may be 50 to 100% by mass, 55 to 95% by mass, or 60 to 90% by mass, based on the total mass of the organic dispersion medium, from the viewpoints of improving the printability of the copper paste and suppressing cracking and peeling of the pillars during sintering.

As described above, by selecting an organic dispersion medium that is suitable from the perspectives of sinterability, printability, etc., it is possible to achieve both excellent sinterability and excellent printability, and to form sintered copper pillars even when the openings 2a in the mask layer 2 are made even finer.

However, depending on the combination of the organic dispersion medium and the material forming the mask layer 2, the mask layer 2 may be dissolved by the organic dispersion medium. Therefore, in the above-mentioned methods for manufacturing a circuit member with copper pillars and for manufacturing a bonded body, it is preferable to select an organic dispersion medium from the perspective of the solubility of the mask layer 2, in addition to the sinterability and printability of the copper paste. For example, when the material forming the mask layer 2 is paraffin wax, examples of the organic dispersion medium include isobornylcyclohexanol (MTPH, manufactured by Nippon Terpene Co., Ltd.), butyl stearate, Exepar BS (manufactured by Kao Corporation), stearyl stearate, Exepar SS (manufactured by Kao Corporation), 2-ethylhexyl stearate, Exepar EH-S (manufactured by Kao Corporation), isotridecyl stearate, Exepar TD-S (manufactured by Kao Corporation), isooctadecanol, Fine Oxocol 180 (manufactured by Nissan Chemical Industries, Ltd.), Fine Oxocol 180T (manufactured by Nissan Chemical Industries, Ltd.), 2-hexyldecanol, Fine Oxocol 1600 (manufactured by Nissan Chemical Industries, Ltd.), tributyrin, tetraethylene glycol, heptadecane, octadecane, nonadecane, eicosane, heneicosane, docosane, and methylheptadecane. , tridecylcyclohexane, tetradecylcyclohexane, pentadecylcyclohexane, hexadecylcyclohexane, undecylbenzene, dodecylbenzene, tetradecylbenzene, tridecylbenzene, pentadecylbenzene, hexadecylbenzene, heptadecylbenzene, nonylnaphthalene, diphenylpropane, octyl octanoate, methyl myristate, ethyl myristate, methyl linoleate, methyl stearate, triethylene glycol bis(2-ethylhexanoate), tributyl citrate, pentylphenol, dibutyl sebacate, oleyl alcohol, cetyl alcohol, methoxyphenethyl alcohol, benzylphenol, hexadecanenitrile, heptadecanenitrile, benzyl benzoate, cinmethylin, and the like are preferably used.

The content of the organic dispersant may be 1% by mass or more, 5% by mass or more, 10% by mass or more, or 15% by mass or more, based on the total mass of the copper paste, in order to adjust the viscosity of the copper paste to a more appropriate level. The content of the organic dispersant may be 70% by mass or less, 65% by mass or less, 60% by mass or less, or 50% by mass or less, based on the total mass of the copper paste, in order to further improve the sinterability of the copper particles. From these perspectives, the content of the organic dispersant may be 1 to 70% by mass, 5 to 70% by mass, 5 to 65% by mass, 10 to 60% by mass, or 15 to 50% by mass, based on the total mass of the copper paste.

The types of organic dispersants contained in copper paste can be analyzed, for example, using high-temperature desorption gas gas chromatography-mass spectrometry and TOF-SIMS. Other analytical methods include separating particle components by centrifugation and identifying the supernatant using conventional organic analysis, such as FT-IR, NMR, liquid chromatography, or a combination of these. The ratio of types of organic dispersants can be quantified using liquid chromatography, NMR, etc.

(Other ingredients)
The copper paste may further contain components other than the copper particles and the organic dispersion medium, such as metal particles other than copper particles, flexibility-imparting components such as thermally decomposable resins, fillers, dispersants, and fluxes.

The viscosity of the copper paste at 25°C may be 50 Pa·s or more and 2000 Pa·s or less, 100 Pa·s or more and 1750 Pa·s or less, or 200 Pa·s or more and 1500 Pa·s or less. The viscosity of the copper paste refers to the value measured using an E-type viscometer at 25°C and a rotation speed of 0.5 rpm. An example of an E-type viscometer that can be used is the VISCOMETER-TV33 model viscometer manufactured by Toki Sangyo Co., Ltd. A cone rotor measuring jig, for example, 3° x R14, SPP, can be used.

The thixotropy index (hereinafter also referred to as "TI value") of the copper paste may be 2.0 or more and 20 or less, 3.0 or more and 15 or less, or 4.0 or more and 10 or less. When the TI value of the copper paste is within this range, the viscosity of the copper paste is reduced by shear force, so that the openings in the mask layer can be easily filled by stirring the copper paste manually or with a stirring device (for example, a rotation-revolution type stirring device (Planetary Vacuum Mixer ARV-310, manufactured by Thinky Corporation) or the like) before application. The TI value of the copper paste is a value calculated by the following formula, where μ0.5 is the viscosity measured with an E-type viscometer at 25 ° C. and a rotation speed of 0.5 rpm, and μ5 is the viscosity measured with an E-type viscometer at 25 ° C. and a rotation speed of 5 rpm.
TI value = μ0.5/μ5

The copper paste can be prepared by mixing copper particles, an organic dispersion medium, and optional components (such as components that provide flexibility) that are added as needed. The copper paste can be prepared by mixing these components simultaneously, or by mixing them in multiple batches.

The present invention will be explained in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

Example 1
A circuit board was prepared by sputtering Ni—Cu on a silicon wafer. A mask layer was formed by applying wax (Paraffin Wax-155, manufactured by Nippon Seiro Co., Ltd.) to the entire surface of this circuit board, except for the areas where openings would be formed, using a 3D printer. The thickness of the mask layer (opening depth) was 200 μm, the opening diameter was 100 μm, and the pitch between the openings was 500 μm. The openings were arranged in a grid pattern. Copper paste was filled into the openings using a urethane squeegee. Next, the circuit board was placed on a hot plate at 65°C for 10 minutes to dry the copper paste. Next, the circuit board was placed on a hot plate at 100°C to melt the mask layer (wax), and the circuit board was tilted to remove the mask layer (wax) from the circuit board. This resulted in a circuit board with pillar precursors formed on the circuit board. The copper paste used was prepared by mixing copper particles and two types of organic dispersion medium.

The circuit board with the pillar precursors was then heated in a formic acid atmosphere at 250°C for 1 hour to sinter the pillar precursors, resulting in a circuit board with sintered copper pillars (circuit board with copper pillars). The shape of the sintered copper pillars was measured using a 3D scanner, revealing a height of 150 μm, a diameter of 80 μm, and an aspect ratio of 1.9.

Example 2
A circuit board was prepared by sputtering Ni-Cu on a silicon wafer. A positive photoresist was applied to the entire surface of the circuit board by spin coating, forming a 100 μm thick coating. The entire surface, excluding the areas where openings would be formed, was then exposed and developed to form cylindrical posts with a height of 100 μm and a diameter of 70 μm. The posts were arranged in a grid pattern with a 200 μm pitch. The periphery of the circuit board was covered with 5 mm-wide polyimide tape to prevent the molten wax from spilling. The circuit board was placed on a hot plate at 100°C, and molten wax (paraffin wax, Paraffin Wax-155, manufactured by Nippon Seiro Co., Ltd.) was poured onto it. The amount of wax poured was adjusted to the same height as the posts. After the circuit board was slowly cooled, the posts were dissolved and removed using a resist stripper. This resulted in the formation of a mask layer with openings of the same shape as the posts.

Subsequently, in the same manner as in Example 1, the openings were filled with copper paste, the mask layer was removed, and sintered copper pillars were formed, thereby obtaining a circuit board with sintered copper pillars (circuit board with copper pillars). When the shape of the sintered copper pillars was measured using a 3D scanner, they were found to have a height of 90 μm, a diameter of 60 μm, and an aspect ratio of 1.5.

1...(first) circuit member, 2...mask layer, 2a...opening, 3...laminated body, 4...copper paste, 5...copper pillar precursor, 6...sintered copper pillar, 7...circuit member with copper pillar precursor, 10...circuit member with copper pillar, 12...second circuit member, 20...first bonding body, 21...bonding layer, 22...bonding material, 30...second bonding body.

Claims (9)

A step a) of preparing a laminate including a circuit member and a heat-meltable mask layer having an opening provided on the circuit member;
a step b of filling the openings in the mask layer with a copper paste containing copper particles and an organic dispersion medium to form a copper pillar precursor;
a step c of melting and removing the mask layer by heat;
and step d) of sintering the copper pillar precursor to form a sintered copper pillar. The method for manufacturing a circuit member with copper pillars according to claim 1, wherein in step c, the mask layer is melted and removed by heating to 40 to 150°C. The method for manufacturing a circuit member with a copper pillar according to claim 1 or 2, wherein in step d, the copper pillar precursor is sintered by heating to 150 to 300°C to form a sintered copper pillar. The method for manufacturing a circuit member with copper pillars according to any one of claims 1 to 3, wherein the mask layer is formed from wax. The method for manufacturing a circuit member with a copper pillar according to any one of claims 1 to 4, wherein the diameter of the opening is 200 μm or less. A method for manufacturing a circuit member with a copper pillar according to any one of claims 1 to 5, wherein the ratio of the depth of the opening to the diameter of the opening is 0.5 or greater. A method for manufacturing a joined body comprising: a first circuit member; a second circuit member joined to the first circuit member; and a sintered copper pillar positioned between the first circuit member and the second circuit member, the method comprising:
A method for manufacturing a bonded body, comprising the step of forming a sintered copper pillar on the first circuit member by the method according to any one of claims 1 to 6. The method for manufacturing a bonded body described in claim 7, wherein after step c, the second circuit member is mounted on the first circuit member and then step d is performed, thereby forming the sintered copper pillar and bonding the first circuit member and the second circuit member together by the sintered copper pillar. 8. The method for producing a joined body according to claim 7, wherein after step d, a joining material is placed on the joining surface of the sintered copper pillar and/or the joining surface of the second circuit member, and then the second circuit member is mounted on the first circuit member, and the first circuit member and the second circuit member are joined by the joining material.