JP7675522B2 - Thermosetting sheets and dicing die bond films - Google Patents

Description

The present invention relates to a thermosetting sheet and a dicing die bond film.

2. Description of the Related Art In the manufacture of semiconductor devices, it has been known to use a thermosetting sheet as a method for bonding a semiconductor element to an adherend such as a metal lead frame (die bonding method) (see, for example, Patent Document 1).
Patent Document 1 discloses a thermosetting sheet that contains conductive particles and a thermosetting resin.

In such a method, for example, a thermosetting sheet is attached to one side of a semiconductor wafer (the side opposite to the circuit-forming surface), and the semiconductor wafer and the thermosetting sheet are diced to obtain a plurality of thermosetting sheets each having a semiconductor element attached to one side.
The thermosetting sheet having the semiconductor element attached to one side thereof is temporarily attached to an adherend such as a metal lead frame on the other side at a predetermined temperature (e.g., 70° C.), and then is thermally cured at a higher temperature (e.g., 200° C.) to be bonded to the adherend. In other words, the semiconductor element is bonded to the adherend with the thermosetting sheet interposed therebetween.

JP 2019-21813 A

However, when a thermosetting sheet having a semiconductor element attached to one side thereof is adhered to the adherend, the semiconductor element may peel off from the thermosetting sheet. If such peeling occurs, electrical conduction and thermal conduction via the conductive particles become insufficient, which is undesirable.
The above-described peeling occurs more significantly when the semiconductor wafer and the thermosetting sheet are diced (the semiconductor element is more likely to fly off the thermosetting sheet).
However, it cannot be said that sufficient research has been conducted yet on preventing the peeling of the semiconductor element from the thermosetting sheet.

Furthermore, when a power semiconductor element is used in a semiconductor device, the power semiconductor element is used at a large power of several MVA or more, and generates a large amount of heat.
Therefore, when the above-mentioned thermosetting sheet is used for a power semiconductor element, it is preferable that the thermosetting sheet after being adhered to an adherend, that is, the thermosetting sheet after being cured, has high heat dissipation properties.

The above-mentioned heat generation problem also occurs when using semiconductor elements other than power semiconductor elements, but it cannot be said that sufficient research has been done yet on improving the heat dissipation properties of the thermosetting sheet after curing.

The present invention aims to provide a thermosetting sheet that can relatively suppress peeling of semiconductor elements and has relatively high heat dissipation properties after curing, and a dicing die bond film that includes the thermosetting sheet.

As a result of intensive research, the inventors have found that by making the thermosetting sheet contain a thermosetting resin, a thermoplastic resin, and conductive particles, the conductive particles contain silver particles having an average particle diameter _D50 of 0.01 μm or more and 10 μm or less and a circularity in cross section of 0.7 or more, and further making the thermosetting sheet have a viscosity at 100° C. of 20 kPa·s or more and 3000 kPa·s or less, peeling of the semiconductor element is relatively suppressed and heat dissipation after curing is relatively high, and have arrived at the present invention.

That is, the thermosetting sheet according to the present invention is
A thermosetting sheet comprising a thermosetting resin, a thermoplastic resin, and conductive particles,
The conductive particles include silver particles having an average particle diameter _D50 of 0.01 μm or more and 10 μm or less and a circularity in cross section of 0.7 or more,
The viscosity at 100°C is 20 kPa·s or more and 3000 kPa·s or less.

According to this configuration, since the conductive particles contain silver particles having an average particle diameter _D50 of 10 μm or less, the outer surfaces of the silver particles can be melted to a degree that allows sintering at a temperature (e.g., 200° C.) sufficient to cure the thermosetting resin.
Furthermore, since the average particle diameter _D50 of the silver particles is 0.01 μm or more, the silver particles are relatively easily dispersed in the thermosetting sheet. In addition, the specific surface area of the silver particles is prevented from becoming excessively large, which would otherwise make the surfaces of the silver particles more susceptible to oxidation, thereby ensuring sufficient electrical conductivity for the silver particles.
This allows the outer surfaces of the silver particles to be melted to a degree that allows them to be sintered while still having sufficient conductivity and being sufficiently dispersed, so that the conductive particles can be sintered together by the silver particles.
In addition, since the circularity of the silver particles in the cross section is 0.7 or more, the silver particles can be more thoroughly dispersed in the thermosetting sheet, and therefore the conductive particles can be sintered together by the silver particles thoroughly dispersed in the thermosetting sheet.
As a result, after curing, the thermosetting sheet according to the present invention has high heat dissipation properties while maintaining sufficient electrical conductivity.
Furthermore, since the viscosity at 100°C is 20 kPa·s or more and 3000 kPa·s or less, the wettability to an adherend (e.g., a semiconductor wafer) can be improved, thereby ensuring relatively sufficient adhesion to the adherend.
Furthermore, since it contains a thermoplastic resin, the viscosity at 100°C can be relatively easily adjusted to be within the above numerical range, and it can also have relatively low elasticity after curing.
Therefore, peeling of the semiconductor element can be relatively suppressed.
As described above, the thermosetting sheet according to the present invention can relatively prevent peeling of the semiconductor element, and has relatively high heat dissipation properties after curing.

In the thermosetting sheet,
It is preferable that the particle filling rate P of the conductive particles in the thermosetting sheet after curing is 30 volume % or more.

This configuration can further improve the heat dissipation properties of the thermosetting sheet after curing.

In the thermosetting sheet,
It is preferable that the thermal conductivity after curing is 3 W/m·K or more.

This configuration can further increase the electrical conductivity of the thermosetting sheet after curing.

In the thermosetting sheet,
It is preferable that the peeling force against a silicon wafer at room temperature is 1 N/10 mm or more.

This configuration can further prevent the semiconductor element from peeling off.

In the thermosetting sheet,
Contains volatile components,
The volatile component preferably contains one or more hydroxyl groups and has a boiling point of 250° C. or higher.

This configuration can further improve the heat dissipation properties of the thermosetting sheet after curing.

In the thermosetting sheet,
The volatile component is preferably a terpene compound.

This configuration can further improve the heat dissipation properties of the thermosetting sheet after curing.

The dicing die bond film according to the present invention is
A base layer;
a dicing tape having a pressure-sensitive adhesive layer laminated on the base layer;
a thermosetting sheet laminated on the adhesive layer of the dicing tape;
The thermosetting sheet is any one of the thermosetting sheets described above.

With this configuration, the dicing die bond film is provided with a thermosetting sheet that can relatively suppress peeling of the semiconductor element and has relatively high heat dissipation properties after curing.

The present invention provides a thermosetting sheet that can relatively suppress peeling of semiconductor elements and has relatively high heat dissipation properties after curing, and a dicing die bond film that includes the thermosetting sheet.

1 is a cross-sectional view showing a configuration of a dicing die bond film according to one embodiment of the present invention.

One embodiment of the present invention is described below.

[Thermosetting sheet]
The thermosetting sheet according to this embodiment contains a thermosetting resin, a thermoplastic resin, and conductive particles.
In this specification, the conductive particles refer to particles having an electrical conductivity of 100 μS/cm or less as measured in accordance with JIS K 0130 (2008).

The mass % of the thermosetting resin per 100 mass % (parts by mass) of the thermosetting sheet is preferably 1 mass % or more and 30 mass % or less, and more preferably 3 mass % or more and 15 mass % or less.
The mass % of the thermoplastic resin in 100 mass % of the thermosetting sheet is preferably 0.5 mass % or more and 10 mass % or less, and more preferably 1 mass % or more and 7 mass % or less.
The mass % of the conductive particles relative to 100 mass % of the thermosetting sheet is preferably 60 mass % or more and 95 mass % or less, and more preferably 80 mass % or more and 93 mass % or less.
The mass proportion of the thermosetting resin in 100 mass% of resins (thermosetting resin and thermoplastic resin) is preferably 30 mass% or more and 90 mass% or less, and more preferably 50 mass% or more and 80 mass% or less.

Examples of thermosetting resins include epoxy resins, phenolic resins, amino resins, unsaturated polyester resins, polyurethane resins, silicone resins, and thermosetting polyimide resins. Of these, it is preferable to use epoxy resins.

Examples of epoxy resins include bisphenol A type, bisphenol F type, bisphenol S type, brominated bisphenol A type, hydrogenated bisphenol A type, bisphenol AF type, biphenyl type, naphthalene type, fluorene type, phenol novolac type, cresol novolac type, orthocresol novolac type, trishydroxyphenylmethane type, tetraphenylolethane type, hydantoin type, trisglycidyl isocyanurate type, and glycidylamine type epoxy resins. Among these, it is preferable to use at least one of bisphenol A type epoxy resin and cresol novolac type epoxy resin, and it is more preferable to use a combination of bisphenol A type epoxy resin and cresol novolac type epoxy resin.
The bisphenol A type epoxy resin includes an aliphatic modified bisphenol A type epoxy resin.

Examples of phenolic resins that can be used as curing agents for epoxy resins include novolac-type phenolic resins, resol-type phenolic resins, biphenyl-type phenolic resins, and polyoxystyrenes such as polyparaoxystyrene. Of the above phenolic resins, it is preferable to use biphenyl-type phenolic resins.

In addition, as the thermosetting resin, a thermoplastic resin having a thermosetting functional group can also be used. As the thermoplastic resin having a thermosetting functional group, for example, a thermosetting functional group-containing acrylic resin can be mentioned. As the acrylic resin in the thermosetting functional group-containing acrylic resin, a monomer unit derived from a (meth)acrylic acid ester can be mentioned.
In the case of a thermoplastic resin having a thermosetting functional group, a curing agent is selected depending on the type of the thermosetting functional group.

The thermoplastic resin functions as a binder.
Since the thermosetting sheet according to this embodiment contains a thermoplastic resin as a binder, the viscosity of the thermosetting sheet at 100°C can be relatively easily adjusted to be 20 kPa·s or more and 3000 kPa·s or less, as described below.
Examples of the thermoplastic resin include natural rubber, butyl rubber, isoprene rubber, chloroprene rubber, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, polybutadiene resin, polycarbonate resin, thermoplastic polyimide resin, polyamide resin such as polyamide 6 and polyamide 6,6, phenoxy resin, acrylic resin, saturated polyester resin such as PET and PBT, polyamideimide resin, fluororesin, etc. Only one type of the thermoplastic resin may be used, or two or more types may be used in combination. As the thermoplastic resin, acrylic resin is preferable from the viewpoint that it has a small amount of ionic impurities and has high heat resistance, making it easier to ensure connection reliability by a thermosetting sheet.

The acrylic resin is preferably a polymer containing a monomer unit derived from a (meth)acrylic acid ester as the most abundant monomer unit in terms of mass ratio. Examples of the (meth)acrylic acid ester include an alkyl (meth)acrylic acid ester, a cycloalkyl (meth)acrylic acid ester, and an aryl (meth)acrylic acid ester. The acrylic resin may contain a monomer unit derived from another component that is copolymerizable with the (meth)acrylic acid ester. Examples of the other components include functional group-containing monomers such as carboxyl group-containing monomers, acid anhydride monomers, hydroxyl group-containing monomers, glycidyl group-containing monomers, sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, acrylamides, and acrylonitriles, and various polyfunctional monomers.
The acrylic resin is preferably a carboxyl-containing acrylic rubber.

The conductive particles include silver particles having an average particle diameter _D50 of 0.01 μm or more and 10 μm or less and a circularity of 0.7 or more in a cross section cut in the thickness direction.
Since the conductive particles contain silver particles having an average particle diameter _D50 of 10 μm or less, the outer surfaces of the silver particles can be melted to a degree that allows sintering at a temperature (e.g., 200° C.) sufficient to cure the thermosetting resin.
Furthermore, when the average particle diameter _D50 of the silver particles is 0.01 μm or more, the silver particles are relatively easily dispersed in the thermosetting sheet. In addition, the specific surface area of the silver particles is prevented from becoming excessively large, which would otherwise make the surfaces of the silver particles more susceptible to oxidation, thereby ensuring sufficient electrical conductivity of the silver particles.
This allows the outer surfaces of the silver particles to be melted to a degree that allows them to be sintered while still having sufficient conductivity and remaining relatively dispersed, thereby allowing the silver particles to sinter the conductive particles together (or to sinter the silver particles together if the conductive particles are only silver particles).
In addition, since the circularity of the silver particles in cross section is 0.7 or more, the silver particles can be more thoroughly dispersed in the thermosetting sheet, and therefore the silver particles thoroughly dispersed in the thermosetting sheet can sinter the conductive particles together (or between the silver particles when the conductive particles are only silver particles).
As a result, after curing, the thermosetting sheet according to the present invention has high heat dissipation properties while maintaining sufficient electrical conductivity.

The average particle size _D50 of the silver particles is preferably 0.1 μm or more and 5 μm or less, and more preferably 0.5 μm or more and 2 μm or less.
The circularity of the silver particles in a cross section taken along the thickness direction is preferably 0.8 or more.
The upper limit of the circularity is 1.

The average particle diameter _D50 of the silver particles can be measured on a volume basis using, for example, a laser diffraction/scattering type particle size distribution measuring device (Microtrac MT3000II series, manufactured by Microtrac-Bell).

Circularity is an index for determining the complexity of a shape based on the area and perimeter values. Circularity is expressed as 4πS/ ^L2 , where S is the area and L is the perimeter. A circularity value of 1 indicates a perfect circle, and the smaller the circularity value is below 1, the more distant the shape is from a circle.
The circularity can be obtained by cutting the thermosetting sheet in the thickness direction, taking an SEM image of the cut surface, and analyzing the SEM image using a powder image analyzer (PITA-3, manufactured by Seishin Enterprise Co., Ltd.) (specifically, by analyzing the image using image analysis software such as "Image J").
Analysis using the powder image analyzer is performed on 10 silver particles randomly selected in the SEM image, and the circularity can be determined by arithmetically averaging the circularity values obtained for the 10 silver particles.
In addition, when the thermosetting sheet contains conductive particles other than silver particles, the silver particles can be distinguished from the conductive particles other than silver particles by observing the reflected electron images so that light and dark appear due to differences in composition.

The silver particles may be silver particles composed of silver element and other elements (metal elements, etc.) contained as unavoidable impurity elements, or may be silver particles that have been subjected to a surface treatment (for example, silane coupling treatment). Examples of the surface treatment agent for silver particles include fatty acid-based, amine-based, and epoxy-based coating agents. Examples of silver particles surface-treated with a fatty acid-based coating agent include HP02 and HP02A manufactured by Mitsui Mining & Smelting Co., Ltd., and examples of silver particles treated with an epoxy-based coating agent include a modified coating agent (epoxy-coated product) of HP02A manufactured by Mitsui Mining & Smelting Co., Ltd.
In the thermosetting sheet according to the present embodiment, it is preferable to use silver particles surface-treated with an epoxy-based coating agent. As described above, the thermosetting sheet according to the present embodiment contains a thermosetting resin. Therefore, when silver particles surface-treated with an epoxy-based coating agent are used as silver particles, the silver particles will exhibit a relatively high affinity with the thermosetting resin in the thermosetting sheet, and will be more easily dispersed in the thermosetting sheet. And, since the silver particles are more easily dispersed in the thermosetting sheet, the heat conductivity (heat dissipation) of the thermosetting sheet can be improved because the silver particles can be contained in the thermosetting sheet in a larger amount. In addition, when the surface treatment agent of the silver particles is an epoxy-based coating agent, the thermosetting resin contained in the thermosetting sheet is preferably an epoxy resin. In this way, the affinity between the silver particles and the thermosetting resin can be further increased, so that the silver particles can be further dispersed in the thermosetting sheet. As a result, the heat conductivity (heat dissipation) of the thermosetting sheet can be further improved.

In addition to silver particles, the conductive particles may include nickel particles, copper particles, aluminum particles, carbon black, carbon nanotubes, particles in which the surface of a metal particle serving as a core is plated with a metal such as gold or silver (hereinafter also referred to as plated metal particles), and particles in which the surface of a resin particle serving as a core is coated with a metal (hereinafter also referred to as metal-coated resin particles). Only one of these conductive particles may be used, or two or more types may be used in combination.

As the plated metal particles, for example, particles having a nickel particle or copper particle as a core, the surface of which is plated with a noble metal such as gold or silver, can be used.
As the metal-coated resin particles, for example, particles having a resin particle as a core, the surface of which is coated with a metal such as nickel or gold, can be used.
When the thermosetting sheet according to the present embodiment contains conductive particles other than silver particles, it is preferable to use plated metal particles as the conductive particles, and it is preferable to use particles (silver-coated copper particles) in which a copper particle is used as a core and the surface of the core is plated with silver as the plated metal particles. Commercially available silver-coated copper particles include 1200YP (trade name) manufactured by Mitsui Smelting & Co., Ltd. and AOP-TCY-2 (EN) (trade name) manufactured by Dowa Electronics Co., Ltd.
When the thermosetting sheet according to this embodiment contains conductive particles other than silver particles, the mass percentage of silver particles in 100 mass% of the conductive particles is preferably 10 mass% or more and 95 mass% or less, and more preferably 20 mass% or more and 90 mass% or less.

The conductive particles other than silver may be, for example, flake-shaped, needle-shaped, filament-shaped, spherical, or flat (including scale-shaped) in shape. Among these, flat particles are preferred because they have a large specific surface area and therefore a large contact area with the silver particles. The product name 1200YP, manufactured by Mitsui Smelting & Co., Ltd., mentioned above, is a flat conductive particle.

The conductive particles other than silver particles preferably have an average particle diameter _D50 of 0.01 μm or more and 20 μm or less, and more preferably 0.05 μm or more and 10 μm or less.
The average particle diameter _D50 of conductive particles other than silver particles can also be measured in the same manner as the average particle diameter _D50 of silver particles described above.

The thermosetting sheet according to this embodiment may contain a thermosetting catalyst in order to sufficiently advance the curing reaction of the resin component and to increase the curing reaction rate. Examples of the thermosetting catalyst include imidazole-based compounds, triphenylphosphine-based compounds, amine-based compounds, and trihalogen borane-based compounds.

The thermosetting sheet according to this embodiment has a viscosity at 100° C. of 20 kPa·s or more and 3000 kPa·s or less.
By having a viscosity at 100°C of 20 kPa·s or more and 3000 kPa·s or less, the wettability to an adherend (e.g., a semiconductor wafer) can be improved, thereby ensuring relatively sufficient adhesion to the adherend.
Therefore, peeling of the semiconductor element can be relatively suppressed.
In particular, when the thermosetting sheet is attached to one side of a semiconductor wafer and diced to obtain multiple thermosetting sheets with semiconductor elements attached to one side, peeling of the semiconductor elements from the thermosetting sheet can be relatively suppressed.

The viscosity at 100°C can be evaluated using a rheometer (Thermo Fisher Scientific, rotational rheometer HAAKE MARS). Specifically, it can be obtained by reading the indication at 100°C when the temperature is increased from 30°C to 180°C at a heating rate of 10°C/min.

The thermosetting sheet according to this embodiment may contain a volatile component.
The thermosetting sheet according to this embodiment preferably contains 5% by mass or more and 50% by mass or less of the volatile components relative to the total mass of the organic components (thermosetting resin, thermoplastic resin, volatile components) contained in the thermosetting sheet, and more preferably contains 10% by mass or more and 40% by mass or less of the volatile components.
Examples of the volatile component include an organic compound containing one or more hydroxyl groups and having a boiling point of 250°C or higher. The boiling point of the organic compound is preferably 350°C or lower. Examples of such organic compounds include terpene compounds. Among terpene compounds, isobornylcyclohexanol represented by the following formula (1) is preferable as the volatile component. Isobornylcyclohexanol is an organic compound having a boiling point of 308 to 318°C. When heated from room temperature (23±2°C) to 600°C under a nitrogen gas flow of 200mL/min and at a temperature increase rate of 10°C/min, it has the property of undergoing a large weight loss from 100°C or higher and volatilizing and disappearing at 245°C (no further weight loss is observed). It also has the property of exhibiting an extremely high viscosity of 1,000,000 mPa·s at 25°C, but a relatively low viscosity of 1,000 mPa·s or lower at 60°C. The weight loss is a value when the weight loss rate at the measurement start temperature (room temperature) is set to 0%.
Thus, isobornylcyclohexanol exhibits extremely high viscosity at 25° C. as described above, and is therefore capable of maintaining a sheet shape at room temperature, but exhibits relatively low viscosity at 60° C. as described above, and thus becomes tacky. In other words, a thermosetting sheet containing isobornylcyclohexanol exhibits excellent sheet shape retention at room temperature, and becomes tacky at temperatures of 60° C. or higher.
Here, when mounting a semiconductor element attached to one side of a thermosetting sheet on a metal lead frame or the like, the semiconductor element is usually temporarily attached (temporarily fixed) to an adherend such as a metal lead frame via the thermosetting sheet at a temperature of 60 to 80° C., but since isobornylcyclohexanol becomes tacky at 60° C. or higher as described above, when the thermosetting sheet according to this embodiment contains isobornylcyclohexanol as a volatile component, the thermosetting sheet has improved temporary adhesion to an adherend such as a metal lead frame. In other words, in the temporarily attached state, the attachment position of the semiconductor element is not shifted and the thermosetting sheet is prevented from lifting off the adherend.
Therefore, when the thermosetting sheet is thermally cured to bond the semiconductor element to the adherend, the semiconductor element can be bonded to the adherend with high reliability.

In the thermosetting sheet according to this embodiment, the particle filling rate P of the conductive particles in the thermosetting sheet before curing is preferably 30% by volume or more, more preferably 40% by volume or more, and even more preferably 50% by volume or more.
The particle packing ratio P is preferably 70% by volume or less, and more preferably 60% by volume or less.
When the particle filling rate P satisfies the above numerical range, the heat dissipation property of the thermosetting sheet after curing can be further improved.

The particle packing ratio P can be determined according to the following procedure.

(1) The cured thermosetting sheet is mechanically polished to expose a cross section, and the exposed cross section is then subjected to ion polishing using an ion polishing device (for example, product name: Cross Section Polisher SM-09010, manufactured by JEOL Ltd.).
(2) An SEM image (scanning electron microscope image) of an arbitrary cross-sectional region of the exposed cross-section that has been ion-polished is taken using a field emission scanning electron microscope (e.g., Hitachi High-Technologies Corporation, product name SU8020), and a reflected electron image is obtained as image data. The imaging conditions can be an acceleration voltage of 5 kV and a magnification of 5000 times.
(3) The obtained image data is subjected to an automatic binarization process using image analysis software (e.g., ImageJ) to binarize the metal parts and the resin parts.
(4) The total area of the conductive particle parts and the total area (conductive particle parts + resin part) are calculated from the binarized image, and the total area of the conductive particle parts is divided by the total area to calculate the particle filling rate P of the conductive particles for the cured thermosetting sheet.

The particle packing ratio P of the conductive particles is preferably determined by arithmetically averaging the packing ratios determined for five cross-sectional regions on the exposed cross-section subjected to ion polishing.

The thickness of the thermosetting sheet according to the present embodiment is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more. The thickness of the thermosetting sheet is preferably 150 μm or less, more preferably 100 μm or less, and even more preferably 80 μm or less.
When the thickness of the thermosetting sheet is 150 μm or less, the thermal conductivity (heat dissipation property) can be further improved.
The thickness of the thermosetting sheet can be determined, for example, by measuring the thickness at five randomly selected points using a dial gauge (Model R-205, manufactured by PEACOCK) and calculating the arithmetic average of these thicknesses.

The thermosetting sheet according to this embodiment preferably has a thermal conductivity of 3 W/m·K or more, and more preferably 10 W/m·K or more, after curing.
When the thermal conductivity after curing is within the above range, the electrical conductivity of the thermosetting sheet after curing can be further increased.
In the thermosetting sheet according to this embodiment, the upper limit of the thermal conductivity after curing is usually 100 W/m·K.
The thermal conductivity after curing can be calculated by subjecting the thermosetting sheet according to this embodiment to heat curing at 200°C for 1 hour in a pressure cooker while applying a pressure of 0.5 MPa, and using the following formula for the heat-cured thermosetting sheet.

The thermal diffusivity (m ² /s) in the above formula can be measured by a TWA method (temperature wave thermal analysis method, measuring device: iPhase Mobile, manufactured by iPhase Corporation).
The specific heat (J/g ° C.) in the above formula can be measured by a DSC method. The specific heat measurement is performed using a DSC6220 manufactured by SII Nanotechnology Inc. under conditions of a heating rate of 10° C./min and a temperature range of 20 to 300° C., and the specific heat can be calculated based on the obtained data by the method described in the JIS Handbook (specific heat capacity measurement method K-7123).
Furthermore, the specific gravity in the above formula can be measured by Archimedes' method.

The thermosetting sheet according to this embodiment preferably has a peel strength against a silicon wafer at room temperature (23±2° C.) of 1 N/10 mm or more, more preferably 5 N/10 mm or more, and even more preferably 10 N/10 mm or more.
Furthermore, the thermosetting sheet according to this embodiment preferably has a peel strength against a silicon wafer at room temperature (23±2° C.) of 20 N/10 mm or less, and more preferably 15 N/10 mm or less.
By ensuring that the peeling force against the silicon wafer satisfies the above numerical range, peeling of the semiconductor element during dicing can be further suppressed.
The peel strength against a silicon wafer at room temperature can be measured by a peel test using a tensile tester (product name: Autograph AG-X, manufactured by Shimadzu Corporation) under conditions of room temperature (23±2° C.), a peel angle of 180°, and a tensile speed of 300 mm/min.
Specifically, it can be measured as follows.

(1) A thermosetting sheet is laminated on one surface of a silicon wafer (bare wafer) to obtain a laminate.
(2) The laminate is placed on a hot plate heated to 70° C. The laminate is placed so that the surface of the silicon wafer is in contact with the surface of the hot plate.
(3) The laminate is pressed with a pressure roller (roller mass: 2 kg) to bond the silicon wafer and the thermosetting sheet together, and then the laminate is left on a hot plate for 2 minutes.
(4) The laminate that has been left standing is removed from the hot plate and left at room temperature (23±2° C.) for 20 minutes to obtain a test specimen.
(5) A peel test is carried out on the test specimen under the above conditions using the above tensile tester to measure the peel force against a silicon wafer even at room temperature.

The thermosetting sheet according to this embodiment may contain one or more other components as necessary. Examples of the other components include a filler dispersant, a flame retardant, a silane coupling agent, and an ion trapping agent.

[Dicing die bond film]
Next, the dicing die bond film 20 will be described with reference to Fig. 1. In the following description, the description of the parts that overlap with the thermosetting sheet will not be repeated.

As shown in FIG. 1, the dicing die bond film 20 according to this embodiment comprises a base layer 1, a dicing tape 10 having an adhesive layer 2 laminated on the base layer 1, and a thermosetting sheet 3 laminated on the adhesive layer 2 of the dicing tape 10.
In the dicing die bond film 20, a semiconductor element is attached onto the thermosetting sheet 3. The semiconductor element may be a bare wafer.
The bare wafer attached to the dicing die bond film 20 according to this embodiment is cleaved into a plurality of bare chips by blade dicing, DBG (dicing before grinding), SDBG (stealth dicing before grinding), or the like. During the cleavage, the thermosetting sheet 3 is also cleaved together with the bare wafer. The thermosetting sheet 3 is cleaved into pieces of a size corresponding to the size of the individual bare chips. This allows a plurality of bare chips with the thermosetting sheet 3 to be obtained.

As described above, the thermosetting sheet 3 of the dicing die bond film 20 is a thermosetting sheet containing a thermosetting resin, a thermoplastic resin, and conductive particles, the conductive particles including silver particles having an average particle diameter _D50 of 0.01 μm or more and 10 μm or less and a circularity in a cross section of 0.7 or more, and a viscosity of 20 kPa·s or more and 3000 kPa·s or less.

The base layer 1 supports the adhesive layer 2 and the thermosetting sheet 3 laminated on the adhesive layer 2. The base layer 1 contains a resin. Examples of the resin include olefin-based resins such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymers; copolymers containing ethylene as a monomer component, such as ethylene-vinyl acetate copolymers (EVA), ionomer resins, ethylene-(meth)acrylic acid copolymers, and ethylene-(meth)acrylic acid ester (random, alternating) copolymers; polyesters such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polybutylene terephthalate (PBT); acrylic resins; polyvinyl chloride (PVC); polyurethane; polycarbonate; polyphenylene sulfide (PPS); amide-based resins such as polyamide and fully aromatic polyamide (aramid); polyether ether ketone (PEEK); polyimide; polyetherimide; polyvinylidene chloride; ABS (acrylonitrile-butadiene-styrene copolymer); cellulose-based resins; silicone resins; and fluororesins.
Among these, it is preferable to use polyethylene terephthalate.

The substrate layer 1 may contain one of the above resins, or may contain two or more of the above resins.

Materials for the base layer 1 include polymers such as crosslinked products of the resins (e.g., plastic films). The plastic films may be used without stretching, or may be stretched uniaxially or biaxially as necessary. When a resin sheet is provided with heat shrinkability by stretching or the like, the base layer 1 can be heat-shrunk after dicing to reduce the adhesive area between the adhesive layer 2 and the thermosetting sheet 3, facilitating the recovery of the semiconductor chips (semiconductor elements).

The surface of the base layer 1 may be subjected to a general surface treatment to improve adhesion and retention with adjacent layers. Examples of such surface treatments include chemical or physical treatments such as chromate treatment, ozone exposure, flame exposure, high-voltage shock exposure, and ionizing radiation treatment, as well as coating with a primer.

The thickness of the base layer 1 is preferably from 1 μm to 1000 μm, more preferably from 10 μm to 500 μm, further preferably from 20 μm to 300 μm, and particularly preferably from 30 μm to 200 μm.
The thickness of the base layer 1 can be determined using a dial gauge (Model R-205, manufactured by PEACOCK) in the same manner as the thickness of the thermosetting sheet 3 described above.

The substrate layer 1 may contain various additives. Examples of the various additives include colorants, fillers, plasticizers, antioxidants, antioxidants, surfactants, and flame retardants.

The adhesive used to form the adhesive layer 2 is not particularly limited, and may be, for example, a general pressure-sensitive adhesive such as an acrylic adhesive or a rubber adhesive. As the pressure-sensitive adhesive, an acrylic adhesive having an acrylic polymer as a base polymer is preferred from the viewpoint of cleaning and washing properties with ultrapure water or organic solvents such as alcohol for electronic components such as semiconductor wafers and glass that are sensitive to contamination.

Examples of the acrylic polymer include acrylic polymers using one or more of (meth)acrylic acid alkyl esters and (meth)acrylic acid cycloalkyl esters as monomer components. Examples of the (meth)acrylic acid alkyl esters include methyl esters, ethyl esters, propyl esters, isopropyl esters, butyl esters, isobutyl esters, s-butyl esters, t-butyl esters, pentyl esters, isopentyl esters, hexyl esters, heptyl esters, octyl esters, 2-ethylhexyl esters, isooctyl esters, nonyl esters, decyl esters, isodecyl esters, undecyl esters, dodecyl esters, tridecyl esters, tetradecyl esters, hexadecyl esters, octadecyl esters, and eicosyl esters, and the like, which are linear or branched alkyl esters having 1 to 30 carbon atoms, particularly 4 to 18 carbon atoms. Examples of the (meth)acrylic acid cycloalkyl esters include cyclopentyl esters and cyclohexyl esters.
The (meth)acrylic acid ester means at least one of an acrylic acid ester and a methacrylic acid ester, and all (meth) in the present invention have the same meaning as defined above.

The acrylic polymer may contain units corresponding to other monomer components that are copolymerizable with the (meth)acrylic acid alkyl ester or (meth)acrylic acid cycloalkyl ester, if necessary, for the purpose of modifying the cohesive strength, heat resistance, etc. Examples of such monomer components include carboxyl-containing monomers such as acrylic acid, methacrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid; acid anhydride monomers such as maleic anhydride and itaconic anhydride; 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, and 10-hydroxydecyl (meth)acrylate. Examples of the copolymerizable monomers include hydroxyl group-containing monomers such as 12-hydroxylauryl (meth)acrylate, (4-hydroxymethylcyclohexyl)methyl (meth)acrylate, etc.; sulfonic acid-containing monomers such as styrenesulfonic acid, allylsulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, (meth)acryloyloxynaphthalenesulfonic acid, sulfopropyl (meth)acrylate, (meth)acryloyloxynaphthalenesulfonic acid, etc.; phosphoric acid-containing monomers such as 2-hydroxyethylacryloylphosphate, etc.; acrylamide, acrylonitrile, etc. These copolymerizable monomer components can be used alone or in combination. The amount of these copolymerizable monomers used is preferably 40% by mass or less of the total monomer components.

Furthermore, the acrylic polymer may contain a polyfunctional monomer or the like as a copolymerization monomer component for crosslinking, if necessary. Examples of such polyfunctional monomers include hexanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, epoxy (meth)acrylate, polyester (meth)acrylate, and urethane (meth)acrylate. These polyfunctional monomers may also be used alone or in combination. The amount of polyfunctional monomer used is preferably 30% by mass or less of the total monomer components in terms of adhesive properties, etc.

The acrylic polymer can be obtained by polymerizing a single monomer or a mixture of two or more monomers. The polymerization may be carried out by any method, such as solution polymerization, emulsion polymerization, bulk polymerization, or suspension polymerization. From the viewpoint of preventing contamination of clean adherends, it is preferable that the content of low molecular weight substances is small. From this viewpoint, the number average molecular weight of the acrylic polymer is preferably 300,000 or more, and more preferably about 400,000 to 3,000,000.

In addition, an external crosslinking agent can be appropriately added to the adhesive to increase the number average molecular weight of the base polymer, such as an acrylic polymer. Specific examples of the external crosslinking method include a method of adding a crosslinking agent such as a polyisocyanate compound, an epoxy compound, an aziridine compound, or a melamine crosslinking agent and reacting it. When an external crosslinking agent is used, the amount used is appropriately determined taking into consideration the balance with the base polymer to be crosslinked and the intended use as an adhesive. In general, it is preferable to mix about 5 parts by mass or less of the external crosslinking agent per 100 parts by mass of the base polymer, and more preferably 0.1 to 5 parts by mass.

In addition to the above components, the adhesive may contain various known additives such as tackifiers and antioxidants, if necessary.

The adhesive layer 2 can be formed from a radiation-curable adhesive. The degree of crosslinking of a radiation-curable adhesive can be increased by irradiation with radiation such as ultraviolet light, and the adhesive strength can be easily reduced. In other words, by forming the adhesive layer 2 from a radiation-curable adhesive, the adhesive layer 2 can be sufficiently adhered to the thermosetting sheet 3 without being irradiated with radiation before dicing, and after dicing, the adhesive layer 2 can be irradiated with radiation to reduce the adhesive strength of the adhesive layer 2, allowing the semiconductor chip (semiconductor element) to be easily picked up (recovered).

The radiation-curable adhesive can be any adhesive that has a radiation-curable functional group such as a carbon-carbon double bond and exhibits adhesive properties. Examples of radiation-curable adhesives include additive-type radiation-curable adhesives that combine a radiation-curable monomer component or oligomer component with a general pressure-sensitive adhesive such as an acrylic adhesive or a rubber adhesive.

Examples of the radiation-curable monomer component include urethane (meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and 1,4-butanediol di(meth)acrylate. Examples of the radiation-curable oligomer component include various oligomers such as urethane-based, polyether-based, polyester-based, polycarbonate-based, and polybutadiene-based oligomers, and those having a molecular weight in the range of about 100 to 30,000 are preferred. The amount of the radiation-curable monomer component or the radiation-curable oligomer component to be blended is preferably an amount that can suitably reduce the adhesive strength of the adhesive layer 2 after radiation exposure. In general, the amount of the radiation-curable monomer component or the radiation-curable oligomer component is, for example, preferably 5 to 500 parts by mass, and more preferably 40 to 150 parts by mass, per 100 parts by mass of the base polymer, such as an acrylic polymer, that constitutes the adhesive.

In addition to the additive-type radiation-curable adhesives described above, examples of the radiation-curable adhesive include internal-type radiation-curable adhesives that use a base polymer having a carbon-carbon double bond in the polymer side chain, in the main chain, or at the end of the main chain. The internal-type radiation-curable adhesive does not need to contain low molecular weight oligomer components or the like, or the content of the oligomer components or the like is relatively small. Therefore, when the internal-type radiation-curable adhesive is used, the oligomer components or the like are prevented from moving over time in the adhesive layer 2. As a result, the adhesive layer 2 can have a relatively stable layer structure.

The base polymer having a carbon-carbon double bond can be any polymer that has a carbon-carbon double bond and is adhesive, without any particular limitations. As such a base polymer, one having an acrylic polymer as the basic skeleton is preferable. Examples of the basic skeleton of the acrylic polymer include the acrylic polymers described above.

The method of introducing a carbon-carbon double bond into the acrylic polymer is not particularly limited, and various methods can be used, but adopting a method of introducing a carbon-carbon double bond into a polymer side chain makes molecular design easier. For example, there is a method in which a monomer having a functional group is copolymerized into the acrylic polymer in advance, and then a compound having a functional group and a carbon-carbon double bond that can react with the functional group is subjected to a condensation reaction or addition reaction while maintaining the radiation curability of the carbon-carbon double bond.

Examples of combinations of these functional groups include a carboxylic acid group and an epoxy group, a carboxylic acid group and an aziridyl group, and a hydroxyl group and an isocyanate group. Among these combinations of functional groups, a combination of a hydroxyl group and an isocyanate group is preferred from the viewpoint of ease of reaction tracking. In addition, as long as the combination of these functional groups produces an acrylic polymer having a carbon-carbon double bond, either of the functional groups may be on the acrylic polymer side or on the compound side having the carbon-carbon double bond. In the case of the above preferred combination, it is preferred that the acrylic polymer has a hydroxyl group and the compound having the carbon-carbon double bond has an isocyanate group. In this case, examples of isocyanate compounds having a carbon-carbon bond include methacryloyl isocyanate, 2-methacryloyloxyethyl isocyanate, m-isopropenyl-α,α-dimethylbenzyl isocyanate, and the like. In addition, acrylic polymers that are used are copolymers of the above-mentioned hydroxyl group-containing monomers and ether compounds such as 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, and diethylene glycol monovinyl ether.

The inherent radiation-curable adhesive can use the base polymer having a carbon-carbon double bond (particularly an acrylic polymer) alone, but can also contain the radiation-curable monomer component or the radiation-curable oligomer component to the extent that the properties are not deteriorated. The radiation-curable oligomer component is usually contained in an amount of 30 parts by mass or less per 100 parts by mass of the base polymer, and preferably in an amount of 1 to 10 parts by mass or less.

The radiation-curable adhesive contains a photopolymerization initiator when curing with ultraviolet light or the like. Examples of photopolymerization initiators include α-ketol-based compounds such as 4-(2-hydroxyethoxy)phenyl(2-hydroxy-2-propyl)ketone, α-hydroxy-α,α'-dimethylacetophenone, 2-methyl-hydroxypropiophenone, and 1-hydroxycyclohexylphenylketone; acetophenone-based compounds such as methoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxyacetophenone, and 2-methyl-1-[4-(methylthio)-phenyl]-2-morpholinopropane-1; benzoin ether-based compounds such as benzoin ethyl ether, benzoin isopropyl ether, and anisoin methyl ether; and ketal-based compounds such as benzyl dimethyl ketal. Examples of the photopolymerization initiator include aromatic sulfonyl chloride compounds such as 2-naphthalenesulfonyl chloride; photoactive oxime compounds such as 1-phenone-1,1-propanedione-2-(o-ethoxycarbonyl)oxime; benzophenone compounds such as benzophenone, benzoylbenzoic acid, and 3,3'-dimethyl-4-methoxybenzophenone; thioxanthone compounds such as thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-dichlorothioxanthone, 2,4-diethylthioxanthone, and 2,4-diisopropylthioxanthone; camphorquinone; halogenated ketones; acylphosphinoxides; and acylphosphonates. The amount of the photopolymerization initiator is, for example, 0.05 to 20 parts by mass relative to 100 parts by mass of the base polymer, such as an acrylic polymer, that constitutes the adhesive.

Examples of radiation-curable adhesives include rubber-based adhesives and acrylic-based adhesives that contain photopolymerizable compounds such as addition-polymerizable compounds with two or more unsaturated bonds and alkoxysilanes with epoxy groups, and photopolymerization initiators such as carbonyl compounds, organic sulfur compounds, peroxides, amines, and onium salt compounds, as disclosed in JP-A-60-196956.

If oxygen inhibits curing during radiation exposure, it is desirable to block oxygen (air) from the surface of the radiation-curable adhesive layer 2 in some way. For example, the surface of the adhesive layer 2 may be covered with a separator, or radiation such as ultraviolet light may be irradiated in a nitrogen gas atmosphere.

The thickness of the adhesive layer 2 is not particularly limited, but in order to prevent chipping of the cut surface of the chip and to maintain the thermosetting sheet 3 in a fixed state, it is preferably 1 to 50 μm, more preferably 2 to 30 μm, and even more preferably 5 to 25 μm.

The thermosetting sheet and dicing die bond film according to the present invention are not limited to the above-mentioned embodiment. The thermosetting sheet and dicing die bond film according to the present invention are not limited by the above-mentioned action and effect. The thermosetting sheet and dicing die bond film according to the present invention can be modified in various ways without departing from the gist of the present invention.

Next, the present invention will be described in more detail with reference to examples. The following examples are intended to explain the present invention in more detail and are not intended to limit the scope of the present invention.

[Example 1]
A varnish was prepared by stirring a mixture containing each material in the mass ratio shown in the section of Example 1 in Table 1 for 3 minutes using a hybrid mixer (manufactured by Keyence Corporation, product name: HM-500). This varnish was applied to one side of a release-treated film (manufactured by Mitsubishi Chemical Corporation, product name: MRA38, thickness 38 μm) and then dried at a temperature of 100° C. for 2 minutes to obtain a thermosetting sheet having a thickness of 30 μm.
The materials used in the following Table 1 are as follows:

Phenolic resin: MEHC-7851S (biphenyl type phenolic resin, phenol equivalent 209 g/eq) manufactured by Meiwa Kasei Co., Ltd.
Solid epoxy resin: KI-3000-4 (cresol novolac type multifunctional epoxy resin, epoxy equivalent 200 g/eq) manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.
Liquid epoxy resin: EXA-4816 manufactured by DIC Corporation (aliphatic modified bisphenol A type epoxy resin (bifunctional type), epoxy equivalent 403 g/eq)
Silver (Ag)-coated copper (Cu) particles: 1200YP manufactured by Mitsui Mining & Smelting Co., Ltd. (flat copper particles coated with 10% by mass of silver particles, average particle size 3.5 μm, irregular shape)
Silver (Ag) particles: HP02A manufactured by Mitsui Mining & Smelting Co., Ltd. (silver particles surface-treated with a fatty acid-based coating agent)
- Volatile material (isobornylcyclohexanol (MTPH))
MTPH manufactured by Nippon Terpene Chemical
Acrylic resin solution: Teisan Resin SG-70L manufactured by Nagase Chemitec Co., Ltd. (containing MEK and toluene as solvents, solid content 12.5%, glass transition temperature -13°C, mass average molecular weight 900,000, acid value 5 mg/KOH, carboxyl group-containing acrylic copolymer)
Coupling agent: Shin-Etsu Chemical Co., Ltd.'s KBE-846 (bis(triethoxysilylpropyl)tetrasulfide)
Catalyst: TPP-K (tetraphenylphosphonium tetraphenylborate) manufactured by Hokko Chemical Industry Co., Ltd.
・Solvent: Methyl ethyl ketone (MEK)

In addition, the mass proportions of the silver-coated copper particles and silver particles in 100 parts by mass of the conductive particles (silver-coated copper particles and silver particles), the mass proportions of the epoxy resin (solid and liquid) in 100 parts by mass of the thermosetting sheet, the mass proportions of the phenol resin in 100 parts by mass of the thermosetting sheet, the mass proportions of the acrylic resin in 100 parts by mass of the thermosetting sheet, and the mass proportions of isobornylcyclohexanol in 100 parts by mass of the organic components (phenol resin, epoxy resin (solid and liquid), acrylic resin solution, isobornylcyclohexanol) are shown in Table 2 below.

[Example 2]
A thermosetting sheet according to Example 2 was obtained in the same manner as in Example 1, except that the silver particles were a modified coating agent (epoxy-coated product) of HP02A manufactured by Mitsui Mining & Smelting Co., Ltd., did not contain TPP-K as a catalyst, and used a mixture containing each material in the mass ratio shown in the Example 2 section of Table 1 below.

[Example 3]
A thermosetting sheet according to Example 3 was obtained in the same manner as in Example 1, except that TPP-K was not used as a catalyst and a mixture containing each material in the mass ratio shown in the section of Example 3 in Table 1 below was used.

[Example 4]
A thermosetting sheet according to Example 4 was obtained in the same manner as in Example 1, except that the silver particles were HP02 manufactured by Mitsui Mining & Smelting Co., Ltd., TPP-K was not used as a catalyst, and a mixture containing each material in the mass ratio shown in the section on Example 4 in Table 1 below was used.

[Example 5]
A thermosetting sheet according to Example 5 was obtained in the same manner as in Example 1, except that the silver particles were AG-2-8F (silver particles surface-treated with a fatty acid-based coating agent) manufactured by Dowa Electronics Co., Ltd., the silver (Ag)-coated copper (Cu) particles were AOP-TCY-2 (EN) manufactured by Dowa Electronics Co., Ltd., and a mixture containing each material in the mass ratio shown in the section of Example 5 in Table 1 below was used.

[Comparative Example 1]
A thermosetting sheet according to Comparative Example 1 was obtained in the same manner as in Example 1, except that the silver particles were SPH02J (aggregated nano Ag particles, irregular shape, average particle size of the aggregates: 1.8 μm) manufactured by Mitsui Mining & Smelting Co., Ltd., no TPP-K was added as a catalyst, and a mixture containing each material in the mass ratio shown in the Comparative Example 1 section of Table 1 below was used.

[Comparative Example 2]
A thermosetting sheet according to Comparative Example 1 was obtained in the same manner as in Example 1, except that the silver particles were SPH02J manufactured by Mitsui Mining & Smelting Co., Ltd., and a mixture containing each material in the mass ratio shown in the Comparative Example 2 section of Table 1 below was used.

[Comparative Example 3]
A thermosetting sheet according to Comparative Example 3 was obtained in the same manner as in Example 1, except that the silver particles were SPH02J manufactured by Mitsui Mining & Smelting Co., Ltd., and a mixture containing each material in the mass ratio shown in the Comparative Example 3 section of Table 1 below was used without containing a volatile material (isobornylcyclohexanol).

<Average particle diameter _D50 of silver (Ag) particles>
Before blending, the particle size distribution was measured using a laser diffraction/scattering type particle size distribution measuring device (Microtrac MT3000II series, manufactured by Microtrac Bell).
The average particle diameter _D50 of the silver particles contained in the heat-cured sheet of each example was measured, and the results are shown in Table 2 below.

<Circularity of Silver (Ag) Particles>
The thermosetting sheet according to each example was cut in the thickness direction, and an SEM image of the cut surface was taken. The SEM image was then analyzed using a powder image analyzer (PITA-3, manufactured by Seishin Enterprise Co., Ltd.).
The analysis using the powder image analyzer was performed on 10 silver particles randomly selected in the SEM image, and the circularity was determined by arithmetically averaging the circularity values obtained for the 10 silver particles.
In the thermosetting sheets according to each example, the silver particles and the silver (Ag)-coated copper (Cu) particles were distinguished by observing backscattered electron images so that light and dark areas were observed due to the difference in composition.
The circularity of the silver particles of the thermosetting sheets according to each example was measured, and the results are shown in Table 2 below.

<Filling rate of conductive particles>
The particle packing ratio P was determined for the thermosetting sheet according to each example according to the following procedure.

(1) The cured thermosetting sheet is mechanically polished to expose a cross section, and the exposed cross section is then subjected to ion polishing using an ion polishing device (manufactured by JEOL Ltd., product name: Cross Section Polisher SM-09010).
(2) An SEM image (image by a scanning electron microscope) of an arbitrary cross-sectional region of the exposed cross-section that has been ion-polished is taken using a field emission scanning electron microscope SU8020 (manufactured by Hitachi High-Technologies Corporation), and a backscattered electron image is obtained as image data. The imaging conditions are an acceleration voltage of 5 kV and a magnification of 5000 times.
(3) The obtained image data is subjected to an automatic binarization process using image analysis software ImageJ to binarize the metal parts and the resin parts.
(4) The total area of the metal parts and the area of the whole (metal parts + resin parts) are calculated from the binarized image, and the total area of the metal parts is divided by the total area to calculate the particle filling rate P of the conductive particles for the cured thermosetting sheet.

The particle packing ratio P of the conductive particles was determined by arithmetically averaging the particle packing ratios determined for five cross-sectional regions on the exposed cross-section that had been ion-polished.
The particle filling rate P of the conductive particles was determined for each of the thermosetting sheets according to the examples, and the results are shown in Table 2 below.

<Viscosity of thermosetting sheet at 100° C.>
The viscosity of the thermosetting sheet according to each example at 100° C. was evaluated using a rheometer (HAAKE MARS rotational rheometer manufactured by Thermo Fisher Scientific Co., Ltd.) by reading the indicated value at 100° C. when the temperature was increased from 30° C. to 180° C. at a rate of 10° C./min.
The viscosity at 100° C. of the thermosetting sheets of each example was measured, and the results are shown in Table 2 below.

<Thermal conductivity of thermosetting sheet>
The thermosetting sheet according to each example was heat-cured in a pressure cooker at 200° C. for 1 hour while applying a pressure of 0.5 MPa. The thermal conductivity of the heat-cured thermosetting sheet according to each example was calculated according to the following formula.

The thermal diffusivity α (m ² /s) was measured by a TWA method (temperature wave thermal analysis method, measuring device: iPhase Mobile, manufactured by iPhase Corporation).
The specific heat C _p (J/g·° C.) was measured by the DSC method. The specific heat measurement was performed using a DSC6220 manufactured by SII Nanotechnology Inc. under conditions of a heating rate of 10° C./min and a temperature range of 20 to 300° C., and the specific heat was calculated based on the obtained data by the method described in the JIS Handbook (specific heat capacity measurement method K-7123).
The specific gravity was measured by the Archimedes method.
The thermal conductivity of the cured thermosetting sheets of each example was calculated, and the results are shown in Table 2 below.

<Peeling force against silicon wafer>
The adhesive strength of the thermosetting sheet according to each example to a silicon wafer was measured. The peeling strength against the silicon wafer was measured at room temperature (23±2°C). The peeling strength against the silicon wafer was measured by a peeling test using a tensile tester (product name: Autograph AG-X, manufactured by Shimadzu Corporation) under the conditions of room temperature (23±2°C), a peeling angle of 180°, and a pulling speed of 300 mm/min.
Specifically, the measurements were carried out as follows.

(1) A thermosetting sheet is laminated on one surface of a silicon wafer (bare wafer) to obtain a laminate.
(2) The laminate is placed on a hot plate heated to 70° C. The laminate is placed so that the surface of the silicon wafer is in contact with the surface of the hot plate.
(3) The laminate is pressed with a pressure roller (roller mass: 2 kg) to bond the silicon wafer and the thermosetting sheet together, and then the laminate is left on a hot plate for 2 minutes.
(4) The laminate that has been left standing is removed from the hot plate and left at room temperature (23±2° C.) for 20 minutes to obtain a test specimen.
(5) A peel test is carried out on the test specimen under the above conditions using the above tensile tester to measure the peel force against a silicon wafer even at room temperature.

The peel strength of the thermosetting sheet according to each example against a silicon wafer was measured, and the results are shown in Table 2 below.

<Peeling during dicing>
The evaluation of the peelability during dicing was performed using a dicing die bond film in which a thermosetting sheet was laminated on the adhesive layer of a dicing tape, and a bare wafer.
In detail, the following steps were followed:

(1) A Si bare wafer having a thickness of 100 μm and a diameter of 8 inches (200 mm) is attached onto the thermosetting sheet while being pressed by a pressing means (pressure roller).
(2) Using a fully automatic dicing saw (DISCO Corporation, FULLY AUTOMATIC DISCING SAW, DFD6361), blade dicing is performed on the thermosetting sheet and the Si bare wafer under conditions of spindle rotation speed: 45,000 rpm (min ^-1 ), feed speed: 30 mm/s, and pitch: 5 mm to obtain a plurality of thermosetting sheets on which bare chips are stacked. At this time, if no bare chips are found to have peeled off from the thermosetting sheet to a level that is problematic for practical use, the peelability during dicing is evaluated as ◯, and if even one bare chip is found to have peeled off to a level that is problematic for practical use (chip skipping), the peelability during dicing is evaluated as ×.

The adhesive layer, dicing tape, and dicing die bond film were prepared as follows.

(Preparation of Adhesive Layer)
Synthesis of acrylic polymer
The following raw materials were placed in a reaction vessel equipped with a cooling tube, a nitrogen inlet tube, a thermometer, and a stirrer so that the monomer concentration was about 55% by mass, and a polymerization reaction was carried out at 60° C. for 10 hours under a nitrogen stream, thereby synthesizing an acrylic polymer intermediate.
2-Ethylhexyl acrylate (2HEA): 100 parts by mass 2-Hydroxyethyl acrylate (HEA): 20 parts by mass Polymerization initiator: appropriate amount Polymerization solvent: toluene An acrylic polymer was synthesized by performing an addition reaction between 100 parts by mass of the synthesized acrylic polymer intermediate and 1.4 parts by mass of 2-methacryloyloxyethyl isocyanate (MOI) in the presence of dibutyltin dilaurate (0.1 part by mass) in an air stream at 50° C. for 60 hours.
Preparation of adhesive layer
(1) A solution containing the following raw materials is obtained, and an appropriate amount of toluene is added to the solution to prepare a pressure-sensitive adhesive solution having a viscosity of 500 mPa·s.
- Synthesized acrylic polymer: 100 parts by weight - Polyisocyanate compound (manufactured by Nippon Polyurethane Co., Ltd., product name "Coronate L"): 1.1 parts by weight - Photopolymerization initiator (manufactured by Ciba Specialty Chemicals, product name "Irgacure 184"): 3 parts by weight (2) A PET film is prepared as a release sheet. The adhesive solution prepared as described above is applied to one side of the release sheet using an applicator. Note that the above-mentioned one side of the release sheet (PET film) is silicone-treated as a release treatment. After application, a drying treatment is performed by heating at 120°C for 2 minutes, and an adhesive layer with a thickness of 30 μm is formed on the release sheet.

(Preparation of dicing tape and dicing die bond film)
Preparation of dicing tape
A supporting substrate made of a polyethylene film having a thickness of 80 μm was attached to the exposed surface of the pressure-sensitive adhesive layer prepared on the release sheet at room temperature using a laminator to prepare a dicing tape.
In addition, the portion of the adhesive layer of the dicing tape to be attached to the Si bare wafer having a diameter of 8 inches was irradiated with ultraviolet light at an intensity of 300 mJ/cm ² to cure the portion to be attached.
Preparation of dicing die bond film
A thermosetting sheet was placed on the adhesive layer of the dicing tape after UV curing, so that the side opposite the laminated side of the release sheet was in contact with the adhesive layer, and the dicing tape was passed through a laminator at a speed of 0.8 mm/min to bond the thermosetting sheet to the dicing tape. The release sheet was then removed to produce a dicing die bond film in which the thermosetting sheet was laminated to the dicing tape.

The results of evaluating the peelability during dicing for the thermosetting sheets of each example are shown in Table 2 below.

From Table 2, it can be seen that the thermosetting sheets according to each Example all contain, as conductive particles, silver particles having an average particle size _D50 of 0.01 μm or more and 10 μm or less and a circularity in cross section of 0.7 or more, and further have a viscosity at 100° C. in the range of 20 kPa·s or more and 3000 kPa·s or less.
In addition, the thermosetting sheets of each of the examples had a thermal conductivity of 3 W/m·K or more after curing, which means that they have sufficient heat dissipation properties for practical use. In addition, the peel force against the silicon wafer was a relatively high value of 1.0 N/10 mm or more, and the peelability during dicing was rated as good.

In contrast, the thermosetting sheets of Comparative Examples 1 and 2 contained silver particles having a cross-sectional circularity of less than 0.7, and were found to have a viscosity at 100°C of more than 3000 kPa·s.
The thermosetting sheets of Comparative Examples 1 and 2 had a thermal conductivity of 3 W/m·K or more after curing, and thus exhibited sufficient heat dissipation for practical use; however, the peel force against the silicon wafer was below 1.0 N/10 mm, and the peelability during dicing was evaluated as ×.
In addition, it was found that the thermosetting sheet of Comparative Example 3 contains silver particles having a circularity in cross section of less than 0.7, and has a viscosity at 100°C in the range of 20 kPa·s or more and 3000 kPa·s or less.
The thermosetting sheet of Comparative Example 3 had a relatively high peel force against the silicon wafer of 7.63 N/10 mm, and the peelability during dicing was evaluated as good; however, the thermal conductivity was 1.5 W/m·K, which did not provide sufficient heat dissipation for practical use.

From these results, it was found that by making the thermosetting sheet contain, as conductive particles, silver particles having an average particle diameter _D50 of 0.01 μm or more and 10 μm or less and a circularity in cross section of 0.7 or more, and having a viscosity at 100° C. in the range of 20 kPa·s or more and 3000 kPa·s or less, peeling of the semiconductor element during dicing can be relatively suppressed, and the heat dissipation properties after curing can be relatively high.

REFERENCE SIGNS LIST 1 Base material layer 2 Pressure sensitive adhesive layer 3 Thermosetting sheet 10 Dicing tape 20 Dicing die bond film

Claims (8)

A thermosetting sheet comprising a thermosetting resin, a thermoplastic resin, and conductive particles,
the thermosetting resin includes an epoxy resin,
The conductive particles include silver particles having an average particle diameter _D50 of 0.01 μm or more and 10 μm or less and a circularity in cross section of 0.7 or more,
the mass % of the conductive particles is 83 mass % or more and 95 mass % or less based on 100 mass % of the thermosetting sheet;
A thermosetting sheet having a viscosity at 100°C of 20 kPa·s or more and 3000 kPa·s or less. The mass % of the conductive particles per 100 mass % of the thermosetting sheet is 89 mass % or more and 95 mass % or less.
The thermosetting sheet according to claim 1 . The thermosetting sheet according to claim 1 or 2 , wherein the conductive particles have a particle filling rate P of 30 volume % or more in the thermosetting sheet after curing. The thermosetting sheet according to claim 1 , which has a thermal conductivity after curing of 3 W/m·K or more and 100 W/m·K or less. The thermosetting sheet according to claim 1 , which has a peel strength from a silicon wafer of 1 N/10 mm or more and 20 N/10 mm or less at room temperature. Contains volatile components,
The thermosetting sheet according to claim 1 , wherein the volatile component contains one or more hydroxyl groups and has a boiling point of 250° C. or more and 350° C. or less. The thermosetting sheet according to claim 6 , wherein the volatile component is a terpene compound. A base layer;
a dicing tape having a pressure-sensitive adhesive layer laminated on the base layer;
a thermosetting sheet laminated on the adhesive layer of the dicing tape;
A dicing die bond film, wherein the thermosetting sheet is the thermosetting sheet according to claim 1 .