JP7722181B2 - Electronic component mounting boards and displays - Google Patents

Description

The present invention relates to an electronic component mounting board and a display.

In recent years, electronic components and the electronic component mounting boards on which they are mounted have become increasingly smaller and thinner in order to meet market demands for higher integration. Currently, in the mounting of logic IC chips such as semiconductor processors and memory, the flip-chip mounting method, in which electrodes are placed under the chip and directly connected to the electrodes on the substrate, is widely used instead of the conventional wire bonding method in order to increase the degree of integration of electronic components.

Meanwhile, in the display field, there has been active research into structures using LED chips with sides of 100 μm or less, known as μLEDs. These are particularly well suited to flip-chip mounting methods, but because the chip size, thickness, and electrode size are significantly different from those of logic IC chips, conventional methods using solder connections pose the problem of solder leaking to adjacent electrodes, causing short circuits between the electrodes. Therefore, many connection structures and methods, not just solder, are being considered. One specific method for mounting μLEDs is known, for example, of using a sheet material commonly known as ACF, which is formed on the surface of a printed wiring board and contains conductive particles with a particle size roughly equal to the thickness of the adhesive layer arranged in a fixed pattern within the adhesive layer (see, for example, Patent Document 1).

WO 2019/74058

However, with the ACF-based construction method described in Patent Document 1, the following reliability issues are likely to become apparent as electronic components become smaller. Specifically, as shown in Figure 2, to prevent short circuits between the electrodes of electronic components, the particle size of the conductive particles used in the ACF must be smaller than the distance between the electrodes. Consequently, the thickness of the adhesive layer must also be thin, so that it is roughly equal to the particle size of the conductive particles. Within such a thin adhesive layer, heat generated when the circuit is running can cause stress due to the thermal expansion coefficient of the adhesive layer and the conductive particles (hereinafter referred to as thermal shock), which can impair electrical connection.

The present invention aims to provide a highly reliable electronic component mounting board that is sufficiently resistant to thermal shock during operation, even in a structure in which electronic components are miniaturized and low-profile.

In order to solve the above problems, the present invention mainly has the following configuration.
The substrate has electronic components thereon,
a conductive composite material containing a resin and a conductive material is disposed between the electrode of the substrate and the electrode of the electronic component;
an electronic component mounting substrate having an insulating resin in a portion between the electronic component and the substrate that does not have the conductive composite material,
When the thickness (μm) of the conductive composite material is T _E and the average diameter (μm) of the conductive material is R _M , the relationship 3.0<T _E /R _M <20.0 is satisfied;
The electronic component mounting substrate has an insulating resin containing inorganic particles in an amount of 40 parts by weight or less, based on 100 parts by weight of the insulating resin.

The electronic component mounting board of the present invention has sufficient thermal shock resistance.

1 is a cross-sectional view schematically illustrating an example of an electronic component mounting board according to the present invention. 1 is a cross-sectional view showing an example of a state of a joint of an electronic component mounting board using an ACF;

The following describes in detail an embodiment of an electronic component mounting board according to the present invention, using the drawings. Note that the drawings are schematic. Furthermore, the present invention is not limited to the embodiment described below.

Figure 1 is a schematic diagram illustrating an example of an electronic component mounting substrate 8 according to an embodiment of the present invention. The electronic component mounting substrate 8 has an electronic component 2 on a substrate 1, a conductive composite material 3 containing a resin and a conductive material between an electrode 5a of the substrate 1 and an electrode 5b of the electronic component 2, and an insulating resin 4 in the portion between the electronic component 2 and the substrate 1 that does not have the conductive composite material 3. Each of these components will be described below.

<Substrate>
Substrates are typically used to form the wiring of electronic components mounted on them. Materials include organic materials such as printed circuit boards and inorganic materials such as glass and silicon. Functionality includes, but is not limited to, those containing elements such as transistors and those functioning as interposers for reconnecting to larger substrates. From the perspective of mounting low-profile electronic components using flip-chip mounting, inorganic substrates with high in-plane flatness are preferred because they can reduce in-plane variations in residual stress after mounting. Furthermore, TFT substrates or silicon substrates incorporating transistor-based driving circuits within the substrate are more preferred because they can compensate for variations in resistance values between electrodes. When a substrate is heated during processing, a temperature gradient generated in the thickness direction of the substrate can warp the substrate and increase thermal shock. To prevent this, the substrate thickness is preferably 1.0 mm or less, and from the perspective of handling, 0.1 mm or more is preferred.

<Electronic Components>
The electronic component mounting board of the present invention has electronic components mounted on a substrate. Here, the term "electronic component" refers to any element mounted on a substrate with electrical connections and functioning based on the input or output of electrical signals, or both. Specific examples include, but are not limited to, semiconductor chips and interposers. The electronic component mounting board of the present invention may have multiple electronic components mounted on the substrate.

One suitable electronic component is an optical element. Optical elements include LEDs, photoresistors, phototransistors, photodiodes, micromirrors, solar cells, etc., but μLEDs with sides of 100 μm or less are particularly preferred because they can achieve particularly high reliability when using the structure of the present invention.

The ratio of the area occupied by the electrodes of an electronic component to the total area of the surface of the electronic component bearing the electrodes (hereinafter sometimes referred to as the "electrode area ratio") is preferably 0.3 to 0.9. Increasing the bonding area between the electrodes and the conductive composite material prevents delamination at the interface between the electrodes and the conductive composite material due to thermal shock, so a large electrode area is preferred; specifically, the electrode area ratio of an electronic component is preferably 0.3 or greater. The electrode area ratio of an electronic component is more preferably 0.5 or greater. On the other hand, setting the electrode area ratio of an electronic component to 0.9 or less makes it easier to prevent short circuits between electrodes. The electrode area ratio of an electronic component is more preferably 0.8 or less. The area of the surface of an electronic component bearing the electrodes and the area of the electrodes can be measured by separating the electronic component from the substrate by peeling or polishing, and then observing the electronic component using an optical microscope or a scanning electron microscope (SEM), respectively.

<Conductive composite material>
The electronic component mounting board of the present invention has a conductive composite material containing a resin and a conductive material between an electrode of the board and an electrode of the electronic component.

<Resin>
The resin may be one whose main component is an acrylic copolymer, an epoxy resin, a silicone resin, a polyimide resin, a phenolic resin, or the like, and preferably contains an acrylic copolymer and an epoxy resin having a carboxyl group.

<Conductive materials>
The conductive material has the function of electrically connecting electrodes in contact with the conductive composite material. The conductive material may be a material that uses conductive particles (hereinafter referred to as conductive particles) and that achieves electrical connection by dispersing the conductive particles in a resin and bringing multiple conductive particles into contact with each other. Alternatively, the conductive particles may be sintered to achieve electrical connection.

Conductive particles include, for example, particles of silver, gold, copper, platinum, lead, tin, nickel, aluminum, tungsten, molybdenum, chromium, titanium, indium, magnesium, zinc, iron, and alloys of these. Two or more of these may be contained. Of these, from the viewpoint of conductivity, particles of a metal selected from silver, gold, and copper are preferred, and from the viewpoint of cost and stability, silver particles are more preferred. Conductive particles may also be those coated with a resin, inorganic oxide, or the like. Metal particles are preferred because conductive particles in which the surface of resin particles or inorganic oxide particles is coated with a metal will experience elastic repulsion due to the resin particles during mounting.

The average particle diameter of the conductive particles is preferably 0.01 to 1.0 μm. By having an average particle diameter of 0.01 μm or more, interactions between particles can be appropriately suppressed, improving the dispersibility of the conductive particles in the resin. The average particle diameter of the conductive particles is more preferably 0.1 μm or more. On the other hand, by having an average particle diameter of 1.0 μm or less, the surface smoothness, pattern accuracy, and dimensional accuracy of the resulting conductive pattern can be improved.

The thickness of the conductive composite material is preferably 2.0 μm or more to obtain sufficient die shear strength, and is preferably 6.0 μm or less to reduce the height of the electronic component mounting board.

It is important that the electronic component mounting board of the present invention satisfies the relationship 3.0 < _TE / RM < 20.0, where _TE is the thickness (μm) of the conductive composite material and _RM is the average diameter ( _μm ) of the conductive material. If _TE / _RM is 3.0 or less, the electrical connection path formed by the conductive material is less likely to branch within the conductive composite material, reducing the number of connection points with the electrodes and making the board more susceptible to disconnection due to thermal shock. _TE / _RM is more preferably 5.0 or more. On the other hand, if _TE / _RM is 20.0 or more, the diameter of the conductive material becomes too small and therefore more susceptible to disconnection due to thermal shock. _TE / _RM is more preferably 15.0 or less. _TE and _RM can be measured by observing a cross section perpendicular to the board at a portion of the electronic component mounting board where the conductive composite material is located between an electrode of the board and an electrode of the electronic component. R _M is calculated by the following formulas 1 and 2, which represent the average value weighted by the area and deviation of the cross-sectional diameters of 50 randomly selected conductive materials. Here, the cross-sectional diameter is the distance between the two most distant points on the outline of the cross section of the conductive material, R _n represents the nth measured cross-sectional diameter, and Σ means the sum of σ _V ×R _n ² or σ _V ×R _n , where n corresponds to 1 to 50. R _AVE means the arithmetic mean of R _n , where n corresponds to 1 to 50.
R _M =Σ(σ _V ×R _n ² )/Σ(σ _V ×R _n ) (Formula 1)
σ _V =10 ^{−|RAVE−Rn|} (Formula 2).

<Insulating resin>
The electronic component mounting board of the present invention has an insulating resin in the portion between the electronic component and the board that does not have the conductive composite material.

The insulating resin can be a resin commonly used as an underfill material. The insulating resin can be supplied before mounting electronic components by laminating a sheet of the insulating resin onto the substrate, or it can be filled in liquid form after mounting electronic components to allow for remounting in the event of a defect in the electronic components.

The insulating resin can be composed of, for example, acrylic polymer, epoxy resin, and curing accelerator.

Acrylic polymers with an average molecular weight of 3000 or more are preferably used.

Epoxy resins include bisphenol A, cresol novolac, phenol novolac, bisphenol A novolac, dicyclopentadiene, and naphthalene types. Curing accelerators include imidazoles, dicyandiamide derivatives, quaternary ammonium salts, triphenylphosphine, and tetraphenylphosphonium tetraphenylborate.

The insulating resin may also contain inorganic particles. Examples of inorganic particles include silicates such as mica and glass; oxides such as titanium oxide, alumina, and silica; carbonates such as calcium carbonate and magnesium carbonate; hydroxides such as aluminum hydroxide, magnesium hydroxide, and calcium hydroxide; sulfates or sulfites such as barium sulfate, calcium sulfate, and calcium sulfite; borates such as zinc borate, barium metaborate, aluminum borate, calcium borate, and sodium borate; and nitrides such as aluminum nitride, boron nitride, and silicon nitride. Among these, silica is preferred from the standpoints of cost and dispersibility.

In the electronic component mounting substrate of the present invention, it is important that the content of inorganic particles contained in the insulating resin be 40 parts by weight or less, based on 100 parts by weight of the entire insulating resin. If the inorganic particle content is greater than 40 parts by weight, increased stress occurs within the insulating resin when displacement occurs due to thermal shock, resulting in insufficient resistance to thermal shock. A content of inorganic particles of 30 parts by weight or less is more preferable. On the other hand, while a lower content of inorganic particles improves thermal shock resistance, a content of 10 parts by weight or more is preferable from the perspective of improving heat resistance. The content of inorganic particles can be calculated by mechanically peeling the electronic components from the electronic component mounting substrate and measuring the ash content of the insulating resin remaining on the substrate using a thermogravimetric analyzer. Here, heat resistance can be evaluated by measuring the initial current value of the obtained electronic component mounting substrate, heating it at 230°C for 1 hour, and then measuring the current value again to determine the ratio to the initial current value.

The insulating resin fills the space below the electronic components excluding the conductive composite material, and the area of the insulating resin is preferably 0.5 or less, more preferably 0.4 or less, relative to the area of the substrate. By making the area of the insulating resin 0.5 or less relative to the area of the substrate, warping due to a mismatch in the linear expansion coefficients of the substrate and the insulating resin when heat is generated during circuit operation is reduced, resulting in higher thermal shock resistance. Here, the "area of insulating resin" refers to the total area of all insulating resin on the substrate, and it may be connected to the insulating resin filled below other electronic components as shown in Figure 1, or it may be divided into pieces of any size.

The electronic component mounting substrate of the present invention can be used for any purpose, but it can be particularly well suited for use in displays that require high reliability for a large number of elements and large areas.

<Method of manufacturing an electronic component mounting substrate>
The method for manufacturing an electronic component mounting substrate of the present invention will be exemplified below, but the present invention is not limited to the examples described below.

The conductive composite material that constitutes the electronic component mounting substrate of the present invention can be formed, for example, by applying a paste made by kneading raw materials onto the substrate, but there is no particular limitation to this.

The paste can be produced by mixing conductive particles into an organic material that is an appropriate mixture of thermosetting resin, curing agent, curing catalyst, photopolymerization initiator, compound with unsaturated double bonds, solvent, and additives.

The conductive particle content in the paste is preferably 30 to 90% by weight. If the conductive particle content is 30% by weight or more, the probability of contact between conductive particles during heat sintering increases, improving conductivity. A conductive particle content of 50% by weight or more is more preferable. On the other hand, if the conductive particle content is 90% by weight or less, the light transmittance of the coating film during the exposure process improves, improving fine processability.

The paste is preferably photosensitive, as this improves positional and dimensional accuracy when it is molded into protruding electrodes suitable for flip-chip mounting. Examples of photosensitive components include photopolymerization initiators, compounds with unsaturated double bonds, and carboxyl group-containing resins with photopolymerizable groups.

Examples of photopolymerization initiators include benzophenone derivatives, acetophenone derivatives, thioxanthone derivatives, benzil derivatives, benzoin derivatives, oxime compounds, α-hydroxyketone compounds, α-aminoalkylphenone compounds, phosphine oxide compounds, anthrone compounds, and anthraquinone compounds.

"Compounds having an unsaturated double bond" refers to monomers and oligomers having an unsaturated double bond. Examples of compounds having an unsaturated double bond include bifunctional monomers such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, glycerin dimethacrylate, tripropylene glycol diacrylate, ethoxylated (4) bisphenol A diacrylate, ethoxylated (10) bisphenol A diacrylate, and acrylic acid adduct of ethylene glycol diglycidyl ether; trifunctional monomers such as pentaerythritol triacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxy triacrylate, and glycerin propoxy triacrylate; and tetrafunctional monomers such as dipentaerythritol hexaacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxy tetraacrylate, and ditrimethylolpropane tetraacrylate. Two or more of these may be contained.

Examples of carboxyl group-containing resins with photopolymerizable groups include carboxyl group-containing acrylic copolymers, carboxylic acid-modified epoxy resins, carboxylic acid-modified phenolic resins, polyamic acids, and carboxylic acid-modified siloxane polymers. Two or more of these may be used.

The paste is preferably thermosetting, since it can be mounted in a softened state by thermocompression bonding and then cured to achieve high reliability. The thermosetting component is preferably an epoxy resin, which enhances the adhesive strength between the conductive composite material and the electrodes to be connected, and preferably contains either a curing agent or a curing catalyst, or both. The adhesive strength between an electronic component and a conductive composite material can be evaluated, for example, by die shear strength. Here, "die shear strength" is an index representing the bonding strength when a horizontal force (shear force) is applied to an adhesive member adhered to a member to be joined. Die shear strength can be measured using a general die shear strength measuring device. Examples of equipment for mixing the paste include dispersers and kneaders such as a three-roller mill, ball mill, and planetary ball mill.

One method for manufacturing an electronic component mounting substrate of the present invention includes the steps of forming a dry film of the paste on a substrate, exposing and developing the dry film to form a conductive composite material on the electrodes of the substrate, forming an insulating resin on at least the electrodes, and heat-pressing an electronic component having an electrode onto the conductive composite material.

In the process of forming a dried film of the paste on a substrate, examples of application methods include spin coating using a spinner, spray coating, roll coating, screen printing, and application using a blade coater, die coater, calendar coater, meniscus coater, or bar coater.

The thickness of the dried paste film is preferably 1 to 5 μm. A dry film thickness of 1 μm or more can suppress variations in the resistance value of the conductive composite material and improve the bonding strength between the substrate and electronic components. On the other hand, a dry film thickness of 5 μm or less allows light to more easily penetrate deep into the dried film during exposure, widening the development margin and suppressing short circuits caused by the spreading of the conductive composite material during mounting. A dry film thickness of 2 to 5 μm is more preferable. The thickness of the dried paste film can be measured using a stylus-type step profiler such as the "Surfcom (registered trademark)" 1400 (manufactured by Tokyo Seimitsu Co., Ltd.). More specifically, the film thickness at three random positions is measured using a stylus-type step profiler (measurement length: 1 mm, scanning speed: 0.3 mm/sec), and the average value is used as the film thickness.

Drying methods include, for example, heat drying using an oven, hot plate, infrared rays, etc., and vacuum drying. The drying temperature is preferably 50 to 180°C, and the drying time is preferably 1 minute to several hours.

The dried film is then exposed and developed to form a conductive composite material on the electrode on the substrate.

Exposure methods include vacuum suction exposure, proxy exposure, projection exposure, and direct writing exposure, using light sources that emit i-lines (wavelength 365 nm), h-lines (wavelength 405 nm), or g-lines (wavelength 436 nm), such as high-pressure mercury lamps, ultra-high-pressure mercury lamps, and LEDs.

Developing methods include, for example, spraying a developer onto the surface of the dried film of exposed photosensitive conductive paste while the substrate bearing the dried film is left stationary or rotated, immersing a substrate bearing the dried film of exposed photosensitive conductive paste in a developer, or applying ultrasound to a substrate bearing the dried film of exposed photosensitive conductive paste while immersing it in a developer.

An alkaline aqueous solution is preferred as the developer, and after development, a rinse treatment with a rinse solution may be performed. Examples of rinse solutions include water, or aqueous solutions of water to which alcohols such as ethanol or isopropyl alcohol or esters such as ethyl lactate or propylene glycol monomethyl ether acetate have been added.

Next, the insulating resin molded into a sheet is laminated onto the substrate. One method for molding the insulating resin is to apply a paint made by dissolving the raw material in an organic solvent onto a release film and then dry it. A diaphragm laminator, roll laminator, etc. can be used to laminate the insulating resin.

After this, electronic components with electrodes are thermocompression bonded onto the conductive composite material.

In the process of thermocompression bonding electronic components having electrodes onto a conductive composite material, the heating temperature is preferably 60°C or higher and 250°C or lower. A heating temperature of 60°C or higher reduces the storage modulus of the conductive bumps, improving adhesion to the electrodes of the electronic components. Furthermore, a heating temperature of 250°C or lower reduces thermal expansion and contraction of the substrate and electronic components, thereby further improving the positional accuracy of mounting.

For heat and pressure bonding, a heat and pressure bonding tool for a flip chip bonder or a vacuum diaphragm laminator can be used.

The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

The materials used in the examples and comparative examples are as follows:

[Photosensitive component]
(Synthesis Example) Carboxyl-containing acrylic copolymer (A) having unsaturated double bonds
A reaction vessel under a nitrogen atmosphere was charged with 150 g of diethylene glycol monobutyl ether (hereinafter, "DGME") and heated to 80°C using an oil bath. A mixture consisting of 20 g of ethyl acrylate (hereinafter, "EA"), 40 g of 2-ethylhexyl methacrylate (hereinafter, "2-EHMA"), 20 g of n-butyl acrylate (hereinafter, "BA"), 15 g of N-methylolacrylamide (hereinafter, "MAA"), 0.8 g of 2,2'-azobisisobutyronitrile, and 10 g of DGME was added dropwise over 1 hour. After completion of the dropwise addition, the mixture was heated at 80°C for an additional 6 hours to carry out the polymerization reaction. Subsequently, 1 g of hydroquinone monomethyl ether was added to terminate the polymerization reaction. Subsequently, a mixture consisting of 5 g of glycidyl methacrylate (hereinafter, "GMA"), 1 g of triethylbenzylammonium chloride, and 10 g of DGME was added dropwise over 0.5 hours. After the dropwise addition was completed, the mixture was heated for an additional 2 hours to carry out the addition reaction. The resulting reaction solution was purified with methanol to remove unreacted impurities, and then vacuum dried for 24 hours to obtain a carboxyl group-containing acrylic copolymer (A) having an unsaturated double bond with a copolymerization ratio (by mass): EA/2-EHMA/BA/GMA/AA=20/40/20/5/15.

[Photopolymerization initiator]
"IRGACURE" OXE04 (manufactured by BASF Japan Ltd.) (hereinafter referred to as OXE04).

[Compounds having unsaturated double bonds]
"Light Acrylate" BP-4EA (manufactured by Kyoeisha Chemical Co., Ltd.) (hereinafter referred to as BP-4EA).

[Conductive materials]
- Silver particles with a particle diameter (D50) of 0.3 μm - Silver particles with a particle diameter (D50) of 0.5 μm - Silver particles with a particle diameter (D50) of 1.0 μm - Silver particles with a particle diameter (D50) of 2.0 μm.

[Epoxy resin]
"EPICLON" HP-7200L (manufactured by DIC Corporation) (hereinafter referred to as HP-7200L)
"EPICLON" N-865 (manufactured by DIC Corporation) (hereinafter referred to as N-865)
"jER" YL-980 (manufactured by Mitsubishi Chemical Corporation) (hereinafter referred to as YL-980).

[Novolac-type phenolic resin]
MEH-7600-4H (manufactured by Meiwa Kasei Co., Ltd.) (hereinafter referred to as MEH-7600).

[Curing accelerator]
"Curezol" C11Z-A (manufactured by Shikoku Kasei Co., Ltd.) (hereinafter referred to as C11Z-A)
"Curezol" C11Z-CN (manufactured by Shikoku Kasei Co., Ltd.) (hereinafter referred to as C11Z-CN).

[Insulating resin]
・XER-32C (manufactured by JSR Corporation).

[Inorganic particles]
"Admanano" Y50-SP-AL1 (manufactured by Admatechs Co., Ltd.) (hereinafter referred to as Y50-SP-AL1).

<Preparation of insulating resin sheet>
An insulating resin solution was obtained by dissolving 5 parts by weight of XER-32C, 15 parts by weight of N-865, 20 parts by weight of YL-980, and 2 parts by weight of C11Z-CN in PGMEA and mixing them with Y50SP-AL1 so that the content of inorganic particles in the insulating resin was the value listed for each Example and Comparative Example in Table 1. Here, the "content of inorganic particles in the insulating resin" refers to the weight ratio of inorganic particles in the insulating resin of the electronic component mounting board obtained in each Example and Comparative Example when the weight of the insulating resin is 100 parts by weight. The insulating resin solution was applied to a release film PET25AL-5 (trade name, PET film, thickness 25 μm, manufactured by Lintec Corporation) using a comma coater so that the film thickness after drying was 5 μm, and then dried at 100°C for 5 minutes to obtain an insulating resin sheet corresponding to each Example and Comparative Example in Table 1.

<Preparation of conductive composite material paste>
A conductive composite material paste was obtained by mixing 30 parts by weight of the acrylic copolymer (A), 20 parts by weight of BP-4EA, 3 parts by weight of OXE04, 15 parts by weight of HP-7200L, 5 parts by weight of MEH-7600, and 0.2 parts by weight of C11Z-A into a resin paste so that the content of the conductive material in the conductive composite material would be the value shown in each Example and Comparative Example in Table 1. Here, the "content of the conductive material in the conductive composite material" refers to the ratio by weight of the conductive material when the weight of the conductive composite material obtained by drying the conductive composite material paste is taken as 100 parts by weight.

The evaluation methods used in each example are as follows:

<Die shear strength>
The conductive composite material paste was applied to a glass substrate by screen printing, and the applied film was dried for 10 minutes in a drying oven at 100°C to form a dry film on the glass substrate. Then, using an exposure device (PEM-6M; manufactured by Union Optical Co., Ltd.) equipped with an ultra-high pressure mercury lamp, the entire surface of the dried film on the MAM substrate was exposed to i-line light (wavelength 365 nm) at an exposure dose of 2000 mJ/ ^cm2 .

Next, a 0.525 mm thick silicon wafer cut into 2 mm squares was placed on the dried film and thermocompressed using a vacuum diaphragm laminator (MVLP500/600; manufactured by Meiki Shiseisho Co., Ltd.). The resulting chip was then heated in a drying oven at 140°C for 60 minutes to obtain a sample for die shear strength measurement. The mounting conditions were a temperature of 100°C, a pressure of 0.5 MPa, and a compression time of 30 seconds. The die shear strength was then measured using a die shear strength measuring device (Dage Series 4000; manufactured by Dage Corporation). Measurements were performed at 25°C and a shear rate of 200 μm/s. A die shear strength of 20 MPa or greater was rated A, and a die shear strength of less than 20 MPa was rated B. The die shear strength obtained here is considered to be equivalent to that of the electronic component mounting substrates produced in the examples and comparative examples.

<Thermal shock resistance>
The current value when 3.0 V was applied to an electronic component mounting board prepared by the method described in the following Examples and Comparative Examples was defined as the initial current value. After measuring the initial current value, 300 cycles were performed using a thermal shock tester, with the tester moving between chambers at -40°C and 85°C every 30 minutes, and the current value measured in the same manner was defined as the post-thermal cycle current value. At this time, a ratio of the post-thermal cycle current value to the initial current value was rated as A when it was 0.95 or more, B when it was less than 0.95 and 0.90 or more, C when it was less than 0.90 and 0.85 or more, and D when it was less than 0.85.

<Film thickness of conductive composite material>
The electronic component mounting substrates obtained in the examples and comparative examples were cleaved along a plane passing through the center of the μLED chip, and the cross section was observed using an SEM to measure the thickness T _E of the conductive composite material between the electrode on the μLED chip and the electrode on the wiring substrate.

<Area ratio of insulating resin>
The ratio of the area of the insulating resin to the area of the substrate was calculated. In Examples 10 and 11, the area of the insulating resin was determined by dividing the total area of the conductive composite material by the area where the insulating resin sheet was laminated. The total area of the conductive composite material was determined by multiplying the average area of 30 randomly selected conductive composite materials by the total number of conductive composite materials. In Examples and Comparative Examples other than those described above, the area of the insulating resin was determined by multiplying the average area of the insulating resin below 30 randomly selected μLED chips by the total number of μLED chips.

<Electrode area ratio of electronic components>
The ratio of the total area of the electrodes formed on the μLED chip to the total area of the electrode-bearing surface of the μLED chip was calculated by SEM measurement. The area of the μLED chip and its electrodes was calculated using the average value measured using 30 randomly selected μLED chips.

<Heat resistance>
The current value when 3.0 V was applied to an electronic component mounting substrate produced by the method described in the following Examples and Comparative Examples was defined as the initial current value. The sample was heated at 230°C for 1 hour and then the current value was measured in the same manner as above. A ratio of the current value after heating to the initial current value of 0.9 or more was rated as A, and a ratio of less than 0.90 was rated as B.

Example 1
An insulating resin sheet was prepared by the method shown in <Preparation of insulating resin sheet>, and a conductive composite material paste was prepared by the method shown in Method for preparing conductive composite material paste. Using a 0.73 mm thick wiring board having wiring in which 0.05 μm of chromium and 0.2 μm of gold were laminated in this order on a glass substrate by sputtering, the conductive composite material paste was dried to form a dry film on the surface of the wiring board in the same manner as described in Method for measuring die shear strength.

The entire surface of the dried film on the wiring substrate was then exposed to i-line light (wavelength 365 nm) at a dose of 2000 mJ/ ^cm² using an exposure device (PEM-6M; manufactured by Union Optical Co., Ltd.) equipped with an ultra-high pressure _mercury lamp. After exposure, the film was shower-developed for 50 seconds using a 0.1 wt% _Na2CO3 aqueous solution and rinsed with ultrapure water to form a 20 µm square conductive bump array made of the conductive composite material in positions corresponding to the electrodes of the μLEDs that would be mounted on the wiring substrate later. The conductive bump array consisted of pairs of bumps corresponding to the anode/cathode electrodes of the μLEDs, forming a 125 row x 60 column pattern with a 120 µm pitch.

Next, the insulating resin sheet was laminated at 80°C and 0.6 MPa on the surface of the wiring board bearing the conductive bump array using a vacuum diaphragm laminator (MVLP500/600; manufactured by Meiki Shiseisho Co., Ltd.) to form an insulating resin. A μLED chip (short side 30 μm, long side 60 μm, electrode spacing 18 μm) was then mounted on the conductive bumps laminated with the insulating resin using a flip-chip bonder (manufactured by Toray Engineering Co., Ltd., FC-3000WS) under the following conditions: stage temperature 40°C, head temperature 150°C, load 24 N, pressure applied for 10 seconds, cooling for 20 seconds until the head temperature reached 40°C, and then the load was released. The insulating resin outside the μLED chip was then removed using plasma treatment.

Then, the substrate was cured for 60 minutes in a drying oven at 140°C to obtain an electronic component mounting substrate. The obtained electronic component mounting substrate was evaluated as described above. The results are shown in Tables 1 and 2.

(Examples 2 to 9 and Comparative Examples 1 to 6)
Electronic component mounting substrates were produced in the same manner as in Example 1, except that the conductive composite material and insulating resin were changed as shown in Tables 1 and 2.

Example 10
An electronic component mounting substrate was produced in the same manner as in Example 1, except that the area ratio of the insulating resin was set to 0.67 by not performing plasma treatment after mounting the μLED chip.

Example 11
An electronic component mounting substrate was produced in the same manner as in Example 1, except that the electrode area ratio of the electronic component was set to 0.25 by setting the inter-electrode distance of the μLED chip to 45 μm.

All of Examples 1 to 11 satisfied the condition 3.0<T _E /R _M <20.0, and the content of inorganic particles contained in the insulating resin was 40 parts by weight or less per 100 parts by weight of the insulating resin, and therefore exhibited high thermal shock resistance. On the other hand, Comparative Examples 1 and 2 had a content of inorganic particles in the insulating resin of 50 parts by weight, and therefore exhibited low thermal shock resistance. All of Comparative Examples 3 to 5 had a T _E /R _M of 3.0 or less, and Comparative Example 6 had a T _E /R _M exceeding 20.0, and therefore exhibited low thermal shock resistance.

1: Substrate 2: Electronic component 3: Conductive composite material 4: Insulating resin 5b: Electrode on electronic component 5a: Electrode on substrate 6: Conductive particles in ACF 7: Short circuit defect between adjacent electrodes 8: Electronic component mounting substrate

Claims (6)

The substrate has electronic components thereon,
a conductive composite material containing a resin and a conductive material is disposed between the electrode of the substrate and the electrode of the electronic component;
an electronic component mounting substrate having an insulating resin in a portion between the electronic component and the substrate that does not have the conductive composite material,
When the thickness (μm) of the conductive composite material is T _E and the average diameter (μm) of the conductive material is R _M , the relationship 3.0<T _E /R _M <20.0 is satisfied;
The electronic component mounting substrate has an insulating resin containing inorganic particles in an amount of 40 parts by weight or less, based on 100 parts by weight of the insulating resin. The electronic component mounting board according to claim 1, wherein the ratio of the area occupied by the electrodes of the electronic component to the total area of the surface having the electrodes of the electronic component is 0.3 to 0.9. An electronic component mounting board according to claim 1 or 2, wherein the area of the insulating resin is 0.5 or less relative to the area of the board. The electronic component mounting board according to any one of claims 1 to 3, wherein the electronic component is an optical element. The electronic component mounting board according to claim 4, wherein the optical element is a μLED. A display having an electronic component mounting substrate according to any one of claims 1 to 5.