JP7537573B2 - Electronic component mounting substrate and electronic device using same - Google Patents

Description

The present invention relates to an electronic component mounting substrate having a protective layer. It also relates to an electronic device equipped with the electronic component mounting substrate.

Smartphones, wearable devices, and other terminal electronic devices are used in a wide variety of environments, so they require high reliability to prevent malfunctions even under harsh conditions. These electronic devices are equipped with electronic components such as semiconductor elements. Electronic components such as semiconductor elements are usually formed on a substrate and are used in electronic devices in a state where they are pre-encapsulated with epoxy resin or the like to prevent physical damage from the outside and deterioration due to heat, light, and humidity.

JP 2003-145687 A

Patent Document 1 discloses a moisture-proof sheet for electronic components for preventing deterioration of electronic components due to humidity. The sheet has a problem that the resin components of electronic components and substrates deteriorate and the sheet peels off in severe environmental tests such as pressure cooker tests (hereinafter, sometimes abbreviated as "PCT"). (Hereinafter, adhesion after PCT may be referred to as "PCT adhesion".) In addition, there is a problem that warping occurs as the substrate deteriorates (hereinafter, the resistance of the substrate to warping may be referred to as "substrate protection".).
Furthermore, there was a demand for optimal surface properties for fixing and peeling the electronic components with dicing tape during the subsequent dicing and mounting processes. (Hereinafter, the suitability for peeling after fixing with dicing tape may be referred to as "process workability.")

The present invention was made in consideration of the above problems, and aims to provide a highly reliable electronic component mounting substrate that has excellent PCT adhesion, substrate protection, and process operability, and an electronic device using the same.

After extensive research, the inventors discovered that the problems of the present invention could be solved in the following manner, and thus completed the present invention.

The present invention relates to
A substrate;
An electronic component mounted on at least one surface of the substrate;
a protective layer covering at least a portion of the substrate and the electronic component;
Equipped with
the protective layer contains a binder resin and a flaky metal filler,
The electronic part mounting substrate has a contact angle of 90 to 130° with water on the surface of the protective layer after a pressure cooker test at 135° C., 85% RH, 0.23 MPa for 96 hours.

The protective layer preferably has a Martens hardness of 50 to 250 N/mm ² .

The glass transition temperature of the protective layer is preferably 20 to 100°C.

The protective layer preferably has a developed interface area ratio (Sdr) of 1.0% to 4.0% and a maximum valley depth (Sv) of 1.5 μm to 4.5 μm, as determined in accordance with ISO 25178-2:2012.

The protective layer further comprises:
It is preferred that the filler metal is dendritic or acicular.

The present invention also relates to an electronic device equipped with the electronic component mounting board.

The present invention, configured as described above, has the excellent effect of providing an electronic component mounting substrate with excellent long-term reliability and an electronic device using the same, with little deterioration of the substrate or electronic components even after PCT.

FIG. 1 is a schematic perspective view showing an example of an electronic component mounting board. FIG. 2 is a cross-sectional view taken along line II-II of FIG. FIG. 11 is a schematic cross-sectional view showing another example of an electronic component mounting board. FIG. 2 is a schematic cross-sectional view showing an example of a laminate. Schematic cross-sectional views showing an example of a manufacturing process for an electronic component mounting board. Schematic cross-sectional views showing an example of a manufacturing process for an electronic component mounting board. Schematic cross-sectional views showing an example of a manufacturing process for an electronic component mounting board. Schematic cross-sectional view showing a test substrate used in the examples.

An example of an embodiment to which the present invention is applied is described below. The numerical values specified in this specification are values determined by the methods disclosed in the embodiments or examples. Furthermore, the sheet in this specification includes not only sheets as defined in JIS, but also films. In order to clarify the explanation, the following description and drawings have been appropriately simplified. Unless otherwise noted, the various components described in this specification may be used independently, either alone or in combination of two or more types.

<Electronic component mounting board>
FIG. 1 is a schematic perspective view showing an example of an electronic component mounting board according to the present invention, and FIG.
The electronic component mounting board 51 includes a substrate 20, an electronic component 30, a protective layer 1, and the like.

<Substrate>
The substrate 20 can be selected arbitrarily as long as it can mount the electronic component 30 and can withstand the thermocompression bonding process described later. For example, a work board on which a conductive pattern made of copper foil or the like is formed on or inside, a mounting module board, a printed wiring board, or a build-up board formed by a build-up method or the like can be mentioned. A film or sheet-like flexible substrate may also be used. The conductive pattern is, for example, an electrode/wiring pattern (not shown) for electrically connecting with the electronic component 30, and a ground pattern 22 for electrically connecting with the protective layer 1. An electrode/wiring pattern, a via (not shown), and the like can be arbitrarily provided inside the substrate. The substrate 20 may be not only a rigid substrate but also a flexible substrate.

<Electronic Components>
In the example of Fig. 1, the electronic components 30 are arranged in a 5 x 4 array on the substrate 20. A protective layer 1 is provided to cover the exposed surfaces of the substrate 20 and the electronic components 30. That is, the protective layer 1 is coated so as to conform to the unevenness formed by the electronic components 30. The protective layer 1 protects the electronic components 30 or the substrate 20 from high temperature and high humidity environments and physical shocks. In addition, when the protective layer 1 is conductive, it can block unnecessary radiation generated from signal wiring and the like built into the electronic components 30 or the substrate 20, and can prevent malfunctions due to external magnetic fields and radio waves.

The number, arrangement, shape and type of electronic components 30 are arbitrary. Instead of arranging the electronic components 30 in an array, the electronic components 30 may be arranged in any position. When the electronic component mounting substrate 51 is singulated into unit modules, as shown in FIG. 2, a half dicing groove 25 may be provided in the substrate 20 so as to partition the unit modules from the upper surface of the substrate in the thickness direction of the substrate. The electronic component mounting substrate in the present invention includes both the substrate before singulation into unit modules and the substrate after singulation into unit modules. That is, in addition to the electronic component mounting substrate 51 on which a plurality of unit modules (electronic components 30) are mounted as shown in FIG. 1 and FIG. 2, the electronic component mounting substrate 52 after singulation into unit modules as shown in FIG. 3 is also included. In the present invention, the substrate may be singulated to include only one unit module as shown in FIG. 3, or may be singulated to include two or more unit modules (not shown). Of course, the electronic component mounting substrate also includes an electronic component mounting substrate in which one electronic component 30 is mounted on the substrate 20 and covered with a protective layer 1 without undergoing a singulation process. That is, the electronic component mounting substrate according to the present invention includes a structure in which at least one electronic component is mounted on the substrate, and at least a portion of the step formed by mounting the electronic component is covered with a protective layer 1.

The electronic component 30 includes all components in which electronic elements such as semiconductor integrated circuits are integrally coated with an insulator such as epoxy resin. For example, a semiconductor chip 31 (see FIG. 3) on which an integrated circuit (not shown) is formed is molded with a sealing material (molding resin 32). The substrate 20 and the semiconductor chip 31 are electrically connected to wiring or electrodes 21 formed on the substrate 20 via their contact area, or via bonding wires 33, solder balls (not shown), etc. Examples of electronic components include semiconductor chips, inductors, thermistors, capacitors, resistors, etc.

The electronic component 30 and the substrate 20 can be widely applied to known embodiments. In the example of FIG. 3, the semiconductor chip 31 has solder balls 24 connected to the rear surface of the substrate 20 through inner vias 23. In addition, in the substrate 20, a ground pattern 22 for electrically connecting to the protective layer 1 may be formed if the protective layer 1 is conductive. In addition, one or more electronic elements can be mounted in the electronic component 30.

<Protective Layer>
The protective layer contains a binder resin and a flaky metal filler, and the contact angle of the protective layer surface with water after a pressure cooker test at 135°C, 85% RH, 0.23 MPa for 96 hours (hereinafter, sometimes abbreviated as "water contact angle after PCT") is 90 to 130°. The protective layer is formed from a protective sheet. The protective sheet can be formed by mixing and stirring a composition containing a flaky metal filler and a thermosetting resin (hereinafter, this composition is also referred to as a "composition for forming a protective sheet"), applying it onto a releasable substrate, and drying it as necessary if it contains a solvent or the like. It can also be formed by directly applying it to a releasable cushion member 3 described later, and drying it as necessary if it contains a solvent or the like.

<Binder resin>
The binder resin in the present invention is a cured thermosetting resin. The thermosetting resin has a reactive functional group. In addition to the above, a curing agent can be used in combination. A self-crosslinking resin or a plurality of resins that crosslink with each other may be used. In addition to these resins, a thermoplastic resin that does not have reactivity in the protective sheet forming composition may be used in combination.
Note that the protective sheet may be in a B-stage (semi-cured state) due to partial crosslinking. For example, the thermosetting resin and the curing agent may be in a semi-cured state due to partial reaction.

Suitable examples of thermosetting resins include polyurethane resins having reactive functional groups, polycarbonate resins, polystyrene resins, phenoxy resins, polyurethane urea resins, polyamide resins, polyimide resins, polycarbonate imide resins, polyamide imide resins, epoxy resins, epoxy ester resins, acrylic resins, polyester resins, polyester amide resins, and polyether ester resins.

Among these, when used under harsh conditions during reflow, the thermosetting resin preferably contains at least one of polyurethane resin, polyurethane urea resin, polycarbonate resin, polystyrene resin, phenoxy resin, polyamide resin, polyimide resin, epoxy resin, and epoxy ester resin. Furthermore, by using a resin having a polycarbonate skeleton, PCT adhesion resistance (adhesion between the protective layer and the substrate after a pressure cooker test) is improved.
The thermosetting resin may be used alone or in combination of two or more kinds at any ratio.

In addition to polycarbonate resin, examples of resins having a polycarbonate skeleton include polyurethane resins, polyamide resins, and polyimide resins having a polycarbonate skeleton. For example, polycarbonate-imide resins can improve heat resistance, insulating properties, and chemical resistance by having a polyimide skeleton. On the other hand, by having a polycarbonate skeleton, PCT adhesion and substrate protection can be effectively improved.

As the polyol component used in the polycarbonate urethane resin, diols such as 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,4-cyclohexanedimethanol, 1,9-nonanediol, or 2-methyl-1,8-octanediol are preferred. The above polyols may be used alone or in combination of two or more kinds.

The thermosetting resin may have multiple functional groups that can be used in a crosslinking reaction by heating. Examples of reactive functional groups include hydroxyl groups, phenolic hydroxyl groups, carboxyl groups, amino groups, epoxy groups, oxetanyl groups, oxazoline groups, oxazine groups, aziridine groups, thiol groups, isocyanate groups, blocked isocyanate groups, and silanol groups.

The curing agent has a functional group that can crosslink with the reactive functional group of the thermosetting resin. Crosslinking can further strengthen adhesion and improve PCT adhesion. The curing agent is preferably an epoxy compound, an acid anhydride group-containing compound, an isocyanate compound, a polycarbodiimide compound, an aziridine compound, a dicyandiamide compound, an imidazole compound, an amine compound such as an aromatic diamine compound, a phenolic compound such as a phenol novolac resin, an organometallic compound, or the like. The curing agent may be a resin. In this case, the thermosetting resin and the curing agent are distinguished by the one with a higher content being the thermosetting resin and the one with a lower content being the curing agent.

The epoxy compound is a compound having two or more epoxy groups in one molecule. The epoxy compound may be liquid or solid. As the epoxy compound, for example, glycidyl ether type epoxy compound, glycidyl amine type epoxy compound, glycidyl ester type epoxy compound, cyclic aliphatic (alicyclic) epoxy compound, etc. are preferable.

Examples of glycidyl ether type epoxy compounds include bisphenol A type epoxy compounds, bisphenol F type epoxy compounds, bisphenol S type epoxy compounds, bisphenol AD type epoxy compounds, cresol novolac type epoxy compounds, phenol novolac type epoxy compounds, α-naphthol novolac type epoxy compounds, bisphenol A type novolac type epoxy compounds, dicyclopentadiene type epoxy compounds, tetrabromobisphenol A type epoxy compounds, brominated phenol novolac type epoxy compounds, tris(glycidyloxyphenyl)methane, tetrakis(glycidyloxyphenyl)ethane, etc.

Examples of glycidylamine type epoxy compounds include tetraglycidyldiaminodiphenylmethane, triglycidyl paraaminophenol, triglycidyl meta-aminophenol, and tetraglycidyl meta-xylylenediamine.

Examples of glycidyl ester type epoxy compounds include diglycidyl phthalate, diglycidyl hexahydrophthalate, and diglycidyl tetrahydrophthalate.

Examples of cyclic aliphatic (alicyclic) epoxy compounds include epoxycyclohexylmethyl-epoxycyclohexanecarboxylate, bis(epoxycyclohexyl)adipate, etc. Liquid epoxy compounds can also be used.

Examples of imidazole compounds include imidazole compounds such as 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, 2,4-dimethylimidazole, and 2-phenylimidazole. Further examples include latent curing accelerators with improved storage stability, such as a type insoluble in a solvent by reacting an imidazole compound with an epoxy resin, or a type in which an imidazole compound is encapsulated in a microcapsule. Among these, latent curing accelerators are preferred from the viewpoint of initiating curing after the protective sheet is thermally melted.

The structure and molecular weight of the curing agent can be selected appropriately depending on the application. From the viewpoint of improving the flexibility of the protective sheet, it is preferable to use two or more types of curing agents with different molecular weights. By using two or more types of curing agents, a sufficient three-dimensional crosslinking structure is established within the protective layer, and PCT adhesion can be improved.

The hardener is preferably contained in an amount of 1 to 70 parts by mass, more preferably 3 to 65 parts by mass, and even more preferably 3 to 60 parts by mass, per 100 parts by mass of the thermosetting resin. When two or more types of hardeners are used in combination, the main hardener is preferably contained in an amount of 5 to 60 parts by mass, more preferably 10 to 60 parts by mass, and even more preferably 20 to 60 parts by mass, per 100 parts by mass of the thermosetting resin.

Suitable examples of thermoplastic resins that are not reactive in the protective sheet-forming composition include polyester, acrylic resin, polyether, urethane resin, polystyrene, polycarbonate, butadiene rubber, polyamide, esteramide resin, polyisoprene, and cellulose. Examples of tackifier resins include rosin resin, terpene resin, alicyclic petroleum resin, and aromatic petroleum resin. Conductive polymers can also be used. Examples of conductive polymers include polyethylenedioxythiophene, polyacetylene, polypyrrole, polythiophene, and polyaniline.

<<Flake-like metal filler>>
The flake-like metal filler is a flake-like metal powder, and in the present invention includes what are called plate-like, thin flake-like, and plate-like. There may be notches or the like around the filler.
The average particle diameter _D50 of the scaly metal filler is preferably 0.1 μm to 100 μm, more preferably 0.5 μm to 70 μm, and even more preferably 1.0 μm to 40 μm. The thickness of the scaly metal filler is preferably 0.05 μm to 3 μm, more preferably 0.07 μm to 1.5 μm, and even more preferably 0.1 μm to 1 μm. Here, the thickness of the scaly metal filler is measured using an image magnified about 1,000 to 50,000 times with an electron microscope, and the average value of the measurements is used.

Suitable types of metal for the flake metal filler include metal powders such as gold, silver, copper, and nickel, alloy powders such as solder, and core-shell type fillers such as silver-coated copper powder, gold-coated copper powder, silver-coated nickel powder, and gold-coated nickel powder. From the viewpoint of obtaining excellent conductive properties, flake metal fillers containing silver or copper are preferred. From the viewpoint of cost, silver-coated copper powder in which copper powder is coated with silver is particularly preferred.

The silver content in the silver-coated copper powder is preferably 3 to 20 mass%, more preferably 8 to 17 mass%, and even more preferably 10 to 15 mass%, based on 100 mass% of the total of silver and copper. In the case of a core-shell type filler, the coverage of the coating layer with respect to the core is preferably 60% or more on average, more preferably 70% or more, and even more preferably 80% or more. The core may be non-metallic, but from the viewpoint of electrical conductivity, a conductive material is preferred, and a metal is more preferred.

As the flake-like metal filler, an electromagnetic wave absorbing filler may be used. For example, iron alloys such as iron, Fe-Ni alloy, Fe-Co alloy, Fe-Cr alloy, Fe-Si alloy, Fe-Al alloy, Fe-Cr-Si alloy, Fe-Cr-Al alloy, and Fe-Si-Al alloy, and ferrite-based materials such as Mg-Zn ferrite, Mn-Zn ferrite, Mn-Mg ferrite, Cu-Zn ferrite, Mg-Mn-Sr ferrite, and Ni-Zn ferrite can be used.

The protective layer preferably further contains metal fillers of other shapes, such as dendritic (branch)-like fillers, needle-like fillers, botryoid fillers, fibrous fillers, spherical fillers, etc. More preferably, it contains needle-like fillers or dendritic fillers. By using both scale-like and dendritic metal fillers, the surface shape can be optimized and the process workability can be improved.
Here, the term "acicular" refers to a shape in which the major axis is three or more times the minor axis, and includes not only a so-called needle shape, but also a spindle shape, a cylindrical shape, and the like. The term "dendritic" refers to a shape in which a plurality of branches extend two-dimensionally or three-dimensionally from a rod-like main axis when observed under an electron microscope (500 to 20,000 times magnification). In the dendritic shape, the branches may be bent, or further branches may extend from each other.

These metal fillers may be used alone or in combination of two or more. Examples include a combination of a scaly metal filler and a spherical metal filler, a combination of a scaly metal filler and a dendritic metal filler, a combination of a scaly metal filler and a needle-shaped metal filler, and a combination of a scaly metal filler, a dendritic metal filler, and a needle-shaped metal filler. Nano-sized spherical metal fillers may also be used in combination with these.

The use of scaly metal fillers tends to increase the hardness of the protective layer surface, while spherical and dendritic fillers tend to decrease the Martens hardness. In addition, the Martens hardness tends to increase as the content of scaly metal fillers increases. Furthermore, the presence of scaly metal fillers in the protective layer improves the water repellency of the protective layer surface, improving the substrate protection.
Electromagnetic wave shielding properties can be imparted by including highly conductive flake metal fillers made of silver or copper, or electromagnetic wave absorbing fillers.

When highly conductive flake-like metal filler is contained, the resistance value of the protective layer is preferably 200 mΩ or less, more preferably 100 mΩ or less, and even more preferably 50 mΩ or less. By keeping the value within the above numerical range, excellent electromagnetic wave shielding properties can be achieved.

In addition, by using flake-like metal filler in combination with dendritic or needle-like metal filler, the number of contact points between the metal fillers can be increased, improving the electromagnetic wave shielding properties.

The content of the flake metal filler is preferably 40 to 85% by mass, and more preferably 50 to 80% by mass, of the solid content (100% by mass) of the protective layer.

The total amount of acicular metal fillers or dendritic metal fillers in the protective layer is preferably 0.5 to 50 mass% relative to 100 mass% of the total metal fillers in the protective layer. More preferably, it is 1 to 40 mass%, even more preferably 2 to 35 mass%, and particularly preferably 3 to 30 mass%. By containing 0.5 to 50% or less by mass, a protective sheet with superior film strength after PCT can be provided.

The average particle diameter _D50 of the acicular metal filler is preferably 2 to 100 μm, more preferably 2 to 80 μm, even more preferably 3 to 50 μm, and particularly preferably 5 to 20 μm. Similarly, the average particle diameter _D50 of the dendritic metal filler is preferably in the range of 2 to 100 μm, more preferably 2 to 80 μm, even more preferably 3 to 50 μm, and particularly preferably 5 to 20 μm.

The average particle diameter _D50 can be measured by a laser diffraction/scattering method. Specifically, for example, it is a value obtained by measuring each conductive filler with a laser diffraction/scattering method particle size distribution measuring device LS 13320 (manufactured by Beckman Coulter) using a Tornado dry powder sample module, and is the diameter of the particle size at which the integrated value of the filler is 50%. The refractive index is set to 1.6 for measurement.

The protective layer may further contain colorants, flame retardants, inorganic additives, lubricants, anti-blocking agents, etc.

Colorants include, for example, organic pigments, carbon black, ultramarine, red iron oxide, zinc oxide, titanium oxide, graphite, etc. From the viewpoint of quality stability, organic pigments are preferred. From the viewpoints of coloring power and dispersion stability, carbon black is particularly preferred.

Examples of flame retardants include halogen-containing flame retardants, phosphorus-containing flame retardants, nitrogen-containing flame retardants, inorganic flame retardants, etc.

Examples of inorganic additives include glass fiber, silica, talc, ceramics, etc.

Examples of lubricants include fatty acid esters, hydrocarbon resins, paraffin, higher fatty acids, fatty acid amides, fatty alcohols, metal soaps, and modified silicones.

Examples of the anti-blocking agent include calcium carbonate, silica, polymethylsilsesquioxane, and aluminum silicate.

The use of small additives with particle sizes of several tens to several hundreds of nanometers reinforces the binder resin, increasing the hardness after curing and providing a protective layer with better PCT adhesion.

<Water contact angle>
The protective layer in the present application has a water contact angle after PCT of 90 to 130°. The water contact angle after PCT is preferably 95 to 125°, and more preferably 100 to 120°. When the water contact angle is 90° or more, the water repellency of the protective layer is improved and the PCT adhesion is improved. When the water contact angle is 130° or less, the adhesion to the dicing tape is improved and the process workability is improved.

PCT is a resistance test under high pressure, high temperature, and high humidity, and by maintaining the contact angle of water on the protective layer surface after PCT at 90° or more, it is possible to prevent water from penetrating into the electronic components and boards inside the protective layer. As a result, it is believed that deterioration of these electronic components and boards is significantly suppressed.

To achieve a water contact angle of 90 to 130° after PCT, the balance between the hydrophobicity and hydrophilicity of the binder resin is adjusted. Also, the balance between the hydrophobicity and hydrophilicity of the surface of the scaly metal filler used is adjusted.

By incorporating highly water-resistant and heat-resistant thermosetting resins and curing agents into the protective sheet, and by adding hydrophobically treated metal fillers and colorants, the hydrolysis resistance and moisture absorption resistance of the protective layer after thermal curing are improved, and the water contact angle after PCT is less likely to decrease.

<Martens hardness>
The Martens hardness of the protective layer is preferably 50 to 250 N/ ^mm2 , more preferably 80 to 240 N/ ^mm2 , and even more preferably 105 to 230 N/ ^mm2 . If it is less than 50 N/ ^mm2 , the protective layer has poor scratch resistance and low adhesion. If it exceeds 250 N/ ^mm2 , cracks may occur due to impact after processing.

The Martens hardness is measured using a Fischerscope H100C hardness tester (manufactured by Fisher Instruments Co., Ltd.) The Martens hardness affects the scratch resistance and warpage of the electronic component mounting board after PCT.
The Martens hardness of the protective layer can be adjusted by the hardness of the binder component and the type and amount of metal filler added. The hardness of the binder component reflects the hardness of the cured product of the thermosetting resin that is its constituent material, so the desired Martens hardness can be easily obtained by selecting the type of resin. Furthermore, the higher the content of metal filler, the higher the Martens hardness, but this effect is particularly noticeable in scaly metal filler, and the effect of spherical metal filler and dendritic metal filler is inferior to that of scaly metal filler.

<Glass transition temperature>
The glass transition temperature of the protective layer is preferably 20°C to 100°C, more preferably 30°C to 80°C, and even more preferably 40°C to 60°C. By adjusting the glass transition temperature of the protective layer within the above range, both high adhesion and substrate protection can be achieved. When the glass transition temperature is 20°C or higher, the strength of the protective layer is ensured, and the hardness is maintained even after PCT. When the glass transition temperature is 100°C or lower, the protective layer has little thermal shrinkage, and peeling of the protective layer is suppressed.

<Developed interface area ratio (Sdr), maximum valley depth (Sv)>
The developed interface area ratio (Sdr) is a parameter that indicates how much the developed area (surface area) of a defined region has increased relative to the area of the defined region. Sdr has a value of 0 for a completely flat surface, i.e., a state in which there are no irregularities at all, and has a higher value as the surface becomes rougher.
The value of r can be adjusted by changing the particle size and content of the flaky metal filler.

The maximum valley depth (Sv) is the absolute value of the minimum height from the average surface of the surface, and is a parameter indicating the depth of the unevenness. Sv can be adjusted by changing the shape and average particle diameter _D50 of the metal filler and its blending amount, as well as the viscosity of the thermosetting resin when softened by heating. It is preferable to use a combination of a scale-like metal filler, a dendritic metal filler, and a needle-like metal filler as the metal filler.

The Sdr of the surface of the protective layer is preferably 1.0% to 4.0%, more preferably 1.5% to 3.5%, and even more preferably 2.0% to 3.0%. The maximum valley depth (Sv) is preferably 1.5 μm to 4.5 μm, more preferably 2.0 μm to 4.0 μm, and even more preferably 2.5 μm to 3.5 μm.

By setting Sdr and Sv within the above ranges, process operability is improved. In other words, by appropriately adjusting the depth and surface area of the unevenness of the protective layer, it is possible to provide appropriate adhesion to the dicing tape, and it will not peel off during pick-up or dicing processes, and the protective layer can be peeled off after the above processes without being damaged.

<Method of manufacturing electronic component mounting substrate>
An example of a method for manufacturing an electronic component mounting substrate will be described below with reference to the drawings. However, the method for manufacturing an electronic component mounting substrate of the present invention is not limited to the following manufacturing method.

The method for manufacturing the electronic component mounting substrate includes the steps of: [a] mounting electronic components 30 on substrate 20; [b] placing protective sheet 2 on substrate 20 on which electronic components 30 have been mounted; [c] bonding protective sheet 2 by thermocompression bonding so as to conform to the side of the step formed by mounting electronic components 30 and at least a part of the exposed surface of substrate 20; [d] peeling off releasable cushion member 3; and [e] singulating electronic component mounting substrate 51. Each step is described below.

[a] Mounting electronic components on a substrate:
First, the electronic components 30 are mounted on the substrate 20. For example, a semiconductor chip (not shown) is mounted on the substrate 20, and the substrate 20 on which the semiconductor chip is formed is molded with a sealing resin to obtain the electronic components 30, and the mold resin and the substrate 20 are half-cut by dicing or the like so as to reach the inside of the substrate 20 from above the electronic components 30. A method of arranging the electronic components 30 in an array on the substrate 20 that has been half-cut in advance may also be used. Through these steps, for example, the substrate 20 on which the electronic components 30 are mounted as shown in FIG. 5 is obtained. In the example of FIG. 5, the electronic components 30 refer to an integrated body formed by molding a semiconductor chip, and generally refer to electronic elements protected by an insulator. The half-cutting may be performed not only in a mode in which the semiconductor chip is molded to reach the inside of the substrate 20, but also in a mode in which the electronic components 30 are cut to the surface of the substrate 20. The entire substrate 20 may also be cut at this stage. In this case, it is preferable to place the substrate 20 on a base with an adhesive tape to prevent misalignment. The material of the mold resin used in molding is not particularly limited, but a thermosetting resin is usually used. The method of forming the mold resin is not particularly limited, and examples thereof include printing, lamination, transfer molding, compression, casting, etc. The molding method is optional, and the mounting method of the electronic component 30 can also be changed as desired.

[b] Step of placing a protective sheet on a substrate:
Next, a laminate 4 is prepared, which is melted by thermocompression to cover the substrate 20 on which the electronic components 30 are mounted (see FIG. 4). The laminate 4 is placed on the top surface of the electronic components 30 so that the protective sheet 2 of the laminate 4 faces the electronic components 30. Depending on the manufacturing equipment or the size of the substrate 20, a plurality of laminates 4 may be used for each region of the substrate 20. Also, a laminate 4 may be used for each electronic component 30. From the viewpoint of simplifying the manufacturing process, it is preferable to use one laminate 4 for all the electronic components 30 mounted on the substrate 20.

[c] Step of forming a protective layer:
Next, the laminate 4 is sandwiched between a pair of press substrates 40 and thermocompression bonded (see FIG. 6). The protective sheet 2 and the releasable cushion member 3 are melted by heat and stretched by pressing so as to follow the half-cut grooves provided in the manufactured substrate, and cover the electronic component 30 and the substrate 20. The protective sheet 2 is bonded to the electronic component 30 and the substrate 20, and is thermoset by thermocompression bonding to function as the protective layer 1. After thermocompression bonding, a separate heat treatment can be performed for the purpose of further promoting thermosetting, etc.

When the laminate 4 is hot-pressed, a heat-softening material, cushion paper, or the like may be used between the laminate 4 and the press substrate 40, if necessary.

The temperature and pressure of the thermocompression bonding process can be set independently and arbitrarily within a range that ensures the coverage of the protective sheet 2, depending on the heat resistance and durability of the electronic component 30, the manufacturing equipment, or needs. The pressure range is not limited, but is preferably about 0.1 to 15 MPa, and more preferably 0.5 to 10 MPa. Releasing the pressed substrate 40 gives a manufactured substrate as shown in FIG. 7. In this way, the top and side surfaces of the electronic component and the exposed surface of the substrate are covered with the protective layer 1.

The heating temperature in the thermocompression bonding process is preferably 60°C or higher, more preferably 80°C or higher, and even more preferably 100°C or higher. The upper limit depends on the heat resistance of the electronic component 30, but is preferably 220°C, more preferably 200°C, and even more preferably 180°C.

The thermocompression bonding time can be set depending on the heat resistance of the electronic component 30, the thermosetting resin used in the protective sheet 2, the production process, etc., but is preferably in the range of about 1 minute to 2 hours. The thermocompression bonding time is more preferably about 1 minute to 1 hour. This thermocompression bonding hardens the thermosetting resin to form the protective layer 1. However, the thermosetting resin may be partially hardened or substantially hardened before thermocompression bonding as long as it is capable of flowing.

The thickness of the protective sheet 2 is set to a thickness that allows it to cover the top and side surfaces of the electronic components 30 and the exposed surface of the substrate 20 to form the protective layer 1. This can vary depending on the fluidity of the thermosetting resin used and the distance and size between the electronic components 30, but is usually preferably about 10 to 200 μm, more preferably about 15 to 100 μm, and even more preferably about 20 to 70 μm. This improves coverage of the electronic components and substrate, and effectively exerts PCT adhesion.

The releasable cushion member 3 softens to promote the covering of the protective sheet 2, and has the function of covering the top and side surfaces of the electronic components 30 and the exposed surface of the substrate 20, and a material with excellent releasability can be used in the peeling process. If necessary, a heat-softening material that functions as a cushioning material may be used for the upper layer of the releasable cushion member 3. If the protective layer is conductive, the covering of the protective layer 1 electrically connects the ground pattern 22 formed in the substrate 20 to the protective layer 1 (see FIG. 7).

[d] Step of peeling off the releasable cushion member:
The releasable cushion member 3 laminated on the upper layer of the protective layer 1 is peeled off. In this way, an electronic component mounting substrate 51 having the protective layer 1 covering the electronic components 30 is obtained (see FIGS. 1 and 2). For example, the releasable cushion member 3 may be peeled off manually from the end, or the outer surface of the releasable cushion member 3 may be sucked and peeled off from the protective layer 1. Peeling by suction is preferred from the viewpoint of improving yield through automation.

[e] Slicing step:
Using a cutting tool such as a dicing blade, the individual product areas of the electronic component mounting substrate 51 are diced into individual pieces. Through these steps, the electronic components 30 are covered with the protective layer 1, and an individualized electronic component mounting substrate is obtained. The dicing method is to fix the front side of the protective layer 1 with a dicing tape and perform dicing from the substrate 20 side. This is because solder balls are often attached to the substrate side. Once dicing is completed, the individualized electronic component mounting substrates are peeled off from the dicing tape and mounted in the respective electronic devices.

Dicing tape can be of the low adhesive type or the type that loses adhesiveness when exposed to UV light.

The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. Note that the "parts" and "%" below are values based on "parts by mass" and "% by mass", respectively.

(Preparation of test substrate)
A substrate was prepared in which 5 x 5 mold-sealed electronic components (1 cm x 1 cm) were mounted in an array on a substrate (1) made of glass epoxy. The thickness of the substrate was 300 μm, and the mold sealing thickness, i.e., the height from the top surface of the substrate (1) to the top surface of the mold sealing material (component height), was 700 μm. Then, half dicing was performed along the grooves between the components to obtain a test substrate (see FIG. 8). The half-cut groove depth was 800 μm (the cut groove depth of the substrate 20 was 100 μm), and the half-cut groove width was 200 μm.

The materials used in the examples are shown below.
<Thermosetting resin>
Thermosetting resin 1 (polycarbonate resin): manufactured by Toyochem Co., Ltd., acid value = 10 mg KOH/g, amine value = 0.1 mg KOH/g
Thermosetting resin 2 (polyurethane urea resin): manufactured by Toyochem Co., Ltd., acid value = 10 mg KOH/g, amine value = 0.1 mg KOH/g
Thermosetting resin 3 (phenoxy resin): manufactured by Toyochem Co., Ltd., acid value = 10 mg KOH/g, amine value = 0.1 mg KOH/g
<Hardening agent>
Curing agent 1: Bisphenol A type epoxy resin "jER828" (epoxy equivalent = 189 g/eq) manufactured by Mitsubishi Chemical Corporation. Curing agent 2: Modified bisphenol A type epoxy resin "EXA4850-150" (epoxy equivalent = 450 g/eq) manufactured by DIC Corporation. Curing agent 3: Bisphenol F type epoxy resin "JER806H" (epoxy equivalent = 171 g/eq) manufactured by Mitsubishi Chemical Corporation. Curing agent 4: Aziridine compound "Chemitite PZ-33" manufactured by Nippon Shokubai Co., Ltd. (metal filler).
・Scaly metal filler: scaly silver powder (average particle diameter _D50 , 11.0 μm) manufactured by Fukuda Metal Foil & Powder Co., Ltd. ・Dendrite-shaped metal filler: dendritic silver-coated copper powder (average particle diameter _D50 , 4.2 μm) manufactured by Fukuda Metal Foil & Powder Co., Ltd. ・Spherical metal filler: spherical silver powder (average particle diameter _D50 , 5.0 μm) manufactured by Fukuda Metal Foil & Powder Co., Ltd. ・Releasable sheet: polyethylene terephthalate (PET) film with a thickness of 50 μm, the surface of which is coated with a silicone release agent. ・Releasable cushioning material: 3-layer TPX "Opulant CR1040" with a thickness of 150 μm.
" Mitsui Chemicals Tocello

[Example 1]
(Preparation of protective sheet)
A container was charged with 100 parts of thermosetting resin 1, 265 parts of scaly metal filler, and 53 parts of dendritic metal filler, and 50 parts of curing agent 1 and 0.5 parts of curing agent 4 were added, followed by adding toluene so that the non-volatile concentration became 32%. The mixture was stirred with a disperser for 10 minutes to obtain a composition for forming a protective sheet, and this composition was applied to a release sheet using a doctor blade so that the dry thickness became 30 μm, and then dried in an electric oven at 120° C. for 2 minutes to obtain a protective sheet according to Example 1.

(Preparation of Laminate)
Thereafter, a releasable cushion member was prepared, and the protective sheet surface and the releasable cushion member were laminated to obtain a laminate according to Example 1.

(Preparation of electronic component mounting board)
Next, this laminate was cut to 8 cm x 3.5 cm, and after peeling off the release sheet, the laminate was placed on the 8 cm x 3.5 cm test substrate (see FIG. 8) so that the protective sheet side of the laminate was in contact with the substrate and temporarily attached. Then, the laminate was thermocompressed from above to the substrate surface at 10 MPa and 170° C. for 5 minutes. After thermocompression, the release cushioning member was peeled off and the substrate was further heated at 180° C. for 2 hours to produce the electronic component mounting substrate according to Example 1.

[Examples 2 to 11, Comparative Examples 1 to 3]
This was obtained in the same manner as in Example 1, except that the components other than toluene in the protective sheet-forming composition of Example 1 were changed to the types and amounts shown in Table 1 (note that toluene is not shown in Table 1).

<Measurement of Martens Hardness of Protective Layer>
The Martens hardness of the electronic component-mounted substrate was measured using a Fischerscope H100C hardness tester (manufactured by Fisher Instruments) in accordance with ISO14577-1. The measurement was performed on the protective layer using a Vickers indenter (a diamond indenter with a spherical tip of 100φ) in a thermostatic chamber at 25°C under the conditions of a test force of 0.3 N, a test force holding time of 20 seconds, and a test force application time of 5 seconds. The average value of the values obtained by repeatedly measuring 10 random locations on the same cured film surface was taken as the Martens hardness. The test force was adjusted according to the thickness of the protective layer. Specifically, the test force was adjusted so that the maximum indentation depth was about one-tenth of the thickness of the protective sheet.

<Water contact angle after PCT>
The above electronic component mounting board was subjected to a pressure cooker test at 135°C, 85% RH, and 0.23 MPa for 96 hours. Immediately after removing from the tester, the water contact angle was measured by the following method. That is, the water contact angle of the protective layer was measured using an automatic contact angle meter DM-501/analysis software FAMAS manufactured by Kyowa Interface Science Co., Ltd. The measurement was performed by the sessile drop method. The measurement was performed at seven points with 1 cm intervals, and the average value was recorded.

<Glass Transition Temperature of Protective Layer After Curing>
The protective sheets of each Example and Comparative Example were heated at 180°C for 2 hours, and the glass transition temperature was measured in accordance with JIS K7198 using a copper viscoelasticity measuring device DVA-200 (manufactured by IT Measurement & Control Co., Ltd.). For the measurement, each protective sheet was cut to 0.5 cm x 3 cm, heated at 180°C for 2 hours, and the release sheet was peeled off. The deformation mode was tensile, and the glass transition temperature was determined as the temperature at which the main dispersion peak of the loss tangent (tan δ) appeared, measured at a strain of 0.08%, a frequency of 10 Hz, and a heating rate of 10°C/min.

<Resistance value>
The resistance value of the electronic component mounting board of each of the examples and comparative examples was measured by the following method.
That is, according to JIS K 7194, pin-type leads L2103 (manufactured by Hioki E.E. Corporation) were connected to a resistance meter RM3544 (manufactured by Hioki E.E. Corporation) and measurements were taken at 5 mm intervals on the surface layer.

<Development interface area ratio (Sdr) and maximum valley depth (Sv)>
For each of the electronic component mounting boards of the examples and comparative examples, the surface shape of the portion corresponding to the upper surface of electronic component 30 was measured using the following method.
That is, in accordance with ISO 25178-2:2012, measurements were taken from directly above the protective layer at a magnification of 50x using a digital microscope VHX-7000 (manufactured by KEYENCE Corporation). The developed interface area ratio (Sdr) and maximum valley depth (Sv) were obtained from the average values of five measurements taken at different locations.

<PCT Adhesion>
The electronic component mounting boards of the examples and comparative examples were subjected to a pressure cooker test (PCT) at 135°C, 85% RH, and 0.23 MPa for 96 hours. Then, using a cross-cut guide in accordance with JIS K5600, 100 grids with a spacing of 1 mm were made on the protective layer surface, and then an adhesive tape was pressed and the end of the tape was peeled off at a 45° angle in one go to perform a cross-cut test. The adhesive tape used was a 18 mm wide adhesive tape made by Nichiban. The state (cross-cut remaining rate) of the protective layer remaining on FR4 (a glass epoxy plate made by impregnating glass fiber with epoxy resin and subjecting it to a heat-curing treatment, with a thickness of 1 mm) was evaluated according to the following criteria.
◎: Remaining rate is 100/100 (very good)
◯: Shows a residual rate of 95 to 99/100 (good)
△: Remaining rate is 85 to 94/100 (lower practical limit)
×: The remaining rate is less than 85/100 (poor).

<Substrate protection>
A 1 mm thick FR4 was cut to 5 x 6 cm to prepare a substrate. On the other hand, a laminate of protective sheets according to each of the Examples and Comparative Examples was cut to 5 cm x 6 cm, and after peeling off the release sheet, the laminate was placed on the substrate so that the protective sheet side of the laminate was in contact with the substrate and temporarily attached. Then, the laminate was thermocompressed from above to the substrate surface at 10 MPa and 170°C for 5 minutes. After thermocompression, the release cushion member was peeled off and heated at 180°C for 2 hours to prepare a test substrate. Then, a pressure cooker test (PCT) was performed on the test substrate at 135°C, humidity 85% RH, and 0.23 MPa for 96 hours. One side of the test substrate was fixed, and the amount of warping on the opposite side was measured. The amount of warping was measured for each of the four sides and the average was taken, and the average amount of warping before and after PCT was calculated, and the difference (after PCT - before PCT) was used for evaluation. The evaluation criteria are as follows.
◎: Difference is less than 1 mm (very good)
◯: Difference is 1 mm or more and less than 2 mm (good)
△: Difference is 2 mm or more and less than 3 mm (lower practical limit)
×: Difference is 3 mm or more (defective)

<Process workability>
The workability was evaluated by carrying out a peel strength test of a dicing tape.
A dicing tape cut to a width of 2.5 cm was adhered to the protective layer of the electronic component mounting substrate in each of the Examples and Comparative Examples, and allowed to stand for 30 minutes in a temperature-controlled room at 23°C and 50% humidity. The dicing tape was then UV-cured using a UV irradiator, and a peel test was performed using the following method.
That is, a 180° peel test was performed at 300 mm/sec using a TENSILON single column type material testing machine STB-1225S (manufactured by A&D Co., Ltd.) in accordance with JIS Z 0237:2009. The dicing tape used was dicing tape UHP-110AT (UV type, PET substrate, total thickness 110 μm (including adhesive layer thickness 10 μm)) manufactured by Denka Co., Ltd. The measurement was performed twice, and the average value was recorded, and the results were evaluated according to the following criteria.

◎: 4.0N<peel force≦5.5N (very good)
○: 3.5N<peel force≦4.0N, or 5.5N<peel force≦6.0N (good)
△: 3.0N<peeling force≦3.5N, or 6.0N<peeling force≦7.0N (lower practical limit)
×: Peel strength ≦ 3.0 N, or 7.0 N < peel strength (bad)

REFERENCE SIGNS LIST 1 Protective layer 2 Protective sheet 3 Release cushion member 4 Laminate 20 Substrate 21 Electrode 22 Ground pattern 23 Inner via 24 Solder ball 25 Half dicing groove 30 Electronic component 31 Semiconductor chip 32 Molding resin 33 Bonding wire 40 Press substrate 51, 52 Electronic component mounting substrate

Claims (5)

A substrate;
An electronic component mounted on at least one surface of the substrate;
a protective layer covering at least a portion of the substrate and the electronic component;
A protective sheet for forming a protective layer of an electronic mounting board, comprising:
the protective layer formed from the protective sheet contains a binder resin and a flaky metal filler,
A protective sheet, wherein the contact angle of the protective layer surface with water after a pressure cooker test at 135° C., 85% RH, 0.23 MPa for 96 hours is 90 to 130°. 2. The protective sheet according to claim 1, wherein the protective layer formed from the protective sheet has a Martens hardness of 50 to 250 N/ ^mm2 . 3. The protective sheet according to claim 1, wherein the protective layer formed from the protective sheet has a glass transition temperature of 20 to 100°C. The protective layer formed from the protective sheet has a developed interface area ratio (Sdr) of 1.0% to 4.0% and a maximum valley depth (Sv) of 1.5 μm to 4.5 μm , as determined in accordance with ISO 25178-2:2012. The protective layer formed from the protective sheet further comprises:
The protective sheet according to any one of claims 1 to 4, which contains dendritic metal filler or needle-like metal filler.

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