Molded underfill sealing sheet and method for sealing electronic component mounting substrates using the same

Abstract

A sheet for molding / underfill encapsulation of a printed circuit board comprising a plurality of electronic components and a substrate and having spaces between the electronic components and the substrate, the sheet being made of a heat-curable resin composition. When examined at 125°C over 150 seconds, the sheet has an increase in viscosity, which is a ratio (V90 / V0) of the viscosity V90 measured at 90 seconds after initiation of the examination of the sheet to the viscosity V0 measured at 0 second thereafter, of less than 9.

Description

Technical Field

[0001] The present invention relates to a sheet for mold underfill encapsulation and a method for encapsulating an electronic component-mounted substrate using the same. Background Art

[0002] For encapsulating electronic components connected by the flip-chip connection method, a general method is to perform underfill on the gap between the electronic component and the substrate with a fluid liquid encapsulating material, and then perform overmolding with another liquid encapsulating material or an encapsulating film (see Patent Documents 1 to 3).

[0003] On the other hand, in order to reduce the number of processes, a mold underfill encapsulation material capable of simultaneously performing underfill encapsulation and overmold encapsulation has been proposed (see Patent Document 4). Prior Art Documents Patent Documents

[0004] Patent Document 1 Japanese Patent Application Laid-Open No. 2014-131016 Patent Document 2 Japanese Patent Application Laid-Open No. 2014-229769 Patent Document 3 Japanese Patent Application Laid-Open No. 2015-178635 Patent Document 4 Japanese Patent Application Laid-Open No. 2015-71670 Summary of the Invention Problems to be Solved by the Invention

[0005] In mold underfill encapsulation where overmold encapsulation is performed together with underfill encapsulation, non-penetrating portions (voids) of the encapsulating material may occur in the spaces between a plurality of electronic components and the substrate, making it difficult to stably perform sufficient underfill encapsulation. Means for Solving the Problems

[0006] One aspect of the present invention relates to a sheet of thermosetting resin composition, wherein the viscosity increase ratio (V90 / V0), which is the ratio of the viscosity V90 at 90 seconds from the start of measurement to the viscosity V0 at 0 seconds, is less than 9, at a measurement temperature of 125°C and a measurement time of 150 seconds, is less than 9, and the sheet comprises a plurality of electronic components and a substrate, with a space provided between the electronic components and the substrate, for use as a mold underfill sealing sheet for electronic component mounting substrates.

[0007] Another aspect of the present invention relates to a method for sealing an electronic component mounting substrate, comprising the steps of (a) preparing an electronic component mounting substrate comprising a plurality of electronic components and a substrate, wherein a space is provided between the electronic components and the substrate; (b) placing the sheet on the electronic component mounting substrate so as to be in contact with the electronic components; and (c) heat-molding the placed sheet to fill the space between the electronic components and the substrate with molten material from the sheet and harden it, wherein the heating temperature in the heat-molding is 110°C or higher and 175°C or lower. [Effects of the Invention]

[0008] According to the above aspects of the present invention, when molding an electronic component mounting substrate in which a space is provided between the electronic component and the substrate, it becomes less likely for voids (uninfiltrated portions of the sealing material) to form in the space between the electronic component and the substrate, and stable and sufficient underfill sealing can be achieved.

[0009] While novel features of the present invention are described in the appended claims, the present invention, both in terms of its structure and content, will be better understood by the following detailed description in conjunction with the drawings, along with other objects and features of the present invention. [Brief explanation of the drawing]

[0010] [Figure 1] This is a conceptual diagram showing an example of an electronic component mounting circuit board. [Figure 2]This diagram shows an example of a circuit board with a center C, a frame line F that encloses all the electronic components and minimizes the enclosed area, an arbitrary point P on the frame line, the outer edge S of the thermosetting sheet, and a point Q that is the intersection of the line Lcp passing through point P and center C and the outer edge S. [Figure 3] This is a process diagram for the sealing method of electronic component mounting boards. [Modes for carrying out the invention]

[0011] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values ​​and materials may be applied as long as the effects of this disclosure are obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B". In the following description, when lower and upper limits of numerical values ​​relating to specific physical properties or conditions are given as examples, either of the given lower limits and either of the given upper limits can be arbitrarily combined, as long as the lower limit is not greater than or equal to the upper limit. When multiple materials are given as examples, one of them may be selected and used alone, or two or more may be used in combination.

[0012] Furthermore, this disclosure encompasses any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims. In other words, any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims, is possible, provided that no technical inconsistency arises.

[0013] In the following explanation, the terms "contains" or "includes" encompass expressions such as "contains (or includes)," "substantially consists of," and "consists of."

[0014] In this disclosure, "thermosetting resin" may be referred to as "sealant" regardless of whether it has cured or not.

[0015] A sheet of thermosetting resin composition (mold underfill encapsulation sheet) according to an embodiment of the present invention is an encapsulating material used for mold underfill encapsulation in which overmold encapsulation is performed together with underfill encapsulation. The object to be encapsulated is an electronic component-mounted substrate comprising a plurality of electronic components and a substrate, with a space provided between the electronic components and the substrate. In mold underfill encapsulation, encapsulation of electrode portions connecting the electronic components and the substrate (i.e., underfill encapsulation) and overall encapsulation including the outer surfaces of the electronic components (i.e., overmold encapsulation) are performed in a single process.

[0016] A mold underfill encapsulation sheet (hereinafter also referred to as "MUFS sheet") is a sheet of an uncured or semi-cured (B-stage) thermosetting resin composition. A semi-cured product (B-stage) refers to a thermosetting resin composition that is solid at room temperature, exhibits fluidity for a certain period of time when heated to a temperature equal to or higher than a predetermined temperature, and then loses fluidity as the curing reaction progresses.

[0017] <Thickening rate> By controlling the thickening rate of the sheet to less than 9, the ease with which the encapsulating material penetrates into the space between the electronic components and the substrate (hereinafter also referred to as "space S") (hereinafter also referred to as "MUF property") is significantly improved.

[0018] Here, the thickening rate is the thickening rate measured under the measurement conditions of a measurement temperature of 125°C and a measurement time of 150 seconds (hereinafter referred to as measurement condition (A)). The thickening rate is the ratio (V90 / V0) of the viscosity V90 at 90 seconds after the start of viscosity measurement to the viscosity V0 at 0 seconds after the start of measurement. An example of a specific measurement method using measurement condition (A) is shown below.

[0019] As a thickening rate measuring device, for example, MCR102 (manufactured by Anton-paar) is used. The measuring device has an attached upper measurement plate and lower measurement plate.

[0020] First, the temperature of the lower plate is raised to 125°C to stabilize the temperature.

[0021] Next, a 25mm diameter test specimen is placed on the surface of the lower plate at 125°C. This causes the specimen to begin heating towards 125°C. The test specimen is prepared by cutting it from a MUFS sheet.

[0022] Within 30 seconds of placing the specimen on the lower plate, set the apparatus so that the gap between the upper and lower plates is 0.25 mm. Remove any excess material from the specimen when setting the gap.

[0023] Measurement is started 30 seconds after the test specimen is placed on the lower plate. The viscosity of the sealant at 0 seconds (i.e., at the start of measurement) (V0) and the viscosity of the sealant at 90 seconds (V90) are measured, and the ratio of the two (V90 / V0) is calculated as the viscosity increase rate.

[0024] The parameters for measurement condition (A) are summarized below. Measurement temperature: 125℃ Measurement time: 0-150 seconds Specimen size: 25mm diameter circle Shear rate: 20 (1 / s) Thickness of thermosetting resin composition (encapsulant): 0.25 mm Viscosity increase ratio: Viscosity after 90 seconds / Viscosity after 0 seconds

[0025] To further improve MUF properties, the viscosity may be set to 8.2 or less, 6.0 or less, or 3.0 or less. In mold underfill sealing, the timing of the sealant's penetration into space S is late, and the sealant needs to have sufficient fluidity until space S is sufficiently filled. By controlling the viscosity within the above range, the sealant can maintain sufficient fluidity until space S is sufficiently filled.

[0026] In the above measurement, the viscosity of the encapsulant at 125°C should preferably be 1000 Pa·s or less, and more preferably 100 Pa·s or less. Such low viscosity further significantly improves the MUF (Mutually Unused Fiber) properties. The viscosity at 125°C can be measured simultaneously with the measurement of the viscosity increase rate. Here, the viscosity of the encapsulant (V20) 20 seconds after the start of the above measurement is measured.

[0027] <tanδ> For mold underfill sealing sheets, it is desirable that the maximum value of tanδ (loss tangent) under the measurement conditions of a measurement temperature of 125°C and a measurement time of 0 to 70 seconds (hereinafter referred to as measurement condition (B)) be less than 6, but it may also be less than 3, 2.9 or less, 2.7 or less, or 2.5 or less. When the maximum value of tanδ under measurement condition (B) is within the above range, the warping of the mold underfill sealed electronic component mounting substrate is significantly reduced.

[0028] For example, when a MUFS sheet is placed on a silicon wafer with a diameter of 12 inches (Φ) and a thickness of 775 μm and the MUFS sheet is heat-molded under the following conditions, the curing warpage can be reduced to 12 mm or less.

[0029] <Condition> Molding pressure: 5 MPa Molding temperature: 125℃ Molding time: 10 minutes Minimum vacuum degree: 200Pa Post-mold curing: 150°C / 3 hours or 180°C / 1.5 hours

[0030] When the maximum value of tanδ falls within the above range, the residual stress in the cured sealant (especially the overmolded portion) is more easily reduced, which is thought to reduce warping. An example of a specific measurement method using measurement condition (B) is shown below.

[0031] For measuring tanδ, for example, an ARES-LS2 (manufactured by TA Instruments) is used.

[0032] A test specimen with a diameter of 25 mm is placed in the measuring device. The test specimen is prepared by cutting it out from a MUFS sheet.

[0033] Next, for example, the tanδ is measured under the condition of a frequency of 1 Hz.

[0034] The parameters for measurement condition (B) are summarized below. Measurement temperature: 125℃ Measurement time: 0-70 seconds Specimen size: 25mm diameter circle Thickness of thermosetting resin composition (encapsulant): 0.25 mm

[0035] From the viewpoint of improving the ease with which the sealing material penetrates the space (space S) between the electronic component and the substrate (MUF property), the tanδ under measurement condition (B) may be set to 0.2 or higher, or to 0.3 or higher. For example, the tanδ under measurement condition (B) is preferably 0.8 or higher and less than 3.

[0036] The method for controlling tanδ in measurement condition (B) to the above range is not particularly limited, but examples include increasing the filler content, applying a surface treatment agent to the surface of the filler, and selecting a main resin and a curing agent.

[0037] <Storage modulus> The storage modulus of the cured MUFS sheet is, for example, 3 GPa or higher, and may also be 5 GPa or higher, and may also be, for example, 40 GPa or lower, and may also be 30 GPa or lower.

[0038] The measurement of the storage modulus of a cured product of the MUFS sheet is carried out according to the following procedure. First, a measurement sample of 50 mm length × 10 mm width × 2 mm thickness is prepared from the cured product of the MUFS sheet. As the cured product, a cured product obtained by heating and curing the MUFS sheet at 175°C for 1 hour is used. Next, the measurement sample is set on a bending measurement jig, and the bending storage modulus in a temperature range of -50 to 300°C is measured using a viscoelasticity measuring device (DMA6100, manufactured by Hitachi High-Tech Science Corporation) under the conditions of a frequency of 1 Hz and a temperature increase rate of 2.5°C / min. The storage modulus at 25°C is read from the measurement result. The storage modulus serves as an indicator of the rigidity of the sheet. A MUFS sheet whose cured product has a storage modulus within the above range is excellent in handleability.

[0039] <Structure of MUFS Sheet> The MUFS sheet may be a sheet with a single-layer structure. A single-layer structure sheet refers to a sheet composed of a single thermosetting resin composition. The MUFS sheet may be attached to one release sheet or sandwiched between two release sheets to improve handleability.

[0040] However, the MUFS sheet may have a multilayer structure. A multilayer structure refers to a structure in which two or more layers of thermosetting resin compositions having different compositions are laminated. On the other hand, a multilayer structure sheet has a more complicated manufacturing process than a single-layer structure sheet. From the viewpoint of simplifying the manufacturing process, a single-layer structure sheet is more preferable.

[0041] The thickness of the MUFS sheet is not particularly limited, but is, for example, 50 µm or more, may be 100 µm or more, may be 200 µm or more, or may be 400 µm or more. The thickness of the MUFS sheet is, for example, 1000 µm or less, and may be 800 µm or less.

[0042] <Method for Producing MUFS Sheet> A single-layer MUFS sheet is formed by molding a thermosetting resin composition into a single sheet. Examples of molding methods include calendering, casting, inflation extrusion, T-die extrusion, and dry lamination. Alternatively, the MUFS sheet may be formed on a release sheet, which is then peeled off before use.

[0043] The release sheet is not particularly limited, but examples include plastic films, paper, nonwoven fabrics, and metals. Examples of plastic films include polyolefin films, vinyl halogenated polymer films, acrylic resin films, rubber films, cellulose films, polyester films, polycarbonate films, polystyrene films, polyphenylene sulfide films, and cycloolefin polymer films. A release sheet treated with silicone or the like may also be used.

[0044] <Thermosetting resin composition> The thermosetting resin composition constituting the MUFS sheet includes, for example, a main resin, a curing agent, and a filler.

[0045] (Filler) The filler is a solid component dispersed in the thermosetting resin composition that does not melt during the sealing process. The solid component may be either an inorganic or organic material. The solid component may be particulate, plate-like, or fibrous. The thermosetting resin composition may also contain inorganic powder as a filler.

[0046] As inorganic powders, fused silica, crystalline silica, quartz glass powder, calcium carbonate, aluminum hydroxide, etc., can be used. Among these, silica is preferred, and fused silica is more preferred.

[0047] The filler content in the thermosetting resin composition is not particularly limited, but may be, for example, 50% by mass or more, 60% by mass or more, or 70% by mass or more. A filler content of 70% by mass or more is desirable in that it makes it easier to keep tanδ below 3 under measurement condition (A). The upper limit of the filler content in the thermosetting resin composition is not particularly limited, but may be, for example, 90% by mass or less, or 85% by mass or less.

[0048] The maximum particle size (Dmax) of the filler is preferably smaller than the minimum distance between the electronic components to be sealed (the distance between the closest outer edges of adjacent electronic components) (W) and the height of the space between the electronic components and the substrate (H), and can be appropriately selected according to the above distance (W) and height (H). The maximum particle size (Dmax) of the filler may be, for example, 35 μm or less, 25 μm or less, 20 μm or less, or 10 μm or less.

[0049] The average particle size (D50) of the filler can be appropriately selected according to the above distance (W) and height (H), but for example it may be 0.5 μm or more, 1 μm or more, or 2 μm or more. The average particle size (D50) of the filler may be 20 μm or less, 10 μm or less, or 5 μm or less (for example, 3 μm or less). The average particle size (D50) of the filler is the median diameter at 50% of the cumulative volume of the volume particle size distribution.

[0050] The average particle size (D50) and maximum particle size (Dmax) of the filler can be measured by laser diffraction scattering using a laser diffraction particle size distribution analyzer.

[0051] (Main material resin) The main resin material is not particularly limited, but epoxy resin is superior in terms of heat resistance and cost.

[0052] The epoxy resin is not particularly limited, but biphenyl-type epoxy resin, bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, bisphenol AD-type epoxy resin, naphthalene-type epoxy resin, glycidylamine-type epoxy resin, phenol novolac-type epoxy resin, phenolphthalein-type epoxy resin, polyglycol-modified epoxy resin, polyolefin-modified bisphenol A-type epoxy resin, alicyclic epoxy resin, dicyclopentadiene-type epoxy resin, polyether-type epoxy resin, silicone-modified epoxy resin, etc. These may be used individually or in combination of two or more. For example, when using bisphenol A-type epoxy resin, the content of bisphenol A-type epoxy resin in the main resin is, for example, 50% by mass or more and 90% by mass or less, and may also be 60% by mass or more and 90% by mass or less. For example, when using phenol novolac-type epoxy resin, the content of phenol novolac-type epoxy resin in the main resin is, for example, 50% by mass or more and 90% by mass or less, and may also be 60% by mass or more and 90% by mass or less.

[0053] In particular, from the viewpoint of improving the glass transition temperature, it is desirable that the main resin component includes a solid epoxy resin with a melting point of 50°C or higher.

[0054] In terms of easily suppressing warping of the electronic component mounting substrate after encapsulation, it is desirable that the main resin includes, as part of the main resin, at least one selected from the group consisting of epoxy resins having alkylene chains, epoxy resins having polyoxyalkylene chains, and phenolphthalein-type epoxy resins. A phenolphthalein-type epoxy resin may be used in combination with an epoxy resin having alkylene chains and / or an epoxy resin having polyoxyalkylene chains.

[0055] (Epoxy resin containing alkylene chains) The content of the epoxy resin having alkylene chains in the main resin is, for example, 5% by mass or more and 30% by mass or less, and may be 5% by mass or more and 20% by mass or less. The type of epoxy resin having alkylene chains is not particularly limited as long as it has alkylene chains, but it may be an epoxy modified product of a polyol having 8 or more carbon atoms. It may also have a bisphenol A type epoxy resin as its basic skeleton.

[0056] The epoxy resin having alkylene chains may be of any type, such as glycidyl ether type, glycidyl ester type, glycidylamine type, or alicyclic epoxy compound. From the viewpoint of ease of availability, glycidyl ethers having alkylene chains (specifically, glycol-modified epoxy resins) are used.

[0057] The number of carbon atoms in the alkylene chain is, for example, 1 or more, but may also be 2 or more, or 3 or more. The number of carbon atoms in the polyolefin chain is preferably 10 or less, but may also be 8 or less, or 6 or less.

[0058] Examples of epoxy resins containing alkylene chains include 1,6-hexanediol diglycidyl ether, resorcinol diglycidyl ether, propylene glycol diglycidyl ether, and cyclohexanedimethanol diglycidyl ether. Other examples include epoxy-modified polybutadiene, epoxy-modified polyisoprene, epoxy-modified polyethylene, epoxy-modified polypropylene, epoxy-modified (meth)acrylic polymer, and epoxy-modified natural rubber.

[0059] (Epoxy resin containing polyoxyalkylene chains) The content of the epoxy resin having polyoxyalkylene chains in the main resin is, for example, 5% by mass or more and 30% by mass or less, and may also be 5% by mass or more and 20% by mass or less. The epoxy resin having polyoxyalkylene chains may have a bisphenol A type epoxy resin as its basic skeleton.

[0060] Epoxy resins containing polyoxyalkylene chains are not particularly limited in type, as long as they contain polyoxyalkylene chains, and may be glycidyl ether type, glycidyl ester type, glycidylamine type, alicyclic epoxy compound, etc. From the viewpoint of ease of availability, glycidyl ethers containing polyoxyalkylene chains (specifically, polyalkylene glycol glycidyl ethers) are used.

[0061] Examples of glycidyl ether type epoxy resins include polyoxyethylene diglycidyl ether, polyoxypropylene diglycidyl ether, polyoxytrimethylene diglycidyl ether, polyoxybutylene diglycidyl ether, polyoxyhexamethylene diglycidyl ether, and polyoxyethylene-polyoxypropylene diglycidyl ether.

[0062] The number of carbon atoms in the alkylene group contained in the polyoxyalkylene chain is, for example, 2 or more, preferably 3 or more, and more preferably 4 or more. The number of carbon atoms in the alkylene group is preferably 16 or less, and may be 10 or less or 6 or less.

[0063] Specific examples of alkylene groups include ethylene, propylene, trimethylene, butylene (1,2-butylene, 1,3-butylene, 1,4-butylene (or tetramethylene), etc.), hexamethylene, octamethylene, and decamethylene.

[0064] The number of repeating oxyalkylene units n in the polyoxyalkylene chain is, for example, 3 or more, preferably 4 or more or 5 or more. The number of repeating oxyalkylene units n is, for example, 70 or less, may be 30 or less, or 10 or less.

[0065] (Phenolphthalein-type epoxy resin) The content of phenolphthalein-type epoxy resin in the main resin is, for example, 50% by mass or more and 90% by mass or less, and may be 60% by mass or more and 90% by mass or less.

[0066] Phenolphthalein-type epoxy resins are bifunctional epoxy resins that have a bulky phenolphthalein backbone within their molecules. For example, phenolphthalein-type epoxy resins may have glycidyl ether groups at the para positions of two phenyl groups that are not bonded to a nitrogen atom. Specifically, phenolphthalein-based diglycidyl ethers (N-phenylphenolphthalein diglycidyl ethers) can be cited.

[0067] The thermosetting resin composition may contain at least one selected from the group consisting of a polyol having an alkylene chain, a polyol having a polyoxyalkylene chain, an epoxy resin having an alkylene chain, an epoxy resin having a polyoxyalkylene chain, and a phenolphthalein-type epoxy resin.

[0068] (Polyols containing alkylene chains) The content of the alkylene chain-containing polyol in the thermosetting resin composition is, for example, 5% by mass or more and 30% by mass or less, and may also be 5% by mass or more and 20% by mass or less. The type of alkylene chain-containing polyol is not particularly limited as long as it contains an alkylene chain, but it may be a polyol with 8 or more carbon atoms. Examples of polyols with 8 or more carbon atoms include 1,4-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 2-methyl-1,1-cyclohexanedimethanol, and tricyclo[5.2.1.0 2,6 Examples include decanedimethanol, 1,9-nonanediol, 2-methyl-1,8-octanediol, 1,10-decadiol, 1,12-todecanediol, dimergol, hydrogenated dimergol, etc. Other examples include alcohol-modified polybutadiene, alcohol-modified polyisoprene, alcohol-modified polyethylene, alcohol-modified polypropylene, alcohol-modified (meth)acrylic polymer, and alcohol-modified natural rubber.

[0069] (Polyols containing polyoxyalkylene chains) The content of polyols having polyoxyalkylene chains in the thermosetting resin composition is, for example, 5% by mass or more and 30% by mass or less, and may also be 5% by mass or more and 20% by mass or less. The type of polyol having polyoxyalkylene chains is not particularly limited as long as it has polyoxyalkylene chains.

[0070] Examples of polyols having polyoxyalkylene chains include polyoxyethylene polyol, polyoxypropylene polyol, polyoxytetramethylene polyol, polyoxyethylene polyoxypropylene polyol, polyoxyethylene polyoxytetramethylene polyol, and polyoxypropylene polyoxytetramethylene polyol. These polyoxyalkylene polyols may be used individually or in combination of two or more. For example, a polyoxyalkylene polyol may have 2 to 6 hydroxyl groups or 2 to 4 hydroxyl groups.

[0071] Examples of polyols that constitute polyols having polyoxyalkylene chains include diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, dibutylene glycol, tributylene glycol, polybutylene glycol, polytetramethylene glycol, diglycerin, triglycerin, polyglycerin, polyoxyalkylene glycol (containing one or more alkylene oxides such as ethylene oxide, propylene oxide, and butylene oxide as constituent units of oxyalkylene), and mixtures thereof, polyoxyethylene glycerin, polyoxypropylene glyceryl ether, polyoxybutylene glyceryl ether, and polyoxyalkylene glyceryl ether (containing one or more alkylene oxides such as ethylene oxide, propylene oxide, and butylene oxide as constituent units of oxyalkylene).

[0072] (Hardening agent) Phenolic resins, acid anhydrides, amine compounds, etc., can be used as curing agents for the main resin. Among these, phenolic resins are preferred because they easily suppress warping of the electronic component mounting substrate after encapsulation.

[0073] While there are no particular limitations on the phenolic resin, phenol novolac resins are preferred. Phenolic novolac resins are obtained by condensation polymerization of phenols or naphthols (e.g., phenol, cresol, naphthol, alkylphenol, bisphenol, terpene phenol, naphthol, etc.) with formaldehyde. More specifically, examples include phenol novolac resins, cresol novolac resins, aralkylphenol novolac resins, biphenylphenol novolac resins, terpene phenol novolac resins, α-naphthol novolac resins, and β-naphthol novolac resins. Of these, naphthol novolac resins are preferred from the viewpoint of water resistance. These may be used individually or in combination of two or more types.

[0074] In particular, from the viewpoint of increasing the glass transition temperature, it is desirable that the curing agent contains a solid phenol novolac resin with a melting point of 60°C or higher.

[0075] The amount of curing agent can be appropriately controlled within a range of, for example, 30 parts by mass or more and 80 parts by mass or less per 100 parts by mass of the main resin, and may be in the range of 45 parts by mass or more and 60 parts by mass or less.

[0076] (Curing accelerator) The thermosetting resin composition may contain a curing accelerator. While not particularly limited, examples of curing accelerators include imidazole-based accelerators, phosphorus-based accelerators, phosphonium salt-based accelerators, bicyclic amidines and their derivatives, organometallic complexes, and polyamine ureas. The curing accelerator is preferably latent, and examples of latent curing accelerators include imidazole-based accelerators and phosphorus-based accelerators. Among latent curing accelerators, encapsulated imidazole-modified products (microcapsule-type curing accelerators) are particularly preferred.

[0077] The viscosity can be controlled, for example, by appropriately selecting the type and amount of curing accelerator. It is preferable to use an imidazole-based accelerator because it is easier to control the viscosity.

[0078] The amount of curing accelerator can be appropriately controlled, for example, between 1 and 10 parts by mass per 100 parts by mass of the main resin, and may be between 2 and 5 parts by mass.

[0079] (Additives) The thermosetting resin composition may further contain additives. Examples of additives include, but are not limited to, silane coupling agents, carbon black, defoaming agents, leveling agents, pigments, stress relaxants, thermoplastic resins, and ion scavenging agents.

[0080] There are various types of silane coupling agents, and the properties of the resin composition (e.g., viscosity at room temperature) may change depending on the type used. Therefore, a suitable and desirable one is selected as appropriate. Silane coupling agents have hydrolyzable groups (alkoxy groups, hydroxyl groups, etc.) and may also have alkyl groups, aliphatic or aromatic amino groups (phenylamino groups, etc.), acrylic groups, methacrylic groups, etc.

[0081] Thermoplastic resins contribute to suppressing warping of electronic component mounting substrates after encapsulation, and also contribute to the gelation or solidification of MUFS sheets.

[0082] The weight-average molecular weight (Mw) of the thermoplastic resin may be, for example, 300,000 or less, 200,000 or less, or 100,000 or less. Mw may also be, for example, 5,000 or more. When the Mw of the thermoplastic resin is within this range, its dispersibility is high, and the elasticity of the cured product is easily reduced, thus further enhancing the effect of suppressing warping.

[0083] In this specification, the weight-average molecular weight Mw is the weight-average molecular weight on a polystyrene basis, measured using gel permeation chromatography (GPC).

[0084] Thermoplastic resins may have reactive functional groups. Examples of reactive functional groups include epoxy groups, carboxyl groups, hydroxyl groups, amino groups (including imino groups), amide groups, nitrile groups, and groups having polymerizable carbon-carbon unsaturated bonds (e.g., vinyl groups, allyl groups, acryloyl groups, methacryloyl groups, etc.).

[0085] Examples of thermoplastic resins include diene-based thermoplastic resins (isoprene rubber, butadiene rubber, styrene-butadiene rubber, chloroprene rubber, etc.), acrylic-based thermoplastic resins (acrylic rubber, etc.), nitrile-based thermoplastic resins (nitrile rubber, etc.), urethane-based thermoplastic resins (urethane rubber, etc.), silicone-based thermoplastic resins (silicone rubber, epoxy-modified silicone, etc.), polyester-based thermoplastic resins (crystalline polyester, amorphous polyester, polyester elastomer, etc.), polyamide-based thermoplastic resins (polyether esteramide, polyamide elastomer, etc.), butyl rubber, and ethylene propylene rubber. These may be used individually or in combination of two or more.

[0086] Acrylic thermoplastic resins may be used because they allow for easy control of molecular weight and molecular weight distribution, easy introduction of reactive functional groups, and easy dispersion in curable resin compositions. Acrylic thermoplastic resins contain (meth)acrylate units. Examples of (meth)acrylate units include alkyl (meth)acrylate units. Examples of alkyl (meth)acrylate units include C 1-6 Examples include alkyl (meth)acrylate units (ethyl (meth)acrylate units, propyl (meth)acrylate units, butyl (meth)acrylate units, etc.), C 1-4 Alkyl (meth)acrylate units may also be used. Note that acrylate and methacrylate are collectively referred to as (meth)acrylate.

[0087] The amount of thermoplastic resin is, for example, 5 parts by mass or more and 30 parts by mass or less per 100 parts by mass of the main resin, and may also be 5 parts by mass or more and 20 parts by mass or less.

[0088] <Method for sealing electronic component mounting boards> The following describes an example of an embodiment of a method for sealing an electronic component mounting substrate using MUFS sheets.

[0089] The method for sealing an electronic component mounting substrate according to this embodiment includes the steps of: (a) preparing an electronic component mounting substrate comprising a plurality of electronic components and a substrate, with a space provided between the electronic components and the substrate; (b) placing an MUFS sheet on the electronic component mounting substrate so as to be in contact with the electronic components; and (c) heating and molding the placed MUFS sheet to fill the space between the electronic components and the substrate with molten material from the sheet and harden it. The heating temperature in the heat molding is, for example, 110°C or higher and 175°C or lower.

[0090] According to the above sealing method, an electronic component mounting substrate (hereinafter also referred to as "sealed body") is obtained, comprising a substrate, electronic components mounted on the substrate, and a cured product of a sealing material that seals the electronic components. Therefore, the sealing method according to this embodiment is also a method for manufacturing an electronic component mounting substrate (sealed body). Specifically, the method can be described as "a method for manufacturing a sealed body for an electronic component mounting substrate, comprising an electronic component mounting substrate comprising a plurality of electronic components and a substrate, with a space provided between the electronic components and the substrate, and a cured product of a mold underfill sealing sheet that undermoldes the space and overmoldes the electronic components." The electronic component mounting substrate may be a single-sided sealed body in which only one side of the substrate is sealed with the sealing material, or it may be a double-sided sealed body in which both sides are sealed with the sealing material.

[0091] In the electronic component mounting substrate prepared in process (a), multiple electronic components are connected to the substrate (specifically, electrodes provided on the substrate) using, for example, a flip-chip connection method. In the flip-chip connection method, electronic components are mounted on the substrate by arrays of protruding terminals (also called "bumps"). Multiple bumps are provided on the surface of the electronic component facing the substrate. The bumps constitute part of the electronic component. The space between the electronic component and the substrate is generally occupied by the gaps between the multiple bumps.

[0092] The MUFS sheet used in process (b) has the property of melting upon heating and then hardening. The MUFS sheet may also be from the B stage.

[0093] In process (c), the MUFS sheet is heat-molded using a mold. The mold presses the MUFS sheet, which is placed on the electronic component mounting substrate so as to cover multiple electronic components, against the substrate. The mold is heated at any time. The heating melts the MUFS sheet, and the molten material covers the surface of the electronic components, filling the space between the electronic components and the substrate, as well as filling the spaces between each electronic component, and then hardens. In other words, underfill sealing and overmolding sealing, which seals the entire electronic component, are performed in one step. Overmolding sealing means sealing at least the surface of the electronic component with the sealing material. The pressing surface of the mold may be covered with a release film.

[0094] In the above encapsulation method, the size and shape of the MUFS sheet in plan view may be designed according to a frame line (hereinafter also referred to as "frame line F") that encloses all of the multiple electronic components while minimizing the enclosed area. The size of the MUFS sheet in plan view may be larger than the size of the substrate, but from the viewpoint of simplifying the encapsulation process and cost, it is desirable that it be the same size as the substrate or smaller.

[0095] Specifically, let Lp be the distance between any point P on the border line F and the center of the substrate (hereinafter also referred to as "center C"). Also, let Q be the intersection point of the line passing through point P and center C (hereinafter also referred to as "line Lcp") and the outer edge of the MUFS sheet (hereinafter also referred to as "outer edge S"). In this case, the distance between point Q and center C (hereinafter also referred to as "Lq") may be restricted to 0.9Lp or greater.

[0096] The distance Lq may be 0.91Lp or greater, 0.93Lp or greater, or 0.96Lp or greater. Furthermore, Lp and Lq may satisfy the above relationship for 70% or more, and even more so for 90% or more, of the length of the trajectory of the frame line F, and it is desirable that Lp and Lq satisfy the above relationship for 98% to 100%.

[0097] Considering the tolerances of the MUFS sheet, the substrate tolerances, and the mold tolerances, Lq may be set to 1.0Lp or greater. Furthermore, the substrate may be completely covered by the thermosetting sheet when viewed from above.

[0098] If the MUFS sheet is circular, the radius R of such a MUFS sheet corresponds to the distance Lq. In this case, the distance Lq (radius R) and the maximum value MLp of the distance Lp must satisfy the above relationship, such as Lq ≥ 0.9MLp. Note that MLp, which is the maximum value of Lp, is the distance Lp when point P is located at the point furthest from the center of the substrate among all electronic component locations on the substrate.

[0099] In other words, in this embodiment, when viewed from above, the MUFS sheet is placed on the substrate so as to completely or most of the multiple electronic components. Even when the outer edge S of the MUFS sheet is inward (closer to the center C) than the frame line F, the distance between point P and point Q is small. In this case, more of the pressure energy applied to the MUFS sheet from the mold is used to fill the space between the electronic components and the substrate with the molten thermosetting sheet. Therefore, the space between the electronic components and the substrate is easily filled with the molten material (making it difficult for unimpregnated areas of the sealant to form), and stable and sufficient underfill sealing can be achieved. Such effects are particularly noticeable in packaging technologies such as panel-level packages (PLP) and wafer-level packages (WLP) when sealing multiple electronic components mounted on a large-area substrate all at once.

[0100] In step (c), the pressure applied from the pressing surface of the mold to the MUFS sheet (or its molten material) may be, for example, 0.5 MPa or more and 15 MPa or less, or 2 MPa or more and 12 MPa or less. This can promote the penetration of the molten material into the narrow space.

[0101] The upper limit of the distance Lq between point Q and center C is not particularly limited from the viewpoint of providing stable and sufficient underfill sealing. However, considering the manufacturing cost and handling ease of the MUFS sheet, Lq may be, for example, 1.45 Lp or less, 1.2 Lp or less, 1.1 Lp or less, or 1.05 Lp or less.

[0102] The heat molding of the MUFS sheet may be carried out in a reduced pressure atmosphere. In this case, a better underfill portion can be formed. A reduced pressure atmosphere is any pressure atmosphere lower than atmospheric pressure, but for example, a pressure atmosphere of 10,000 Pa (Pascals) or less, i.e., 100 hectopascals (hPa) or less is preferred, 5,000 Pa (Pascals) or less is also acceptable, less than 500 Pa (5 hPa) is preferred, and less than 200 Pa (2 hPa) is more preferred.

[0103] In the encapsulant obtained through process (c), the cured encapsulant consists of an underfill portion that fills the space between the substrate and the electronic component, and an overmolded portion that encapsulates the side of the electronic component that does not face the substrate. The structure of the underfill portion and the overmolded portion are continuous. The boundary between the underfill portion and the overmolded portion is not observed even under a microscope, and there is no substantial difference in the morphology (tissue state) of the underfill portion and the overmolded portion.

[0104] The type of substrate is not particularly limited and includes, for example, wafers, panels, glass substrates, resin substrates, and printed circuit boards. Examples of wafers include silicon wafers, sapphire wafers, and compound semiconductor wafers. Examples of panels include plate-shaped members used in liquid crystal panels and organic (or inorganic) LED panels. Examples of resin substrates include bismaleimidotriazine substrates, polyimide substrates, and fluororesin substrates. The substrate itself may be an assembly of electronic components. An example of an assembly of electronic components is an assembly of semiconductor chips before they are separated into multiple individual chips.

[0105] Electronic components may be active or passive elements. Electronic components may be semiconductor elements or other materials. Electronic components may be semiconductor packages such as BGA (Ball grid array) or CSP (Chip size package). Specific examples of electronic components include RFIC (Radio frequency identifier), chip multilayer LC filters, dielectric filters, and multilayer ceramic capacitors (MLCCs).

[0106] It is desirable that the outer shape of the substrate and the outer shape of the MUFS sheet correspond in general. The outer shapes of the substrate and the MUFS sheet may also be similar. For example, if the outer shape of the substrate is circular, the outer shape of the MUFS sheet may also be circular. If the outer shape of the substrate is rectangular, the outer shape of the MUFS sheet may also be rectangular. If the substrate has an outer shape that is generally circular, such as an orientation flat wafer, the outer shape of the MUFS sheet may also be circular. In addition, it is acceptable for 70% or more of the length of the trajectory of the outer edge S of the MUFS sheet to satisfy the similarity relationship with the outer shape of the substrate.

[0107] The size of electronic components is not particularly limited, but the surface area of ​​the electronic component facing the substrate is, for example, 1 mm² per electronic component. 2 It may be greater than or equal to 3mm 2 The above may also be the case. Furthermore, the surface area of ​​the surface of the electronic component facing the substrate may be, for example, 1600 mm² per electronic component. 2 The following are also acceptable, and 2500mm 2 The following may also be used: The size of an electronic component can be measured using any number of electronic components (e.g., 10) on the circuit board, and the average value can be calculated.

[0108] The height of the electronic component is not particularly limited, but may be, for example, 5 μm or more and 800 μm or 10 μm or more and 600 μm or less. The height of the electronic component is, for example, the distance from the contact point between the bump and the substrate to the maximum height of the electronic component. In other words, this embodiment can perform good underfill sealing and overmolding sealing simultaneously even for substrates on which multiple minute electronic components with a height of about 5 μm are mounted.

[0109] The distance between electronic components is not particularly limited, but may be, for example, 5 μm or more and 2000 μm or 10 μm or more and 1000 μm or less. The minimum distance (W) between electronic components is the distance between the closest outer edges of adjacent electronic components (i.e., the gap between them). In other words, this embodiment can perform good underfill sealing and overmolding sealing simultaneously even on a high-density mounted substrate with a gap between components of about 5 μm. The distance (W) between electronic components can be measured over any multiple pairs of electronic components on the substrate (e.g., 10 pairs) and the average value can be calculated.

[0110] The height (H) of the space between the electronic component and the substrate may be, for example, 2 μm or more, 5 μm to 100 μm, or 10 μm to 80 μm. In other words, this embodiment can perform good underfill sealing and overmolding sealing simultaneously even on substrates with small bumps and a space height of about 2 to 5 μm. The height of the space between the electronic component and the substrate may be, for example, 40 μm or less, or 15 μm or less. Note that the height of the space between the electronic component and the substrate refers to the minimum distance between the surface of the electronic component facing the substrate and the substrate. The minimum distance can be measured for any number of electronic components on the substrate (for example, 10) and the average value can be calculated.

[0111] In an electronic component mounting substrate (encapsulant), the maximum thickness T of the cured encapsulant may be, for example, 1.2 mm or less, 1.0 mm or less, 0.8 mm or less, or 0.4 mm or less (i.e., 400 μm or less). According to this embodiment, it is effective not only when forming a thin encapsulant as described above in package applications such as PLP and WLP, but also when performing good underfill encapsulation and overmolding encapsulation in a single process.

[0112] In a encapsulant, the maximum thickness T of the cured encapsulant is the maximum distance from the surface of the substrate to the surface of the cured material opposite the substrate. The maximum thickness T can be measured at multiple locations on the substrate (e.g., 10 locations) and the average value can be calculated.

[0113] The sealing method will be explained in more detail below, with reference to the diagrams.

[0114] Process (a) First, a substrate with multiple electronic components mounted on it is prepared. A space is provided between the electronic components and the substrate. Figure 1 is a conceptual diagram showing an example of an electronic component mounting substrate 10. The substrate 11 of the electronic component mounting substrate 10 is a notched wafer with a circular outer shape. Multiple rectangular semiconductor chips are mounted on the surface of the substrate 11 as electronic components 12. Note that Figure 1 is a conceptual diagram and does not necessarily reflect the actual size of the electronic components.

[0115] Process (b) Next, the MUFS sheet 20 is placed on the substrate 11 so as to be in contact with the electronic components 12. Here, point P is an arbitrary point on the border line F that encloses all of the electronic components 12 and minimizes the enclosed area. Let Lp be the distance between point P and the center C of the substrate. Let Q be the point where the line Lcp passing through point P and the center C of the substrate intersects with the outer edge S of the MUFS sheet. At this time, the distance Lq between point Q and the center C of the substrate 11 satisfies 0.9Lp or more.

[0116] Figure 2 shows an example of a circuit board 11 with a center C, a frame line F that encloses all of the electronic components 12 and minimizes the enclosed area, an arbitrary point P on the frame line F, the outer edge S of the MUFS sheet 20, and the intersection point Q of the line Lcp passing through point P and center C and the outer edge S. The frame line F is shown as a thicker solid line. The outer edge S of the MUFS sheet 20 is shown as a dashed line. Here, the case where Lq > Lp is shown, but there is also a case where Lq ≤ Lp. Also, here the size of the MUFS sheet 20 is larger than the size of the circuit board 11 when viewed from above, but the size of the MUFS sheet 20 may be less than or equal to the size of the circuit board 11.

[0117] Process (c) Next, the MUFS sheet 20 placed on the electronic component mounting substrate 10 is heated and molded to fill the space between the electronic component 12 and the substrate 11 with the molten MUFS sheet 20, and the molten material is then hardened. Figure 3 is a process diagram of the method for sealing the electronic component mounting substrate 10.

[0118] Specifically, as shown in Figure 3(a), the electronic component mounting substrate 10 is set in the compression molding machine 50. The compression molding machine 50 has an upper mold 51, a lower mold 52, and a flange portion 53 that also serves as part of the mold and is fixed to the periphery of the upper mold 51 via an elastic member such as a spring. The upper mold 51 has a flat pressing surface that presses the MUFS sheet 20. The pressing surface of the upper mold 51, the substrate mounting surface of the lower mold 52, the flange portion 53, etc., may be covered with a release sheet.

[0119] Multiple electronic components 12 are each connected to the surface of the substrate 11 via bumps 121. A space 10S is provided between the surface of the electronic component 12 facing the substrate 11 and the substrate 11. The majority of the space 10S is occupied by the gaps between the bumps.

[0120] In the heat molding process, as shown in Figure 3(b), the MUFS sheet 20 placed on the electronic component mounting substrate 10 is covered with the pressing surface of the mold, and the MUFS sheet 20 is compressed while being heated. At this time, a portion of the molten material of the MUFS sheet 20 penetrates into the space 10S, and the hardening reaction of the molten material proceeds.

[0121] At least one of the lower mold 52 and the upper mold 51 is heated to a temperature at which the curing reaction of the molten MUFS sheet 20 proceeds. As the curing reaction of the molten material proceeds, the underfill portion 221 and the overmolded portion 222 are formed simultaneously. As a result, a sealant 100 is obtained in which the electronic component mounting substrate 10 is sealed with the cured material 22.

[0122] At least part of step (c) may be carried out under atmospheric pressure or under reduced pressure as already described. When heat molding is performed under reduced pressure, air can be drawn from the space in which the compression molding machine 50 is installed.

[0123] The heating temperature is, for example, 80-200°C, but 100-180°C is also acceptable, and 110-140°C is preferable. The heating time is, for example, 30 seconds to 30 minutes, but 2 minutes to 20 minutes is also acceptable.

[0124] Post-mold cure (post-curing) may be further performed on the sealing body 100 unloaded from the compression molding machine 50. Post-mold cure may be performed, for example, at 100 to 180°C for about 30 minutes to 3 hours.

[0125] [Examples] Hereinafter, the present invention will be described in further detail based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[0126] <<Examples 1 to 28 and Comparative Examples 1 to 6>> <Preparation of MUFS Sheet> (1) Materials were blended according to the formulations shown in each table, and kneaded using a roll kneader to prepare a thermosetting resin composition. All numerical values indicating the formulations in the tables are parts by mass.

[0127] (2) The obtained thermosetting resin composition was applied onto a release sheet by a T-die extrusion method under the condition of 100°C, and molded into a sheet shape to prepare a MUFS sheet having a thickness of 500 µm. A polyethylene terephthalate film having a thickness of 50 µm subjected to silicone release treatment was used as the release sheet.

[0128] [Evaluation] <Measurement of Thickening Rate> For each of Examples (Ex. 1 to 28) and Comparative Examples (Comp. 1 to 6), the thickening rate of the MUFS sheet obtained above was measured by the method described above.

[0129] <MUF Property> Five evaluation electronic components (TEG) were mounted on a circular glass substrate with an outer diameter of 300 mmΦ to prepare a sample of an electronic component-mounted substrate for evaluation. The electronic components were arranged at the center C of the substrate and at four positions angularly equivalent with respect to the center C (0°, 90°, 180°, and 270°) such that the maximum distance between a point P on each electronic component and the center C of the substrate was Lp=140 mm.

[0130] The TEG has a bump height of 30 μm, corresponding to the height of the space between the electronic component and the substrate; a size of 25 mm × 25 mm × 300 μm (the height of the electronic component including the bump is 330 μm); a bump size of 20 μm; and a pitch between the centers of the bumps of 40 μm.

[0131] A substrate with Lq=140mm=1.0Lp and a similarly shaped (circular) MUFS sheet were placed on the sample, with the center of the substrate and the center of the MUFS sheet aligned so that they were in contact with the electronic components. The MUFS sheet was then heat-molded under the following conditions.

[0132] Molding pressure: 5 MPa Molding temperature: 125℃ Molding time: 10 minutes Minimum vacuum degree: 200Pa Post-mold curing: 175°C / 1 hour

[0133] The condition (penetration) of the underfill portion filling the space between the substrate and the electronic component was visually evaluated. Direct observation from the back surface of the glass substrate was performed, and the size of the unpenetrated areas (voids) of the cured sealant was evaluated according to the following criteria. The largest void size was identified among five evaluation electronic components (TEGs). The results are shown in the respective tables.

[0134] ◎: The void size is 500 μm or less. ○: The void size is greater than 500 μm and less than or equal to 750 μm. △: The void size is greater than 750 μm and less than or equal to 1000 μm. ×: The void size is greater than 1000 μm.

[0135] [Table 1]

[0136] [Table 2]

[0137] [Table 3]

[0138] It can be understood from Tables 1 to 3 that when the thickening rate is 9 or less, the MUF property is significantly improved.

[0139] <Measurement of maximum value of tanδ> tanδ was measured by the method already described for the MUFS sheet obtained above.

[0140] <Warpage amount> A MUFS sheet was placed on a silicon wafer having a diameter of 12 inches Φ and a thickness of 775 μm, and the MUFS sheet was heat-molded under the following conditions.

[0141] Molding pressure: 5 MPa Molding temperature: 125°C Molding time: 10 minutes Minimum degree of vacuum: 200 Pa Post-mold cure: 150°C for 3 hours or 180°C for 1.5 hours

[0142] The laminate of the silicon wafer and the sealing material after post-mold cure was cooled to room temperature, and the warpage amount was evaluated according to the following criteria. Using a laser displacement meter, on the surface of the silicon wafer not provided with the sealing material, the height difference between the center of the wafer and two points at the edge of the wafer was measured, and the average of these values was calculated and taken as the warpage amount. The warpage amount was evaluated according to the following criteria. The results are shown in each table.

[0143] ○: Warpage is 12 mm or less. △: Warpage is greater than 12 mm.

[0144] [Table 4]

[0145] [Table 5]

[0146] [Table 6]

[0147] From Tables 4-6, it can be seen that when tanδ is less than 6, the amount of warpage is significantly reduced in MUF sealing.

[0148] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention. [Industrial applicability]

[0149] The mold underfill sealing sheet according to the present invention can reduce warping of the substrate when molding underfill sealing an electronic component mounting substrate in which a space is provided between the electronic component and the substrate. Furthermore, it can realize a sealing method for electronic component mounting substrates with excellent MUF (Mold Underfill) properties. The present invention can be used, for example, for sealing integrated circuits and large-scale integrated circuits used in IoT, autonomous driving, etc. [Explanation of Symbols]

[0150] 10: Electronic component mounting board 10S: Space 11: Circuit board 12: Electronic components 121: Bump 20: MUFS Seat 22: Cured product 221: Underfill section 222: Overmolded part 50: Compression molding machine 51: Upper mold 52: Lower mold 53: Flange section F: Border C: Center of the circuit board Point P: Any point on the border line. Lp: Distance between point P and center C Lcp: A straight line passing through point P and center C. S: Outer edge of thermosetting sheet Q: Intersection of Lcp and outer edge S Lq: Distance between point Q and center C

Claims

1. A sheet of thermosetting resin composition, The viscosity increase ratio (V90 / V0), which is the ratio of the viscosity V90 at 90 seconds from the start of viscosity measurement to the viscosity V0 at 0 seconds, is less than 9, and the timing of the start of viscosity measurement is 30 seconds after heating to 125°C. A mold underfill sealing sheet for an electronic component mounting substrate, comprising multiple electronic components and a substrate, wherein a space is provided between the electronic components and the substrate.

2. The sheet according to claim 1, wherein the viscosity at 125°C 20 seconds after the start of the viscosity measurement is 1000 Pa·s or less.

3. The sheet according to claim 1, wherein the maximum value of the tanδ (loss tangent) of the sheet at a measurement temperature of 125°C and a measurement time of 0 to 70 seconds is 0.2 or more.

4. The sheet according to claim 3, wherein the maximum value of tanδ is less than 6.

5. The thermosetting resin composition comprises a main resin, a curing agent, and a filler. The sheet according to claim 1, wherein the content of the filler is 70% by mass or more.

6. The sheet according to claim 5, wherein the maximum particle size of the filler is 35 μm or less.

7. The sheet according to claim 5, wherein the average particle size of the filler is 20 μm or less.

8. The sheet according to claim 1, wherein the thermosetting resin composition comprises at least one selected from the group consisting of a polyol having an alkylene chain, an epoxy resin having an alkylene chain, a polyol having a polyoxyalkylene chain, an epoxy resin having a polyoxyalkylene chain, and a phenolphthalein-type epoxy resin.

9. The sheet according to claim 5, wherein the curing agent comprises a solid phenol novolac resin.

10. A sheet according to any one of claims 1 to 9, having a single-layer structure.

11. The sheet is placed on a silicon wafer with a diameter of 12 inches (Φ) and a thickness of 775 μm. The following conditions: Molding pressure: 5 MPa Molding temperature: 125℃ Molding time: 10 minutes Minimum vacuum degree: 200Pa Post-mold curing: The sheet according to any one of claims 1 to 9, wherein when the sheet is heat-molded at 150°C for 3 hours or 180°C for 1.5 hours, the curing warp after curing is 12 mm or less.

12. (a) A step of preparing an electronic component mounting substrate comprising a plurality of electronic components and a substrate, wherein a space is provided between the electronic components and the substrate; (b) A step of placing a mold underfill sealing sheet, which is a sheet of thermosetting resin composition, on the electronic component mounting substrate so as to be in contact with the electronic component, (c) A step of heating and molding the placed sheet, filling the space between the electronic component and the substrate with the molten sheet and hardening it, Includes, The heating temperature in the aforementioned heat molding is 110°C or higher and 175°C or lower. A method for sealing an electronic component mounting substrate, wherein the viscosity increase ratio (V90 / V0), which is the ratio of the viscosity V90 at 90 seconds from the start of viscosity measurement of the sheet to the viscosity V0 at 0 seconds, is less than 9, and the timing of the start of viscosity measurement is 30 seconds after heating to 125°C.

13. When Lp is the distance between the center of the substrate and any point P on the frame line that encloses all of the aforementioned electronic components and minimizes the enclosed area, The method for sealing an electronic component mounting substrate according to claim 12, wherein the distance Lq between the point Q where the line passing through point P and the center of the substrate intersects with the outer edge of the sheet and the center of the substrate is 0.9Lp or more.

14. A method for sealing an electronic component mounting substrate according to claim 12 or 13, wherein the maximum particle diameter of the filler is smaller than the height (H) of the space between the electronic component and the substrate, and the minimum distance (W) between the electronic components.

15. An electronic component mounting board comprising multiple electronic components and a substrate, wherein a space is provided between the electronic components and the substrate, The present invention comprises a cured mold underfill sealing sheet, which is a sheet of thermosetting resin composition that undermolds the space and overmolds the electronic components, An electronic component mounting substrate encapsulant, wherein the viscosity increase ratio (V90 / V0), which is the ratio of the viscosity V90 at 90 seconds from the start of viscosity measurement to the viscosity V0 at 0 seconds, is less than 9, at a measurement temperature of 125°C and a measurement time of 150 seconds, and the timing of the start of viscosity measurement is 30 seconds after heating to 125°C.

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