Electronic component mounting method and reinforcing adhesive

Abstract

This reduces bonding defects in the reflow process, which involves mounting electronic components onto a substrate using solder paste containing solder particles with a melting point of 150°C or lower, and then bonding the electronic components to the substrate with a reinforcing adhesive. [Solution] An electronic component mounting method comprising: (i) applying a solder paste containing solder particles with a melting point of 150°C or less to the pads of a substrate; (ii) applying a reinforcing adhesive containing a thermosetting resin that hardens at a temperature higher than the melting point of the solder particles and at a temperature of 210°C or less to the substrate; (iii) mounting electronic components on the substrate such that the electronic components and the reinforcing adhesive are in contact, and the terminal electrodes of the electronic components are in contact with the solder paste; and (iv) a reflow process in which the solder particles are melted at a temperature of 210°C or less and the reinforcing adhesive is softened, the reinforcing adhesive is hardened, and then cooled, wherein the consistency of the reinforcing adhesive at room temperature is 240 to 420.

Description

Technical Field

[0001] The present invention relates to an electronic component mounting method for mounting an electronic component on a substrate and a reinforcing adhesive.

Background Art

[0002] Patent Document 1 proposes "an electronic device having a plurality of electronic components each having two or more electrodes, wherein one electronic component and another electronic component among the plurality of electronic components are electrically connected, and an electrode of the one electronic component and an electrode of the other electronic component are joined via a metal, and two or more electrode joints that are electrically insulated from each other are formed, and a gap between one of the electrode joints and the other electrode joint is filled with a thermosetting resin".

[0003] Patent Document 2 proposes "a mounting structure including a semiconductor package having a first electrode, a circuit board having a second electrode, a bonding material including solder disposed between the second electrode and a bump formed on the first electrode for electrically joining the bump and the second electrode, a first reinforcing resin covering the periphery of the bonding material, and a second reinforcing resin covering a gap between an outer peripheral portion of the semiconductor package disposed on the circuit board and the circuit board".

[0004] Patent Document 3 proposes "an electronic component connection structure for electrically connecting an electronic component to a substrate via bumps, wherein an alignment protrusion or depression is provided on an electrode arrangement surface of the electronic component, and a depression or protrusion is provided on the substrate to match the alignment protrusion or depression for mounting the electronic component thereon, and the protrusion melts at a temperature lower than the melting temperature of the bumps, and the protrusion hardens after ensuring the bonding of the bumps".

[0005] Patent Document 4 proposes an electronic component mounting substrate in which an electronic component having a first electrical connection portion and a substrate having second electrical connection portions located at positions corresponding to each of the first electrical connection portions are connected via a current-carrying member that electrically connects the first electrical connection portions and the second electrical connection portions by melting, wherein the electronic component mounting substrate is equipped with a mechanism to prevent crushing of the current-carrying member, which generates a resistance force on the electronic component in the direction opposite to the direction of gravity when the current-carrying member melts, and which also enables horizontal movement of the electronic component. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2013 / 047137 [Patent Document 2] International Publication No. 2013 / 168352 [Patent Document 3] Japanese Patent Publication No. 2002-373914 [Patent Document 4] Japanese Patent Application Publication No. 11-054654 [Overview of the project] [Problems that the invention aims to solve]

[0007] From a carbon-neutral perspective, the process of mounting electronic components onto substrates should ideally be environmentally friendly and low-cost. To achieve this low environmental impact, there is a growing trend towards developing electronic component mounting methods that utilize solder particles that melt at low temperatures. For example, while SnAgCu-based solder has a melting point of around 230°C, SnBi-based solder has a melting point of around 140°C. Using solder particles that melt at low temperatures reduces the power consumption of reflow ovens and eliminates the need for high-heat-resistant materials, thus broadening the range of material choices.

[0008] On the other hand, solder, which melts at low temperatures, has relatively low impact strength, so the development of mounting techniques that use reinforcing adhesives in combination is progressing. Reinforcing adhesives need to have a curing temperature higher than the melting point of solder so as not to interfere with the solder joint of electronic components. Reinforcing adhesives need to have the characteristic of dramatically decreasing shape retention near the melting point of solder so as not to hinder the sinking of electronic components. At the same time, at room temperature, they need to have a certain degree of shape retention so as to be able to contact the electronic components mounted on the substrate, and excessive wetting and spreading must be suppressed. [Means for solving the problem]

[0009] One aspect of the present invention relates to an electronic component mounting method for mounting an electronic component having a component body and terminal electrodes onto a substrate, comprising: (i) applying a solder paste containing solder particles having a melting point of 150°C or less to a land on the substrate; (ii) applying a reinforcing adhesive containing a thermosetting resin that has a melting point higher than the melting point of the solder particles and hardens at a temperature of 210°C or less to the substrate; (iii) mounting the electronic component onto the substrate such that the component body and the reinforcing adhesive are in contact, and the terminal electrodes are in contact with the solder paste; and (iv) a reflow step of melting the solder particles and softening the reinforcing adhesive at a temperature of 210°C or less, hardening the reinforcing adhesive, and then cooling, wherein the consistency of the reinforcing adhesive at room temperature is 240 to 420.

[0010] Another aspect of the present invention relates to a reinforcing adhesive which is applied to a substrate on which a solder paste containing solder particles with a melting point of 150°C or less is applied to the lands, before mounting an electronic component having a component body and terminal electrodes, and which hardens after softening in the reflow process of the solder particles to bond the component body to the substrate, and which contains a thermosetting resin that hardens at a temperature higher than the melting point of the solder and 210°C or less, and has a consistency of 240 to 420 at room temperature. [Effects of the Invention]

[0011] According to the present invention, in a reflow process in which electronic components are mounted on a substrate using solder paste containing solder particles with a melting point of 150°C or lower, and the electronic components are bonded to the substrate with a reinforcing adhesive, bonding defects can be reduced. [Brief explanation of the drawing]

[0012] [Figure 1] This is an explanatory diagram of an electronic component mounting method relating to one embodiment of the present invention. [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described below with examples, but the present invention 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 other materials may be applied as long as the effects of the present invention 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 "numerical value A or greater and numerical value B or less". In the following description, when lower and upper limits are given as examples for numerical values ​​of specific physical properties or conditions, either of the given lower limits and either of the given upper limits can be arbitrarily combined as long as the lower limit does not exceed the upper limit.

[0014] 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.

[0015] <Electronic component mounting method> An electronic component mounting method according to an embodiment of the present invention is an electronic component mounting method for mounting an electronic component having a component body and terminal electrodes on a substrate, comprising: (i) a step of applying a solder paste containing solder particles having a melting point of 150°C or less to the lands of the substrate; (ii) a step of applying a reinforcing adhesive containing a thermosetting resin that has a melting point higher than that of the solder particles and hardens at a temperature of 210°C or less to the substrate; (iii) a step of mounting the electronic component on the substrate such that the component body and the reinforcing adhesive are in contact and the terminal electrodes and the solder paste are in contact; and (iv) a reflow step of melting the solder particles and softening the reinforcing adhesive at a temperature of 210°C or less, hardening the reinforcing adhesive, and then cooling. Here, the consistency of the reinforcing adhesive at room temperature (25°C) is 240 or more and 420 or less.

[0016] Electronic components having a component body and terminal electrodes are electronic components that require reinforcement with a reinforcing adhesive. Such electronic components may also be leaded components having a component body and lead terminals that protrude from the component body as terminal electrodes. Electronic components that require reinforcement with a reinforcing adhesive are typically SOP (Small Outline Package) components, but are not limited to SOP components.

[0017] The substrate on which an electronic component having a component body and terminal electrodes is mounted is not particularly limited. Examples of substrates include semiconductor substrates, glass substrates, resin substrates, and ceramic substrates. Examples of semiconductor substrates include silicon substrates, compound semiconductor substrates, and substrates made of other semiconductors. The substrate has lands (electrodes) formed thereon that are soldered to the terminal electrodes of the electronic component.

[0018] Hereinafter, an electronic component mounting method according to an embodiment of the present invention will be described in detail with reference to the drawings as necessary.

[0019] ≪Process (i)≫ Step (i) is a step of applying cream solder to the lands of the substrate. The cream solder is a mixture of solder particles and flux. Here, cream solder containing solder particles with a melting point of 150°C or lower is used. The solder particles with a melting point of 150°C or lower are alloy particles, and for example, particles such as Sn - Bi - based alloys and Sn - Bi - Ag - based alloys are used. The composition of the flux is not particularly limited.

[0020] FIG. 1(a) is a cross - sectional conceptual diagram of a substrate 100 with lands 101 formed on its surface. FIG. 1(b) shows a state where cream solder 102 is applied to the lands 101.

[0021] In step (i), the method of applying cream solder to the lands of the substrate is not particularly limited, but cream solder may be applied to the lands by screen printing. In screen printing, cream solder can be applied to a plurality of lands on the substrate in a single printing step. For example, a mask plate having a plurality of through - holes is arranged such that the through - holes are located above the lands, and the cream solder supplied to the upper surface of the mask plate is moved with a squeegee to apply the cream solder to the lands through the through - holes.

[0022] ≪Step (ii)≫ Step (ii) is a step of applying a reinforcing adhesive to the substrate. This step is usually performed after step (i). The reinforcing adhesive contains a thermosetting resin. The thermosetting resin has a temperature higher than the melting point of the solder particles and cures at a temperature of 210°C or lower. When the thermosetting resin cures, the reinforcing adhesive also cures.

[0023] Reinforcement adhesive is an insulating material used to bond (adhere) electronic components to a circuit board so that the electronic components mounted on the board by soldering do not fall off the board. Therefore, the reinforcement adhesive 103 needs to be in contact with the electronic components when they are mounted on the circuit board. In other words, at room temperature (for example, 25°C), it needs to have a certain degree of shape retention so that it can contact the electronic components mounted on the circuit board. If the reinforcement adhesive spreads excessively on the circuit board, the height of the reinforcement adhesive will become lower than the gap between the electronic component body and the circuit board, and the reinforcement adhesive will not be able to contact the electronic component.

[0024] On the other hand, in the reflow process, the solder particles contained in the solder paste melt to form molten solder, but it is necessary for the molten solder to wet and spread over the terminal electrodes of the electronic components. This wetting and spreading of the molten solder over the terminal electrodes of the electronic components enables a strong solder joint. Furthermore, it does not hinder the horizontal movement of the electronic components (self-alignment phenomenon). To achieve this, the reinforcing adhesive needs to have a curing temperature higher than the melting point of the solder. In addition, the reinforcing adhesive needs to have a dramatically reduced shape retention near the melting point of the solder so as not to hinder the phenomenon of the electronic components moving closer to the surface of the substrate 100 as the solder particles melt (sinking of the electronic components).

[0025] However, finding a reinforcing adhesive formulation that satisfies the above requirements is not easy. When soldering electronic components to a substrate using solder paste containing solder particles with a melting point of 150°C or lower, the heating temperature in the reflow process is set lower than when using solder paste containing general solder particles, such as Sn-Ag-Cu alloy. In this case, in the temperature range where the solder particles begin to melt, the shape retention of the reinforcing adhesive does not decrease dramatically, resulting in insufficient sinking of the electronic components and defects in the solder joint between the electronic components and the substrate. Adding a considerable amount of thermoplastic resin to the reinforcing adhesive to accelerate the sinking of the electronic components can be considered, but this can lead to a significant decrease in adhesive strength or bonding defects due to incompatibility with the solder.

[0026] In contrast, when mounting electronic components onto a substrate, if contact can be made not only between the reinforcing adhesive and the component body of the electronic component, but also between the solder paste and the terminal electrodes of the electronic component, then it is not necessary to consider the sinking of the electronic component. To achieve this, a reinforcing adhesive should be used that, at room temperature (e.g., 25°C), has sufficient shape retention to allow contact with the electronic component before mounting it onto the substrate, and that, once mounted onto the substrate, can deform sufficiently so that the distance between the terminal electrodes and the land is reduced, allowing the terminal electrodes to contact the solder paste. Specifically, the consistency of the reinforcing adhesive at room temperature (25°C) should be controlled to be between 240 and 420. When mounting electronic components onto a substrate via a reinforcing adhesive with a consistency between 240 and 420, contact between the reinforcing adhesive and the component body of the electronic component, and contact between the solder paste (molten solder) and the terminal electrodes of the electronic component can be ensured.

[0027] It should be noted that when electronic components are mounted on a substrate, it is not necessary for the terminal electrodes of all electronic components mounted on the substrate to be in contact with the solder paste. Typically, multiple electronic components that require reinforcement with reinforcing adhesive are mounted on a substrate. It is sufficient that at least one terminal electrode of the electronic components requiring reinforcement with reinforcing adhesive be in contact with the solder paste. In that case, even for electronic components whose terminal electrodes are not in contact with the solder paste, the distance between the terminal electrode and the land is considered to be sufficiently reduced. Therefore, even if the shape deformation of the reinforcing adhesive due to heating during the reflow process is slight, the terminal electrode can come into contact with the solder paste and the solder paste can spread and wet the terminal electrode. However, it is preferable that the terminal electrodes of the majority of the electronic components requiring reinforcement with reinforcing adhesive be in contact with the solder paste when the electronic components are mounted on the substrate.

[0028] If the consistency is less than 240, when electronic components are mounted on the substrate via reinforcing adhesive, the reinforcing adhesive does not deform sufficiently, and the distance between the terminal electrodes and the pads cannot be sufficiently reduced. As a result, the terminal electrodes of many electronic components cannot make contact with the solder paste.

[0029] On the other hand, if the consistency exceeds 420, when the reinforcing adhesive is applied to the substrate, the reinforcing adhesive spreads excessively over the substrate, causing the height of the reinforcing adhesive to become lower than the gap between the electronic component body and the substrate, preventing the reinforcing adhesive from making contact with the electronic component. From the viewpoint of sufficiently suppressing such defects, it is necessary, for example, for 90% or more of the electronic component requiring reinforcement with the reinforcing adhesive to be in contact with the reinforcing adhesive, and preferably for 99% or more to be in contact with the reinforcing adhesive.

[0030] In this specification, the consistency of the reinforcing adhesive is the value (mixed consistency) measured according to the procedure of the mixing consistency test specified in JIS (Japanese Industrial Standards) K2220:2013. In the examples, the consistency was measured using a 1 / 2 cone. The measured consistency was then converted to the consistency when using a standard cone according to the above JIS standard. The converted consistency was then used as the consistency of the reinforcing adhesive.

[0031] The consistency of the reinforcing adhesive is 240 or higher, but may be 245 or higher, 250 or higher, or 300 or higher. The consistency of the reinforcing adhesive is 420 or lower, but may be 415 or lower, or 400 or lower. The consistency of the reinforcing adhesive is in the range of 240 to 420, may be in the range of 245 to 420, or may be in the range of 250 to 400.

[0032] In step (ii), a suitable method for applying the reinforcing adhesive to the substrate is, for example, using a dispenser. Using a dispenser allows the reinforcing adhesive to be applied in a protruding manner to the area on the substrate where the electronic component body will be mounted. By applying the reinforcing adhesive in a protruding manner, the probability of the reinforcing adhesive coming into contact with the component body when the electronic component is mounted on the substrate can be increased.

[0033] Figure 1(c) shows the state in which the reinforcing adhesive 103 is applied in a protruding manner to the area on the substrate 100 where the component body of the electronic component is mounted, using a dispenser. By applying the reinforcing adhesive 103 in a protruding manner, the reinforcing adhesive can be made to come into contact only with the component body without coming into contact with the terminal electrodes.

[0034] ≪Process (iii)≫ Step (iii) is the process of mounting electronic components onto a substrate such that the component body and the reinforcing adhesive are in contact, and the terminal electrodes are in contact with the solder paste. The reinforcing adhesive is applied, for example, to a location opposite the center of the component body of the electronic component. The solder paste is applied, for example, to multiple locations surrounding the component body. The reinforcing adhesive has a consistency of 240 to 420, so it has high shape retention, and the peaks of the reinforcing adhesive are higher than the peaks of the solder paste. Therefore, the electronic component in the process of mounting first comes into contact with the reinforcing adhesive. Subsequently, the reinforcing adhesive is deformed as it is pressed towards the substrate by the electronic component. At this time, the reinforcing adhesive deforms easily because it has a consistency of 240 to 420. As a result, the terminal electrodes of the electronic component come into contact with the solder paste on the land.

[0035] Figure 1(d) shows the state in which the electronic component 200, which is an SOP component, is mounted on the substrate 100 such that the component body 202 of the electronic component 200 is in contact with the reinforcing adhesive 103, and the terminal electrodes 201 are in contact with the solder paste 102. If the consistency of the reinforcing adhesive 103 is less than 240, the reinforcing adhesive 103 cannot be deformed by the load during component mounting as shown in the example, and the probability that the terminal electrodes 201 will not be in contact with the solder paste 102 increases. Furthermore, in the subsequent reflow process, the heating temperature is set low according to the melting point of the solder, so the reinforcing adhesive 103 cannot be sufficiently softened. As a result, defects occur in the solder joint. On the other hand, if the consistency of the reinforcing adhesive 103 exceeds 420, dripping (spreading onto the substrate) of the reinforcing adhesive 103 becomes significant, and the reinforcing adhesive 103 cannot be applied in a protruding shape as shown in Figure 1(c), and the probability that the electronic component 200 will not be in contact with the reinforcing adhesive 103 increases.

[0036] ≪Process (iv)≫ Step (iv) is the reflow process for the substrate on which the electronic components are mounted. The substrate on which the electronic components are mounted passes through a reflow oven set to a maximum temperature of 210°C or less. During heating, the solder particles melt and the reinforcing adhesive softens. Since the curing temperature of the reinforcing adhesive is higher than the melting temperature of the solder particles, the reinforcing adhesive remains in a molten state for a while before curing. During this time, the movement of the electronic components is not hindered, so the solder paste spreads sufficiently over the terminal electrodes. In this state, a self-alignment phenomenon may occur, but the reinforcing adhesive does not hinder this self-alignment phenomenon. Subsequently, the reinforcing adhesive hardens. After that, as the substrate cools, the solder solidifies and the solder joint is completed.

[0037] Figure 1(e) shows the state of the substrate after soldering is complete. The terminal electrodes 210 of the electronic component 200 and the lands 102 of the substrate 100 are joined by solder 102a that has solidified after melting, and the component body 210 of the electronic component 200 and the substrate 100 are joined by reinforcing adhesive 103a that has hardened after softening.

[0038] In step (iv), the maximum temperature of the reflow process is 210°C or lower, but may also be 195°C or lower, or 180°C or lower. When using solder paste containing solder particles with a melting point of 150°C or lower, the temperature at which the solder particles melt and the reinforcing adhesive softens and hardens can be set as low as described above.

[0039] (Reinforcement adhesive) The reinforcing adhesive is a resin composition containing a thermosetting resin (i.e., a thermosetting resin composition). The thermosetting resin composition applied using a dispenser is a liquid composition that is fluid at room temperature (25°C) before curing. The reinforcing adhesive (thermosetting resin composition) can be prepared by mixing a thermosetting resin with, for example, a curing agent, a filler, a coupling agent, a pigment, etc.

[0040] The reinforcing adhesive has a consistency of 240 to 420, resulting in low viscosity while maintaining high shape retention. The consistency of the reinforcing adhesive can be adjusted by changing the components and their ratios.

[0041] The thermosetting resin is not particularly limited, but may include epoxy resins, urethane resins, acrylic resins, polyimide resins, polyamide resins, bismaleimide, phenolic resins, polyester resins, silicone resins, oxetane resins, and the like. These may be used individually or in combination of two or more types. Among these, epoxy resins are particularly preferred due to their excellent heat resistance and adhesive properties.

[0042] Suitable epoxy resins include, for example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, biphenyl type epoxy resin, naphthalene type epoxy resin, phenol novolac type epoxy resin, and cresol novolac type epoxy resin. Modified epoxy resins of these can also be used. These may be used individually or in combination of two or more types.

[0043] Thermosetting resins include liquid epoxy resins and solid epoxy resins at room temperature (25°C). Since reinforcing adhesives are liquid compositions, it is preferable that they contain liquid thermosetting resin as the main component. Liquid epoxy resin is preferred as the liquid thermosetting resin. Furthermore, mixing a small amount of solid epoxy resin with liquid epoxy resin at room temperature (25°C) makes it easier to control the consistency of the reinforcing adhesive between 240 and 420.

[0044] When using both liquid and solid epoxy resins, a good mass ratio of solid epoxy resin to 100 parts by mass of liquid epoxy resin is, for example, 1 to 15 parts by mass, but may also be 3 to 12 parts by mass, or 5 to 10 parts by mass.

[0045] Examples of curing agents that can be used in combination with the thermosetting resins described above include thiol compounds, modified amine compounds, polyfunctional phenol compounds, imidazole compounds, and acid anhydride compounds. These may be used individually or in combination of two or more. The amount of curing agent used is appropriately selected depending on the type and equivalent amount of the thermosetting resin. As a curing agent, a solid curing agent at room temperature (25°C) is preferred because it makes it easy to control the consistency of the reinforcing adhesive between 240 and 420. For example, when using epoxy resin as the thermosetting resin, an imidazole compound that is solid at room temperature (25°C) is preferred.

[0046] By appropriately selecting fillers, various physical properties can be imparted to reinforcing adhesives. For example, a reinforcing adhesive may include a first filler that controls the consistency of the reinforcing adhesive. The reinforcing adhesive may further include a second filler that enhances the thixotropy of the reinforcing adhesive.

[0047] As the first filler, an inorganic material that can impart high strength to the cured product of the reinforcing adhesive is preferred. For example, fused silica, crystalline silica, alumina, magnesium oxide, silicon nitride, talc, mica, and kaolin can be used as the first filler. The higher the content of the first filler in the reinforcing adhesive, the higher the strength of the cured product of the reinforcing adhesive and the lower the consistency of the reinforcing adhesive. Among the first fillers, fused silica is preferred because it has few impurities and excellent fluidity, and spherical fused silica is particularly preferred.

[0048] When epoxy resin is used as the thermosetting resin, a good mass ratio of the first filler to 100 parts by mass of liquid epoxy resin is, for example, 5 to 35 parts by mass, and may also be 10 to 30 parts by mass. The volume-based average particle diameter D50 of spherical fused silica, measured by a laser diffraction scattering particle size distribution analyzer, is, for example, 1 μm to 50 μm, and may also be 1 to 30 μm.

[0049] As the second filler, from the viewpoint of improving the shape retention of the reinforcing adhesive, fumed silica, alumina, titania, modified urea, amide wax, etc., having an average particle size smaller than spherical fused silica are preferred. When epoxy resin is used as the thermosetting resin, a good mass ratio of the second filler to 100 parts by mass of liquid epoxy resin is, for example, 0.5 to 5 parts by mass, and may also be 1 to 3 parts by mass. The volume-based average particle diameter D50 of fumed silica, measured by a laser diffraction scattering particle size distribution analyzer, is, for example, 100 nm or less.

[0050] While it is permissible to use a small amount of thermoplastic resin to adjust the physical properties of the reinforcing adhesive, it is preferable that the reinforcing adhesive does not contain thermoplastic resin from the viewpoint of enhancing the reinforcing effect of the solder joint. That is, the content of thermoplastic resin that may be included in the reinforcing adhesive is preferably 3% by mass or less, more preferably 1% by mass or less, and most preferably 0% by mass.

[0051] (Note) The following technologies are disclosed as described above. (Technology 1) An electronic component mounting method for mounting an electronic component having a component body and terminal electrodes onto a substrate, (i) A step of applying solder paste containing solder particles with a melting point of 150°C or lower to the pads of a substrate, (ii) A step of applying a reinforcing adhesive to the substrate, which includes a thermosetting resin that hardens at a temperature higher than the melting point of the solder particles and at a temperature of 210°C or lower, (iii) A step of mounting the electronic component onto the substrate such that the component body and the reinforcing adhesive are in contact and the terminal electrodes and the solder paste are in contact, (iv) A reflow process in which the solder particles are melted at a temperature of 210°C or lower, the reinforcing adhesive is softened, the reinforcing adhesive is cured, and then cooled; It is equipped with, An electronic component mounting method wherein the consistency of the reinforcing adhesive at room temperature is 240 to 420. (Technology 2) In step (i) above, the solder paste is applied to the land by screen printing, The electronic component mounting method according to Technology 1, wherein in step (ii) above, the reinforcing adhesive is applied to the substrate in a protruding manner using a dispenser. (Technology 3) The electronic component mounting method according to Technology 1 or 2, wherein the electronic component is a leaded component having a component body and lead terminals protruding from the component body as terminal electrodes. (Technology 4) The reinforcing adhesive comprises a first filler and a second filler. The first filler has the effect of increasing the consistency of the reinforcing adhesive, The method for mounting electronic components according to any one of the technologies 1 to 3, wherein the second filler has the effect of increasing the thixotropy of the reinforcing adhesive. (Technology 5) The first filler contains spherical fused silica, The method for mounting electronic components according to any one of the technologies 1 to 4, wherein the second filler comprises fumed silica having an average particle size smaller than that of the spherical fused silica. (Technology 6) An electronic component mounting method according to any one of the technologies 1 to 5, wherein in step (iv), the solder particles are melted at a temperature of 195°C or lower, the reinforcing adhesive is softened, and then the reinforcing adhesive is cured. (Technology 7) A reinforcing adhesive is applied to a substrate on which a solder paste containing solder particles with a melting point of 150°C or less has been applied to the land, before mounting an electronic component having a component body and terminal electrodes, and which hardens after softening during the reflow process of the solder particles to bond the component body to the substrate, It contains a thermosetting resin that hardens at a temperature higher than the melting point of the aforementioned solder and at 210°C or lower. A reinforcing adhesive having a consistency of 240 to 420 at room temperature. (Technology 8) A reinforcing adhesive according to Technical Reference 7, which is applied to the substrate in a protruding manner by a dispenser. (Technology 9) The reinforcing adhesive according to Technical Reference 7 or 8, wherein the electronic component is a leaded component having a component body and lead terminals protruding from the component body as terminal electrodes. (Technology 10) A first filler and a second filler are included. The first filler has the effect of increasing the consistency of the reinforcing adhesive, The second filler is a reinforcing adhesive according to any one of the technologies 7 to 9, wherein the second filler has the effect of increasing the thixotropy of the reinforcing adhesive. (Technology 11) The first filler contains spherical fused silica, The reinforcing adhesive according to Art 10, wherein the second filler comprises fumed silica having an average particle size smaller than that of the spherical fused silica. (Technology 12) A reinforcing adhesive according to any one of the technologies 7 to 11, comprising a hardening agent that is solid at room temperature. (Technology 13) The reinforcing adhesive according to any one of the arts 7 to 12, wherein the thermosetting resin comprises an epoxy resin that is solid at room temperature. (Technology 14) A reinforcing adhesive described in any one of the technologies 7 to 13, which does not contain thermoplastic resins.

[0052] [Examples] The present disclosure will be further explained below based on examples and comparative examples. In the following examples and comparative examples, several reinforcing adhesives with different consistencys were prepared and evaluated.

[0053] <Examples 1-3, Comparative Examples 1 and 2> Thermosetting resin compositions with the compositions shown in Table 1 were prepared as reinforcing adhesives. The reinforcing adhesives of Examples 1 to 3 are referred to as adhesives A1 to A3, and the reinforcing adhesives of Comparative Examples 1 and 2 are referred to as adhesives B1 and B2.

[0054] Specifically, each adhesive contains epoxy resin A (bisphenol A type epoxy resin) that is liquid at room temperature (25°C), epoxy resin B (novolac type epoxy resin) that is solid at room temperature (25°C), an imidazole-based curing agent that is solid at room temperature (25°C), a first filler (spherical fused silica (average particle size D50 = 200 μm)) for adjusting consistency, and a second filler (fumed silica (average particle size D50 = 30 nm)) that enhances thixotropy.

[0055] The consistency of adhesives A1-A3, B1, and B2 was measured at 25°C using the method described above. The results are shown in Table 1.

[0056] [Table 1]

[0057] Tests were conducted to reproduce the conditions for mounting electronic components (SOP components: PI-SOP8 JEDEC 150mil-JA) using the prepared adhesives A1-A3, B1, and B2. Specifically, as shown in Figure 1(b), solder paste was screen printed onto multiple lands (0.72mm x 1.27mm, Cu-OSP (organic coating for rust prevention)) on a copper-clad laminate substrate (0.8mm thick) using a 150μm thick metal mask. The solder paste used was made from Sn-Bi alloy particles (particle size 20-38μm) with a melting point of approximately 140°C.

[0058] Next, the adhesive was applied to one location on the circuit board opposite the center of the SOP component body using a dispenser, creating a protrusion. The application area (maximum diameter D of the contact area between the circuit board and the reinforcing adhesive) was set to 0.8 mmΦ ± 0.1 mm.

[0059] Next, the center of the adhesive on the substrate was aligned with the center of the component body of the SOP component, and the SOP component was mounted on the substrate. A predetermined mounting load (2N) was then applied to the SOP component from above using a pressing member for approximately 2 seconds. Ten SOP components were mounted on the substrate for each adhesive.

[0060] Subsequently, the substrate lands and the terminal electrodes of the SOP components were soldered together in a nitrogen stream in the reflow oven, and the adhesive was cured. The maximum temperature of the reflow oven was set to 180°C.

[0061] [evaluation] The number of defective solder joints was visually counted, and the defect rate relative to the total was calculated. Additionally, the number of defects where the adhesive and SOP components were not in contact was visually identified, and the defect rate relative to the total was calculated. The results are shown in Table 1.

[0062] Table 1 shows that when the consistency of the adhesive at room temperature (25°C) is between 240 and 420, it is possible to achieve highly reliable reinforcement of solder joints with the reinforcing adhesive in an electronic component mounting process in which solder paste containing solder particles with a melting point of 150°C or less is applied to the pads of a substrate. [Industrial applicability]

[0063] This disclosure can be used for electronic component mounting, which involves mounting electronic components onto a substrate using solder paste containing solder particles with a melting point of 150°C or lower, and joining the electronic components to the substrate with a reinforcing adhesive. [Explanation of Symbols]

[0064] 100: Circuit board, 101: Land, 102: Solder paste, 102a: Solder that has solidified after melting, 103: Reinforcement adhesive, 103a: Reinforcement adhesive that has hardened after softening, 200: Electronic component, 201: Terminal electrode, 202: Component body

Claims

1. An electronic component mounting method for mounting an electronic component having a component body and terminal electrodes onto a substrate, (i) A step of applying a solder paste containing solder particles with a melting point of 150°C or lower to the pads of a substrate, (ii) A step of applying a reinforcing adhesive to the substrate, which includes a thermosetting resin that hardens at a temperature higher than the melting point of the solder particles and at a temperature of 210°C or lower, (iii) A step of mounting the electronic component on the substrate such that the component body and the reinforcing adhesive are in contact and the terminal electrodes and the solder paste are in contact, (iv) A reflow process in which the solder particles are melted at a temperature of 210°C or lower, the reinforcing adhesive is softened, the reinforcing adhesive is cured, and then cooled. It is equipped with, An electronic component mounting method wherein the consistency of the reinforcing adhesive at room temperature is 240 to 420.

2. In step (i) above, the solder paste is applied to the land by screen printing, The method for mounting electronic components according to claim 1, wherein in step (ii) above, the reinforcing adhesive is applied to the substrate in a protruding manner using a dispenser.

3. The method for mounting an electronic component according to claim 1, wherein the electronic component is a leaded component having a component body and lead terminals protruding from the component body as terminal electrodes.

4. The reinforcing adhesive comprises a first filler and a second filler. The first filler has the effect of controlling the consistency of the reinforcing adhesive, The method for mounting electronic components according to claim 1, wherein the second filler has the effect of increasing the thixotropy of the reinforcing adhesive.

5. The first filler contains spherical fused silica, The method for mounting electronic components according to claim 1, wherein the second filler comprises fumed silica having an average particle size smaller than that of the spherical fused silica.

6. The method for mounting electronic components according to claim 1, wherein in step (iv), the solder particles are melted at a temperature of 195°C or lower, the reinforcing adhesive is softened, and then the reinforcing adhesive is cured.

7. A reinforcing adhesive is applied to a substrate on which a solder paste containing solder particles with a melting point of 150°C or less has been applied to the land, before mounting an electronic component having a component body and terminal electrodes, and which hardens after softening during the reflow process of the solder particles to bond the component body to the substrate, The material contains a thermosetting resin that hardens at a temperature higher than the melting point of the solder and at 210°C or lower. A reinforcing adhesive having a consistency of 240 to 420 at room temperature.

8. The reinforcing adhesive according to claim 7, which is applied to the substrate in a protruding manner by a dispenser.

9. The reinforcing adhesive according to claim 7, wherein the electronic component is a leaded component having a component body and a lead terminal protruding from the component body as a terminal electrode.

10. A first filler and a second filler are included. The first filler has the effect of controlling the consistency of the reinforcing adhesive, The reinforcing adhesive according to claim 7, wherein the second filler has the effect of increasing the thixotropy of the reinforcing adhesive.

11. The first filler contains spherical fused silica, The reinforcing adhesive according to claim 10, wherein the second filler comprises fumed silica having an average particle size smaller than that of the spherical fused silica.

12. The reinforcing adhesive according to claim 7, comprising a curing agent that is solid at room temperature.

13. The reinforcing adhesive according to claim 7, wherein the thermosetting resin includes an epoxy resin that is solid at room temperature.

14. A reinforcing adhesive according to claim 7, which does not contain a thermoplastic resin.

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