JP2018126787A - Solder paste and mounting structure acquired with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solder paste that solves existing problems and strikes a balance between excellent repairing property and high-adhesion maintained at service temperature of a semiconductor component, and to provide a mounting structure.SOLUTION: A solder paste is constituted of solder powder and flux. The flux contains an epoxy resin, a hardening agent, a rubber modified epoxy resin and an organic acid. The solder paste includes 3 wt.% to 35 wt.% the rubber modified epoxy resin based on the total weight of the flux.SELECTED DRAWING: Figure 1

Description

  The present invention mainly relates to a solder paste containing an epoxy resin in a flux component among solder pastes used when soldering a semiconductor component or an electronic component to a circuit board, and a mounting structure obtained thereby. .

  In recent years, mobile devices such as mobile phones and PDAs (Personal Digital Assistants) are becoming smaller and more functional. As mounting technology that can cope with this, mounting structures such as BGA (Ball Grid Array) and CSP (Chip Scale / Size Package) are often used. Mobile devices are subject to mechanical loads such as drop impacts. A QFP (Quad Flat Package) is used to absorb an impact at the lead portion. It has become important to ensure impact resistance reliability even in BGA, CSP, and the like that do not have a lead that reduces impact.

  The melting point of Sn-Pb eutectic solder, which is a conventional representative solder, is 183 ° C, but the melting point of Ag-Sn-Cu based solder, which is a typical lead-free solder, is Sn-Pb eutectic solder. The maximum temperature of the profile of the reflow furnace is as high as 220 to 260 ° C. For this reason, when a component with low resistance to high temperature is mounted on a circuit board, only that component is spot soldered in a separate process, and the productivity is significantly reduced.

  Therefore, low melting point Pb-free solders such as Sn—Zn, Sn—Ag—In, and Sn—Bi, which have a lower melting point than Sn—Ag—Cu solder (hereinafter referred to as SAC solder), are used. I'm starting. However, the connection reliability of the solder connection portion of the BGA connection using Sn—Zn, Sn—Ag—In, and Sn—Bi solder, in particular, the shock resistance reliability has not been sufficiently established yet. .

  Therefore, as described in Patent Documents 1 and 2, a resin flux solder paste (hereinafter also simply referred to as a solder paste) in which a thermosetting resin is contained in a flux in order to increase the impact resistance reliability of the connection portion is used. A semiconductor mounting structure and a method for manufacturing the same have been proposed. Conventional solder pastes as described in Patent Documents 1 and 2 form a reinforcing structure in which the periphery of the solder is covered with the resin by separating the resin and the solder in the process of heating to melt and connect the solder. As a result of this reinforcement, the strength of the solder connection portion can be increased and the impact resistance reliability can be improved. Such a mounting process is actually performed by printing a solder paste on a predetermined position such as a wiring electrode of a circuit board using a metal mask or the like and then heating in a reflow furnace. At this time, the resin flux expresses the action of chemically removing the oxide film on the surface of the metal to be soldered and the oxide film on the surface of the solder powder by a reduction reaction, that is, the flux action, and in addition, melts the connection part Connecting. Thereafter, since the curing of the epoxy resin proceeds, it is possible to perform the bonding of the circuit board wiring electrode and the component and the resin reinforcement in one heating reflow process.

Japanese Patent No. 5373464 Japanese Patent No. 5357784

  It is preferable that the solder paste can be removed, that is, repaired after the mounted semiconductor component is inspected. It is important for cost reduction to remove only defective semiconductor components and re-install new semiconductor components instead of discarding the entire board when a connection failure occurs due to the mounting of expensive semiconductor components. This is because. However, since the solder paste described in Patent Document 1 or 2 uses a thermosetting resin for the reinforcing epoxy resin of the solder coating portion, it is considered that it cannot be removed by being melted with heat like solder. Since the joint formed by the solder paste described in Patent Document 1 or 2 is slightly softened by heating to a glass transition temperature Tg or higher, it is removed by applying a mechanically strong force at a temperature of Tg or higher. It is considered possible, but its removal is considered to be very time consuming. Also, since many conventional solder pastes use general bisphenol-based epoxies, they have high adhesion even at Tg or higher, so they can be peeled off together with the solder resist on the circuit board due to the force of peeling. Therefore, it is very difficult to re-mount (repair) a good semiconductor element.

  The present invention solves the above-mentioned conventional problems, and provides a solder paste and a mounting structure that have excellent repair properties at high temperatures while having high adhesion at room temperature, which is the operating temperature of semiconductor components. With the goal.

  The solder paste of the present invention is composed of solder powder and a flux, and the flux contains an epoxy resin, a curing agent, a rubber-modified epoxy resin, and an organic acid, and the rubber-modified epoxy resin is the whole of the flux. It is contained at a ratio of 3% to 35% by weight with respect to the weight. The mounting structure of the present invention is a mounting structure in which an electronic component is mounted using the solder paste, wherein the electronic component and the circuit board are metal-bonded, and the periphery of the conductive portion is the And a reinforcing part formed by being covered with a cured product of flux.

  According to the solder paste of the present invention, it is possible to form a joint that can be easily removed at high temperatures while having high adhesion at room temperature, which is the operating temperature of the semiconductor component.

It is sectional drawing of the ball | bowl part of CSP joined using the solder paste in embodiment of this invention. It is sectional explanatory drawing which showed typically the joining process of the ball | bowl part of CSP using the solder paste in embodiment of this invention. It is sectional explanatory drawing which showed typically the joining process of the ball | bowl part of CSP using the solder paste in embodiment of this invention. It is sectional explanatory drawing which showed typically the joining process of the ball | bowl part of CSP using the solder paste in embodiment of this invention. It is sectional explanatory drawing which showed typically the joining process of the chip components using the solder paste in embodiment of this invention. It is sectional explanatory drawing which showed typically the joining process of the chip components using the solder paste in embodiment of this invention. It is sectional explanatory drawing which showed typically the joining process of the chip components using the solder paste in embodiment of this invention. It is the cross-sectional schematic diagram which showed the shear strength measuring method of chip components.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  The solder paste of the present invention contains solder powder and flux, and may contain other components as necessary. FIG. 1 is a cross-sectional view of a CSP bonded using the solder paste of the present invention. The solder for joining the circuit boards 1 and 3 contains solder powder and flux so that the solder bumps 5 and the circuit board 3 are joined metallically, and the conductive part 9 derived from the solder powder part, and the conductive part The joint part which consists of the reinforcement part 6b formed by the circumference | surroundings being covered with the hardened | cured material of flux is obtained. As described above, the presence of the flux-derived reinforcing portion 6b around the conductive portion 9 to be joined metallically can increase the strength of the solder joint portion and improve the impact resistance reliability.

  The flux contained in the solder paste of the present invention contains an epoxy resin, a curing agent, a rubber-modified epoxy resin, and an organic acid, and may contain other components as necessary. When the rubber-modified epoxy resin is contained in the flux contained in the solder paste of the present invention, the solder paste has toughness. Further, the rubber-modified epoxy resin is reacted and crosslinked to form a jungle gym structure. In this structure, the rubber-modified epoxy resin tends to cause a spring-like molecular vibration, and thus exhibits a low elastic modulus at a high temperature. Therefore, the solder joint formed by the solder paste of the present invention can be removed with a slight external force at a high temperature and has excellent repairability. The rubber-modified epoxy resin is used in a proportion of 3% to 35% by weight with respect to the total weight of the flux. By using the rubber-modified epoxy resin in such a range of content, it is possible to form a joint having particularly excellent repair properties at high temperatures.

  Furthermore, by using an epoxy resin having a butadiene skeleton as the rubber-modified epoxy resin, the adhesiveness of the solder paste at a high temperature is reduced as compared with those not containing an epoxy resin having a butadiene skeleton, thereby facilitating removal. And the repair process can be made easier. The epoxy resin having a butadiene skeleton can be used in an arbitrary ratio with respect to the other components, but is preferably used in a ratio of 2 wt% to 30 wt% with respect to the total weight of the flux. By using the epoxy resin having a butadiene skeleton in such a content range, the adhesiveness of the solder paste at a high temperature can be more effectively reduced.

  In addition, by using an epoxy resin having a urethane skeleton as a rubber-modified epoxy resin, the adhesion of the solder paste at room temperature can be improved as compared with a product that does not contain an epoxy resin having a urethane skeleton. It becomes possible to improve the connection reliability. The epoxy resin having a urethane skeleton can be used in an arbitrary ratio with respect to the other components, but is preferably used in a ratio of 1% by weight to 20% by weight with respect to the total weight of the flux. When the epoxy resin having a urethane skeleton is used in such a content ratio, the adhesion of the solder paste at room temperature can be more effectively improved.

  As the rubber-modified epoxy resin, both an epoxy resin having a butadiene skeleton and an epoxy resin having a urethane skeleton can be used. As a result, a solder paste having both high adhesion at room temperature and low adhesion at high temperature can be obtained. can get. The epoxy resin having a butadiene skeleton can be used in any ratio with respect to the other components, but is preferably used in a ratio of 2 wt% to 20 wt% with respect to the total weight of the flux. The epoxy resin having a urethane skeleton can be used in an arbitrary ratio with respect to other components, but is preferably used in a ratio of 1% by weight to 15% by weight with respect to the total weight of the flux. When the rubber-modified epoxy resin is used in such a content range, high adhesion at room temperature and excellent repairability at high temperature can be effectively realized.

  The solder powder contained in the solder paste of the present invention is an arbitrary solder powder containing Sn, and is 22 wt% to 68 wt% Bi, 0 wt% to 2 wt% Ag, and 0 wt% to A solder powder containing 73 wt% In and the balance being Sn can be used. Specifically, 42Sn-58Bi, 42Sn-57Bi-1.0Ag, 16Sn-56Bi-28In, and the like can be used, but are not limited thereto. When the ratio of each component of the solder powder is in the above range, the melting point of the solder powder used in the solder paste of the present invention is lower than 200 ° C.

  Examples of other components of the flux contained in the solder paste of the present invention include commonly used modifiers and additives. Moreover, a solvent or diluent having a low boiling point can be added for the purpose of reducing the viscosity of the solder paste and imparting fluidity. Furthermore, it is also effective to add hardened castor oil or stearamide as a thixotropic agent for maintaining the printed shape.

  Below, the component of the solder paste of this invention is demonstrated in detail.

<Solder powder>
In the solder paste of one embodiment of the present invention, it is preferable to use a solder powder having a melting point of 200 ° C. or lower as the solder powder. Although the minimum of melting | fusing point of a solder particle is not specifically limited, It is preferable that it is 130 degreeC or more. When the melting point of the solder powder is 200 ° C. or less, the solder paste has a lower melting point than the melting point (220 ° C.) of the tin-silver-copper (SAC) solder powder used for the solder balls of BGA and CSP semiconductors. Therefore, the remelting of the SAC solder powder can be prevented. The composition of the solder powder is not particularly limited. For example, an alloy based on Sn can be used, and 22 wt% to 68 wt% Bi, 0 wt% to 2 wt% Ag, and 0 wt%. A solder powder containing ˜73 wt% In and the balance being Sn can be used. Specifically, SnBi-based 42Sn-58Bi, 42Sn-57Bi-1.0Ag, 16Sn-56Bi-28In, and the like are preferably used. The content of the solder powder with respect to the total mass of the solder paste of the present invention is in the range of 40 wt% to 95 wt%, more preferably 78 wt% to 85 wt%. When the content of the solder powder in the solder paste of the present invention is in the above range, it is possible to effectively realize high connection reliability of the joint and excellent printing workability of the paste.

  The composition of the solder powder in this specification is expressed by connecting element symbols of elements contained in the solder powder with hyphens. In the present specification, to describe the metal composition of the solder powder, a numerical value or a numerical range may be indicated immediately before the metal element, which is generally used in the art. The mass% (=% by weight) of each element in the composition is indicated by a numerical value or a numerical range. As long as the solder powder is substantially composed of the elements listed, the solder powder is inevitably mixed in and may contain a metal such as Ni, Zn, Sb, or Cu.

  The melting point of the solder powder in this specification refers to the temperature at the end of melting when a change in the state of the sample in the process of heating and heating is observed, and can be measured using DSC, TG-DTA, or the like.

<Flux>
The flux in the present invention includes an epoxy resin, a rubber-modified epoxy resin, a curing agent, and an organic acid (activator). Moreover, the flux in this invention can also contain a hardening accelerator other than an epoxy resin and a hardening | curing agent as a resin component as needed. The content of the flux with respect to the total mass of the solder paste of the present invention is in the range of 5% to 60% by weight, more preferably 22% to 15% by weight. When the content of the flux in the solder paste of the present invention is within the above range, high connection reliability of the joint and excellent printing workability of the paste can be effectively realized. Hereinafter, each component contained in the resin flux will be described in more detail.

(Epoxy resin)
The epoxy resin generally refers to a thermosetting resin that has an epoxy group in the structure and can be cured by heating. In the present invention, an epoxy resin that is liquid at room temperature is used. When the epoxy resin is liquid at room temperature, other components such as solder powder can be easily dispersed. In the present specification, the term “liquid at normal temperature” means having fluidity in a temperature range of 5 to 28 ° C. under atmospheric pressure, particularly around 20 ° C. at room temperature. The epoxy resin that is liquid at room temperature is not particularly limited as long as it has two or more epoxy groups in one molecule, and various types can be used. Specifically, for example, various liquid epoxy resins such as glycidyl ether type, glycidyl amine type, glycidyl ester type, and olefin oxidation type (alicyclic) can be used. More specifically, for example, bisphenol type epoxy resins such as bisphenol A type epoxy resins and bisphenol F type epoxy resins, hydrogenated bisphenol type epoxy resins such as hydrogenated bisphenol A type epoxy resins and hydrogenated bisphenol F type epoxy resins, Biphenyl type epoxy resin, naphthalene ring-containing epoxy resin, alicyclic epoxy resin, dicyclopentadiene type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, triphenylmethane type epoxy resin, aliphatic epoxy resin, tri Glycidyl isocyanurate or the like can be used. These may be used alone or in combination of two or more. Among these, bisphenol-type epoxy resins and hydrogenated bisphenol-type epoxy resins are preferred as liquid epoxy resins at room temperature in consideration of lowering the viscosity of the liquid epoxy resin composition for semiconductor encapsulation and improving the physical properties of the cured product. Moreover, a solid epoxy resin can also be used together at normal temperature. As an epoxy resin that is solid at room temperature, for example, a biphenyl type epoxy resin, a dicyclopentadiene type epoxy resin, a triazine skeleton epoxy resin, or the like can be used. The epoxy resin is preferably used in the range of 50% by mass to 90% by mass, particularly in the range of 66% by mass to 82% by mass with respect to the total mass of the flux. When the content of the epoxy resin in the flux of the present invention is in the above range, the connection reliability of the joint can be effectively improved.

  In general, epoxy resins are used for adhesives, paints, electrical and electronic materials and the like because of their advantages such as high adhesion and insulating properties. However, an essential drawback is a lack of toughness. Since it is rigid, cracks and the like are likely to occur due to mechanical load. Specifically, since the parts are peeled off when a mechanical load is applied to the connection parts of the parts, the reliability life is shortened. To make the epoxy resin tough, flexible resin polymer alloy (IPN interpenetrating network polymer, that is, tough thermoplastic polymer added to form various mixed forms) or sea-island structure Forming various rubber skeletons, for example, forming a polymer alloy of an epoxy resin and an acrylic resin, and forming a sea-island structure of an epoxy resin and a silicone resin, etc. . These are techniques for producing special low-elasticity properties by creating micro-localized states of a plurality of different types of resins, but it is quite difficult to stably produce the dispersed state. Therefore, the solder paste of the present invention is added with a rubber-modified epoxy resin containing an epoxy group that is a functional group that imparts crosslinkability in the structure and a functional group that imparts toughness to the solder paste. Yes.

(Rubber-modified epoxy resin)
As the rubber-modified epoxy resin in the present invention, an epoxy resin having a structure including an epoxy group and a functional group that imparts toughness to the solder paste is used. The functional group that imparts toughness to the solder paste is a functional group that is excellent in elasticity against mechanical and thermal stimuli, and in order to impart high toughness to the epoxy resin, A functional group capable of imparting toughness to a cured product. The functional group for imparting toughness to the hardened product of the solder paste has a structure capable of improving stretchability, and an example thereof is a structure bent at a certain angle. Examples of the functional group include, but are not limited to, a butadiene group, a urethane group, an alkylene ether group, and a fatty acid group. The rubber-modified epoxy resin in the present invention has the above-described structure, and thus exhibits a spring-like stretchability at room temperature. However, at a high temperature, particularly at Tg or more, the molecular mobility becomes very large and the elasticity becomes low. Therefore, since the solder paste of the present invention includes the rubber-modified epoxy resin having the above structure, the formed joint can be removed by a slight external force, and therefore, the joint having excellent repairability at high temperature can be obtained. Can be formed.

（Ｘ，Ｙは、繰り返し係数） A rubber-modified epoxy resin having a butadiene skeleton in a molecule has both a butadiene structure and an epoxy group in the molecule, and thus has both high adhesive strength and toughness. The arrangement of the butadiene skeleton in the rubber-modified epoxy resin having a butadiene skeleton in the molecule includes those in the main chain (including 1,4-polybutadiene) and those in the side chain (including 1,2-polybutadiene). However, both can exhibit rubber properties and can be used suitably. In addition, polybutadiene hydrogenated to the double bond portion exhibits similar rubber properties, and since it has no double bond, it is difficult to oxidize and exhibits excellent heat resistance. It is preferably liquid because it is used as a flux component, but it is liquefied by using it together with a liquid epoxy resin, or liquefied by adding a solvent, and is a rubber-modified epoxy having a butadiene skeleton in the molecule. Resin can be used. When a rubber-modified epoxy resin having a butadiene skeleton in the molecule reacts with a curing agent and is incorporated into a crosslinked structure, even if it has a relatively hard structure at room temperature, in a high temperature environment (specifically, 160 ° C., etc.) Since the molecular motion becomes intense, the butadiene skeleton expands and contracts like rubber, and the cured product becomes very low elastic. Therefore, by using a rubber-modified epoxy resin having a butadiene skeleton in the molecule as the rubber-modified epoxy resin, a solder paste that adheres firmly to the substrate at room temperature and has low adhesion under a high temperature environment can be obtained. This solder paste can be easily removed by applying a physical force with a spatula or the like in a high-temperature environment. An example of a rubber-modified epoxy resin having a butadiene skeleton in the molecule is shown in Chemical Formula 1, but the structure is not limited to Chemical Formula 1. Any epoxy resin having a butadiene skeleton and an epoxy group in the molecule. Can be used. Specific examples of commercially available materials include Epolide PB3600, PB4700 (both are Daicel Chemical), Nisseki Polybutadiene E-1000-3.5 (Nippon Petrochemical), R-15EPT, R-45EPT (Nagase Chemtech), and the like. It is done.

(X and Y are repetition factors)

（Ｒはアルキル基、Ｚは脂肪族骨格、ｍ，ｎは繰り返し係数） A rubber-modified epoxy resin having a urethane skeleton in the molecule has both high adhesive strength and toughness by having both a urethane structure and an epoxy group in the molecule. One example is shown in Chemical Formula 2, but the structure is not limited to Chemical Formula 2, and any epoxy resin having a urethane skeleton and an epoxy group in the molecule can be used. The urethane skeleton is generally formed by a reaction between a polyol and a polyisocyanate, and is further prepared by introducing an epoxy group therein, but the preparation process is not particularly limited. As long as it has both a urethane skeleton and an epoxy group, other main chain skeletons may have various structures (for example, an aliphatic skeleton). Also, it is preferably liquid because it is used as a flux component, but it is liquefied by using it together with a liquid epoxy resin, or liquefied by adding a solvent. Epoxy resins can be used. When a rubber-modified epoxy resin having a urethane skeleton in a molecule reacts with a curing agent and is incorporated into a cross-linked structure, a high shear adhesive force is exhibited at room temperature due to the tough structure of the urethane skeleton. Therefore, by using a rubber-modified epoxy resin having a urethane skeleton in the molecule as a rubber-modified epoxy resin, even if a shearing force is applied to a chip component or the like at room temperature, the urethane skeleton does not easily crack, A solder paste having characteristics that do not easily peel off can be obtained. As described above, the cured product of the rubber-modified epoxy resin having a urethane skeleton can exhibit high shear peeling resistance. Specific examples of commercially available materials include EPU-7N and EPU-73B (ADEKA).

(R is an alkyl group, Z is an aliphatic skeleton, m and n are repetition coefficients)

  The rubber-modified epoxy resin is preferably contained in the solder paste at a ratio of 3% to 35% by weight with respect to the total weight of the flux. By including the rubber-modified epoxy resin in the solder paste so as to have such a ratio with respect to the total weight of the flux, it is possible to effectively improve the connection reliability of the formed joint part and the repair property at high temperature. Can be increased.

  The adhesion strength when the chip component is mounted and connected to the circuit board using the solder paste using the rubber-modified epoxy resin containing the butadiene skeleton described above is rubber-modified in the high temperature range above Tg of the resin flux. This is significantly reduced as compared with the case where a solder paste not containing an epoxy resin is used. That is, the joint formed by the solder paste using the rubber-modified epoxy resin containing the butadiene skeleton described above can be easily removed by raising the temperature. Furthermore, when the epoxy resin containing a butadiene skeleton is used as the rubber-modified epoxy resin in the solder paste and the content is 2 wt% to 30 wt% with respect to the total weight of the flux, the solder paste is excellent. The printability is also shown.

  The adhesion strength when a chip component is mounted and connected to a circuit board using a solder paste using a rubber-modified epoxy resin containing a urethane skeleton of the present invention is a solder that does not contain a rubber-modified epoxy resin at room temperature. It becomes high compared with the case where a paste is used. An epoxy resin containing a urethane skeleton as a rubber-modified epoxy resin is used for the solder paste, and particularly when the content is 1 wt% to 20 wt% with respect to the total weight of the flux, excellent printing The sex etc. were shown. On the other hand, the adhesion strength when the chip component is mounted and connected to the circuit board using the solder paste using the rubber-modified epoxy resin containing the urethane skeleton described above is in a high temperature range above Tg of the resin flux. Compared with the case of using a solder paste containing no rubber-modified epoxy resin, it is significantly reduced. That is, the solder paste using the rubber-modified epoxy resin containing the butadiene skeleton described above can be easily removed by raising the temperature.

  Further, both a rubber-modified epoxy resin containing a butadiene skeleton and a rubber-modified epoxy resin containing a urethane skeleton can be used in combination. The content of the epoxy resin containing the butadiene skeleton is 2% by weight to 20% by weight with respect to the total weight of the flux, and the content of the epoxy resin containing the urethane skeleton is the total weight of the flux. The adhesion strength when the chip component is mounted and connected to the circuit board using a solder paste of 1% to 15% by weight with respect to the solder paste includes a rubber-modified epoxy resin in the high temperature range above the Tg of the resin flux. It has been found that it is low compared to a solder paste that does not contain rubber-modified epoxy resin at room temperature. That is, it has been clarified that by adjusting the content ratios of the two kinds of rubber-modified epoxy resins, it is possible to realize a high adhesion property at room temperature and a low adhesion property at high temperature.

(Curing agent)
As the curing agent, general epoxy resin curing agents can be used, such as acid anhydrides, phenol novolacs, various thiol compounds, various amines, dicyandiamide, imidazoles, metal complexes and their adduct compounds. For example, an adduct modification product of polyamine can be used, but it is not limited thereto. In particular, various imidazoles can be preferably used because they are excellent in both compatibility with one component and solder meltability. Examples of imidazoles include 2MZ, C11Z, 2PZ, 2E4MZ, 2P4MZ, 1B2MZ, 1B2PZ, 2MZ-CN, 2E4MZ-CN, 2PZ-CN, C11Z-CN, 2PZ-CNS, C11Z-CNS, 2MZ-A, and C11Z. -A, 2E4MZ-A, 2P4MHZ, 2PHZ, 2MA-OK, 2PZ-OK (manufactured by Shikoku Kasei Kogyo Co., Ltd., product name) and compounds obtained by adding these imidazoles to an epoxy resin can be used. However, it is not limited to these. In addition, it is also possible to use a microcapsule obtained by coating these curing agents with a polyurethane-based or polyester-based polymer substance. The amount of the curing agent used can be appropriately set, but it is preferable that the stoichiometric equivalent ratio of the curing agent to the epoxy equivalent of the epoxy resin is in the range of 0.8 to 1.2. When the content of the curing agent is in the above range, the connection reliability of the formed joint part and the repair property at a high temperature can be effectively enhanced.

(Curing accelerator)
As the curing accelerator, in addition to the imidazoles, for example, tertiary amines, 1,8-diazabicyclo (5.4.0) undecene-7, 1,5-diazabicyclo (4.3.0) nonene-5, etc. Cyclic amines and their tetraphenylborate salts, trialkylphosphines such as tributylphosphine, triarylphosphines such as triphenylphosphine, tetraphenylphosphonium tetraphenylborate and tetra (n-butyl) phosphonium tetraphenylborate Metal complexes such as quaternary phosphonium salts and Fe acetylacetonate and their adduct compounds can be used. The blending amount of these curing accelerators is appropriately set in consideration of gelation time and storage stability. When the content of the curing accelerator in the flux of the present invention is in the above range, the connection reliability of the formed joint part and the repair property at high temperatures can be effectively enhanced.

(Organic acid)
The kind of organic acid (activator) is not particularly limited, and any organic compound acid can be used. For example, rosin component materials represented by abietic acid, various amines and salts thereof, sebacin salt, adipine Acid, glutaric acid, succinic acid, malonic acid, citric acid, pimelic acid, and the like can be used. In particular, the organic acid has an excellent flux action (here, the flux action is a reduction action that removes the oxide film formed on the metal surface to which the solder paste is applied, and the surface tension of the molten solder is reduced. , Meaning the action of promoting the wettability of the solder to the metal surface. These organic acids may be one type of component or a mixture of two or more types of components. Of these organic acids, adipic acid and glutaric acid are preferable because they are excellent in fluxing action and have high stability as compounds. The amount of the organic acid used can be appropriately set, but it is preferable that the stoichiometric equivalent ratio of the organic acid to the epoxy equivalent of the epoxy resin is in the range of 0.8 to 1.2. When the content of the organic acid is in the above range, the connection reliability of the formed joint part and the repair property at high temperatures can be effectively enhanced.

  An example of the method for adjusting a solder paste and the method for manufacturing a mounting structure according to the present invention will be described below.

  First, an epoxy resin, a curing agent, a rubber-modified epoxy resin and an organic acid, and optionally a curing accelerator are weighed and mixed to create a flux. Furthermore, the solder paste of this invention is obtained by adding and mixing and kneading solder powder to the created flux.

  Using the obtained solder paste of the present invention, a semiconductor component can be mounted on a circuit board or the like having a conductor wiring, and the mounting structure of the present invention can be manufactured. The solder paste is applied to the circuit board by, for example, stacking a metal mask having a plurality of through holes at the same position as each electrode on the circuit board on the circuit board, and then applying the solder paste of the present invention to the surface of the metal mask. It can be performed by supplying and filling the through hole with a squeegee. Thereafter, the metal mask is removed from the circuit board to obtain a circuit board on which a solder paste is applied to each electrode.

  Next, the chip component or the semiconductor component is stacked on the circuit board using a chip mounter or the like so that the terminal of the chip component or the semiconductor component and the electrode of the circuit board face each other while the solder paste is in an uncured state. Here, chip resistors, chip capacitors, and the like are mounted as chip components. In addition to semiconductor packages such as CSP and BGA formed by providing solder balls as terminals and QFP formed by providing leads as terminals, the semiconductor components were formed by providing terminals without being accommodated in the package. A semiconductor element (bare chip) can be used.

  In this state, the printed wiring board on which the chip components are arranged is heated to a predetermined heating temperature in a reflow furnace. The heating temperature can be appropriately set to a temperature at which the solder powder is sufficiently melted and the curing reaction of the resin component sufficiently proceeds. The heating temperature is preferably set so that the curing reaction of the epoxy resin proceeds before the solder powder is completely melted and the aggregation and melting of the solder particles are not hindered. A preferable heating temperature for this is equal to or higher than the melting point of the solder powder and equal to or higher than the curing temperature of the flux containing the resin. Specifically, the heating temperature is 10 ° C. higher than the melting point of the solder powder. The temperature does not exceed ℃.

  Through the above-described steps, the semiconductor device of the present invention can be manufactured that includes a joint portion in which the terminals of the semiconductor component and the electrodes of the circuit board are connected via the solder paste of the present invention. The joint portion includes a solder powder, a conductive portion in which the solder balls are fused and integrated, and a reinforcing portion that is a cured epoxy resin portion that covers the periphery of the conductive portion. As described above, according to the solder paste of the present invention, it is possible to manufacture a mounting structure in which a component and a substrate are electrically joined by a conductive portion and mechanically reinforced by a reinforcing portion.

  2A to 2C are cross-sectional explanatory views schematically showing a process of connecting the CSP ball portion in the embodiment of the present invention. 2A, the electrode 2 provided on the circuit board 1 and the electrode 4 provided on the circuit board 3 are joined with a solder bump 5 and a solder paste 7, and then shown in FIG. 2B. As shown in FIG. 2C, the mounting structure having the reinforcing portion 6b and the conductive portion 9 is manufactured by heat curing with the dryer 8 as described above.

  3A to 3C are cross-sectional explanatory views schematically showing a joining process of chip components joined using the solder paste in the embodiment of the present invention. As shown in FIG. 3A, a chip component 10 is mounted on a solder paste 7 applied on an electrode 4 provided on a circuit board 1 and is heated and cured by a dryer 8, whereby solder contained in the solder paste. A structure as shown in FIG. 3B is formed in which the powder is melted and / or agglomerated and the periphery of the solder and the lower part of the chip are covered with the epoxy resin 6a extruded by the surface tension and / or agglomeration force of the solder powder. The Thereafter, the epoxy resin 6a is cured by heating and curing with the dryer 8, and a mounting structure having the reinforcing portion 6b and the conductive portion 9 as shown in FIG. 3C is manufactured.

  FIG. 4 is a schematic view showing a method for measuring the shear strength of chip components joined using the solder paste of the present invention shown in FIG. The chip parts are fixed to a heatable hot plate stage 12 and are pressed horizontally using a shearing jig 11 to measure the adhesion strength.

  Examples of the present invention and comparative examples are shown below. The following embodiments of the present invention and comparative examples are merely illustrative, and do not limit the present invention.

(Creation of solder paste)
First, the epoxy resin, the rubber-modified epoxy resin, the organic acid, and the curing agent are respectively weighed so as to occupy the weight parts shown in Table 1 in the solder paste, and put in a planetary mixer. Each component was kneaded and uniformly dispersed in the epoxy resin to prepare fluxes of Examples 1 to 10 and Comparative Examples 1 to 4. As the epoxy resin, jER806, which is a bisphenol F type epoxy resin manufactured by Japan Epoxy Resin Co., Ltd., was used. As the rubber-modified epoxy resin, R-15EPT, which is a polybutadiene-modified epoxy resin manufactured by Nagase Chemtech Co., Ltd., and EPU-7N, which is a urethane-modified epoxy resin manufactured by ADEKA Corporation, were appropriately used. As the organic acid, glutaric acid manufactured by Kanto Chemical Co., Ltd. was used. As a curing agent, 2P4MHZ (2-phenyl-4-methyl-5-hydroxymethylimidazole), which is an imidazole-based curing agent manufactured by Shikoku Kasei Kogyo Co., Ltd., was used.

  Next, the solder powder is added to the fluxes of Examples 1 to 10 and Comparative Examples 1 to 4 obtained as described above in such a ratio as to occupy parts by weight described in Table 1, and further kneaded. By doing so, the solder paste was adjusted. For the solder powders of Examples 1 to 6 and 8 to 10, those having the solder composition 42Sn-58Bi defined in JIS H42B: 58A were used, and for the solder powder of Example 7, 42Sn-57Bi-1. 0 Ag was used. Solder powder was produced according to a conventional method. The solder particles had an average particle size of 15 μm and a melting point of 139 ° C.

  In the present specification, the average particle size is a particle size (D50) at which the cumulative value is 50% in a cumulative curve obtained by obtaining a particle size distribution on a volume basis and setting the total volume to 100%. The average particle diameter can be measured using a laser diffraction / scattering particle diameter / particle size distribution measuring apparatus or an electronic scanning microscope.

(Creation of adhesion evaluation element)
The solder paste prepared as described above is printed on the Au-plated electrode on the circuit board (FR-4 board) using a metal mask so that the thickness becomes 0.1 mm, and solder A paste printing part was formed.

  Then, a chip resistor (tin electrode) having a size of 3.2 mm × 1.6 mm was mounted on a solder paste printing portion on the circuit board using a chip mounter. The circuit board was made of copper as the electrode material and glass epoxy material as the board material. Then, the junction part was formed by heating at 160 degreeC for 6 minute (s) using the reflow apparatus, and the evaluation element was created.

(Evaluation)
The printability of the solder paste was evaluated by observing the shape of the solder paste printed using a metal mask. The observation was performed on the state of fitting in the electrode area, the sagging, and the sharp shape by visual observation. The evaluation results of Examples 1 to 10 and Comparative Examples 1 to 4 are shown in Table 1 as the characteristics of the solder paste in each example. In the table, the evaluation of printability was determined by the shape when the paste was transferred onto the electrode of the circuit board through the through hole of the mask. ○ that the shape is held in the electrode part and that can be mounted is ○, that there is a bridge between the electrodes, or that the electrode is exposed ×, that the mounting is possible but the shape is partly collapsed (sag or Those with sharp edges) were marked △.

  By measuring the shear adhesion force at 20 ° C. of the adhesive evaluation element prepared as described above using DAGE's Series 4000 which is a bond tester schematically shown in FIG. The paste was evaluated for room temperature adhesion. The evaluation results of Examples 1 to 10 and Comparative Examples 1 to 4 are shown in Table 1 as the characteristics of the solder paste in each example. In the table, if the load applied to the joint exceeds 20 kgf (196 N), the product where the joint did not break is broken, and the load applied to the joint is damaged within the range of 20 kgf or less, 14 kgf or more (196 N or less, 137.2 N or more) △ was given to cause the damage, and x was given to the case where the load applied to the joint was less than 14 kgf (137.2 N).

  Further, as shown in FIG. 4, the hot plate is heated in a state where the evaluation element is fixed to the hot plate stage 12, the evaluation element is heated to 160 ° C., and the shear adhesion is measured in the same manner as described above. Thus, the high temperature adhesion of the solder paste was evaluated. The evaluation results of Examples 1 to 10 and Comparative Examples 1 to 4 are shown in Table 1 as the characteristics of the solder paste in each example. In the table, when the load applied to the joint is 3 kgf (29.4 N) or less and the joint can be removed, the load applied to the joint is 4 kgf or more and 7 kgf or less (19.6 N or less and 68.6 N or more). The case where the joint part could be removed within the range was indicated by Δ, and the part where the joint part did not come off unless a load applied to the joint part was 8 kgf (78.4 N) or more.

  A comprehensive evaluation ◎ if all three types of evaluations were ◯, a comprehensive determination ◯ if there were two ◯, a comprehensive determination Δ if there was one ◯, and a comprehensive determination × if there was even one x.

  In Example 1, 42Sn-58Bi (shown as SB in the table) was used as the type of solder powder, and the solder powder was used so that 80 parts by weight of solder paste was 100 parts by weight. The polybutadiene-modified epoxy resin is used so as to occupy 30 parts by weight (30 phr) when the weight of the flux (the total weight of components other than the solder powder of the solder paste) is 100 parts by weight. Further, urethane-modified epoxy resin is not included. The activator and the curing agent are contained so as to be 40% by weight and 20% by weight, respectively, when the weight of the epoxy resin (not including the rubber-modified epoxy resin) is 100.

  The printability of Example 1 was determined to be Δ because the shape was slightly sharpened. Since the adhesiveness of the joint part of Example 1 was 14 kgf at room temperature, it was remarkably reduced to 0.5 kgf at 160 ° C. Therefore, it can be said that Example 1 has excellent repairability at high temperatures. .

  In Example 2, the kind of solder powder used was 42Sn-58Bi as in Example 1, and the solder ratio with respect to 100 parts by weight of the solder paste was 82% by weight. The ratio of polybutadiene-modified epoxy resin was 15 phr, and the ratio of urethane-modified epoxy resin was 5 phr. The activator and the curing agent were used so that the ratio to the weight of the epoxy resin was 40% by weight and 20% by weight, respectively, as in Example 1.

  Since the printability of the paste of Example 2 was good, it was evaluated as “Good”. Moreover, although room temperature adhesiveness is high compared with the thing which does not contain the rubber modification epoxy of the comparative example 1, since the adhesiveness in 160 degreeC is reduced compared with room temperature adhesiveness, it has excellent repair property. I could say I have it.

  For Examples 3 to 6 and 8 to 10, the solder paste was prepared in the same manner as in Example 1 except that the ratio of the solder powder and the like to 100 parts by weight of the solder paste was changed as shown in Table 1. The printability and adhesion results were as shown in Table 1.

  In Example 7, the solder paste was adjusted under the same conditions as Example 3 except that the type of solder powder was 42Sn-57Bi-1.0Ag (shown as SBA in the table). The printability and adhesion results were as shown in Table 1.

  In Comparative Example 1, a solder paste was prepared without using a rubber-modified epoxy resin. The ratio of solder powder to 100 parts by weight of the solder paste is as shown in Table 1. Although there was no particular problem in the printability of the solder paste of Comparative Example 1, the room temperature adhesion was x because the breakage occurred due to a load below 15 kgf (147 N), and the overall judgment was x.

  In Comparative Example 2, a polybutadiene-modified epoxy resin was used so that the ratio was 50 phr, and the solder paste was adjusted so that the solder ratio was 78% by weight without using the urethane-modified epoxy resin. The solder paste of Comparative Example 2 was confirmed to be sharp and was damaged by a load of 5 kgf lower than 15 kgf. Therefore, the printability and the room temperature adhesion were x, and the overall judgment was x.

  In Comparative Example 3, the urethane-modified epoxy resin was used so that the ratio became 40 phr, and the solder paste was adjusted so that the solder ratio became 80% by weight without using the polybutadiene-modified epoxy resin. Since the solder paste of Comparative Example 3 was confirmed to be sharp, the printability was x, and the comprehensive judgment was x.

  In Comparative Example 4, the polybutadiene-modified epoxy resin and the urethane-modified epoxy resin were used so as to be 30% by weight and 20% by weight, respectively, with respect to the total weight of the flux. The ratio of solder powder to 100 parts by weight of the solder paste is as shown in Table 1. Since the solder paste of Comparative Example 4 was confirmed to be sharp, the printability was x, and the comprehensive judgment was x.

  From the results shown in Table 1, by including 3 wt% to 35 wt% of the rubber-modified epoxy resin in the solder paste containing the epoxy resin, the curing agent, the organic acid, and the solder powder, the semiconductor component It has been clarified that a solder paste can be obtained that can form a joint that can be easily removed at a high temperature while having high adhesion at room temperature, which is the temperature of use.

  More specifically, when the rubber-modified epoxy resin is an epoxy resin containing a butadiene skeleton and is contained in 2% to 30% by weight in the total flux, the adhesion strength of the chip component is the resin. It has been found that the temperature is lower in the high temperature region above the Tg of the flux as compared with the solder paste not containing the rubber-modified epoxy resin. Further, when the rubber-modified epoxy resin is an epoxy resin containing a urethane skeleton and is contained in 1% to 20% by weight in the total flux, the adhesion strength of the chip component is rubber-modified at room temperature. It was found to be higher than the solder paste that does not contain epoxy resin.

  Furthermore, as a rubber-modified epoxy resin, an improvement in adhesion was also observed for those containing both an epoxy resin containing a butadiene skeleton and an epoxy resin containing a urethane skeleton. More specifically, the epoxy resin containing a butadiene skeleton is contained in an amount of 2 to 20% by weight in the total flux, and 1 to 15% by weight in the total epoxy resin flux containing a urethane skeleton. The solder paste contained shows lower adhesion than the solder paste not containing the rubber-modified epoxy resin in the high temperature range above the Tg of the resin flux, and higher than the solder paste not containing the rubber-modified epoxy resin at room temperature. It has been shown that it can exhibit both high adhesion at room temperature and low adhesion at high temperatures.

  The solder paste and mounting structure of the present invention can be used in a wide range of applications in the field of electric / electronic circuit formation technology. For example, it can be used for connecting electronic parts such as CCD elements, holographic elements, chip parts and the like and joining them to a substrate. Products incorporating these elements, components, or substrates, such as DVDs, mobile phones, etc. It can be used for portable AV devices, digital cameras, and the like.

DESCRIPTION OF SYMBOLS 1 Circuit board 2 Electrode 3 Circuit board 4 Electrode 5 Solder bump 6a Epoxy resin 6b Reinforcement part 7 Solder paste 8 Dryer 9 Conductive part 10 Chip component 11 Shearing jig 12 Hot plate stage

Claims (8)

  A solder paste composed of solder powder and a flux, wherein the flux includes an epoxy resin, a curing agent, a rubber-modified epoxy resin, and an organic acid, and the rubber-modified epoxy resin is a total weight of the flux. Solder paste, contained in a proportion of 3% to 35% by weight.   2. The solder paste according to claim 1, wherein the rubber-modified epoxy resin includes an epoxy resin having a urethane skeleton at a ratio of 1 wt% to 20 wt% with respect to the total weight of the flux.   2. The solder paste according to claim 1, wherein the rubber-modified epoxy resin contains an epoxy resin having a butadiene skeleton at a ratio of 2 wt% to 30 wt% with respect to the total weight of the flux.   The rubber-modified epoxy resin includes an epoxy resin having a butadiene skeleton at a ratio of 2% by weight to 20% by weight with respect to the total weight of the flux, and an epoxy resin having a urethane skeleton at a ratio of 1% by weight to 15% by weight. The solder paste according to claim 1, comprising:   The solder powder contains 22 wt% to 68 wt% Bi, 0 wt% to 2 wt% Ag, and 0 wt% to 73 wt% In, with the balance being Sn. The solder paste according to any one of the above.   A mounting structure in which a component is mounted on a circuit board using the solder paste according to claim 2 or 4, wherein the adhesion strength between the component and the circuit board at room temperature does not include the rubber-modified epoxy resin. Mounting structure that is higher than when used with solder paste.   A mounting structure in which a component is mounted on a circuit board using the solder paste according to claim 3 or 4, wherein the adhesion strength between the component and the circuit board in a high temperature region above the glass transition temperature of the flux is The mounting structure is reduced as compared with the case where the solder paste not containing the rubber-modified epoxy resin is used.   A mounting structure in which a component is mounted on a circuit board using the solder paste according to any one of claims 1 to 5, wherein the component and the circuit board are metal-bonded, and the conductive portion, A mounting structure comprising: a reinforcing portion formed by covering the periphery of the conductive portion with a cured product of the flux.

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