JP2020089897A - Solder paste and mounting structure - Google Patents

Abstract

To provide a solder paste which can be applied for even solder connection which requires a high melting point and has excellent coating workability, high adhesion and excellent solder connection reliability, and a mounting structure in which an electronic component is mounted by use of the solder paste.SOLUTION: A solder paste contains solder powder and flux, the flux contains an epoxy resin, a phenol resin, a benzoxazine compound and an activator, the phenol resin is contained at a ratio less than 58.9% by mass to total mass of the flux, and the activator is contained at a ratio more than 1.3% by mass to total mass of the flux. A mounting structure, in which an electronic component is mounted on a circuit board by use of the solder paste, comprises a conductive part in which the electronic component and the circuit board are metal-joined, and a reinforcement part which is formed in sucha manner that a circumference of the conductive part is covered with the hardened flux.SELECTED DRAWING: Figure 1

Description

The present invention mainly relates to a solder paste containing a epoxy component as a flux component among solder pastes used for soldering semiconductor components or electronic components to a circuit board, and a mounting structure.

In recent years, mobile devices such as mobile phones and PDAs (Personal Digital Assistants) are becoming smaller and more sophisticated. As a mounting technique capable of coping with this, a mounting structure such as BGA (Ball Grid Array) or CSP (Chip Scale Package) is often used. Mobile devices are easily exposed to mechanical loads such as drop impact. In the QFP (Quad Flat Package), the lead portion absorbs impact. However, it is becoming important to secure impact resistance reliability in BGA or CSP which does not have a lead for cushioning impact. In particular, heat cycle resistance and heat resistance have become important with the recent trend toward higher functionality and higher power of conductor devices. For automotive applications, strict vibration resistance and heat resistance due to the mounting of semiconductor devices within the engine rules are required. Therefore, high solder connection reliability in device mounting has become essential, and a structural method and a solder material that can realize it are desired.

As a structural method for improving solder connection reliability, an underfill material is used for mounting BGA and CSP. In the mounting structure using the underfill material, the electronic component and the circuit board are connected by melting solder balls (for example, Sn—Ag—Cu solder balls), and the periphery of the solder is filled with epoxy resin or the like. It is a technique. The underfilled electronic parts are covered with resin around the solder, which allows external forces such as thermal expansion and contraction, vibration, and drop stress to be dispersed in the surrounding resin instead of being concentrated on the solder. it can. Therefore, high connection reliability can be exhibited. However, in such a mounting method, it is necessary to fill the gap between the electronic component and the circuit board of about several tens of microns with the underfill material by the force of the capillary tube. Therefore, the mounting time per device becomes long. Moreover, since the underfill material is thermally cured after the filling, the process is further lengthened and the cost is increased accordingly.

Therefore, as a further measure, a semiconductor mounting structure using a solder paste containing a thermosetting resin for the flux and a method for manufacturing the same have been proposed (for example, refer to Patent Document 1).

A solder paste containing a thermosetting resin (hereinafter, also simply referred to as a solder paste) separates the resin contained in the flux from the solder in the process of heating and melting and connecting the solder, and the resin covers the periphery of the solder. A reinforcing structure may be formed. As a result of the reinforcement, it becomes possible to increase the strength of the solder connection portion.

In the mounting process using the solder paste, the wiring electrodes of the circuit board are printed at predetermined positions using a metal mask, and then heated in a reflow oven. At that time, the flux acts to chemically remove 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, to act as a flux, thereby enabling the melt connection of the solder. Then, the thermosetting resin such as epoxy resin is further cured, and the wiring electrode of the circuit board and the electronic component are bonded and the resin is reinforced in one heating reflow process.

On the other hand, as a solder material, Pb eutectic solder has conventionally been typically used, but nowadays lead-free solder is used in consideration of the environment. For example, lead-free solders include Sn-Bi solders, Sn-Ag-Cu solders (hereinafter also simply referred to as SAC solders), Sn-Cu solders, and the like. In mounting using SAC solder or the like, In-containing solder having a different metal composition has been put into practical use as a measure for achieving high connection reliability. Typical examples of the SAC solder include SAC305 (Sn-3.0Ag-0.5Cu) solder (hereinafter also simply referred to as SAC305 solder) and SAC105 (Sn-1.0Ag-0.5Cu) solder having a lower silver ratio. (Silver ratio 1%) (hereinafter, also simply referred to as SAC105 solder) has been studied and gradually put into practical use.

Japanese Patent No. 5204241

As described above, according to the solder paste containing the thermosetting resin in the flux, the connection reliability can be improved by the reinforcing structure formed of the resin without causing the problems of the process delay and the cost. However, what has been put into practical use as such a solder paste is one that uses a low melting point solder such as Sn—Bi solder as shown in Patent Document 1. For example, a solder paste containing a thermosetting resin using a high melting point solder such as SAC solder has hardly been put into practical use.

Specifically, in the case of Sn—Bi solder having a low melting point as shown in Patent Document 1, since the melting point is about 139° C., the epoxy resin, which is a thermosetting resin after the solder is melted Hardening occurs. Therefore, the solder joint portion (conductive portion) and the resin reinforcing portion can be preferably formed. On the other hand, for example, in order to sufficiently melt the SAC305 solder having a melting point of about 219° C. in the reflow profile, it is necessary to raise the peak temperature of the mounting reflow furnace to 240 to 260° C. Generally, the epoxy resin, which is a thermosetting resin in the flux of the solder paste, usually starts the curing reaction at 100 to 150°C. Therefore, in the reflow profile, before the solder particles dispersed in the solder paste are melted and aggregated, the epoxy resin starts to harden and thickens, which makes it difficult to suitably form a solder joint portion or the like. Further, the epoxy resin has a very high curing speed at a high temperature of around 200° C. as compared with a temperature of around 150° C., and is solidified in a short time. Therefore, particularly in the case of solder having a high melting point, it becomes very difficult to form the solder joint portion and the resin reinforcing portion with the solder paste containing the thermosetting resin.

As described above, there is a demand for a solder paste capable of suitably forming a solder joint portion and a resin reinforcing portion even if a reflow profile that passes through a high melting point is performed.

Therefore, the present invention can be applied to a solder connection requiring a high melting point, and has a solder paste having excellent coating workability, high adhesion, and excellent solder connection reliability, and an electronic component mounted using the same. The purpose of the present invention is to provide a mounting structure.

Even if a mixture containing only the epoxy resin and the phenol resin, which does not contain a commonly used curing accelerator, is heated at a high temperature of about 240° C. for 1 hour, the resin curing hardly progresses. However, it was found that by adding an appropriate amount of the benzoxazine compound to the mixture, resin curing occurs at a high temperature of about 240° C. and a short time of about several minutes. Further, it has been found that a suitable solder paste can be obtained by further adding an appropriate amount of activator to the mixture containing the benzoxazine compound in order to exert the flux effect.

According to the first aspect of the present invention, there is provided a solder paste containing a solder powder and a flux,
The flux contains an epoxy resin, a phenol resin, a benzoxazine compound and an activator,
The phenol resin is contained in a ratio of less than 58.9% by mass with respect to the total mass of the flux,
The activator is contained in a ratio of more than 1.3% by mass based on the total mass of the flux,
Solder paste is provided.

In one aspect of the first aspect of the present invention, the solder powder may be Sn—Ag—Cu based solder or Sn—Cu based solder having a melting point of 200° C. or higher.

In one aspect of the first aspect of the present invention, the epoxy resin is contained in a proportion of 20% by mass or more and 60% by mass or less based on the total mass of the flux,
The phenol resin is contained in a proportion of 10% by mass or more and 40% by mass or less based on the total mass of the flux,
The benzoxazine compound is contained in a proportion of 5% by mass or more and 30% by mass or less with respect to the total mass of the flux,
The activator may be included in a ratio of 3% by mass or more and 40% by mass or less based on the total mass of the flux.

In one aspect of the first aspect of the present invention, the activator may be an organic acid.

In the aspect of the first aspect of the present invention, the organic acid may have a melting point of 130°C or higher and 220°C or lower.

In one aspect of the first aspect of the present invention, the phenol resin may be a phenol novolac resin having a softening point of 60° C. or higher and 110° C. or lower and a hydroxyl equivalent of 70 g/eq or higher and 150 g/eq or lower.

In one aspect of the first aspect of the present invention, the benzoxazine compound may be a polyvalent oxazine having a plurality of oxazine rings in the molecule.

In one aspect of the first aspect of the present invention, the solder powder may be contained in a ratio of 50% by mass or more and 95% by mass or less with respect to the total mass of the solder paste.

According to a second aspect of the present invention, there is provided a mounting structure in which an electronic component is mounted on a circuit board using the solder paste according to the first aspect,
A conductive portion in which the electronic component and the circuit board are metal-bonded, and a reinforcing portion formed by covering the periphery of the conductive portion with a cured product of the flux,
A mounting structure is provided.

The solder paste of the present invention can be applied to solder connection requiring a high melting point, and has excellent coating workability, high adhesion, and excellent solder connection reliability.

It is sectional drawing of the solder joint 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 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 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 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 a cross-sectional schematic diagram which showed the shear adhesive force measuring method of a chip component.

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

The solder paste in the embodiment of the present invention includes solder powder and flux. FIG. 1 is a sectional view of a solder joint portion of a CSP joined by using a solder paste according to an embodiment of the present invention. As shown in FIG. 1, between the electrode 2 provided on the CSP substrate 1 and the electrode 4 provided on the circuit substrate 3 is a conductive portion 5 composed of a molten portion of the solder ball and a portion derived from the solder powder. Are joined together, and the periphery thereof is reinforced by a reinforcing portion 6b which is a solid epoxy resin after curing derived from flux.

The composition of the solder paste in the embodiment of the present invention will be described in detail below.

The solder paste according to the embodiment of the present invention contains solder powder and flux, and may contain other components as necessary. The flux contains an epoxy resin, a phenolic resin, a benzoxazine compound and an activator.

<Flux>
The flux in the solder paste according to the embodiment of the present invention contains an epoxy resin, a phenol resin, a benzoxazine compound and an activator. The amount of the flux with respect to the total mass of the solder paste is preferably 1% by mass or more and 65% by mass or less, more preferably 1% by mass or more and 55% by mass or less, and further preferably 5% by mass or more and 50% by mass or less. When the content of the flux in the solder paste of the present invention is within the above range, it is possible to effectively realize high connection reliability of the joint portion, excellent printing workability of the paste, and stable conductivity. Hereinafter, each essential component contained in the flux will be described in more detail.

(Epoxy resin)
Epoxy resin generally refers to a thermosetting resin that has an epoxy group in its structure and can be cured by heating. In the embodiment of the present invention, the epoxy resin (base epoxy resin) contained in the flux is liquid at room temperature. By blending such an epoxy resin, other components such as solder particles can be easily dispersed. In the present specification, "liquid at normal temperature" means that the material has fluidity in a temperature range of 5°C or more and 28°C or less under atmospheric pressure, particularly around 20°C at room temperature. Alternatively, at normal temperature, a solid epoxy resin may be liquefied by mixing with a liquid epoxy resin, or may be liquefied by adding a reactive epoxy diluent or solvent.

The epoxy resin which is liquid at room temperature is not particularly limited in its molecular weight and molecular structure as long as it has two or more epoxy groups in one molecule, and various resins 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 A type epoxy resin, bisphenol F type epoxy resin or other bisphenol type epoxy resin, hydrogenated bisphenol A type epoxy resin, hydrogenated bisphenol F type epoxy resin or other hydrogenated bisphenol type epoxy resin, 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 resin and hydrogenated bisphenol-type epoxy resin are preferable as the liquid epoxy resin at room temperature in view of lowering the viscosity of the liquid epoxy resin composition for semiconductor encapsulation and improving the physical properties of the cured product. Specific examples of commercially available products include a bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Corporation: product number jER828) and a bisphenol F type epoxy resin (manufactured by Mitsubishi Chemical Corporation: product number jER806).

The epoxy resin is contained in a proportion of preferably 10% by mass or more and 90% by mass or less, more preferably 20% by mass or more and 70% by mass or less, and further preferably 20% by mass or more and 60% by mass or less with respect to the total mass of the flux. Preferably. When the content of the epoxy resin in the flux of the present invention is within the above range, the connection reliability of the joint portion can be effectively improved.

(Phenolic resin)
The phenol resin is not particularly limited as long as it has two or more phenolic hydroxyl groups capable of reacting with the epoxy groups of the epoxy resin in the molecule. Examples thereof include polyfunctional phenols having two or more phenolic hydroxyl groups in the molecule, such as bisphenol A, phenol novolac, and cresol novolac. In particular, from the viewpoint of the solubility of two or more phenolic hydroxyl groups present in the molecule in other components such as epoxy resin, the phenol resin preferably has a softening point of 60° C. or more and 110° C. or less, and a hydroxyl group equivalent. It is 70 g/eq or more and 150 g/eq or less. In the present disclosure, the softening point refers to a temperature at which a phenol resin is softened by an increase in temperature and starts to deform, and refers to a temperature measured using a ring and ball softening point measuring method. Further, in the present disclosure, the hydroxyl group equivalent refers to a numerical value measured by the neutralization titration method based on JIS K0070. Specific commercially available products include, for example, phenol novolac resin (manufactured by Meiwa Kasei Co., Ltd.: product number HF-1M), phenol aralkyl resin (manufactured by Meiwa Kasei Co., Ltd.: product number MEH-7800), and biphenylaralkyl resin. (Maywa Kasei Co., Ltd. product number MEH-7851SS). The form of the phenol resin may be solid or liquid. Further, it is also possible to use a phenol resin having only one phenolic hydroxyl group in the molecule.

The phenol resin is contained in a ratio of less than 58.9% by mass with respect to the total mass of the flux. The lower limit of the content is not particularly limited, but the phenol resin is preferably 10% by mass or more and less than 58.9% by mass, more preferably 10% by mass or more and 50% by mass or less, and further preferably, the total mass of the flux. Is contained in a proportion of 10% by mass or more and 40% by mass or less. By setting the proportion of the phenol resin within such a specific range, it is possible to obtain an appropriate viscosity and the curing reaction of the resin can proceed appropriately.

(Benzoxazine compound)
The benzoxazine compound is not particularly limited as long as it is a compound containing a dihydrobenzoxazine ring. For example, it can be synthesized from various phenols, amines and formaldehyde.

In the benzoxazine compound, the dihydrobenzoxazine ring is chemically stable under normal conditions, and the polymerization reaction does not proceed. However, by heating to about 170° C. or higher, the dihydrobenzoxazine ring is opened and mutated to a polybenzoxazine compound having a diaminodiphenyl structure composed of a phenolic hydroxyl group and a basic amino group. The basic amino group present in the diaminodiphenyl structure formed by this ring opening is higher than the melting point of the solder powder at a high temperature (for example, about 219° C. in the case of SAC solder) between the above epoxy resin and the above phenol resin. It is considered that the resin hardening is accelerated after the solder is melted by accelerating the reaction of (1) and acting as a hardening accelerator. In addition, the dihydrobenzoxazine ring of the benzoxazine compound does not open until it reaches 170° C. Therefore, the reaction between the epoxy resin and the phenol resin does not proceed, so that the melting and agglomeration of the solder as described later is prevented. Do not block. In addition, after ring-opening, the phenolic hydroxyl group can self-polymerize without reacting with by-products or react with the above-mentioned epoxy resin or the like. As described above, after the solder is melted, the flux reacts rapidly due to the opening of the dihydrobenzoxazine ring.

Here, for example, the reaction temperature of the resin can be lowered to a low temperature range of about 150° C. or lower by adding the curing accelerator and the phenol resin to the composition mainly containing the benzoxazine compound and the epoxy resin. The technology is disclosed in, for example, Japanese Patent Laid-Open Nos. 2000-248151 and 2002-047391. When this technique is applied to the solder paste of the present embodiment, the curing temperature of the resin becomes low, and the viscosity increases before reaching the high melting point, which hinders the melting and agglomeration of the solder described later. However, according to the solder paste of the embodiment of the present invention, since the epoxy resin and the phenol resin are the main components and the benzoxazine compound (and the activator) are contained in an appropriate amount, the viscosity is increased before reaching the high melting point. Excellent soldering connection can be made without

In order to further enhance the function as a curing accelerator, the benzoxazine compound is preferably a polyvalent oxazine having a plurality of oxazine rings in the molecule.

The benzoxazine compound is preferably 1% by mass or more and 50% by mass or less, more preferably 1% by mass or more and 40% by mass or less, and further preferably 5% by mass or more and 30% by mass or less with respect to the total mass of the flux. included. By containing the benzoxazine compound in such a ratio, the curing of the epoxy resin and the phenol resin can be sufficiently favorably proceeded.

The structure of the benzoxazine compound produced differs depending on the type of raw material. In the present invention, a benzoxazine compound synthesized from various raw materials can be used. Alternatively, a commercially available product may be used.

（式中、Ｒは、水素またはアリル基を示す。） Typical commercially available compounds include the following compounds.
Pd type benzoxazine compound: Polymer of phenol, diaminodiphenylmethane and formaldehyde (manufactured by Shikoku Chemicals Co., Ltd.)

(In the formula, R represents hydrogen or an allyl group.)

Further, the following compounds having different resin skeletons can also be mentioned.
Fa type benzoxazine compound: a polymer of bisphenol F, aniline and formaldehyde (manufactured by Shikoku Chemicals Co., Ltd.)

(Activator)
The type of activator may be any appropriate type as long as it has a function of removing the metal oxide film, and the type is not limited. For example, in a temperature range where the solder paste is heated, an organic acid, halogen, or amine salt having a reducing power for removing an oxide film that may be present on the electrode, wiring and/or the surface of the solder powder, which is a member to be joined, Can be used. Of these, the activator is preferably an organic acid having excellent insulation resistance and deterioration resistance. The organic acid has a particularly excellent flux action (where, the flux action is a reducing action of removing an oxide film formed on the metal surface to which the solder paste is applied, and a reduction of the surface tension of the molten solder, It means the function of promoting the wettability of the solder to the surface of the joining metal). The type of organic acid is not particularly limited, and an acid of any organic compound can be used. For example, rosin component materials typified by abietic acid, various amines and salts thereof, sebacin salts, adipic acid, glutaric acid, succinic acid, malonic acid, citric acid, pimelic acid, etc. can be used.

INDUSTRIAL APPLICABILITY The present invention more efficiently exerts its effect when a solder (solder powder) having a high melting point of around 200° C. or 200° C. or higher (for example, SAC solder or Sn—Cu based solder) is used. .. Since the carboxyl group of the organic acid reacts with the epoxy group even at 200° C. or lower, it contributes to the thickening of the flux in the solder paste. Therefore, when an organic acid is used as the activator, the melting point of the organic acid is preferably 130°C or higher and 220°C or lower, more preferably 130°C or higher and 200°C or lower, and further preferably 133°C or higher and 186°C or lower. This is because it has been found that the use of such a dibasic organic acid having a high melting point does not easily hinder the melting and agglomeration of solder as described below.

Specifically, for a solder having a high melting point, such as SAC solder, the activating power (that is, the reducing action of removing the oxide film on the solder surface) is small in a low temperature range of 130° C. or less, and the solder is active in a high temperature range. It is desirable to develop power. Examples of the organic acid having a melting point of 130° C. or higher and 220° C. or lower include succinic acid (melting point 186° C.), adipic acid (melting point 152° C.), corkic acid (melting point 142° C.), sebacic acid, which are one of dibasic acids. (Melting point 133° C.) and the like. Although oxalic acid anhydride has a high melting point of 189° C., it has high hygroscopicity and becomes a low-melting point (melting point 101° C.) dihydrate due to moisture absorption. Further, an organic acid having a melting point higher than that of SAC solder, such as isophthalic acid (melting point 340° C.), cannot usually be expected to have a function of removing the oxide film of the solder. However, these organic acids having a melting point of less than 130° C. or more than 220° C. are not excluded from the organic acids that can be used in the present invention, and may be appropriately used depending on the solder to be actually used and the reflow temperature. Good. These organic acids may be one type of component or a mixture of two or more types of components.

The activator is contained in a ratio of more than 1.3% by mass with respect to the total mass of the flux, preferably 1.5% by mass or more and 60% by mass or less, more preferably 2% by mass or more and 50% by mass or less, and It is preferably contained in a proportion of 3% by mass or more and 40% by mass or less. When the content of the activator (particularly organic acid) is within the above range, the flux function works properly, and suitable connection reliability can be obtained.

(Other ingredients)
Examples of other components of the flux contained in the solder paste include modifiers (e.g., rosin) and additives that are commonly used. Further, for the purpose of reducing the viscosity of the solder paste and imparting fluidity, a low boiling point solvent or diluent may be added. Furthermore, it is also effective to add hydrogenated castor oil, stearic acid amide, or the like as a thixotropy imparting agent for maintaining the printed shape.

When a solvent for reducing the viscosity is added to the flux of the solder paste of the present invention, the solvent is not taken into consideration in the conversion of the compounding ratio of each component with respect to the total mass of the flux. The reason is that the solvent is present in the paste in the state of the solder paste, but in the reflow heating step, it does not react with the resin and most of it volatilizes, and it does not exist in the resin cured product, or there is an extremely small amount. This is because there is only one.

<Solder powder>
The solder powder contained in the solder paste of the present invention is not particularly limited, but it is preferable to use solder powder having a melting point of 180° C. or higher, particularly 200° C. or higher. The composition of the solder powder is not particularly limited, but may be in the form of a solder alloy. For example, Sn-based SAC solder, Sn—Cu based solder, Sn—Ag based solder alloy, or the like can be used. Examples of the SAC solder include SAC305 (Sn-3.0Ag-0.5Cu) solder having a melting point of 219°C, SAC405 (Sn-4.0Ag-0.05Cu) solder having a melting point of 220°C, and a melting point of 225°C. SAC105 (Sn-1.0Ag-0.5Cu) solder which is Examples of the Sn-Ag solder include Sn-3.5Ag solder having a melting point of 221°C, and examples of the Sn-Cu solder include Sn-0.7Cu solder having a melting point of 227°C. .. Of these solder alloys, SAC305 solder is preferable. This is because the SAC305 solder is currently widely used in consumer electronic devices, has achieved high connection reliability and low cost, and is also commonly used as solder balls for CSP and BGA packages. This is because it is used.

The content of the solder powder with respect to the total mass of the solder paste of the present invention is preferably 35% by mass or more and 95% by mass or less, more preferably 40% by mass or more and 95% by mass or less, and further preferably 50% by mass or more and 95% by mass or less. Is in the range. When the content of the solder powder is within the above range, it is possible to effectively realize high connection reliability of the joint portion and excellent workability of the paste. If the content of the solder powder is less than about 35% by mass, sufficient connection may not be secured. On the other hand, if the content is more than 95% by mass, the viscosity becomes high, and it may not be possible to secure an appropriate viscosity as a paste, and the flux content may be reduced, so that a sufficient reinforcing effect may not be obtained.

The composition of the solder powder in this specification is expressed by connecting the element symbols of the elements contained in the solder powder with a hyphen. In the present specification, in order to describe the metal composition of the solder powder, a numerical value or numerical range may be shown immediately before the metal element, which is a metal as generally used in the technical field. The mass% (=mass%) of each element in the composition is shown by a numerical value or numerical range. The solder powder may contain trace metals inevitably mixed in, such as Ni, Ge, Zn, Sb, and Cu, as long as they are substantially composed of the listed elements.

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

Next, 1 of the above-described method for preparing a solder paste in the embodiment of the present invention and a specific method for manufacturing (or manufacturing) a mounting structure by mounting an electronic component on a circuit board using the solder paste Here is an example:

First, the above-mentioned epoxy resin, phenol resin, benzoxazine compound and activator are weighed and mixed to form a flux. Solder powder is added to the flux and mixed and kneaded.

The solder paste according to the embodiment of the present invention can be used to mount a semiconductor component on a circuit board having conductor wiring. The mounting structure, for example, a semiconductor device, according to the embodiment of the present invention includes a joint portion in which the terminal of the semiconductor component and the electrode of the circuit board are joined by using the solder paste described above. The solder paste is applied by, for example, overlaying a circuit board with a metal mask having a through hole at the same position as the electrode, supplying the solder paste to the surface of the metal mask, and filling the through hole with a squeegee. You can After that, when the metal mask is separated from the circuit board, a circuit board in which the solder paste is applied to each electrode can be obtained.

Next, while the solder paste is in an uncured state, the chip component or the semiconductor component is overlaid on the circuit substrate using a chip mounter or the like so that the terminals of the chip component or the semiconductor component and the electrodes of the circuit substrate face each other. Here, a chip resistor, a chip contactor, or the like may be mounted as the chip component. As the semiconductor component, a CSP or BGA formed by providing a solder ball as a terminal, a semiconductor package such as QFP formed by providing a lead as a terminal, or a terminal provided without being housed in the package is formed. A semiconductor element (bare chip) or the like can be used.

In this state, the printed wiring board on which the chip parts are arranged is heated to a predetermined heating temperature in a reflow furnace. According to another embodiment of the present invention, in such a method, the terminals of the chip component or the semiconductor component and the electrodes of the circuit board are provided with the conductive portion connected via the solder paste according to the embodiment of the present invention. A semiconductor device can be manufactured. This conductive portion is a solder joint portion (conductive portion) in which solder powder and solder balls are melted and integrated, and a portion formed by covering the periphery with a cured product of flux, that is, an epoxy resin cured portion (reinforcement portion). With. As described above, according to the solder paste in the embodiment of the present invention, it is possible to fabricate a mounting structure in which the conductive portion electrically connects the component and the board, and the reinforcing portion mechanically reinforces the mounting structure. it can.

In the reflow step, it is necessary that the solder powder is sufficiently melted, and further that the curing reaction of the resin component of the flux proceeds sufficiently and appropriately. Specifically, in the reflow step, if the curing reaction of the epoxy resin, which is the flux component in the solder paste, proceeds before the solder powder is completely melted, the flux thickens. Then, agglomeration and melting of the solder particles are hindered, and proper metal conduction cannot be obtained. In order to avoid such a situation, the temperature of the reflow furnace is such that the curing reaction of the resin is slow until the temperature rises to the melting point of the solder powder to be used, and the solder powder melts, for example, the solder balls of the semiconductor component and the melting. After they are combined and melt-bonded to the electrode metal of the circuit component, it is necessary that the resin of the flux completes the curing reaction in a short time (for example, about several minutes).

In the solder paste according to the embodiment of the present invention, the composition of the flux mainly contains an epoxy resin and a phenol resin, and further contains an appropriate amount of a benzoxazine compound (and an activator), so that the temperature of the reflow furnace is the solder paste. It is difficult for the flux to thicken while the temperature is raised to the melting point of the inside solder powder (particularly about 219° C. which is the melting point of the commonly used SAC305 solder). In addition, by additionally using an appropriate amount of activator in the composition of the flux, excellent solder meltability and short-time curing of the resin flux after melting the solder are made possible. The composition of the flux in the solder paste is preferably such that the epoxy resin is contained in a proportion of 20% by mass or more and 60% by mass or less with respect to the total mass of the flux, and the phenol resin is 10% by mass or more with respect to the total mass of the flux. 40 mass% or less, the benzoxazine compound is contained in a ratio of 5 mass% or more and 30 mass% or less with respect to the total mass of the flux, and the activator is 3 mass% or more 40 with respect to the total mass of the flux. It is contained in a proportion of not more than mass %.

In another embodiment, the reflow oven profile may be a two-step profile in which after melting the solder, the temperature is reduced to 150-200° C. for a mild cure. In that case, since the curing rate is slowed only by the ring-opened benzoxazine compound and the activator, it is also possible to use an appropriate amount of a curing accelerator so long as it does not hinder solder melting. Examples of the type of the curing accelerator include imidazoles, tertiary amines, cyclic amines such as DBU salts, triarylphosphines such as TPP salts, quaternary phosphonium salts, and metal complexes such as Fe acetylacetonate. .. Of these, those of high temperature reaction type are suitable.

2A to 2C are cross-sectional explanatory views schematically showing a step of joining the ball portions of the CSP using the solder paste according to the embodiment of the present invention. As shown in FIGS. 2A to 2C, the electrodes 2 provided on the CSP substrate 1 and the electrodes 4 provided on the circuit board 3 are joined with solder balls 8 and a solder paste 7, and then heated with a drier 9. It is cured and completed. The periphery of the formed conductive portion 5 has a structure reinforced by a reinforcing portion 6b which is solid epoxy resin after curing.

3A to 3C are cross-sectional explanatory views schematically showing a step of joining chip components using the solder paste according to the embodiment of the present invention. As shown in FIGS. 3A to 3C, the chip component 10 is mounted on the solder paste 7 applied on the electrodes 4 provided on the circuit board 3, and is cured by heating in a dryer 9. Then, the solder is melted and connected to form the conductive portion 11, and the liquid epoxy resin 6a extruded by the cohesive force of the solder forms a structure that covers the periphery of the solder and/or the lower part of the chip component 10. After that, it is cured by heating to the reinforcing portion 6b which is a solid epoxy resin, and is completed. In this way, the chip part 10 and the circuit board 3 are metal-bonded (metal bond containing metal derived from solder powder in the solder paste of the raw material), and the reinforcing part 6b around the conductive part 11. A mounting structure having is manufactured.

Examples and comparative examples of the present invention will be shown below. The following embodiments and comparative examples of the present invention are merely examples and do not limit the present invention. In Examples and Comparative Examples, "parts" and "%" are based on mass unless otherwise specified.

<Creating solder paste>
First, the epoxy resin, the phenol resin, and the benzoxazine compound occupy 100 parts by mass of the total mass of the solder paste (excluding the solvent), but occupy parts by mass shown in Tables 1 and 2 below. Each of them was weighed in a ratio and heated and melted at 80° C. to prepare a uniform resin mixture. After cooling to room temperature, the weighed organic acid was further added and mixed to prepare the fluxes of Examples 1 to 9 and Comparative Examples 1 to 4. Further, after appropriately adding a solvent as shown in Tables 1 and 2, the mixture was uniformly dispersed using a planetary mixer. In the following, phr is a mass% with respect to the mass of the total flux of the solder paste (total mass of epoxy resin, phenol resin, benzoxazine compound and organic acid). However, the amount of solvent is not included in the total amount of flux.

As the epoxy resin, bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Co., Ltd.: product number jER828) or bisphenol F type epoxy resin (manufactured by Mitsubishi Chemical Co., Ltd.: product number jER806) was used. Phenol novolac (manufactured by Meiwa Kasei Co., Ltd.: product number HF-1M or H-4) was used as the phenol resin. As the benzoxazine compound, Pd type benzoxazine (manufactured by Shikoku Chemicals Co., Ltd.) or Fa type benzoxazine (manufactured by Shikoku Chemicals Co., Ltd.) was used. As the organic acid as an activator, adipic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) or succinic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) was used. HeDG (hexyl diglycol) (manufactured by Nippon Emulsifier Co., Ltd.) was used as the solvent.

Next, solder powders were added to the fluxes of Examples 1 to 9 and Comparative Examples 1 to 4 obtained as described above in proportions so as to occupy parts by mass shown in Table 1 and Table 2, respectively, Further kneading was performed to prepare a solder paste. As the solder powder, SAC305 solder powder (Sn-3.0Ag-0.5Cu) (average particle size: 10 to 25 μm, melting point: 219° C. (manufactured by Mitsui Mining & Smelting Co., Ltd.)) or SAC105 solder powder (Sn-1) 0.0Ag-0.5Cu) (average particle size: 10 to 25 μm, melting point: 225° C. (manufactured by Mitsui Mining & Smelting Co., Ltd.)).

<Production of adhesion evaluation element>
The solder paste prepared as described above is printed on a Au-plated electrode on a circuit board (FR-4 board) using a metal mask so as to have a thickness of 0.1 mm, and the solder paste is printed. A paste print section was formed.

Then, a chip resistor (tin electrode) having a size of 3.2 mm×1.6 mm was mounted on the solder paste printed portion on the circuit board using a chip mounter. In addition, the electrode material of the circuit board was copper, and the board material was a glass epoxy material. After that, a joint portion was formed by heating at 240° C. for 6 minutes using a reflow device, and an evaluation element was produced.

<Evaluation>
The following items were evaluated for Examples 1 to 9 and Comparative Examples 1 to 4. The evaluation results are also shown in Tables 1 and 2 as the characteristics of the solder paste in each example.

(Printability)
The printability of the solder paste was evaluated by observing the shape of the solder paste printed using a metal mask. The observation was visually performed with respect to the state of fitting in the electrode area, the shape of sagging, and the pointed shape. The printability was evaluated by the shape when the paste was transferred to the electrodes of the circuit board through the through holes of the mask. If the electrode part retains its shape, it is evaluated as O, if there is a defect in the shape (occurrence of sagging or sharpness), it can be used, and if it is very bad, it is evaluated as x.

(Adhesion)
FIG. 4 is a schematic cross-sectional view showing a method for measuring the shear adhesion force of a chip component. The chip component 10 is fixed to a heatable stage 13, and the shearing jig 12 is used to horizontally push the chip component 10 to measure the adhesion strength. By using a bond tester device (Series 4000, manufactured by DAGE), which is measured by such a method, to measure the shear adhesive force at room temperature of 20° C. of the adhesiveness evaluation element produced as described above, the solder paste is obtained. Was evaluated. Adhesion was evaluated as follows: ◎ for a load not applied even if the load applied to the joint exceeds 20 Kg/chip, ⊚, for those with damage in the range of 15-20 Kg/chip, ∘, 10-15 Kg/chip When the damage occurred in the range, it was designated as Δ, and when the damage occurred in the range of less than 10 kg/chip, it was designated as x.

(Metallizing property)
The metallization property (solder connection reliability) was evaluated according to the following JIS Z3284-4 solder ball test. A solder cohesion degree of level 1 is ⊚, a solder cohesion degree of level 2 is ◯, a solder cohesion degree of level 3 is Δ, and a solder cohesion degree is level 4. What was there was marked with x. The details of each level of solder cohesion are as follows.
Level 1: The solder (powder) is melted, the solder becomes one large sphere, and there is no solder ball around.
Level 2: Solder (powder) is melted, the solder becomes one large sphere, and there are three or less solder balls with a diameter of 75 μm or less in the periphery.
Level 3: Solder (powder) is melted, the solder becomes one large sphere, and there are four or more solder balls with a diameter of 75 μm or less in the periphery, and they are not arranged in a semi-continuous ring shape.
Level 4: The solder (powder) is melted, the solder becomes one large sphere, and a large number of fine spheres are arranged in a semi-continuous ring around the periphery.

(Comprehensive judgment)
Of the three evaluations of printability, adhesion, and metallization, a comprehensive evaluation is made by using ○ if all items are ○, △ if there is 1 or Δ, and × if there is 1 or X. It was

The blending amounts shown in Tables 1 and 2 below are parts by mass.

For example, as shown in Table 1, in Example 1, the type of solder powder was SAC305 solder. With respect to 100 parts by mass of the solder paste (however, the solvent was not included), the amount of the solder powder was 50 parts by mass, and the solder ratio was also 50% by mass. The epoxy resin in the flux was jER828, and the addition amount was 23.5 parts by mass with respect to the total amount of solder paste and 47.0 phr with respect to the total amount of flux. The phenol resin was HF-1M, and the addition amount was 15.0 parts by mass with respect to the total amount of solder paste and 30.0 phr with respect to the total amount of flux. The benzoxazine compound was a Pd type, and the addition amount was 10.0 parts by mass with respect to the total amount of the solder paste and 20.0 phr with respect to the total flux amount. The organic acid was adipic acid, and the addition amount was 1.5 parts by mass with respect to the total amount of solder paste and 3.0 phr with respect to the total flux amount. No solvent was added. In the evaluation result of the solder paste of Example 1 as described above, the printability was slightly sagging, and was judged as Δ. The adhesiveness was 12 Kg/chip, which was slightly excellent, and was evaluated as Δ. The metallization property was slightly good at level 3, and was Δ. As a result, the overall judgment was Δ. As for the solder pastes of Examples 2 to 9 in which the kinds and amounts of the solder powder, the epoxy resin, the phenol resin, the benzoxazine compound and the organic acid were variously changed, as shown in Table 1 above, similarly good or usable levels were obtained. The printability, adhesiveness, and metallization of the can be confirmed.

In Comparative Example 1, a solder paste having a solder ratio of 30% was used. As a result of the evaluation, the printability was significantly sagging, and the judgment was x. The adhesion was also weak, 7 Kg/chip, and the evaluation was x. The metallization was also level 4 and was judged to be bad. From the result, the comprehensive judgment was x.

In Comparative Example 2, a solder paste containing no benzoxazine compound was used. As a result of the evaluation, the adhesiveness was weak, and the overall judgment was “x”. It is presumed that this is because the benzoxazine compound was not contained and the curing of the epoxy resin and the phenol resin did not proceed sufficiently.

In Comparative Example 3, a solder paste in which the ratio of phenol novolac, which is a phenol resin, was 58.9 phr was used. As a result of the evaluation, the viscosity was high, and the adhesion and metallization were not good either. It is speculated that this is because the curing reaction did not proceed sufficiently because the amount of phenol novolac was excessive.

In Comparative Example 4, a solder paste containing no organic acid was used. As a result of the evaluation, the adhesion and metallization were poor. This is presumably because the metallization of the solder did not proceed because it did not contain an organic acid.

Considering from the results of Table 1 and Table 2, a solder paste mainly composed of an epoxy resin and a phenol resin as a flux component and further appropriately added with a benzoxazine compound has excellent metallization property and high adhesion in a reflow treatment at 240°C. Have sex. This is because the benzoxazine compound is heated to 170° C. or higher, and the dihydrobenzoxazine ring is opened to mutate into a polybenzoxazine compound having a diaminodiphenyl structure, which is present in the diaminodiphenyl structure formed by the ring opening. It is presumed that the basic amino group which is formed accelerates the reaction between the epoxy resin and the phenol resin. In addition, it is presumed that excellent adhesiveness is secured by the fact that the hydroxyl group of itself reacts with the epoxy resin to form a crosslinked structure.

Since such a mutation to the polybenzoxazine compound occurs after the SAC solder is melted, the flux is unlikely to thicken before the SAC solder is melted. Therefore, it is presumed that it is very suitable for melting and joining the solder. Further, the ring opening of the dihydrobenzoxazine ring of the benzoxazine compound hardly occurs at low temperatures, so that the room temperature storability of the solder paste is extremely stable and has a long room temperature pot life.

When further considering from the results of Table 1 and Table 2, the epoxy resin, the phenol resin, the benzoxazine compound and the organic acid (the same applies to other activators having the same effect) contained in the flux of the solder paste are included in the epoxy resin. Is preferably 20 phr or more and 60 phr or less, the phenol resin is 10 phr or more and 40 phr or less, the benzoxazine compound is 5 phr or more and 30 phr or less, and the organic acid (as well as other activators having the same action) is 3 phr or more and 40 phr or less. I also understand.

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

1 CSP board 2 electrode 3 circuit board 4 electrode 5 conductive part 6a epoxy resin (uncured liquid)
6b Reinforcement part 7 Solder paste 8 Solder ball 9 Dryer 10 Chip part 11 Conductive part 12 Shear jig 13 Stage

Claims (9)

A solder paste containing solder powder and flux,
The flux contains an epoxy resin, a phenol resin, a benzoxazine compound and an activator,
The phenol resin is contained in a ratio of less than 58.9% by mass with respect to the total mass of the flux,
The activator is contained in a ratio of more than 1.3% by mass based on the total mass of the flux,
Solder paste. The solder paste according to claim 1, wherein the solder powder is a Sn-Ag-Cu solder or a Sn-Cu solder having a melting point of 200°C or higher. The epoxy resin is contained in a proportion of 20% by mass or more and 60% by mass or less with respect to the total mass of the flux,
The phenol resin is contained in a proportion of 10% by mass or more and 40% by mass or less based on the total mass of the flux,
The benzoxazine compound is contained in a proportion of 5% by mass or more and 30% by mass or less with respect to the total mass of the flux,
The activator is contained in a proportion of 3% by mass or more and 40% by mass or less based on the total mass of the flux.
The solder paste according to claim 1 or 2. The solder paste according to claim 1, wherein the activator is an organic acid. The solder paste according to claim 4, wherein the organic acid has a melting point of 130°C or higher and 220°C or lower. The solder paste according to claim 1, wherein the phenol resin is a phenol novolac resin having a softening point of 60° C. or more and 110° C. or less and a hydroxyl equivalent of 70 g/eq or more and 150 g/eq or less. The solder paste according to claim 1, wherein the benzoxazine compound is a polyvalent oxazine having a plurality of oxazine rings in the molecule. The said solder powder is a solder paste of any one of Claims 1-7 contained in the ratio of 50 mass% or more and 95 mass% or less with respect to the total mass of this solder paste. A mounting structure in which an electronic component is mounted on a circuit board using the solder paste according to claim 1.
A conductive portion in which the electronic component and the circuit board are metal-bonded, and a reinforcing portion formed by covering the periphery of the conductive portion with a cured product of the flux,
Mounting structure.

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