阅读说明：本技术 树脂助焊剂焊膏及安装结构体 (Resin flux paste and mounting structure ) 是由 日野裕久 松野行壮 于 2021-05-08 设计创作，主要内容包括：本发明提供树脂助焊剂焊膏及安装结构体。上述树脂助焊剂焊膏包含焊料粉末和助焊剂,上述助焊剂至少包含环氧树脂、固化剂、固化促进剂和活性剂,上述环氧树脂包含相对于全部环氧树脂为10～90重量％的环氧当量为200～400的联苯芳烷基型环氧树脂、萘型环氧树脂、二环戊二烯型环氧树脂中的一种以上,上述固化剂包含相对于全部固化剂为30～95重量％的羟基当量为150～350的联苯芳烷基酚树脂、以及相对于全部固化剂为5～70重量％的羟基当量为100～200的具有烯丙基的苯酚酚醛树脂。(The invention provides a resin flux solder paste and a mounting structure. The resin flux paste comprises solder powder and flux, wherein the flux at least comprises epoxy resin, curing agent, curing accelerator and activator, the epoxy resin comprises more than one of biphenyl aralkyl type epoxy resin with epoxy equivalent of 200-400, naphthalene type epoxy resin and dicyclopentadiene type epoxy resin in 10-90 wt% relative to the total epoxy resin, and the curing agent comprises biphenyl aralkyl type phenol resin with hydroxyl equivalent of 150-350 in 30-95 wt% relative to the total curing agent and phenol phenolic resin with allyl group with hydroxyl equivalent of 100-200 in 5-70 wt% relative to the total curing agent.)

1. A resin flux solder paste is a solder paste containing solder powder and flux,

the soldering flux at least comprises epoxy resin, a curing agent, a curing accelerator and an active agent,

the epoxy resin contains 10 to 90 wt% of a total of the epoxy resins, and at least one of a biphenyl aralkyl type epoxy resin having an epoxy equivalent of 200 to 400, a naphthalene type epoxy resin, and a dicyclopentadiene type epoxy resin,

the curing agent comprises 30 to 95 wt% of a biphenyl aralkyl phenol resin having a hydroxyl equivalent of 150 to 350 with respect to the total curing agent, and 5 to 70 wt% of a phenol resin having an allyl group having a hydroxyl equivalent of 100 to 200 with respect to the total curing agent.

2. The resin flux paste of claim 1, wherein the flux exhibits a characteristic of an increase in elastic modulus at 220 ℃ or higher when heated at a constant rate of temperature rise of 20 ℃/minute.

3. The resin flux paste of claim 1 or 2, wherein a cured product of the flux has a glass transition temperature Tg of 80 ℃ or higher.

4. The resin flux solder paste of any one of claims 1 to 3, wherein the curing accelerator comprises one or more of an organic phosphine compound and a salt thereof, and a quaternary phosphonium compound and a salt thereof.

5. The resin flux paste of any one of claims 1 to 4, wherein the curing accelerator is one or more of triphenylphosphine, triphenylphosphine-triphenylborane, tetraphenylphosphonium tetraphenylborate, and tetraphenylphosphonium p-tolylborate.

6. The resin flux paste of any one of claims 1 to 5,

the solder powder has a melting point of 200 ℃ or higher,

the solder powder contains Sn alone, or an Sn-Ag alloy, an Sn-Cu alloy, an Sn-Ag-Cu alloy, or the alloy further containing an additional metal.

7. The resin flux paste of any one of claims 1 to 6, wherein the content of the solder powder is 60 to 95 wt% with respect to 100 wt% of the total amount of the resin flux paste.

8. A mounting structure obtained by mounting an electronic component on a circuit board using the resin flux paste according to any one of claims 1 to 7, the mounting structure comprising:

a conductive portion formed by metal bonding the electronic component and the circuit board; and

and a reinforcing portion formed by covering the periphery of the conductive portion with a cured product of the flux.

Technical Field

The present invention relates to a solder paste and a mounting structure, wherein a flux component of the solder paste is composed of an epoxy resin, and the solder paste is used for soldering a semiconductor component, an electronic component, or the like on a circuit board.

Background

In recent years, mobile devices such as mobile phones and PDAs (Personal Digital assistants) have been increasingly downsized and highly functionalized. As a mounting technique that can cope with this, a mounting structure such as BGA (Ball Grid Array) or CSP (Chip Scale Package) is often used. Mobile devices are susceptible to mechanical loads such as drop shock. In a QFP (Quad Flat Package), shock is absorbed at its lead portion. However, in BGA, CSP, or the like which does not have a lead for shock absorption, it is important to ensure shock-resistant reliability. In particular, with the recent trend toward higher functionality and higher power of semiconductor devices, heat cycle resistance and heat resistance have become important. Therefore, high solder connection reliability in device mounting becomes necessary, and a structural method and a solder material capable of realizing the same are desired.

As a further measure, a semiconductor mounted structure using a solder paste containing a thermosetting resin in a flux and a method for manufacturing the same have been proposed (for example, see patent document 1).

In the solder paste containing a thermosetting resin in a flux, in the step of heating and melting and connecting the solder, the resin contained in the flux is separated from the solder, and a reinforcing structure in which the resin covers the periphery of the solder can be formed. As a result of this reinforcement, the strength of the connection portion of the solder can be improved.

However, as shown in patent document 1, a solder paste using a low melting point solder such as Sn — Bi solder has been put to practical use as such a solder paste. For example, a solder paste containing a thermosetting resin using a high melting point solder such as SAC solder has not been practically used.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 5204241

Disclosure of Invention

According to the 1 st aspect of the present invention, there is provided a resin flux solder paste comprising solder powder and a flux,

the soldering flux at least comprises epoxy resin, a curing agent, a curing accelerator and an active agent,

the epoxy resin contains 10 to 90 wt% of the total epoxy resin and at least one of biphenyl aralkyl type epoxy resin, naphthalene type epoxy resin and dicyclopentadiene type epoxy resin having an epoxy equivalent of 200 to 400,

the curing agent comprises 30 to 95 wt% of a biphenyl aralkyl phenol resin having a hydroxyl equivalent of 150 to 350 with respect to the total curing agent, and 5 to 70 wt% of a phenol resin having an allyl group having a hydroxyl equivalent of 100 to 200 with respect to the total curing agent.

According to the 2 nd aspect of the present invention, there is provided a mounted structure in which an electronic component is mounted on a circuit board using the resin flux paste, the mounted structure including:

a conductive portion formed by metal bonding the electronic component and the circuit board; and

and a reinforcing portion formed by covering the periphery of the conductive portion with a cured product of the flux.

Drawings

Fig. 1 is a sectional view of a solder-bonded portion of a CSP bonded using a resin flux paste of an embodiment of the present invention.

Fig. 2A is a cross-sectional explanatory view schematically showing a bonding process of a ball portion of a CSP using the resin flux paste according to the embodiment of the present invention.

Fig. 2B is a cross-sectional explanatory view schematically showing a bonding process of the ball portion of the CSP using the resin flux paste according to the embodiment of the present invention.

Fig. 2C is a cross-sectional explanatory view schematically showing a step of joining a ball portion of a cssp using a resin flux solder paste according to an embodiment of the present invention.

Fig. 2D is a cross-sectional explanatory view schematically showing a bonding process of the ball portion of the CSP using the resin flux paste according to the embodiment of the present invention.

Fig. 3 is a sectional view of a solder bonding portion of the CSP bonded with the conventional solder paste.

Fig. 4 shows the characteristics of the elastic modulus when the flux of the resin flux paste of comparative example 1 was heated and cooled at a constant rate by a rheometer "DHR-2" viscoelasticity measuring apparatus manufactured by TA Instruments.

Fig. 5 shows the characteristics of the elastic modulus when the flux of the resin flux paste of example 2 is heated and cooled at a constant speed by a rheometer "DHR-2" viscoelasticity measuring apparatus manufactured by TA Instruments.

Fig. 6 is a diagram showing characteristics of the resin flux solder paste.

Description of the reference numerals

1: circuit substrate (CSP substrate)

2: electrode for electrochemical cell

3: circuit board

4: electrode for electrochemical cell

5: solder bump

6 b: reinforcing part

8: heating machine

9: conductive part

10: solder

Detailed Description

Fig. 3 is a cross-sectional view of a connection portion joined using a conventional solder paste. As shown in fig. 3, the following structure is obtained: the electrode 2 provided on the circuit board 1 and the electrode 4 provided on the circuit board 3 are joined by the solder bump 5 and the solder conductive portion 9A, and the periphery thereof is reinforced by the reinforcing portion 6b which is a cured solid resin.

In the mounting process using this solder paste, the wiring electrodes of the circuit board and the like are printed at predetermined positions using a metal mask, and then heated in a reflow furnace. In this case, 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, the flux acts, and the solder can be fused and connected. Then, a thermosetting resin such as an epoxy resin is cured, and the wiring electrodes of the circuit board and the electronic component are bonded and reinforced with the resin by 1 heating reflow step.

On the other hand, as a solder material used in a general paste-like solder paste (containing no thermosetting resin), a Pb eutectic solder has been typically used in the past, but a lead-free solder has been used in recent years in consideration of the environment. The lead-free solder includes Sn-Bi solder, Sn-Ag-Cu solder (hereinafter, also referred to as SAC solder), Sn-Cu solder, and the like. In mounting using SAC solder or the like, In-containing solders or the like having different metal compositions have also been put into practical use as a measure for achieving high connection reliability. SAC solder has been studied and put into practical use as a representative of SAC solders, SAC305(Sn-3.0Ag-0.5Cu) solder (hereinafter, also referred to as SAC305 solder) and SAC105(Sn-1.0Ag-0.5Cu) solder (silver ratio 1%) (hereinafter, also referred to as SAC105 solder) having a lower silver ratio.

As described above, by using the solder paste, there is no problem of delay of the process and cost, and the connection reliability can be improved by the reinforcing structure formed of the resin. However, among such solder pastes, a solder paste using a low melting point solder such as Sn — Bi solder as disclosed in patent document 1 has been put to practical use. For example, a solder paste containing a thermosetting resin using a high melting point solder such as SAC solder has not been practically used.

The present inventors have conducted extensive studies and found that the reason why the above-mentioned materials are not put into practical use is as follows. For example, in order to sufficiently melt SAC305 solder having a melting point of about 219 ℃ in a reflow curve, it is necessary to increase the peak temperature of a reflow furnace to 240 to 260 ℃. In general, an epoxy resin, which is a thermosetting resin in a flux of a solder paste, generally starts a curing reaction at 100 to 150 ℃. Therefore, in the reflow profile, the epoxy resin starts to solidify and thickens before the solder particles dispersed in the solder paste melt and aggregate at the melting point, and it is difficult to form solder joints and the like appropriately. In addition, epoxy resins cure at a high temperature around 200 ℃ at a very high rate and in a short time as compared with a temperature around 150 ℃. Therefore, particularly in the case of a high melting point solder, it becomes very difficult to form the solder joint portion and the resin reinforcing portion with a solder paste.

Accordingly, the present inventors have conducted extensive studies on a curing system in which the epoxy resin hardly cures until the melting temperature of the SAC305 solder reaches about 220 ℃ and the reaction starts in a temperature range higher than the melting point of the SAC305 solder about 220 ℃, and as a result, they have found that the phenol novolac resin satisfies the reaction characteristics.

In addition, a mixture in which a phenol novolac resin is dissolved in an epoxy resin (hereinafter referred to as a phenol novolac + epoxy mixture) has low reactivity at room temperature and excellent storage stability. Further, since the reaction rapidly starts in a temperature region of 220 ℃ or higher than the melting point of SAC305 solder, there is an advantage that the solder is extremely unlikely to be inhibited from melting and the solder has excellent connectivity. However, as a disadvantage, it has been clarified that the glass transition temperature (hereinafter, also referred to as Tg) of a cured product of a liquid bisphenol type epoxy resin and a low molecular weight phenol novolac resin which are generally used is as low as about 60 to 80 ℃. As a curing agent for epoxy resins, amine compounds, imidazoles, and acid anhydrides are known as curing agents other than phenol-novolac resins, and cured products thereof often have a Tg of 100 ℃.

As described in the background section above, the present invention includes mounting of a power semiconductor that generates significant heat. That is, heat cycle resistance and heat resistance under a high temperature environment are important, and therefore, heat resistance is also required for a solder portion for connecting a semiconductor and a circuit board. Specifically, as the conditions for reliability, high temperature humidification conditions at 85 ℃ and 85% humidity, thermal cycle test between-40 ℃ and +105 ℃, thermal cycle test between-45 ℃ and +125 ℃, 125 ℃ high temperature standing test, and the like are strict. Therefore, the present resin flux paste also has a problem that the Tg of the cured resin needs to be 80 ℃ or higher in order to overcome the above reliability (japanese patent No. , をクリア, and する). Accordingly, an object of the present invention is to provide a solder paste which can be applied to a solder (for example, SAC (tin-silver-copper) solder) requiring a high melting point and in which Tg of a cured resin is 80 ℃ or higher, and a mounting structure in which an electronic component is mounted using the solder paste.

Hereinafter, embodiments of the present invention will be specifically described. The present invention is not limited to this embodiment. The present invention can be implemented with appropriate modifications within the intended scope of the present invention.

The resin flux paste and the mounting structure are described in detail below.

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

< solder paste of resin flux >

The resin flux solder paste of the embodiment of the present invention is a solder paste containing solder powder and flux,

the soldering flux at least comprises epoxy resin, a curing agent, a curing accelerator and an active agent,

the epoxy resin contains 10 to 90 wt% of the total epoxy resin and at least one of a biphenyl aralkyl type epoxy resin having an epoxy equivalent of 200 to 400, a naphthalene type epoxy resin and a dicyclopentadiene type epoxy resin,

the curing agent comprises 30 to 95 wt% of a biphenyl aralkyl phenol resin having a hydroxyl equivalent of 150 to 350 with respect to the total curing agent, and 5 to 70 wt% of a phenol resin having an allyl group having a hydroxyl equivalent of 100 to 200 with respect to the total curing agent.

The solder paste according to the present invention can be applied to solder connection with a high melting point, and has high heat resistance because the Tg of the cured resin of the solder paste is 80 ℃.

[ solder powder ]

The solder powder contained in the solder paste of the present embodiment is not particularly limited, and a solder powder having a melting point of 180 ℃ or higher, particularly 200 ℃ or higher is preferably used. The composition of the solder powder is not particularly limited, and may be in the form of Sn alone or a solder alloy. As the solder alloy, for example, Sn-based Sn — Ag — Cu-based solder (SAC solder), an alloy of Sn — Cu-based solder or Sn — Ag-based solder, or an alloy in which an additional metal (more specifically, a trace metal or the like described later) is further contained in these alloys can be used. Examples of the SAC solder include SAC305(Sn-3.0Ag-0.5Cu) solder having a melting point of 220 ℃ and SAC105(Sn-1.0Ag-0.5Cu) solder having a melting point of 225 ℃. Examples of the Sn-Ag solder include Sn-3.5Ag solder having a melting point of 221 ℃, and examples of the Sn-Cu solder include Sn-0.7Cu solder having a melting point of 227 ℃. Among these solder alloys, SAC305 solder is preferable. This is because, at present, SAC305 solder is commonly used for consumer electronic devices, realizes high connection reliability and low cost, and is also commonly used for solder balls of CSP, BGA packages.

The content of the solder powder is preferably 5 wt% or more and less than 60 wt% or more and 95 wt% or less with respect to the total amount of the resin flux solder paste of the present embodiment. When the content of the solder powder is 60 wt% or more and 95 wt% or less, the metal ratio of the solder paste is high, and sufficient metal connection can be performed by the metal component of the solder paste itself, and therefore, the solder paste can be used both in the case where a SAC solder ball is present (for example, BGA type) and in the case where a SAC solder ball is not present (for example, LGA type).

When the content of the solder powder is 5 wt% or more and less than 60 wt%, the solder powder is suitably used as a soldering flux for connecting a SAC solder ball and an electrode of a circuit board. In this case, metal bonding such as SAC solder balls become a main body, and the metal of the solder paste also assists metal connection of the solder balls. Further, since the solder paste has a high resin ratio, the periphery of the solder connection portion can be effectively resin-reinforced, and high connection strength can be exhibited.

The composition of the solder powder is marked by connecting the element symbols of the elements contained in the solder powder with hyphens. In the present specification, in order to explain the metal composition of the solder powder, a numerical value or a numerical range is sometimes shown before the metal element, and as is generally used in the art, the weight% of each element in the metal composition is shown in numerical values or numerical ranges (% by mass). The solder powder may be substantially composed of the listed elements, and may contain a trace amount of metal, such as Ni, Ge, Zn, Sb, and Cu, which is inevitably mixed.

The melting point of the solder powder (or solder) in the present specification means a temperature at which melting ends when a state change in the course of heating and temperature rise of the sample is observed, and can be measured by using DSC, TG-DTA, or the like.

[ flux ]

The soldering flux at least comprises epoxy resin, a curing agent, a curing accelerator and an active agent. If the resin flux paste of the present embodiment contains flux, a joint portion having high connection reliability and heat resistance can be formed. When the Tg of the cured resin of the solder paste is 80 ℃ or higher, higher heat resistance can be achieved.

When the flux is heated at a constant temperature of 20 ℃/min, it preferably exhibits a property of increasing the elastic modulus at 220 ℃ or higher. When the solder paste exhibits a property of increasing elastic modulus at 220 ℃ or higher, the solder powder is sufficiently melted at a temperature lower than 220 ℃ when the solder paste is heated, and then the flux is likely to be cured by a curing reaction at 220 ℃ or higher. Therefore, the solder powder is melted to form the conductive portion, and for example, electrical conduction between the electronic component and the circuit board is easily ensured, and the surface of the conductive portion is easily covered with the cured product of the flux, so that the resulting mounting structure has excellent electrical conductivity and mechanical strength. The method for measuring the elastic modulus (storage modulus (G)) is described in detail in examples.

(epoxy resin)

If the flux contains an epoxy resin, other components such as solder powder are easily dispersed in the epoxy resin.

The epoxy resin contains 10 to 90 wt% of the total epoxy resin and at least one of a biphenyl aralkyl type epoxy resin, a naphthalene type epoxy resin and a dicyclopentadiene type epoxy resin having an epoxy equivalent of 200 to 400.

In the present embodiment, the cured product of the epoxy resin is designed to have a high Tg. For this reason, the epoxy resin preferably has a large molecular weight, rigid skeleton. However, many of the high molecular weight epoxy resins are generally solid at normal temperature, and even when mixed with liquid epoxy, they have high viscosity. As a result of intensive studies, the present inventors have found that, among epoxy resins having a rigid skeleton, biphenyl aralkyl type epoxy resins, naphthalene type epoxy resins, and dicyclopentadiene type epoxy resins are preferable as epoxy resins having a relatively low molecular weight. They can be mixed with liquid epoxy resins to make relatively low viscosities.

As a result of further studies, the present inventors have found that when an epoxy having the above rigid skeleton is used to increase Tg of a cured epoxy resin, reactivity with a curing agent is often increased. Generally, when a resin flux paste is heated, the resin reacts and thickens before the temperature of the resin flux paste reaches the melting point of the solder powder (for example, the melting point of SAC solder is 220 ℃). This may cause thickening to inhibit metal bonding of the solder, which may result in poor bonding (see fig. 4).

In addition, the present inventors have thought that the temperature at which the resin reacts to thicken is higher than the melting point of the solder powder by adjusting the epoxy equivalent of the epoxy resin of the rigid skeleton to 200 to 400 (see fig. 5).

Specific commercially available products of such an epoxy resin having a rigid skeleton with an epoxy equivalent of 200 to 400 (high-rigidity epoxy resin) include biphenyl aralkyl type epoxy resins (product No. NC3000 epoxy equivalent 276, manufactured by Nippon Kabushiki Kaisha), naphthalene type epoxy resins (product No. HP6000 epoxy equivalent 215, manufactured by DIC Co., Ltd.), dicyclopentadiene type epoxy resins (product No. HP7200 epoxy equivalent 247, manufactured by DIC Co., Ltd.), and the like. These may be used alone in 1 kind, or may be used in combination of 2 or more kinds.

When the epoxy resin contains 10 to 90 wt% of the above epoxy resin having an epoxy equivalent of 200 to 400, the solder powder can be well dispersed in the epoxy resin. From the viewpoint of further improving the dispersibility, the resin flux solder paste of the present embodiment may further contain a solvent.

The epoxy resin may contain other epoxy resins than the biphenyl aralkyl type epoxy resin described above. The epoxy resin is preferably liquid at ordinary temperature, but may be liquefied by mixing an epoxy resin that is solid at ordinary temperature with a liquid epoxy resin, or by adding a solvent.

As the other epoxy resin which is liquid at room temperature, as long as it is an epoxy resin having 2 or more epoxy groups in 1 molecule, the molecular weight and molecular structure thereof are not particularly limited, and various epoxy resins can be used. For example, various liquid epoxy resins such as a glycidyl ether type, a glycidyl amine type, a glycidyl ester type, and an olefin oxidation type (alicyclic type) can be used. Specific commercially available products include bisphenol A type epoxy resin (product No. jER828 manufactured by Mitsubishi Chemical Co., Ltd.) and YD8125 (product No. NIPPON STEEL Chemical & Material Co., Ltd., epoxy equivalent 170).

(curing agent)

The curing agent cures the epoxy resin. The curing agent comprises 30 to 95 wt% of a biphenyl aralkyl phenol resin having a hydroxyl equivalent of 150 to 350 with respect to the total curing agent, and 5 to 70 wt% of a phenol resin having an allyl group having a hydroxyl equivalent of 100 to 200 with respect to the total curing agent. By adopting such a composition, the epoxy resin can be cured without being cured before the solder powder is melted.

The biphenyl aralkylphenol resin and the phenol novolac resin having an allyl group preferably have 2 or more phenolic hydroxyl groups in 1 molecule that can react with the epoxy group of the epoxy resin. The phenol resin used in the flux of the solder paste of the present embodiment may be 2 or more, but the phenol novolac resin having an allyl group has at least both a phenolic hydroxyl group and an allyl group in 1 molecule.

It is presumed that the phenol novolac resin having an allyl group hinders the arrangement of the phenolic hydroxyl groups by the hydrogen bond due to the steric hindrance effect of the allyl group, and therefore the phenol novolac resin which should be solid originally has a low viscosity due to this effect. In particular, the phenol resin may be a low molecular weight dimer (formula, n is 0) phenol resin in a liquid form. Specific commercially available products include, for example, those manufactured by Minghe chemical Co., Ltd: MEH-8000H (viscosity 1500-3500 mPa.s, hydroxyl equivalent 139-143), MEH-8005 (viscosity 4500-7500 mPa.s, hydroxyl equivalent 133-138), etc. In the present disclosure, the hydroxyl group equivalent means a value measured by a neutralization titration method according to Japanese Industrial Standard (JIS) -K0070.

[ chemical formula 1 ]

The cured product of the phenol novolac resin having an allyl group and the epoxy resin has a high Tg of 80 ℃ or higher. When the phenol novolac resin having an allyl group according to the present embodiment is included, the crosslink density of the cured product can be increased, and as a result, a high Tg can be obtained.

Among the phenol novolac resins, the biphenyl aralkyl phenol resin is most excellent in that both the increase in Tg and the suppression of the increase in viscosity are compatible. Specific examples of the commercial products include biphenyl aralkyl phenol novolac resin and MEHC7851S (product of michaelis chemical co., ltd., hydroxyl group equivalent 210).

(curing accelerators)

The curing accelerator accelerates the reaction between an epoxy resin classified into a relatively low reactivity class and a curing agent (for example, phenol novolac resin), does not substantially react at a temperature lower than the melting point of the solder powder (for example, 220 ℃), and can react in a short time at a temperature equal to or higher than the melting point of the solder powder. Examples of the curing accelerator include phosphorus compounds (more specifically, organophosphine compounds and salts thereof, and quaternary phosphonium compounds and salts thereof) and nitrogen compounds (more specifically, imidazole, DBU salts, tertiary amine compounds, and the like). Among these, for example, when the melting point of the solder powder is 220 ℃, as a curing accelerator which does not substantially react at a temperature lower than 220 ℃ and accelerates the reaction at a temperature of 220 ℃ or higher in a short time, for example, one or more of triphenylphosphine which is a phosphorus-based quaternary phosphonium compound, triphenylphosphine triphenylborane which is a salt thereof, tetraphenylphosphonium tetraphenylborate, and tetraphenylphosphonium p-tolylborate are preferable, and the melting point of tetraphenylphosphonium p-tolylborate is also as high as 305 ℃, and therefore, it is particularly preferable.

(active agent)

The activator removes a metal oxide film that may exist on the surface of the joined members (more specifically, electrodes, wirings, and/or solder powder of the electronic component), for example, in a temperature region where the resin flux solder paste is heated.

The type of the activating agent is not limited as long as it has a function of removing the metal oxide film, and any appropriate activating agent may be used. Examples of the activator include organic acids having a reducing power, halogens, and amine salts. In electrical and electronic applications, if a halogen compound is contained in an epoxy resin cured product, it may cause insulation failure. In addition, since a common amine salt reacts with an epoxy resin, the storage stability tends to be impaired. Therefore, among these active agents, organic acids having excellent resistance to dielectric deterioration are preferable.

The organic acid has a particularly excellent flux action. Here, the flux action refers to a reduction action of removing an oxide film generated on a surface of a metal coated with a solder paste and an action of reducing a surface tension of a molten solder to promote wettability of the solder to the surface of the metal. In addition, the organic acid does not have reactivity with the epoxy resin at room temperature like an amine salt, and can react with the epoxy resin when heated. However, as an exception, Triethanolamine (TEA) is mild in reactivity in amine-based active agents and also excellent in preservability.

The organic acid also hardly causes adverse effects such as corrosion, since it enters into the cured epoxy resin after the oxide film is removed by reducing the solder.

The type of the organic acid is not particularly limited, and any organic compound acid can be used. For example, a rosin component material typified by rosin acid, sebacate, adipic acid, glutaric acid, succinic acid, malonic acid, citric acid, pimelic acid, or the like can be used. In particular, when considering the reaction with the epoxy resin, it is preferable that the dibasic acid does not lower the crosslinking density.

The carboxyl group of the organic acid reacts with the epoxy group even at 200 ℃ or lower, and therefore, the organic acid contributes to thickening of the flux in the solder paste. Therefore, when an organic acid is used as the active agent, the melting point of the organic acid is preferably 130 ℃ or higher and 220 ℃ or lower, more preferably 130 ℃ or higher and 200 ℃ or lower, and still more preferably 133 ℃ or higher and 186 ℃ or lower. This is because the use of the organic acid of the dibasic acid having a high melting point hardly inhibits melting and aggregation of the solder described later.

Specifically, it is desired that a solder having a high melting point, for example, SAC solder, has a small activation force (i.e., a reduction action for removing an oxide film on the surface of the solder) in a low temperature region of 130 ℃. Examples of the organic acid having a melting point of 130 ℃ or higher and 220 ℃ or lower include succinic acid (melting point 186 ℃), adipic acid (melting point 152 ℃), suberic acid (melting point 142 ℃), sebacic acid (melting point 133 ℃) which are one of dibasic acids. Oxalic anhydride has a melting point as high as 189 ℃ but a high hygroscopic property, and absorbs moisture to form 2 hydrate having a low melting point (melting point 101 ℃). Further, organic acids having a melting point higher than that of SAC solder, such as isophthalic acid (melting point 340 ℃ C.), are generally not expected to remove the oxide film of solder. However, these organic acids having a melting point of less than 130 ℃ or more than 220 ℃ are not excluded from the organic acids that can be used in the present embodiment, and may be used as appropriate depending on the solder used in practice, the reflow temperature, and the like. These organic acids may be used in 1 component, or 2 or more components may be mixed.

(other Components)

Examples of other components of the flux contained in the solder paste include a modifier (for example, rosin), an additive, a solvent, and a thixotropy imparting agent, which are generally used. The solvent can reduce the viscosity of the solder paste, reduce the viscosity, or impart fluidity. Examples of the solvent include diethylene glycol monohexyl ether. The thixotropy imparting agent retains the solvent print shape. Examples of the thixotropy imparting agent include hydrogenated castor oil, stearic acid amide, and sorbitol compounds. Specific examples of the thixotropy imparting agent include those manufactured by Nippon chemical Co., Ltd: GELALL D.

(method for producing solder paste)

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

First, the epoxy resin and the curing agent (phenol resin) are dissolved by heating to prepare a uniform resin mixture. Next, the activator, the curing accelerator, and a solvent as needed are weighed and mixed to prepare the flux. Then, solder powder is added to the flux and mixed and kneaded. Thereby producing a resin flux solder paste.

The solvent may be added as necessary before the addition of the activator to lower the viscosity of the flux. In addition, a thixotropy-imparting agent may be added as necessary in order to improve printability.

< mounting Structure >

A mounting structure according to an embodiment of the present invention is a mounting structure for mounting an electronic component on a circuit board using the resin flux paste described above, including: a conductive part formed by metal bonding of the electronic component and the circuit board; and a reinforcing portion formed by covering the periphery of the conductive portion with a cured product of the flux.

The mounting structure of the present embodiment will be described with reference to fig. 1. Fig. 1 is a sectional view of a solder-bonded portion of a CSP bonded using a resin flux solder paste. As shown in fig. 1, the mounting structure (e.g., semiconductor device) includes: the circuit board 1 and the circuit board 3, the electrodes 2 and 4 provided on the circuit boards 1 and 3, the solder bump 5 and the solder conductive portion 9 for metal bonding the electrodes 2 and 4, and the reinforcing portion 6b for covering the surface of the solder conductive portion 9. The circuit substrate 1 provided with the electrodes 2 is an electronic component (e.g., a chip component and a semiconductor component). Chip components include, for example, a chip resistor and a chip capacitor. The circuit board 3 on which the electrodes 4 are provided is, for example, a printed board. Examples of the semiconductor components include CSP or BGA having a solder ball as a terminal, semiconductor packages such as QFP having a lead as a terminal, and semiconductor elements (bare chips) having a terminal not housed in the package. The circuit boards 1 and 3 have conductive wirings. The electrode 2 is a terminal of an electronic component. The electrodes 2, 4 are electrically connected to the solder conductive portion 9 via the solder bump 5. The reinforcing portion 6b is formed of a cured product of the flux, and covers the surface (periphery) of the solder conductive portion 9 to reinforce the solder conductive portion 9, thereby improving the mechanical strength.

(method of manufacturing mounting Structure)

The mounting structure of the present embodiment can be manufactured by mounting a semiconductor component on, for example, a circuit board having conductor wiring using the resin flux paste. A method for manufacturing the mounting structure is described with reference to fig. 2A to 2D. Fig. 2A to 2D are cross-sectional explanatory views schematically showing a bonding process of a ball portion of a CSP using the resin flux paste of the present invention. The method for manufacturing the mounting structure includes, for example, a coating step, a mounting step, and a bonding step.

In the coating step, as shown in fig. 2A, a resin flux paste 7 is coated on the electrodes 4 of the circuit board 3. The resin flux paste 7 can be applied by, for example, superimposing a metal mask having through holes at the same positions as the electrodes 4 on the circuit board 3, then supplying the resin flux paste 7 to the surface of the metal mask, and filling the through holes with a squeegee. Then, when the metal mask is separated from the circuit substrate 3, the circuit substrate 3 coated with the resin flux paste 7 per electrode 4 can be obtained.

In the mounting step, as shown in fig. 2B, the electronic component (circuit board 1) is mounted on the circuit board 3 by using a chip mounter or the like so that the electrodes 4 coated with the resin flux paste 7 and the electrodes 2 of the circuit board 1 face each other. Specifically, the electronic component is superimposed on the circuit board so that the electrodes 4 of the coated circuit board 3 face the terminals of the chip component or the semiconductor component thereon in an uncured state of the applied resin flux paste 7.

In the bonding step (reflow step), as shown in fig. 2C, the circuit board 1 on which the electronic component is mounted is heated by a heater 8. For example, a printed wiring board on which chip components are arranged is heated to a predetermined heating temperature in a reflow oven. As a result, as shown in fig. 2D, a solder joint portion (conductive portion 9) in which the solder powder is melted and integrated with the solder ball and a reinforcing portion 6b in which the surface of the conductive portion 9 is made of a cured product of the flux (cured product of the epoxy resin) are formed. The electronic component and the circuit board 1 are electrically joined via the conductive portion 9.

In the bonding step, it is necessary to sufficiently melt the solder powder and then sufficiently and appropriately perform a curing reaction of the resin component of the flux. Specifically, in the bonding step, if the epoxy resin, which is a flux component in the solder paste, undergoes a curing reaction before the solder powder is sufficiently melted, the flux is thickened. Thus, the aggregation and melting of the solder particles are inhibited, and proper metal conduction cannot be obtained. In order to avoid such a situation and obtain appropriate conduction and good mechanical strength, it is necessary to delay (suppress the progress of) the curing reaction of the resin of the flux until the temperature of the heater 8 (e.g., reflow furnace) is raised to the melting point of the solder powder to be used. When the temperature of the heater 8 reaches the melting point of the solder powder, the solder powder is sufficiently melted, and after the solder powder is fused with the solder ball of the electronic component (e.g., semiconductor component) and fused with the electrode metal of the circuit component, the resin of the flux needs to complete the curing reaction in a short time (e.g., several minutes or so).

[ examples ] A method for producing a compound

The present invention will be described more specifically below with reference to examples. The present invention is not limited to the following examples. In addition, unless otherwise specified, parts and% in the examples are on a weight basis.

< preparation of solder paste >

First, components (solder powder, raw material of flux, and the like) constituting the solder paste shown below are prepared.

[ solder powder ]

SAC 305: sn-3.0Ag-0.5Cu, an average particle diameter of 10 to 25 μm, and a melting point of 219 ℃ (manufactured by Mitsui Metal mining Co., Ltd.)

SAC 105: sn-1.0Ag-0.5Cu, an average particle diameter of 10 to 25 μm, and a melting point of 225 ℃ (manufactured by Mitsui Metal mining Co., Ltd.)

[ flux ]

(epoxy resin: basic epoxy resin)

Bisphenol A epoxy resin, YD8125(NIPPON STEEL Chemical & Material Co., Ltd., epoxy equivalent 170)

(epoxy resin: high rigidity epoxy resin)

Biphenylalkyl epoxy resin, NC3000 (manufactured by Nippon Kagaku K.K., epoxy equivalent 276)

Naphthalene epoxy resin (available from DIC corporation: HP6000, epoxy equivalent 215)

Dicyclopentadiene type epoxy resin (available from DIC corporation: HP7200, epoxy equivalent 247)

(curing agent: phenol novolac resin having allyl group (liquid phenol resin))

Allylated phenol novolac resin (allyl-modified phenol novolac resin): MEH8000H (hydroxyl equivalent 140, manufactured by Minghe Kaisha)

(curing agent: Biphenylaralkylphenol resin (high rigidity phenol resin))

Biphenylalkyl phenol Novolac, MEHC7851S (hydroxyl equivalent 210, product of Minghe Kabushiki Kaisha, used in examples 1 to 9)

General purpose phenol novolac resin: h-4 (hydroxyl equivalent 104, manufactured by Minghe chemical Co., Ltd., used in comparative example 1)

(curing accelerators)

Triphenylphosphine (TPP)

Triphenylphosphine triphenylborane (TPP-S)

Tetraphenylphosphonium tetraphenylborate (TPP-K)

Tetraphenylphosphonium p-tolylborate (TPP-MK)

(active agent: organic acid)

Adipic acid (manufactured by Tokyo chemical industry Co., Ltd.)

[ others ]

(solvent)

Diethylene glycol monohexyl ether

(thixotropic agent)

GELALL D (New Ri Su chemical Co., Ltd.)

Next, the epoxy resin, the phenol resin curing agent, the activator, the curing accelerator, the thixotropic agent, and the solvent were weighed so as to be in the proportions of the parts by weight shown in fig. 6 below. Heating and mixing are carried out, and the uniform resin mixture is prepared into the soldering flux. SAC solder was further added and kneaded by a planetary mixer to prepare resin flux pastes of examples 1 to 9 and comparative examples 1 to 2.

< measuring method >

The following items were evaluated for examples 1 to 9 and comparative examples 1 to 2. The evaluation results are shown in fig. 6 as characteristics of the solder paste in each example.

(measurement of temperature at which increase of modulus of elasticity started)

The change in elastic modulus of the flux during curing under heating and during cooling was measured using a viscoelasticity measuring apparatus ("rheometer DHR-2" manufactured by TA Instruments). Characteristics of the change in elastic modulus (change in storage modulus (G)) are described with reference to fig. 4 and 5. Referring to the compounding amounts shown in fig. 6, flux was prepared as a measurement sample. The flux was heated and cooled according to a predetermined temperature profile, and the elastic modulus at each time was measured in parallel (indicated by a solid line in fig. 4 and 5). The temperature profile is shown by a dotted line (short dashed line) in FIGS. 4 and 5, and the temperature is raised at a constant rate of 20 ℃ per minute from the normal temperature (25 ℃), maintained at 230 ℃ for 8 minutes, and then cooled at a low rate of-20 ℃ per minute. When the flux was heated at a constant temperature of 20 ℃/min, the "temperature at the time of starting a sharp rise" of the elastic modulus accompanying the curing reaction of the resin was read from the graph. Specifically, when a chemical reaction (curing reaction) of the epoxy resin and the phenol novolac resin of the curing agent is initiated by the accelerating effect of the curing accelerator, the reaction proceeds at a time due to a high temperature, the resin of the flux becomes three-dimensional, and the elastic modulus of the cured product is improved. The curve shape showing the change in the elastic modulus changes sharply upward and rightward as the reaction starts, from a substantially flat shape before the reaction starts. The temperature that abruptly rises to the right is referred to as "temperature at the time of onset of abrupt rise". The temperature thus obtained was set as a viscoelasticity increase start temperature.

The resin flux solder paste is determined based on the following determination criteria based on the obtained elastic modulus increase start temperature.

A: the initial temperature of the increase in modulus of elasticity is 220 ℃ or higher

C: the elastic modulus rise starting temperature is lower than 220 DEG C

(measurement of glass transition temperature Tg)

The glass transition temperature Tg (unit:. degree. C.) of the resin flux paste was measured using a viscoelasticity measuring apparatus ("DHR-2" manufactured by TA Instruments). The measurement of the glass transition temperature is explained with reference to fig. 4 and 5. Referring to the compounding amounts shown in fig. 6, a flux was prepared as a measurement sample. The flux was heated and cooled according to a predetermined temperature profile, and loss tangents (tan δ: represented by broken lines (long dashed lines) in fig. 4 and 5) at respective times were plotted in parallel to obtain graphs. Temperature profile the same temperature profile as for the determination of the modulus of elasticity was used. The peak value is detected from the obtained graph of the loss tangent. The temperature at the peak was defined as the glass transition temperature Tg of the cured product of the flux.

< evaluation of Heat resistance: evaluation of Heat cycle reliability >

(production of evaluation element for thermal cycle reliability)

The solder paste prepared as above was printed on the Au-plated electrode on the circuit substrate (FR-4 substrate) using a metal mask in such a manner that the thickness became 0.1mm, thereby forming a solder paste printed portion.

Then, a CSP chip (0.4mm BGA) having a size of 10mm × 10mm, a pitch of 0.4mm, and 360 pins (Japanese: ピン) was mounted on the solder paste printed portion on the circuit board by using a mounter. The electrode material of the circuit board is copper, and the substrate material is glass epoxy. Then, the resultant was heated at 240 ℃ for 6 minutes using a reflow apparatus to form a bonded portion, and a thermal cycle reliability evaluation element was produced.

(reliability of thermal cycle)

As the evaluation of the solder connection reliability, the thermal cycle reliability was evaluated as follows. For the 5 elements for evaluation of thermal cycle reliability (measurement number n is 5) produced as described above, the cycle of cooling to-40 ℃ and then raising the temperature to 125 ℃ was repeated 1000 times. Then, the connection resistance value was measured. The thermal cycle reliability was evaluated from the obtained connection resistance values based on the following evaluation criteria.

(evaluation criteria)

A: the connection resistance values of all 5 evaluation elements were within 2. omega. + -20% of the standard resistance value

B: at least 1 of the 5 evaluation elements is within 2Q + -20% of the standard resistance value

C: all of the connection resistance values of the 5 evaluation elements were not included in the range of 2. omega. + -20% of the standard resistance value

Fig. 5 shows the characteristics of the storage modulus (G) and the loss tangent tan δ of the resin flux of example 2 at the time of heating for curing and at the time of cooling. Specifically, if the temperature is raised at a constant rate from room temperature, the storage modulus (G) of the resin flux decreases as the viscosity decreases, and becomes stable from around 80 ℃. Then, if the temperature is further increased, the storage modulus (G) increases with a sharp viscosity increase at 230 ℃. This indicates that the epoxy resin and curing agent begin to react and gradually bridging occurs. Further, if the temperature in the furnace becomes a constant value at 240 ℃, the storage modulus (G) is also stabilized. As shown in fig. 5, when the reaction start temperature of the resin flux is 230 ℃, the reaction and thickening of the resin do not start at the melting point 220 ℃ of the SAC solder, and therefore the solder melts and aggregates, thereby enabling metal connection.

Fig. 4 shows the characteristics of the storage modulus (G) and the loss tangent tan δ of the resin flux of comparative example 1 at the time of heating for curing and at the time of cooling. In comparison with fig. 5, the resin flux of comparative example 1 has a resin cure initiated at 200 ℃. Therefore, when the temperature in the furnace reaches 220 ℃ which is the melting point of the SAC solder, the curing reaction proceeds and the resin thickens, so that the solder does not melt and aggregate, and remains as a solder ball.

As shown in FIG. 6, the resin flux pastes of examples 1 to 9 include solder powder and flux. The soldering flux comprises epoxy resin, a curing agent, a curing accelerator and an active agent. The epoxy resin has an epoxy equivalent of 200 to 400, and contains 10 to 90 wt% of at least one of a biphenyl aralkyl type epoxy resin, a naphthalene type epoxy resin, and a dicyclopentadiene type epoxy resin, relative to the epoxy resin. The curing agent comprises 30 to 95 wt% of a biphenyl aralkyl phenol resin having a hydroxyl equivalent of 150 to 350 with respect to the total curing agent, and 5 to 70 wt% of a phenol resin having an allyl group having a hydroxyl equivalent of 100 to 200 with respect to the total curing agent.

As shown in FIG. 6, the evaluation results of the heat resistance of the resin flux pastes of examples 1 to 5 were A or B.

As shown in FIG. 6, the resin flux paste of comparative example 1 contains 70.0 wt% of the phenol novolac resin H-4 with respect to the total curing agent, but H-4 does not have allyl groups. In the resin flux paste of comparative example 2, the epoxy resin was not 1 or more of the biphenyl aralkyl type epoxy resin, the naphthalene type epoxy resin, and the dicyclopentadiene type epoxy resin. Phenol novolac resin having allyl group is not included. In addition, the curing agent does not contain 30 to 95 wt% of a biphenyl aralkyl phenol resin and 5 to 70 wt% of a phenol resin having an allyl group with respect to the total curing agent.

As shown in fig. 6, the resin flux paste of comparative example 1 was unable to be connected, and therefore, heat resistance could not be evaluated. The resin flux paste of comparative example 2 was C.

The resin flux pastes of examples 1 to 9 were significantly superior in heat resistance to the resin flux pastes of comparative examples 1 to 2.

When considering the results of fig. 6, consider that: in a flux comprising an epoxy resin having a rigid skeleton (high-rigidity epoxy resin) and a phenol resin (high-rigidity phenol resin), the Tg of the resin can be increased, and by using a resin having a large epoxy equivalent and a large hydroxyl equivalent and using a curing accelerator of a type that accelerates a reaction at a high temperature, the resin does not cure until the SAC solder melts, and after the solder melts, the curing reaction is rapidly caused in a short time to perform three-dimensional bridging, whereby excellent thermal cycle reliability can be obtained.

Industrial applicability

The solder paste and the mounting structure of the present invention can be used in a wide range of applications in the field of electric/electronic circuit forming technology. For example, the present invention can be used for connection of various electronic components and for bonding them to a substrate. Further, the present invention can be used for products incorporating these elements, components, or substrates, for example, DVDs, mobile phones, general-purpose home appliances, and the like.