JP2006124607A - Conductive adhesive and electronic device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive adhesive which is used for connecting an electronic part having Sn electrodes to a circuit substrate and realizes a reduction in the initial value of connection resistance, the inhibition in the increase of the connection resistance under a high temperature, and a high humidity, and the security of a connection strength under a high temperature. <P>SOLUTION: This conductive adhesive 30 used on the connection of an electronic part 20 having Sn electrodes 21 to a circuit substrate 10, comprising a naphthalene skeleton-having epoxy resin as a main agent, an acid anhydride and a phenolic resin as curing agents, imidazole as a curing accelerator, and a conductive filler 32, is characterized in that the conductive filler comprises Ag and the other metal such as Cu which is baser than Ag but nobler than Sn, and the acid anhydride and the phenolic resin are together used in an amount of 0.8 equivalent and in an epoxy equivalent ratio of 95/5 to 5/95. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electronic device in which an electronic component is connected to a conductive adhesive and a circuit board via the conductive adhesive.

  In recent years, in mounting electronic components, a connection method using a conductive adhesive has been adopted as a connection method instead of solder connection (see, for example, Patent Document 1). Since the connection by the conductive adhesive does not use Pb, there are merits such as being able to cope with environmental problems and abolishing the cleaning of the solder flux.

This conductive adhesive is generally formed by containing a conductive filler in a resin, and after contacting the circuit board and the electrode of the electronic component via this conductive adhesive, the resin is cured. Then, contact is made through a conductive filler to make an electrical connection.
JP 2000-319622 A

  Here, the conductive adhesive generally uses an Ag filler as a conductive filler. At present, the conductive adhesive using the Ag filler is reliable for electronic parts having noble metal electrodes, and has been used in in-vehicle electronic devices.

  However, according to the study by the present inventors, this Ag filler was used for an Sn-plated electrode component used in many general-purpose electronic devices such as home appliances, that is, an electronic component having a Sn-based base metal electrode. It has been found that the following problems occur when connecting on a circuit board via a conductive adhesive.

  In the connection between the base metal electrode of the electronic component and the conductive adhesive, (1) increase in the initial value of connection resistance, (2) increase in connection resistance under high temperature and high humidity, and (3) connection under high temperature. There are three problems: strength reduction. These problems are specifically shown in FIG. 2, FIG. 3, and FIG. 4 as experimental results of the present inventors.

  FIG. 2 is a diagram showing the relationship between test time and component connection resistance in a high-temperature standing test at 150 ° C., and FIG. 3 shows the relationship between test time and component connection resistance in a high-temperature and high-humidity test at 85 ° C. and 85% RH. FIG. 4 and FIG. 4 are diagrams showing the relationship between the test time and the component connection strength in a high-temperature standing test at 150 ° C.

  2 to 4, the white triangle plot is the result in the case of an electronic component having a base metal electrode made of Sn, and the black circle plot is the result in the case of an electronic component having a noble metal electrode made of Ag-Pd. . The result of this noble metal electrode has a track record in terms of reliability.

  As shown in FIGS. 2 to 4, the initial value of the connection resistance is increased in the case of the electronic component having the base metal electrode made of Sn, compared to the case of the electronic component having the noble metal electrode made of Ag—Pd. As can be seen (see FIG. 2), an increase in connection resistance is observed under high temperature and high humidity (see FIG. 3), and a decrease in connection strength is observed under high temperature (see FIG. 4).

  The present invention has been made in view of the above problems, and in a conductive adhesive used when connecting an electronic component having a Sn-based base metal electrode on a circuit board, the initial value of the connection resistance is reduced, It is an object to realize suppression of an increase in connection resistance under high temperature and high humidity and securing of connection strength under high temperature. Another object of the present invention is to provide an electronic device using such a conductive adhesive.

  In order to achieve the above object, intensive study was made on three problems: (1) increase in initial value of connection resistance, (2) increase in connection resistance under high temperature and high humidity, and (3) decrease in connection strength under high temperature. Went. This examination will be specifically described with reference to FIGS. 10A and 10B and FIGS. 11A to 11D.

  10A is a schematic cross-sectional view of a general electronic device using the conductive adhesive 30, and FIG. 10B is a conductive adhesive 30 in a portion A surrounded by a circle in FIG. It is an enlarged view which shows the state before hardening of.

  11A is a view showing the shrinkage of the resin 31 in the conductive adhesive 30 shown in FIG. 1B, and FIG. 11B is an Ag filler as a conductive filler in the conductive adhesive 30. It is a figure which shows the mode of 32 contact, (c) is a figure which shows the influence of the conductive adhesive 30 under high temperature, high humidity, (d) is a figure which shows the influence of the conductive adhesive 30 under high temperature. It is.

  As shown in FIG. 10A, the electronic component 20 has an Sn-based base metal electrode 21 and is mounted on the circuit board 10 so that the electrode 11 and the base metal electrode 21 of the circuit board 10 are electrically conductive. It is electrically connected via an adhesive 30.

  As shown in FIG. 10B, Ag filler 32 is dispersed in resin 31 in conductive adhesive 30 before curing in a state where electronic component 20 is mounted on circuit board 10. In this state, heating is performed and the conductive adhesive 30, that is, the resin 31 is cured to perform connection.

  When heating is performed, the resin 31 shrinks as shown in FIG. 11A, and as shown in FIG. 11B, the Ag fillers 32, the Ag filler 32 and the base metal electrode 21, and further the Ag filler. 32 and the electrode 11 of the circuit board 10 are electrically connected by contact or tunnel effect.

  Here, as shown in FIG. 10B, an oxide film (that is, initial oxide film) 21 a originally exists on the surface of the Sn-based base metal electrode 21 of the electronic component 20. Then, as shown in FIG. 10B, the initial oxide film 21a causes a conduction failure between the Ag filler 32 and the base metal electrode 21, so that there is a problem that the initial value of the connection resistance is increased. It is thought to occur.

  Further, since the potential difference between Ag of the Ag filler 32, which is a noble metal, and Sn of the Sn-based base metal electrode 21 is large, as shown in FIG. 11C, the base metal electrode is caused by galvanic corrosion under high temperature and high humidity. Sn on the surface 21 is oxidized and an oxide film 21a grows.

  And since this oxide film 21a causes a poor conduction between the Ag filler 32 and the base metal electrode 21 as an insulating film, it is considered that the above problem of an increase in connection resistance under high temperature and high humidity occurs.

  Further, as shown in FIG. 11 (d), a deteriorated portion 31 a of the resin is generated near the interface between the resin 31 and the base metal electrode 21 in a high temperature environment. The deteriorated portion 31a is a portion where the resin 31 is deteriorated or changed in composition by heat, and has been experimentally confirmed by a composition analysis such as FT-IR. Due to the deteriorated portion 31a, the influence of decreasing the interface strength between the resin 31 and the base metal electrode 21 is great. Prof. Kakinuma, Osaka University, states that tin diffuses into silver and forms a void when alloyed, resulting in a decrease in strength.

  From these examination results, in order to reduce the initial value of the first connection resistance, it is necessary to remove the initial oxide film 21a originally present on the surface of the Sn-based base metal electrode 21 of the electronic component 20. Considering that, we proceeded with the study.

  As a result, it has been experimentally found that if an acid anhydride is used as the curing agent for the conductive adhesive and imidazole is used as the curing accelerator, the initial oxide film 21a can be reduced and removed by the acid anhydride and imidazole. (See FIG. 2).

  In addition, the present inventors formed an oxide film on the surface of the eutectic solder ball for the reducing action by the acid anhydride and imidazole, and mixed the acid film with the acid anhydride and imidazole, followed by heat treatment. The DSC behavior was examined using the solder balls after the oxide film was formed and the solder balls after the heat treatment.

  In this DSC analysis, the more oxide film is present on the surface of the solder ball, the higher the melting point shifts. When reduced by an acid anhydride or imidazole, it approaches the melting point temperature of eutectic solder. The disappearance degree of the oxide film, that is, the reducing action by the acid anhydride and imidazole could be confirmed, and the reducing action was actually confirmed.

  Similarly, in order to suppress an increase in connection resistance under high temperature and high humidity, it is also effective to lower the water absorption rate of the cured resin 31 that plays the role of an electrolyte.

  Therefore, the present inventors adopted an epoxy resin having a naphthalene skeleton as the main agent of the conductive adhesive, adopted an acid anhydride and a phenol resin as a curing agent, and adopted imidazole as a curing accelerator. It was considered that the increase in connection resistance can be reduced by reducing the water absorption rate of the resin 31 and increasing the purity.

  Moreover, in order to suppress the increase in the connection resistance under the second high temperature and high humidity, the galvanic corrosion is suppressed by replacing the conductive filler 32 of the conductive adhesive with not a precious Ag but a base metal. It is possible. However, since Ag is excellent in conductivity as a metal, the use of Ag cannot be stopped in order to ensure the function of the conductive filler 32.

  Thus, as a result of studying the suppression of the connection resistance value under high temperature and high humidity while utilizing the conductivity of Ag as the conductive filler, the present inventors found that the conductive filler is lower than Ag and Ag. Thus, it was considered that the potential difference between the base metal electrode 21 and the conductive filler 32 can be reduced and galvanic corrosion can be suppressed if it is made of other metal that is nobler than Sn.

  And as a result of advancing the study, in the conductive adhesive, the conductive filler is composed of Ag and other metals that are baser than Ag and noble than Sn, and an epoxy resin having a naphthalene skeleton as the main agent It has been experimentally found that if an acid anhydride and a phenol resin are employed as the curing agent and imidazole is employed as the curing accelerator, an increase in connection resistance under high temperature and high humidity can be suppressed (see FIG. 3).

  Further, in order to ensure the connection strength at the third high temperature, the cured resin 31 has less change in functional group that seems to be involved in the adhesive strength, and is heat resistant. Considering that it is necessary that the volume change is smaller and the glass transition point (Tg) is higher, the investigation was advanced.

  As a result, if an epoxy resin having a naphthalene skeleton is used as the main agent of the conductive adhesive, an acid anhydride is used as the curing agent, and imidazole is used as the curing catalyst, high heat resistance and high Tg of the resin can be realized. It was experimentally found that the connection strength was ensured at high temperatures (see FIG. 4).

  Further, as shown in the above examination results, it is preferable to use an acid anhydride and a phenol resin in combination as a curing agent for the conductive adhesive.

  As described above, the acid anhydride can reduce and remove the oxide film, increase the purity and decrease the water absorption rate of the cured resin 31 and increase the Tg, and is effective in improving heat resistance and moisture resistance. is there. However, since it is difficult to ensure the printability of the conductive adhesive and the elasticity of the resin after curing with an acid anhydride alone, the combined use with a phenol resin is preferable.

  As a result of further investigation on this, it was experimentally found that by using phenol as a curing agent, the curing shrinkage stress can be lowered and the flexural modulus can be increased (see FIGS. 5 and 6).

  The curing shrinkage stress and the flexural modulus are not preferable if they are too large or too small. Practically, the preferred ratio between the acid anhydride and the phenolic resin is that the acid anhydride and the phenolic resin are used in combination and the epoxy equivalent ratio is 0.8 equivalent, and the breakdown is 95/5 to 5/95. Within this ratio range, it is effective for improving heat cycle resistance, and further suitable for paste application, and is effective.

  Moreover, if the ratio of the acid anhydride and the phenol resin as the curing agent is in the above range, the Cl ion concentration in the conductive adhesive can be reduced, high purity can be appropriately realized, and high Tg can be achieved. Heat resistance can be appropriately realized (see FIGS. 7 and 8).

  The invention described in claim 1 is created based on such examination results, and connects the electronic component (20) having the Sn-based base metal electrode (21) on the circuit board (10). In a conductive adhesive sometimes used, comprising an epoxy resin having a naphthalene skeleton as a main agent, an acid anhydride and a phenol resin as a curing agent, imidazole as a curing accelerator, and a conductive filler, The conductive filler is composed of Ag and another metal that is more base than Ag and nobler than Sn, and the acid anhydride and the phenol resin are used in combination with an epoxy equivalent ratio of 0.8 equivalent. The breakdown is 95/5 to 5/95.

  According to the present invention, it is used when connecting the electronic component (20) having the Sn-based base metal electrode (21) on the circuit board (10) by appropriately exerting the above-described effects of the respective components. In the conductive adhesive, it is possible to reduce the initial value of the connection resistance, suppress the increase in connection resistance under high temperature and high humidity, and ensure the connection strength at high temperature.

  The invention described in claim 2 is characterized in that, in the conductive adhesive according to claim 1, the imidazole is microencapsulated.

  As described above, it is preferable to microencapsulate imidazole since it is possible to suppress the progress of curing by imidazole, which is a curing accelerator, before heating the conductive adhesive.

  Here, as in the invention according to claim 3, in the conductive adhesive according to claim 1 or 2, novolac phenol can be adopted as the phenol resin.

  Moreover, like the invention of Claim 4, in the electrically conductive adhesive of Claims 1-3, the compounding ratio of the said electrically conductive filler and the resin component is 82 / 18-90 / as a weight ratio. 10 is preferable.

  Further, as in the invention according to claim 5, in the conductive adhesive according to claims 1 to 4, the conductive filler is an alloy filler made of an alloy of Ag and the other metal. Can be.

  Here, in the conductive adhesive according to claim 5, as in the invention according to claim 7, the surface of the alloy filler is coated with fine particles made of a metal nobler than the other metal. It is preferable that

  Since the above alloy filler is baser than Ag alone, it is likely to be oxidized, and the connection resistance between the alloy filler and the counterpart tends to increase. Therefore, if the alloy filler is coated with fine particles made of a noble metal rather than other metals, the fine particles are fused by the thermal curing of the conductive adhesive. Therefore, it is easy to secure the connection resistance.

  Further, as in the invention according to claim 6, in the conductive adhesive according to claims 1 to 4, the conductive filler is a first filler made of Ag and a second filler made of the other metal. It can be a mixture with a filler.

  Here, in the conductive adhesive according to claim 6, as in the invention according to claim 8, the surface of the first filler or the second filler is more than the other metal. It is preferable that fine particles made of a noble metal are coated.

  The reason is the same as that of the invention described in claim 7 above, and by the fusion of the fine particles by heat curing of the conductive adhesive, sufficient connection between the fillers is made and it is easy to ensure the connection resistance.

  In the ninth aspect of the present invention, in the conductive adhesive according to the fifth or sixth aspect, fine particles made of a noble metal than the other metal are mixed between the conductive fillers. It is characterized by having.

  The operational effect of the present invention is the same as that of the invention described in claim 7 above, and by the fusion of the fine particles by the thermal curing of the conductive adhesive, sufficient connection between the fillers is made and it is easy to ensure the connection resistance. .

  As in the invention described in claim 10, in the conductive adhesive described in claims 7-9, the particle diameter of the fine particles can be 1-500 nm.

  As in the invention described in claim 11, in the conductive adhesive described in claims 1-10, Cu can be adopted as the other metal.

  In addition, as described above, an epoxy resin having a naphthalene skeleton is adopted as a main component of the conductive adhesive, an acid anhydride and a phenol resin are adopted as a curing agent, and imidazole is adopted as a curing accelerator, thereby being cured. The electrical conductivity can be reduced by reducing the water absorption rate of the resin and increasing the purity.

  Here, as an index of a resin that is highly purified to reduce electrical conductivity, there is a Cl ion concentration in the conductive adhesive.

  And like invention of Claim 12, in the conductive adhesive of Claims 1-11, it is preferable that the Cl ion concentration in the said conductive adhesive is 10 ppm or less.

  The small amount of Cl ions in the conductive adhesive means that the cured resin is highly purified, the electrical conductivity is reduced, and galvanic corrosion is unlikely to occur.

  According to the study by the present inventors, it has been experimentally confirmed that in the conductive adhesive according to claim 1, the Cl ion concentration in the conductive adhesive is 10 ppm or less (see FIG. 8), such a Cl ion concentration is preferable because galvanic corrosion can be appropriately suppressed.

  Moreover, as a water absorption rate of the cured resin, a moisture resistance test is performed on the cured conductive adhesive, and a change in weight before and after the test corresponds to the water absorption rate.

  In the invention according to claim 13, in the conductive adhesive according to claims 1 to 12, the cured product after curing the conductive adhesive is allowed to stand for 364 hours in an environment of 85 ° C and 85RH%. The weight change after the moisture resistance test is 2% or less.

  According to the study by the present inventors, it has been experimentally confirmed that in the conductive adhesive according to claim 1, the weight change by such a moisture resistance test is 2% or less (see FIG. 9).

  This employs an epoxy resin having a naphthalene skeleton as the main agent of the conductive adhesive, an acid anhydride and a phenol resin as the curing agent, and imidazole as the curing accelerator, thereby absorbing the water absorption of the cured resin. This is probably because the rate dropped.

  Moreover, in invention of Claim 14, in the conductive adhesive of Claims 1-13, in the hardened | cured material after hardening | curing the said conductive adhesive, the glass transition temperature is 110-160 degreeC. It is characterized by being.

  According to the study by the present inventors, in the conductive adhesive according to claim 1, the glass transition temperature of the cured conductive adhesive is increased to about 110 ° C. to 160 ° C. This has been confirmed experimentally (see FIG. 7).

  Further, as in the invention described in claim 15, in the conductive adhesive according to claims 1 to 14, the conductive filler is between the conductive fillers or of the circuit board (10). It can be fused with the electrode (11) or the base metal electrode (21) of the electronic component (20).

  In the invention described in claim 16, an Sn-based base metal electrode (on the circuit board (10) via the conductive adhesive (30) according to any one of claims 1 to 15 is provided. An electronic device comprising the electronic component (20) and the circuit board (10) is provided by mounting the electronic component (20) having 21) and heating and curing the conductive adhesive (30). .

  According to this, an electronic device using a conductive adhesive that can reduce the initial value of connection resistance, suppress the increase in connection resistance under high temperature and high humidity, and ensure the connection strength at high temperature is provided. can do.

  In addition, the code | symbol in the bracket | parenthesis of each said means is an example which shows a corresponding relationship with the specific means as described in embodiment mentioned later.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, parts that are the same or equivalent to each other are given the same reference numerals in the drawings for the sake of simplicity.

  1A is a diagram showing a schematic cross-sectional configuration of an electronic device S1 using a conductive adhesive 30 according to an embodiment of the present invention, and FIG. 1B is a circle B in FIG. It is an enlarged view which shows the state before hardening of the conductive adhesive 30 in a part.

  The electronic component 20 is mounted on the circuit board 10, and the electrode 11 of the circuit board 10 and the electrode 21 of the electronic component 20 are electrically connected via the conductive adhesive 30. Hereinafter, the electrode 11 of the circuit board 10 is referred to as a substrate electrode 11, and the electrode 21 of the electronic component 20 is referred to as a component electrode 21.

  The circuit board 10 can employ a ceramic board, a printed board, a lead frame, or the like, and is not particularly limited.

  The substrate electrode 11 is formed on one surface of the circuit board 10, and is made of, for example, an Ag-based metal such as Ag, AgSn, and AgPd, a Cu-based metal such as Cu and CuNi, a Ni-based metal, or Au. It is composed of the thick film or plating used.

  As the electronic component 20, a surface mount component such as a capacitor, a resistor, or a semiconductor element can be employed. In the example shown in FIG. 1A, the electronic component 20 is shown as an example using a chip capacitor. The component electrode 21 is a Sn-based base metal electrode.

  Examples of the component electrode 21 as such a Sn-based base metal electrode include metals such as Sn, SnCu, SnBi, and SnCu. Here, a plated Sn electrode is used as the component electrode 21.

  The conductive adhesive 30 includes a resin 31 containing a main agent, a curing agent, a curing accelerator (curing catalyst), a coupling agent, and a diluent, and a conductive filler 32 (see FIG. 1B). The material used has a reduction effect function, exhibits a characteristic of becoming a cured product with high purity and low water absorption, and a cured product with heat resistance, and is selected in consideration of workability and paste suitability. Is.

  In such an electronic device S1, the electronic component 20 is mounted on the circuit board 10, the component electrode 21 is brought into contact with the substrate electrode 11 via the conductive adhesive 30, and the conductive adhesive 30 is heated and cured. Thus, the electronic component 20 and the circuit board 10 are connected to each other.

  The conductive adhesive 30 of this embodiment will be specifically described focusing on the characteristic points.

  The conductive adhesive 30 includes an epoxy resin having a naphthalene skeleton as a main agent, an acid anhydride and a phenol resin as a curing agent, imidazole as a curing accelerator, and a conductive filler 32. 32 is composed of Ag and other metals (for example, Cu) that are more base than Sn and nobler than Sn, and an acid anhydride and a phenol resin are used in combination to have an epoxy equivalent ratio of 0.8. The equivalent is 95/5 to 5/95.

  Here, the epoxy resin having a naphthalene skeleton used as the main agent includes a liquid bisphenol type epoxy resin in consideration of workability, a solid biphenyl type epoxy resin and a trifunctional bisphenol resin in order to have heat resistance. A liquid epoxy resin containing a phenol type epoxy resin, a liquid epoxy resin having a naphthalene skeleton, or the like can be employed.

  In the conductive adhesive 30 of this example, dihydroxynaphthalene diglycidyl ether is mainly used as a liquid epoxy resin having a naphthalene skeleton in consideration of moisture resistance and heat resistance.

  The reason why the acid anhydride is used as the curing agent is that the acid anhydride has a reducing effect, so that the cured product has high Tg, low water absorption, and high purity properties. However, it is preferable to select an acid anhydride having a lower hygroscopic property so that curability and characteristic deterioration due to moisture absorption of the acid anhydride itself do not occur.

  In particular, in this example, as a preferable acid anhydride, 1-Isopropyl-4-methylcyclo- [2.2.2] oct-5-ene-2,3-dicboxylic anhydride and 3,4-Dimethyl-6- ( 2-methyl-1-propenyl) -1,2,3,6-tetrahydrophthalic anhydride is employed.

  As the curing agent, a combination of an acid anhydride and a phenol resin is employed in consideration of the printability of the conductive adhesive 30 and the elasticity of the cured product. As the phenolic resin, novolak phenol is preferable, and as the novolak phenol, allylphenol having a lower viscosity is more preferable in consideration of workability.

  The acid anhydride and phenol resin as the curing agent are used in combination, and the epoxy equivalent ratio is preferably 0.8 equivalent, and the breakdown is preferably 95/5 to 5/9, particularly acid anhydride and phenol resin. The ratio is more preferably 50/50.

  In consideration of reducing property, paste pot life, and curability, the curing catalyst employs curable slightly slow powdered imidazole or microencapsulated imidazole, and the addition amount is 3 to 12% by weight. In particular, in this example, microencapsulated imidazole dispersed in a bisphenol A type epoxy resin is preferably used.

  Moreover, although not limited, as a coupling agent, the silane coupling agent containing an epoxy group is employ | adopted as a coupling agent, and the addition amount shall be 0.5 weight%. As the diluent, for example, a non-alcohol reactive diluent and a solvent are employed. In particular, in this example, a cyclic aliphatic epoxy resin is employed.

  Further, as described above, the conductive filler 32 is made of Ag and other metal (eg, Cu) that is more base than Sn and nobler than Sn, but the other metal is Ag. It is included for the purpose of relaxing the potential difference between -Sn.

  In the conductive adhesive 30, the blending ratio of the conductive filler 32 and the resin 31 component is 82/18 to 90/10 as a weight ratio, and in this example, a preferable ratio is 88/12.

  Specifically, the conductive filler 32 is an alloy filler made of an alloy of Ag and another metal, or a mixture of a first filler made of Ag and a second filler made of another metal. Can be adopted. Here, although the shape of each said filler is not specifically limited, For example, it can be made into flake shape.

  In this example, the conductive filler 32 is a flaky alloy filler made of an alloy of Ag and Cu, which is another metal, that is, an AgCu alloy. Here, the ratio of Ag and Cu is preferably in the range of Ag / Cu = 60/40 to 95/5.

  Further, as shown in FIG. 1B, the surface of the alloy filler that is the conductive filler 32 may be coated with fine particles 33 made of a metal that is nobler than other metals.

  In this example, the conductive filler 32 is an alloy filler of Ag and another metal, and the fine particles 33 are coated on the surface thereof, but the conductive filler 32 is the first filler as described above. In the case where the second filler is used, the surface of the first filler or the second filler may be coated with the fine particles 33.

  The fine particles 33 can be formed, for example, by coating nano-sized Ag particles having a particle diameter of 1 to 500 nm on the surface of the alloy filler, and are provided for the purpose of assisting the conductive path. Therefore, the fine particles 33 may not be coated and may be mixed between the conductive fillers 32. The ratio of the fine particles 33 is about 30% or less of the filler.

  As described above, the conductive filler 32 of this example is an alloy filler of Ag and Cu, and the surface thereof is coated with fine particles 33 made of Ag. More specifically, the conductive filler 32 of this example is a flaky filler made of an Ag70Cu30 alloy, and its surface is coated with 15 ± 5% of nano-sized Ag.

In such a conductive filler 32 of this example, the specific surface area is 0.5 ± 0.3 [m ² / g], the Tap density is 3.5 ± 1.5 [g / m ³ ], The particle diameter is D50: 5 ± 2 [um], D90: 10 ± 3 [um].

  Here, the curing conditions of the conductive adhesive 30 of this example described above will be described. The conductive adhesive 30 of this example has a conductive filler 32 coated with nano-sized or sub-micron-sized Ag fine particles 33. The Ag fine particles 33 have a fusion function at a low temperature of about 120 ° C. to 250 ° C. It is possible to demonstrate.

  Moreover, the heat resistance of the electronic component 20 to be mounted is guaranteed only up to the reflow condition. In addition, the resin 31 in the conductive adhesive 30 of this example is accelerated at about 150 ° C., and in order to volatilize the reactive diluent that causes voids in the resin 31, the temperature is 100 ° C. It is effective to preheat.

  In addition, since the component electrode 21 of the electronic component 20 is Sn, when it is raised to the melting point of Sn (231 ° C.) or higher, the connection resistance is deteriorated, and when the component connection strength is evaluated, the fracture site becomes the connection interface. ing.

Considering the above, the curing of the conductive adhesive 30 of this example is 100 ° C./30 minutes → 150 ° C./60 minutes, or 100 ° C./30 minutes → 200 ° C./1 minute → 150 ° C./60 minutes. Alternatively, it is desirable to carry out under the conditions of 100 ° C./30 minutes → 150 ° C./60 minutes → 200 ° C./1 minute. Furthermore, the conductive filler 32 is an AgCu alloy, and in order to suppress the oxidation of Cu, it is desirable that the curing is performed in a nitrogen (N ₂ ) atmosphere.

  As described above, according to the present embodiment, the naphthalene skeleton as the main component in the conductive adhesive 30 used when connecting the electronic component 20 having the Sn-based base metal electrode 21 on the circuit board 10. An epoxy resin having an acid content, an acid anhydride and a phenol resin as a curing agent, an imidazole as a curing accelerator, and a conductive filler 32. The conductive filler 32 is Sn-base and lower than Ag and Ag. The acid anhydride and the phenol resin are used in combination with an epoxy equivalent ratio of 0.8 equivalent, and the breakdown is 95/5 to 5/95. A conductive adhesive 30 is provided.

  First, according to the present embodiment, when an acid anhydride is used as the curing agent of the conductive adhesive 30 and imidazole is used as the curing accelerator, the initial stage formed on the surface of the component electrode 21 by these acid anhydride and imidazole. Reduction removal of the oxide film 21a is realized.

  In addition, the present inventors formed an oxide film on the surface of the eutectic solder ball for the reducing action by the acid anhydride and imidazole, and mixed the acid film with the acid anhydride and imidazole, followed by heat treatment. The DSC behavior was examined using the solder balls after the oxide film was formed and the solder balls after the heat treatment.

  In this DSC analysis, the more oxide film is present on the surface of the solder ball, the higher the melting point shifts. When reduced by an acid anhydride or imidazole, it approaches the melting point temperature of the eutectic solder, so the disappearance degree of the oxide film, that is, the reduction action by the acid anhydride and imidazole can be confirmed. confirmed.

  In this embodiment, an Sn oxide film 21a is formed on the surface of the component electrode 21 which is an Sn electrode in FIG. 1B. This oxide film 21a is formed of an acid anhydride or a curing accelerator as a curing agent. Is reduced and removed by imidazole.

  Therefore, conduction is ensured between the conductive filler 32 and the component electrode 21 which is an Sn-based base metal electrode, and the initial value of the connection resistance is reduced. The concrete effect about this is confirmed about what was illustrated as the conductive adhesive 30 of this embodiment, and the result is shown by FIG.

  FIG. 2 is a diagram showing the relationship between the test time (leaving time) in the high-temperature standing test at 150 ° C. and the component connection resistance. In FIG. 2, the white circle plot is the result when the conductive adhesive 30 of the present embodiment and the component electrode 21 made of the Sn electrode are joined.

  Moreover, in FIG. 2, the white triangle plot is a result of the case where a conductive adhesive using a conventional general Ag filler and an electronic component having a base metal electrode made of Sn are joined (conventional-base metal), The black circle plot is the result when a conductive adhesive using a conventional general Ag filler and an electronic component having a noble metal electrode made of Ag-Pd are joined (noble metal). The result of this noble metal electrode has a track record in terms of reliability.

  As shown in FIG. 2, in the case of this embodiment, the initial value of the connection resistance is reduced as compared with the case where the conventional conductive adhesive is connected to the base metal electrode. Similarly, a practical level is secured.

  Further, according to the conductive adhesive 30 of the present embodiment having the above-described features, the conductive filler 32 is made of Ag and another metal that is lower than Ag and higher than Sn. The potential difference between the component electrode 21 which is a base metal electrode and the conductive filler 32 can be reduced, and galvanic corrosion is suppressed.

  In addition, by employing an epoxy resin having a naphthalene skeleton as the main agent, an acid anhydride and a phenol resin as the curing agent, and imidazole as the curing accelerator, the water absorption rate of the cured resin 31 is reduced, The electrical conductivity can be reduced by purifying.

  For these reasons, the oxidation of Sn on the surface of the component electrode 21 that is a base metal electrode can be suppressed, and the increase in connection resistance under high temperature and high humidity can be suppressed. The concrete effect about this is confirmed about what was illustrated as the conductive adhesive 30 of this embodiment, and the result is shown by FIG.

  FIG. 3 is a diagram showing the relationship between test time and component connection resistance in a high-temperature and high-humidity test at 85 ° C. and 85% RH. In FIG. 3, the white circle plot is a result when the conductive adhesive 30 of the present embodiment and the component electrode 21 made of the Sn electrode are joined.

  Moreover, in FIG. 3, the white triangle plot is a result of the case where a conductive adhesive using a conventional general Ag filler and an electronic component having a base metal electrode made of Sn are joined (conventional-base metal), The black circle plot is the result when a conductive adhesive using a conventional general Ag filler and an electronic component having a noble metal electrode made of Ag-Pd are joined (noble metal). The result of this noble metal electrode has a track record in terms of reliability.

  As shown in FIG. 3, in the case of this embodiment, compared with the case where the conventional conductive adhesive is connected to the base metal electrode, the increase in connection resistance under high temperature and high humidity is realized, and noble metal is realized. A practical level is secured as in the case of the electrode.

  Further, according to the conductive adhesive 30 of the present embodiment having the above features, if an epoxy resin having a naphthalene skeleton is used as a main agent, an acid anhydride is used as a curing agent, and imidazole is used as a curing catalyst, the resin has high heat resistance. A high Tg can be realized, and the deterioration of the resin 31 due to heat is suppressed, thereby ensuring the connection strength at a high temperature.

  The concrete effect about this is confirmed about what was illustrated as the conductive adhesive 30 of this embodiment, and the result is shown by FIG.

  FIG. 4 is a diagram showing the relationship between the test time and the component connection strength in the high-temperature standing test at 150 ° C. In FIG. 4, the white circle plot is a result when the conductive adhesive 30 of the present embodiment and the component electrode 21 made of the Sn electrode are joined. Here, the component connection strength is the tensile strength.

  Moreover, in FIG. 4, the white triangle plot is a result of the case where a conductive adhesive using a conventional general Ag filler and an electronic component having a base metal electrode made of Sn are joined (conventional-base metal), The black circle plot is the result when a conductive adhesive using a conventional general Ag filler and an electronic component having a noble metal electrode made of Ag-Pd are joined (noble metal). The result of this noble metal electrode has a track record in terms of reliability.

  As shown in FIG. 4, in the case of the present embodiment, compared to the case where a conventional conductive adhesive is connected to the base metal electrode, the connection strength is ensured at a high temperature. Similarly, a practical level is secured.

  In this connection strength test, the final form of destruction is the base material destruction in the case of this embodiment and the noble metal, and the case of connecting the conventional conductive adhesive to the non-metallic electrode is Sn interface peeling. there were.

  As described above, in the conductive adhesive 30 of the present embodiment, an acid anhydride and a phenol resin are used in combination as a curing agent.

  As described above, the acid anhydride can reduce and remove the oxide film, increase the purity and decrease the water absorption rate of the cured resin 31 and increase the Tg, and is effective in improving heat resistance and moisture resistance. is there. However, since it is difficult to ensure the printability of the conductive adhesive 30 and the elasticity of the resin 31 after curing with an acid anhydride alone, the combined use with a phenol resin is preferable.

  According to the study by the present inventors, it has been experimentally found that by using phenol as a curing agent, the curing shrinkage stress can be lowered and the flexural modulus can be increased. An example of the experimental results is shown in FIGS.

  FIG. 5 is a graph showing the relationship between the ratio of phenol resin (Ph) / acid anhydride (Anh) and cure shrinkage force, and FIG. 6 is the ratio of phenol resin (Ph) / acid anhydride (Anh) and the maximum bending It is a figure which shows the relationship between stress and a bending elastic modulus. Here, the curing shrinkage force was obtained from a warp test of the cover glass, and the bending maximum stress and the bending elastic modulus were obtained from a bending strength test with a three-point support.

  From the viewpoints of ensuring contact between the conductive fillers 32 due to the shrinkage of the resin 31 and ensuring the above printability and elasticity, it is not preferable that the curing shrinkage stress and the bending elastic modulus of the conductive adhesive 30 are too large or too small.

  Based on the results shown in FIG. 5 and FIG. 6, a practically preferred ratio of the acid anhydride to the phenol resin is a combination of the acid anhydride and the phenol resin, and the epoxy equivalent ratio is 0.8 equivalent. 95/5 to 5/95. Within this ratio range, it is effective for improving heat cycle resistance, and further suitable for paste application, and is effective.

  Moreover, if the ratio of the acid anhydride and the phenol resin as the curing agent is in the above range, the Cl ion concentration in the conductive adhesive 30 can be reduced, high purity can be appropriately realized, and high Tg can be achieved. High heat resistance can be realized properly. Specific experimental results for these are shown in FIGS.

  FIG. 7 is a graph showing the relationship between the ratio of phenol resin (Ph) / acid anhydride (Anh) and glass transition temperature, and FIG. 8 is the ratio of phenol resin (Ph) / acid anhydride (Anh) and Cl ions. It is a figure which shows the relationship with a density | concentration.

  Here, a method for measuring the Cl ion concentration will be described. It is measured by ion chromatographic analysis. The measurement procedure is shown below.

[Conducting conductive adhesive]
The conductive adhesive 30 is applied to the entire surface of a Teflon (registered trademark) sheet masked with a heat-resistant tape in a shape in which the thickness is uniformly thinned.

[Curing conductive adhesive]
The applied conductive adhesive 30 is cured in a constant temperature bath under predetermined curing conditions (for example, 150 ± 5 ° C., 60 ± 5 min).

[Crushing of cured film]
The conductive adhesive 30 that has been cured to become a cured film is taken out of the thermostatic bath, and then returned to room temperature. Then, the cured film of the conductive adhesive 30 is peeled off from the Teflon (registered trademark) sheet and placed in a polyethylene bag. Put in a bag and crush it into a shape of approximately 5 mm □ to make a pulverized powder.

[Preparation of extract]
The above ground powder 0.5 ± 0.1 g was put in a Teflon (registered trademark) container with a cap, and after adding 20 mL of ultrapure water, the cap was put on and a pressure cooker test (121 ° C., 2 atm) was carried out for 20 hours. Then, let the extract which returned to room temperature be a test liquid.

[Measurement]
Measure the Cl concentration of the test solution with a measuring instrument (equipment: equivalent to Ion Chromatograph HIC-6A manufactured by Shimadzu Corporation), and obtain the Cl concentration of the conductive adhesive by multiplying the quantitative calculation value of the obtained chart by 40 times. .

  First, as shown in FIG. 7, according to the conductive adhesive 30 of the present embodiment having the above features, the glass transition temperature of the cured product after curing the conductive adhesive is 110 ° C. to 160 ° C. A high Tg of about 0 ° C. is achieved. This is because the present embodiment employs an epoxy resin having a naphthalene skeleton as the main agent, an acid anhydride as the curing agent, and imidazole as the curing catalyst.

  Further, as described above, the Cl ion concentration in the conductive adhesive is an index of a resin that is highly purified to reduce electrical conductivity. And as FIG. 8 shows, according to the conductive adhesive 30 of this embodiment which has the said characteristic point, the Cl ion density | concentration in a conductive adhesive is 10 ppm or less.

  The small amount of Cl ions in the conductive adhesive means that the cured resin is highly purified, the electrical conductivity is reduced, and galvanic corrosion is unlikely to occur. And in the conductive adhesive 30 of this embodiment, the low Cl ion concentration of 10 ppm or less is implement | achieved, and the galvanic corrosion can be suppressed appropriately.

  As described above, this is because an epoxy resin having a naphthalene skeleton is employed as the main component of the conductive adhesive 30, an acid anhydride and a phenol resin are employed as the curing agent, and imidazole is employed as the curing accelerator. Moreover, by setting it as such a resin structure, the water absorption of the hardened resin can also be lowered | hung.

  Lowering the water absorption rate leads to reduction of electrical conductivity and suppression of the galvanic corrosion. The concrete experimental result about the reduction of this water absorption is shown in FIG.

  FIG. 9 is a diagram showing the relationship between the high temperature and high humidity standing time and the water absorption rate. In FIG. 9, as the water absorption rate of the cured resin, a moisture resistance test is performed on the cured conductive adhesive, and the weight change before and after the test corresponds to the water absorption rate.

  Here, in the moisture resistance test, a cured coating film is prepared only with a resin component without a filler, and an initial weight and a weight after performing a moisture resistance test that is left in an environment of 85 ° C. and 85 RH% for 364 hours are measured. The change in weight was determined as the water absorption rate (%).

  In FIG. 9, the white circle plot shows the result of the naphthalene type epoxy resin which is the main component of the conductive adhesive 30 of the present embodiment, and the black circle plot shows a bisphenol type epoxy which is the main component of the conventional conductive adhesive as a comparative example. The resin results are shown.

  As shown in FIG. 9, in the naphthalene epoxy resin of this embodiment, the weight change, that is, the water absorption rate is reduced to about 1% or less. That is, the conductive adhesive 30 of this embodiment substantially has a weight change of 2% or less after a moisture resistance test in which the cured product after curing is left to stand for 364 hours in an environment of 85 ° C. and 85 RH%. Can be.

  As described above, according to the conductive adhesive 30 of the present embodiment having the above feature points, the Sn-based base metal electrode 21 is formed on the circuit board 10 by appropriately exerting the effects of the above-described components. In the conductive adhesive used when connecting the electronic component 20 having the above, the initial value of the connection resistance is reduced, the increase in the connection resistance under high temperature and high humidity, and the connection strength at high temperature is ensured. can do.

  As described above, the conductive adhesive 30 of the present embodiment is also characterized in that imidazole is microencapsulated.

  As described above, it is preferable to microencapsulate imidazole since it is possible to suppress the progress of curing by imidazole, which is a curing accelerator, before heating the conductive adhesive.

  Moreover, in the conductive adhesive 30 of this embodiment, it is also one of the characteristics that a novolak phenol is employ | adopted as a phenol resin.

  In addition, the conductive adhesive 30 of the present embodiment is also characterized in that the blending ratio of the conductive filler 32 and the resin component 31 is 82/18 to 90/10 as a weight ratio.

  Further, in the conductive adhesive 30 of the present embodiment, the conductive filler 32 is also characterized by being an alloy filler made of an alloy of Ag and the other metal.

  Furthermore, it is preferable that the surface of the alloy filler is coated with fine particles 33 made of a noble metal rather than the other metals.

  Since the above alloy filler is baser than Ag alone, it is likely to be oxidized, and the connection resistance between the alloy filler and the counterpart tends to increase. Therefore, if the alloy filler is coated with the fine particles 33 made of a noble metal rather than the other metal, the fine particles 33 are fused by the heat curing of the conductive adhesive, so that the filler is more than the case of the alloy filler alone. Sufficient connections are made in between, making it easy to ensure the connection resistance.

  As described above, in the conductive adhesive 30 of the present embodiment, the conductive filler 32 can be a mixture of the first filler made of Ag and the second filler made of the other metal.

  Here, as described above, it is preferable that the surface of the first filler or the second filler is coated with the fine particles 33 made of a noble metal rather than the other metal.

  The reason is the same as the configuration in which the surface of the alloy filler 32 is coated with the fine particles 33, and the fine particles 33 are fused by thermal curing of the conductive adhesive 30 so that the filler is sufficiently connected. It is easy to secure resistance.

  As described above, in the conductive adhesive 30 of the present embodiment, instead of coating the fine particles 33, fine particles may be mixed between the conductive fillers.

  The effect of this is also the same as the configuration in which the surface of the alloy filler 32 is coated with the fine particles 33, and the fine particles 33 are fused by the heat curing of the conductive adhesive 30, so that a sufficient connection between the fillers is made. It is easy to secure the connection resistance.

  Thus, in the conductive adhesive 30 of the present embodiment, the conductive filler is fused with the conductive fillers or with the electrode 11 of the circuit board 10 or the base metal electrode 21 of the electronic component 20. be able to.

  In the present embodiment, the electronic component 20 having the Sn-based base metal electrode 21 is mounted on the circuit board 10 via the conductive adhesive 30 having the various features described above. By heating and curing, an electronic device S1 in which the electronic component 20 and the circuit board 10 are connected is provided.

  According to this, the electronic device S1 using the conductive adhesive 30 that can reduce the initial value of the connection resistance, suppress the increase in the connection resistance under high temperature and high humidity, and ensure the connection strength under the high temperature. Can be provided.

(Other embodiments)
In the above-described embodiment, an example in which a chip capacitor is used as an electronic component is illustrated. However, as the electronic component, a surface mount component such as a capacitor, a resistor, a semiconductor element, or the like can be employed.

  Moreover, in the said embodiment, although the electronic component 20 is mounted on the circuit board 10 and the electrode 11 of the circuit board 10 and the electrode 21 of the electronic component 20 are connected via the electroconductive adhesive 30, such as this. After the mounting, a packaging process may be further performed.

  For example, although not shown, in the mounting structure shown in FIG. 1, a structure in which a heat sink made of Al is further attached to a substrate (component mounting board), the heat sink and the case are further bonded, and then sealed with silicone gel It is good.

  However, the package form is not limited to the above, and the silicone gel may or may not be used, or may be replaced with another moisture-proof coating material.

  Further, for example, in FIG. 1, the connection part of the electronic component 20 to the circuit board 10 or its peripheral part may be reinforced with an underfill resin. Moreover, you may employ | adopt the sealing structure by mold resin.

(A) It is a schematic sectional drawing of the electronic device using the conductive adhesive which concerns on embodiment of this invention, (b) is an expansion which shows the state before hardening of the conductive adhesive in the B section in (a). FIG. It is a figure which shows the relationship between the test time and component connection resistance in a high temperature leaving test. It is a figure which shows the relationship between the test time and component connection resistance in a high temperature, high humidity test. It is a figure which shows the relationship between the test time and component connection strength in a high temperature leaving test. It is a figure which shows the relationship between the ratio of a phenol resin / acid anhydride, and hardening shrinkage force. It is a figure which shows the relationship between the ratio of a phenol resin / an acid anhydride, a bending maximum stress, and a bending elastic modulus. It is a figure which shows the relationship between the ratio of a phenol resin / acid anhydride, and glass transition temperature. It is a figure which shows the relationship between the ratio of a phenol resin / acid anhydride, and Cl ion concentration. It is a figure which shows the relationship between high temperature high humidity leaving time and a water absorption. (A) is a schematic sectional drawing of the general electronic device using a conductive adhesive, (b) is an enlarged view which shows the state before hardening of the conductive adhesive in the A section in (a). . (A) is a figure which shows the shrinkage | contraction of resin in a conductive adhesive, (b) is a figure which shows the mode of the contact of the conductive filler in a conductive adhesive, (c) is the influence of high temperature, high humidity in a conductive adhesive. (D) is a figure which shows the influence under the high temperature in a conductive adhesive.

Explanation of symbols

10 ... circuit board, 20 ... electronic components,
21 ... Electronic component electrode as Sn base metal electrode, 30 ... conductive adhesive.

Claims (16)

In the conductive adhesive used when connecting the electronic component (20) having the Sn-based base metal electrode (21) on the circuit board (10),
An epoxy resin having a naphthalene skeleton as a main agent, an acid anhydride and a phenol resin as a curing agent, imidazole as a curing accelerator, and a conductive filler,
The conductive filler is composed of Ag and another metal that is more base than Ag and noble than Sn,
The said acid anhydride and the said phenol resin are used together, an epoxy equivalent ratio is set to 0.8 equivalent, The breakdown is 95/5-5/95, The conductive adhesive characterized by the above-mentioned. The conductive adhesive according to claim 1, wherein the imidazole is microencapsulated. The conductive adhesive according to claim 1, wherein the phenol resin is novolak phenol. 4. The conductive adhesive according to claim 1, wherein a blending ratio of the conductive filler and the resin component is 82/18 to 90/10 as a weight ratio. The conductive adhesive according to any one of claims 1 to 4, wherein the conductive filler is an alloy filler made of an alloy of Ag and the other metal. 5. The conductive adhesive according to claim 1, wherein the conductive filler is a mixture of a first filler made of Ag and a second filler made of the other metal. 6. . 6. The conductive adhesive according to claim 5, wherein the surface of the alloy filler is coated with fine particles made of a metal that is nobler than the other metal. The conductive adhesive according to claim 6, wherein the surface of the first filler or the second filler is coated with fine particles made of a metal that is nobler than the other metal. . 7. The conductive adhesive according to claim 5, wherein fine particles made of a metal nobler than the other metal are mixed between the conductive fillers. The conductive adhesive according to any one of claims 7 to 9, wherein a particle diameter of the fine particles is 1 to 500 nm. The conductive adhesive according to any one of claims 1 to 10, wherein the other metal is Cu. The conductive adhesive according to any one of claims 1 to 11, wherein a Cl ion concentration in the conductive adhesive is 10 ppm or less. The cured product after curing the conductive adhesive has a weight change of 2% or less after performing a moisture resistance test in which it is left for 364 hours in an environment of 85 ° C and 85RH%. The conductive adhesive according to any one of 12. 14. The conductive adhesive according to claim 1, wherein the cured product after curing the conductive adhesive has a glass transition temperature of 110 to 160 ° C. 15. The conductive filler is fused with the conductive fillers or with the electrode (11) of the circuit board (10) or the base metal electrode (21) of the electronic component (20). The conductive adhesive according to any one of claims 1 to 14. An electronic component (20) having an Sn-based base metal electrode (21) is mounted on a circuit board (10) via the conductive adhesive (30) according to any one of claims 1 to 15. An electronic device formed by connecting the electronic component (20) and the circuit board (10) by heat-curing the conductive adhesive (30).

Images