JP2006324629A - Packaging construction and its method of packaging electronic part - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To keep a high connecting reliability under environments of high temperature and cold cycle even when general-purpose Sn system base metal electrode is used for an electrode of electronic part in a packaging construction of the electronic part fabricated, by connecting the electrode of the electronic part and an electrode of substrate through a conductive adhesive. <P>SOLUTION: The packaging construction 100 of the electronic part is fabricated by mounting an electronic part 20 on a substrate 10, and by connecting an electrode 11 of the substrate with an electrode 21 of the electronic part through a conductive adhesive 30. Further, a surface plated layer 21b, a surface layer of the electrode 21 of the electronic part, is formed by plating an Sn system metal and by reforming the Sn system metal plated in the way of heat treatment. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a mounting structure for an electronic component in which an electronic component is mounted on a substrate and the electrode of the substrate and the electrode of the electronic component are connected via a conductive adhesive, and a mounting method for realizing such a mounting structure. In particular, the present invention relates to an electronic component made of a Sn-based base metal electrode.

  In recent years, in the electronics field, as a result of increasing awareness of environmental measures, there is an urgent need to establish a lead-free mounting technology, that is, a technology for mounting electronic components using a material that does not use lead, in order to comply with regulations on lead in solder.

  As lead-free mounting technology, mounting using lead-free solder or conductive adhesive is being studied, but benefits such as stress resistance and lower processing temperature are expected due to the resin connection. There is a growing interest in conductive adhesives.

  Generally, the conductive adhesive is obtained by dispersing metal particles as a conductive filler in a resin component. The electronic component is mounted by supplying a conductive adhesive to the electrode of the substrate, mounting the electronic component, and then heat-curing the resin.

  With this process, as the resin shrinks, the metal particles in the resin are brought into contact with each other, or the metal particles are brought into contact with the component electrodes and the substrate electrodes to obtain conduction, and the connection portion is bonded with the resin. .

  In the above process, the curing temperature of the resin used for the conductive adhesive is generally about 150 ° C., which is considerably lower than that of a solder that requires a melting temperature of about 230 to 240 ° C. For this reason, as the other members constituting the mounting component and the electronic circuit product, an inexpensive member having low heat resistance can be used, and the product cost can be reduced.

For example, in Patent Document 1, a filler that is easily brought into contact with each other due to resin shrinkage has little translation / rotation motion, and can be used as a substitute for solder by using a conductive adhesive dispersed in a resin having a plurality of reactive groups. It is said that good joint strength and connection resistance, and excellent printability can be obtained.
JP 2000-319622 A

  However, according to the study of the present inventor, it has been found that the conductive adhesive is difficult to put into practical use as a solder substitute because the connection reliability when using a general-purpose electronic component is not preferable.

  In general, Sn-based base metal electrodes are used as electrodes of electronic components. Specifically, the Sn-based base metal electrode is mainly composed of an Sn-based metal, that is, Sn such as Sn or SnPb, SnCu, SnAg, SnBi or the like on a base metal plating layer such as Ni plating (50% or more). The Sn-based metal plating layer is used as a surface plating layer.

  However, when an electronic component having an electrode made of such a Sn-based base metal electrode is mounted on a substrate using a conductive adhesive, a resin compared with a solder whose metal electrode is connected to the component electrode. In the case of the connection of the conductive adhesive which is adhesion, it is easily affected by the shape change of the component electrode interface.

  According to the study of the present inventor, a plated Sn system having a lower melting point than the case where the electrode of the electronic component, that is, the component electrode is an electrode made of a noble metal (for example, Ag-based, Au-based, Cu-based metal, etc.) In the case of electrodes made of metal, it was found that, when exposed to a high temperature environment or a cold cycle environment for a long time, atomic movement due to temperature energy tends to become active, so that the plating surface of the component electrode changes in shape. .

  Specifically, when left at high temperature for a long time, volume shrinkage occurs on the surface of the Sn-based metal plating, and cracking of the grain boundary occurs on the surface of the Sn-based metal plating under a long-time cooling cycle environment. did. This is considered to be one of the reasons why it is difficult to ensure the connection reliability between the conductive adhesive and the component electrode interface.

  Even when the conductive adhesive described in Patent Document 1 is used, it is effective only for electronic parts having noble metal electrodes such as AgPd electrodes, and for Sn-based base metal electrodes, In such a high temperature environment and a cold cycle environment, it is not possible to suppress a change in the shape of the electrode plating surface.

  Actually, the present inventor used a conductive adhesive described in the above-mentioned patent document, a commercially available multilayer ceramic capacitor having a Ni—Sn electrode, which is a typical Sn-based base metal electrode, as a component electrode, When connected to the electrode, the connection reliability in the high temperature environment and the thermal cycle environment was significantly deteriorated in connection strength and connection resistance as compared with those of the AgPd electrode (FIGS. 3, 4, and 8 to be described later). (See FIG. 7).

  As described above, in a conductive adhesive, when a general-purpose Sn-based base metal electrode is used as an electrode of an electronic component, it is necessary to use a noble metal electrode because of low connection reliability, resulting in an increase in component cost. It was an impediment to practical use.

  The present invention has been made in view of the above problem, and in a mounting structure of an electronic component in which an electrode of an electronic component and an electrode of a substrate are connected via a conductive adhesive, a general-purpose electrode is used for the electrode of the electronic component. Even when an Sn-based base metal electrode is used, it is an object to ensure high connection reliability in a high-temperature environment and a cold cycle environment.

  In order to achieve the above object, in the invention according to claims 1 to 3, an electronic component (20) is mounted on a substrate (10), and an electrode (11) of the substrate and an electrode (21) of the electronic component are provided. In the electronic component mounting structure in which the electrodes are connected via the conductive adhesive (30), the surface layer of the electrode (21) of the electronic component is formed by plating Sn-based metal, and the plated Sn The system metal is characterized by comprising a surface plating layer (21b) modified by heat treatment.

  In the present invention, the surface layer of the electrode (21) of the electronic component is a Sn-based base metal electrode obtained by plating an Sn-based metal, and the plated Sn-based metal layer (21b) modified by heat treatment. Specifically, the plated Sn-based metal is recrystallized (invention of claim 2), or the base metal diffuses into the surface plating layer (21b). Thus, an alloyed product (invention of claim 3) can be obtained.

  According to the study of the present inventor, the Sn-based base metal electrode (21) of the electronic component (20) of the present invention can be used in a higher temperature environment and a cold cycle environment than the conventional Sn-based base metal electrode. It has been experimentally found that the connection resistance and the connection strength can be secured at a suitable level (see FIGS. 3 to 10 described later).

  Therefore, according to the present invention, in the electronic component mounting structure in which the electrode (21) of the electronic component (20) and the electrode (11) of the substrate (10) are connected via the conductive adhesive (30). Even when a general-purpose Sn-based base metal electrode is used for the electrode (21) of the electronic component (20), high connection reliability can be ensured in a high-temperature environment and a cooling / heating cycle environment.

  Here, as in the invention of claim 3, the surface plating layer (21b) of the electrode (21) of the electronic component is alloyed by diffusion of the underlying metal into the surface plating layer (21b). In this case, an average film thickness of a portion of the surface plating layer (21b) excluding a portion alloyed by diffusing the base metal into the surface plating layer (21b) may be 1.5 μm or less. Preferred (Invention of Claim 4).

  Of the surface plating layer (21b), a portion excluding the portion alloyed by diffusion of the underlying metal into the surface plating layer (21b), that is, the average film thickness of the unalloyed Sn-based metal plating is 1 If it is thicker than 0.5 μm, durability at high temperatures and cold temperatures is inferior.

  In this case, it is preferable that an average film thickness of a portion alloyed by diffusion of a base metal in the surface plating layer (21b) in the surface layer plating layer (21b) is 0.5 μm or more. .

  Moreover, in the electronic component mounting structure according to any one of the first to fifth aspects as in the invention according to the sixth aspect, in the electrode (21) of the electronic component (20), the surface plating layer (21b) The base can be a Ni plating layer (21a) formed by Ni plating.

  According to a seventh aspect of the present invention, the electronic component (20) is mounted on the substrate (10), and the conductive adhesive (30) is connected between the electrode (11) of the substrate and the electrode (21) of the electronic component. In the mounting method of the electronic component connected via the electrode, an electronic component (20) having a surface layer of the electrode (21) consisting of a plating layer (21c) formed by plating Sn-based metal is prepared. Then, the plating layer (21c) is modified by heat treatment, and subsequently, the connection between the electrode (11) of the substrate and the electrode (21) of the electronic component is performed via the conductive adhesive (30). It is characterized by.

  According to this, the plating layer (21c) modified by heat treatment in the prepared electronic component (20) becomes the surface plating layer (21b) according to the first aspect. Thus, according to the present invention, it is possible to provide a mounting method capable of appropriately realizing the electronic component mounting structure according to claims 1 to 6.

  Here, in the invention according to claim 8, in the electronic component mounting method according to claim 7, the heating temperature in the heat treatment is equal to or higher than the heating temperature in the mounting step after the heat treatment, and the plating layer It is characterized by being in the range below the melting point of the plating material of (21c).

  According to this, the plating layer modified by the heat treatment, that is, the surface layer plating layer (21b) according to claim 1 formed by the heat treatment is altered by further heating in the subsequent mounting process. Can be prevented, and can be prevented from melting.

  Here, as in the invention according to claim 9, in the electronic component mounting method according to claim 8, the heating temperature in the mounting step after the heat treatment is the curing temperature of the conductive adhesive (30). Can be.

  According to a tenth aspect of the present invention, in the electronic component mounting method according to any one of the seventh to ninth aspects, the electrode (21) of the electronic component (20) has a base of the plating layer (21c) as a base. It is characterized by being a Ni plating layer (21a) formed by plating. Accordingly, the mounting structure according to the sixth aspect can be appropriately realized.

  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.

[Configuration]
FIG. 1 is a diagram showing a schematic cross-sectional configuration of an electronic component mounting structure 100 according to an embodiment of the present invention.

  An electronic component 20 is mounted on a circuit board 10 as a substrate, and an electrode 11 of the circuit board 10 and an electrode 21 of the electronic component 20 are electrically connected via a 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. 1, the electronic component 20 is shown as an example using a chip capacitor.

  The component electrode 21 is a Sn-based base metal electrode, and is formed on the base electrode 22 in this example. Specifically, the component electrode 21 is obtained by forming a surface plating layer 21b on a base metal plating layer 21a. The base metal plating layer 21a is made of Ni plating or the like, and is the Ni plating layer 21a in this example.

  The surface plating layer 21b, that is, the surface layer of the component electrode 21, is formed by plating an Sn-based metal, and the plated Sn-based metal is modified by heat treatment.

  Here, the Sn-based metal is Sn or made of a Sn alloy containing Sn as a main component (that is, containing 50% or more of Sn) such as SnPb, SnCu, SnAg, SnBi. In this example, the surface plating layer 21b is made of an Sn plating layer made of Sn plating.

  The surface plating layer 21b is a plated Sn-based metal modified by heat treatment. Specifically, the plated Sn-based metal is recrystallized or a base metal. The metal in the plating layer 21a (Ni in this example) is alloyed by diffusing into the surface plating layer 21b (Ni-Sn alloy in this example). Such a state of the surface plating layer 21b can be confirmed by observing an electrode with an electron microscope or performing various elemental analyzes.

  The conductive adhesive 30 is composed of a resin containing a main agent, a curing agent, a curing accelerator (curing catalyst), a coupling agent, a diluent and a conductive filler, and the material used has a reducing effect function. It has characteristics such as having a cured product with high purity and low water absorption, or a cured product with heat resistance, and has been selected in consideration of workability and paste suitability. is there.

  Specifically, as the conductive adhesive 30, a general material composed of an epoxy-based resin and an Ag filler can be used. In order to ensure a high level of connection resistance in a high temperature and high humidity environment. The following is preferably adopted.

  The preferred conductive adhesive 30 of this embodiment comprises 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 other metals (for example, Cu) which are more base than Sn and noble than Sn. The acid equivalent and the phenol resin are used in combination to reduce the epoxy equivalent ratio to 0. 0.8 equivalent, and the breakdown is 95/5 to 5/95.

  By adopting such a conductive adhesive 30, problems such as (1) an increase in the initial value of connection resistance, (2) an increase in connection resistance under high temperature and high humidity, and (3) a decrease in connection strength under high temperature. The point can be solved.

  If an epoxy resin having a naphthalene skeleton as the main agent is used, an increase in connection resistance can be reduced by lowering the water absorption rate of the cured resin 31 and increasing the purity, and an acid anhydride or a curing accelerator as a curing agent. If imidazole is used, the initial oxide film originally present on the surface of the electrode 21 of the electronic component 20 can be reduced and removed, so that an increase in the initial value of the connection resistance can be suppressed as much as possible.

  Also, the conductive filler is made of Ag and other metals that are more base than Ag and nobler than Sn, and the epoxy resin having a naphthalene skeleton as the main agent, acid anhydride and phenol resin as the curing agent, and curing If each imidazole is employ | adopted as an accelerator, the suppression of the raise of connection resistance under high temperature and high humidity will be made.

  Furthermore, by using an epoxy resin having a naphthalene skeleton as the main agent, an acid anhydride as the curing agent, and imidazole as the curing catalyst, high heat resistance and high Tg (Tg: glass transition point) of the resin can be realized. This ensures the connection strength at high temperatures.

  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. Hereinafter, this mixture is referred to as an ID mixture.

  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. In this example, this allylphenol is employed as a curing agent.

  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 in the conductive adhesive 30 is made of Ag and other metals (eg, Cu) that are more base than Ag and noble than Sn. These metals are contained for the purpose of relaxing the potential difference between Ag and Sn.

  Further, in the conductive adhesive 30, the blending ratio of the conductive filler and the resin 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 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 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.

  Moreover, the surface of the alloy filler which is a conductive filler may be coated with fine particles made of a metal that is more noble than other metals.

  In addition, when the conductive filler is an alloy filler of Ag and another metal, the surface is coated with the fine particles, but the conductive filler is composed of the first filler and the second filler as described above. In the case where it is configured from the above, the surface of the first filler or the second filler may be coated with the fine particles.

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

  For example, when the conductive filler is an alloy filler of Ag and Cu as in the above example, the surface is coated with fine particles made of Ag. More specifically, the conductive filler is a flaky filler made of an Ag70Cu30 alloy, and the surface thereof can be coated with 15 ± 5% of nano-sized Ag.

In such a conductive filler, for example, specific surface area: 0.5 ± 0.3 [m ² / g], Tap density: 3.5 ± 1.5 [g / m ³ ], Can be set to D50: 5 ± 2 [um], D90: 10 ± 3 [um].

  Here, the preferable curing conditions for the conductive adhesive 30 described above will be described. Here, the conductive adhesive 30 has a conductive filler 32 coated with nano-sized or sub-micron-sized Ag fine particles. In this case, the Ag fine particles can exhibit a fusion function at a low temperature of about 120 ° C. to 250 ° C.

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

  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. Further, the conductive filler 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.

  Further, in the conductive adhesive 30, the Cl ion concentration in the conductive adhesive 30 is preferably 10 ppm or less. Thus, if the Cl ion in the conductive adhesive 30 is small, the cured resin is highly purified, the electrical conductivity is reduced, and galvanic corrosion is unlikely to occur.

  Further, in the conductive adhesive 30, the weight change after performing a moisture resistance test for 364 hours in an environment of 85 ° C. and 85 RH% in the cured product after the conductive adhesive 30 is cured is 2% or less. Preferably there is.

  Moreover, in the conductive adhesive 30, in the hardened | cured material after hardening the conductive adhesive 30, it is preferable that the glass transition temperature is 110-160 degreeC.

[Mounting method etc.]
Next, a mounting method for realizing the mounting structure of this embodiment shown in FIG. 1 will be described. FIG. 2 is a schematic cross-sectional view for explaining the electronic component mounting method of the present embodiment.

  First, as shown in FIG. 2A, an electronic component 20 having a surface layer of a component electrode 21 made of a plated layer 21c formed by plating Sn-based metal is prepared. Here, in this example, the base metal plating layer 21a of the plating layer 21c is an Ni plating layer 21a formed by Ni plating, and the plating layer 21c is an Sn plating layer made of Sn plating.

  Next, the plating layer 21c on the surface layer of the prepared electronic component 20 is modified by heat treatment. By this modification, the Sn-based metal in the plating layer 21c is recrystallized, or the metal in the base metal plating layer 21a is diffused into the plating layer 21c to form an alloy, which is shown in FIG. 2B. As described above, the surface plating layer 21b is formed.

  Here, the heating temperature in the heat treatment for reforming may be in a range not less than the heating temperature in the mounting process after the heat treatment and not more than the melting point of the plating material of the plating layer 21c, that is, the Sn-based metal. preferable. Furthermore, the heating temperature in the heat treatment is preferably equal to or lower than the heat-resistant temperature of the electronic component 20 in order to prevent deterioration of the electronic component 20 due to heating.

  Specifically, the heating temperature in the mounting process after the heat treatment is the curing temperature of the conductive adhesive 30. For example, the curing temperature of the conductive adhesive 30 is 150 ° C., and the heating temperature is about 175 ° C.

  Thereafter, the substrate electrode 11 and the component electrode 21 are connected via the conductive adhesive 30. First, the conductive adhesive 30 is supplied onto the substrate electrode 11 of the substrate 10 by mask printing or dispensing. Next, the electronic component 20 is mounted on the substrate 10 in a state where the substrate electrode 11 and the component electrode 21 are aligned.

  Next, the conductive adhesive 30 is heated and cured at a curing temperature of about 100 ° C. to 200 ° C. Thereby, the connection between the electronic component 20 and the substrate 10 is completed, and the mounting structure shown in FIG. 1 is completed.

[Effects]
By the way, according to this embodiment, in the electronic component mounting structure in which the electronic component 20 is mounted on the substrate 10 and the electrode 11 of the substrate and the electrode 21 of the electronic component are connected via the conductive adhesive 30. The mounting layer 100 is characterized in that the surface layer of the electrode 21 of the electronic component is formed by plating a Sn-based metal, and the surface layer plating layer 21b is obtained by modifying the plated Sn-based metal by heat treatment. Is provided.

  In the present embodiment, the surface layer of the component electrode 21 is composed of a Sn-based base metal electrode obtained by plating an Sn-based metal, and the plated Sn-based metal is modified by heat treatment. Specifically, as described above, the plated Sn-based metal is recrystallized, or the metal in the base metal plating layer 21a as the base diffuses into the surface plating layer 21b. Can be alloyed.

  According to the study of the present inventor, the Sn-based base metal electrode 21 of the electronic component 20 of the present embodiment is more resistant to connection resistance and high-temperature environments than the conventional Sn-based base metal electrode even in a high temperature environment and a cold cycle environment. It has been experimentally found that the connection strength can be secured at a suitable level. This examination result will be specifically described with reference to FIGS.

  In this examination, a multilayer ceramic capacitor having a commercially available Sn base metal electrode was used as an electronic component. This capacitor is an electronic component 20 as shown in FIG. 2A, that is, a component electrode 21 is a Ni plating layer 21a as a base, and an Sn plating layer 21c as a surface layer of the electrode 21 formed thereon. It will be.

  And this capacitor | condenser was used as the electronic component 20, and the conventional mounting structure and the mounting structure of this embodiment were formed as a comparative example. Here, a ceramic substrate was used as the circuit board 10.

  Moreover, what was shown by the said example as the conductive adhesive 30 and a preferable conductive adhesive was used.

  That is, the conductive adhesive is dihydroxynaphthalene / diglycidyl ether as the main agent, the epoxy equivalent ratio of the ID mixture which is an acid anhydride as the curing agent and allylphenol is 50/50, and the bisphenol A type as the curing catalyst. Microencapsulated imidazole dispersed in an epoxy resin, a silane coupling agent containing an epoxy group as a coupling agent, a cyclic aliphatic epoxy resin as a diluent, and Ag and Cu as a conductive filler in a ratio of 72/28 Ag A Cu alloy and a mixture ratio of conductive filler and resin component of 88/12 as a weight ratio were used. The conductive adhesive was cured under the conditions of 100 ° C./30 minutes → 150 ° C./60 minutes.

  First, as for the comparative example, the conductive adhesive 30 is supplied to the substrate electrode 11 of the circuit board 10 by screen mask printing, and the multilayer ceramic chip capacitor as the electronic component 20 is mounted on the conductive adhesive 30 from above. Agent 30 was heat cured at 150 ° C. for 60 minutes. In this case, the conductive adhesive 30 and the surface Sn of the capacitor electrode 21 are bonded.

  On the other hand, in the case of the mounting structure of this embodiment, before mounting the capacitor as the electronic component 20 via the conductive adhesive 30, heat treatment is performed in advance to modify the Sn plating layer 21c, The surface plating layer 21b of this embodiment was used. Here, the heat treatment was performed at 175 ° C. for 100 hours.

  Thereafter, the capacitor was mounted on the circuit board 10, and the conductive adhesive 30 was heated and cured at 150 ° C. for 60 minutes. In this case, the surface plating layer 21b and the conductive adhesive 30 in a state where the Sn plating is recrystallized or the underlying Ni diffuses into the Sn plating are adhered.

  3 to 10 show the connection reliability of the comparative example in which the heat treatment is not performed and the present embodiment in which the heat treatment is performed. Here, connection resistance and connection strength were investigated as evaluation characteristics.

  The connection resistance is a resistance value when a current of 10 mA is passed between the component electrode 21 and the substrate electrode 11, and the connection strength is the maximum generated when the electronic component 20 is pulled vertically from the circuit board 10. It is strength.

  In addition, as a reliability test item, a cooling cycle test and a high temperature storage test were performed. The cooling / heating cycle test was a cycle test in which each of −40 ° C. and 150 ° C. was repeated for 30 minutes, and the high temperature standing test was a standing test at a temperature of 150 ° C.

  FIG. 3 is a diagram showing a change in connection resistance by a cooling cycle test for the comparative example, FIG. 4 is a diagram showing a change in connection resistance by a high temperature standing test for the comparative example, and FIG. FIG. 6 is a diagram showing a change in connection resistance due to a high temperature storage test for this embodiment.

  FIG. 7 is a diagram showing a change in connection strength by a thermal cycle test for the comparative example, FIG. 8 is a diagram showing a change in connection strength by a high-temperature standing test for the comparative example, and FIG. 9 is a connection by a thermal cycle test for this embodiment. FIG. 10 is a diagram showing a change in strength, and FIG. 10 is a diagram showing a change in connection strength according to a high temperature standing test for this embodiment.

  First, regarding the connection resistance, as shown in FIGS. 3 to 6, there was no difference between the comparative example and the present embodiment in the initial and high temperature storage tests, and both were good connection resistance values.

  However, when the thermal cycle test is performed, as shown in FIG. 3, the connection resistance increases remarkably in the comparative example, whereas in this embodiment, the connection resistance increases as shown in FIG. Stable characteristics could be obtained.

  This is because the component electrode 21 of the present embodiment can suppress brittle fracture and intergranular cracking due to the thermal cycle generated at the interface with the conductive adhesive 30, and the conductive filler and electrode in the conductive adhesive 30. This is considered to be because the contact with 21 was maintained unchanged from the initial stage.

  However, in the present embodiment, if the component electrode 21 is heated too much when it is reformed, generation of excessive oxide film on the electrode surface and exposure of the underlying Ni to the electrode outermost surface occur. Therefore, there is a concern that the connection resistance in the initial and endurance tests will increase.

  Next, regarding the connection strength, as shown in FIG. 7 to FIG. 10, in the initial stage, the present embodiment showed higher strength than the comparative example. This is presumably because the surface of the electrode was appropriately oxidized by the heat treatment, and the number of extremely strong hydrogen bonding portions increased in the adhesion mechanism with the resin.

  Furthermore, when the thermal cycle test and the high temperature storage test are performed, the connection strength is greatly deteriorated in the comparative example, whereas no significant strength deterioration occurs in the present embodiment. This is because, in this embodiment, since it is possible to suppress a change in the shape of the surface of the component electrode 21 at the interface with the conductive adhesive 30, it is possible to maintain a bonding area that is the same as the initial state even if the durability test is performed. it is conceivable that.

  Thus, according to this embodiment, in the electronic component mounting structure 100 in which the electrode 21 of the electronic component 20 and the electrode 11 of the substrate 10 are connected via the conductive adhesive 30, the electrode of the electronic component 20 is provided. Even when a general-purpose Sn-based base metal electrode is used for 21, high connection reliability can be ensured in a high-temperature environment and a thermal cycle environment.

  In addition, in the electronic component mounting structure 100 of the present embodiment, in the electrode 21 of the electronic component 20, the base of the surface plating layer 21b is a Ni plating layer 21a formed by Ni plating. .

  Further, according to this embodiment, in the electronic component mounting method in which the electronic component 20 is mounted on the substrate 10 and the substrate electrode 11 and the component electrode 21 are connected via the conductive adhesive 30, 20, the surface layer of the electrode 21 is prepared of a plated layer 21c formed by plating Sn-based metal, and the plated layer 21c is modified by heat treatment, and then the substrate electrode 11 There is provided a mounting method characterized in that a connection is made to the component electrode 21 via a conductive adhesive 30.

  According to this, the plated layer 21c modified by the heat treatment in the prepared electronic component 20 becomes the surface layer plated layer 21b in the mounting structure of the present embodiment. Thus, according to the present embodiment, it is possible to provide a mounting method that can appropriately realize the electronic component mounting structure 100 of the present embodiment.

  Here, in the electronic component mounting method of the present embodiment, the heating temperature in the heat treatment is not less than the heating temperature in the mounting step after the heat treatment and not more than the melting point of the plating material of the plating layer 21c. It is one of the features.

  According to this, it is possible to prevent the plating layer 21c modified by the heat treatment, that is, the surface plating layer 21b formed by the heat treatment from being deteriorated by further heating in the subsequent mounting process. Moreover, melting can be prevented.

  Furthermore, in the electronic component mounting method of this embodiment, one of the characteristics is that the heating temperature in the mounting process after the heat treatment is the curing temperature of the conductive adhesive 30.

  As described above, the present embodiment heats an electronic component in securing connection reliability with a general-purpose and low-cost Sn-based base metal electrode, which has been a major problem with conventional conductive adhesives. Since the Sn plating is simply modified in advance by treatment, it can be achieved without requiring much man-hours and costs.

[Examination of Ni-Sn alloy layer]
As described above, the surface plating layer 21b is obtained by modifying the plated Sn-based metal by heat treatment, but the metal (Ni in this example) in the base metal plating layer 21a is contained in the surface plating layer 21b. In the case of being alloyed by diffusion (Ni-Sn alloy in this example), the metal in the base metal plating layer 21a out of the surface plating layer 21b diffuses into the surface plating layer 21b. It is preferable that the average film thickness of the part excluding the alloyed part is 1.5 μm or less.

  FIG. 11 is a schematic cross-sectional view for explaining how the alloy layer 21d is formed in the case of this alloying. As described in the manufacturing method, the surface plating layer 21c shown in FIG. 11A is modified by heat treatment.

  As a result, the metal in the base metal plating layer 21a is alloyed by diffusing into the plating layer 21c. Then, as shown in FIG. 11B, a part of the plating layer 21c on the base metal plating layer 21a side becomes an alloy layer 21d made of Ni—Sn alloy, and this alloy layer 21d and the remaining plating layer 21c. Is formed as a surface plating layer 21b.

  At this time, in FIG. 11B, the portion of the surface plating layer 21b that is alloyed by diffusion of the underlying metal into the surface plating layer 21b is the alloy layer 21d. A portion excluding the alloy layer 21d is a plating layer 21c.

  And in this FIG.11 (b), it is preferable that the average film thickness of the plating layer 21c is 1.5 micrometers or less. If it is thicker than 1.5 μm, the durability of the surface plating layer 21b in a high temperature environment or a cold environment is inferior, but if it is 1.5 μm or less, this durability can be ensured.

  The average film thickness of the alloy layer 21d is preferably 0.5 μm or more. If the average film thickness of the alloy layer 21d is set to 0.5 μm or more by performing the modification by the heat treatment described above, high connection reliability can be appropriately ensured in a high temperature environment and a cold cycle environment.

  Here, the state of the surface plating layer 21b shown in FIG. 11B, that is, the average film thickness of the plating layer 21c which is a portion of the surface plating layer 21b excluding the alloy layer 21d is 1.5 μm or less, Making the average film thickness of the alloy layer 21d 0.5 μm or more can be realized, for example, as follows.

  The first method is a case where the average film thickness of the plating layer 21c in FIG. 11A is about 4 μm, which is a conventional normal level.

  In this case, if the heat treatment is performed, for example, at 175 ° C. for about 100 hours, Ni in the base metal plating layer 21a can be diffused into Sn of the plating layer 21c on average by about 2.5 μm or more. Thereby, the average film thickness of the plating layer 21c which is a part which is not alloyed in FIG.11 (b) can be 1.5 micrometers or less.

  The second method is a simpler case. In this case, Sn plating is performed with a uniform thickness so that the average thickness of the plating layer 21c in FIG. 11A is 0.5 to 3.5 μm, which is thinner, and the underlying Ni is not exposed. In this way, the surface plating layer 21b can be brought into a state by heat treatment at a lower temperature and for a shorter time than the first method.

  Here, FIG. 12 shows the treatment time when heat treatment is performed at a temperature of 150 ° C. when the average film thickness of the plating layer 21c in FIG. 11A is 1.75 μm and when the average film thickness is 0.75 μm. It is a figure which shows the result of having investigated the electroconductive joining member connection resistance.

  As shown in FIG. 12, when the average film thickness of the plating layer 21c is 1.75 μm, the heating may be performed at 150 ° C. for 5 to 50 hours. If it is further heated, for example, for 100 hours, the diffusion of the underlying Ni proceeds too much and is exposed to the outermost surface, resulting in abnormal connection resistance.

  In addition, when the average film thickness of the plating layer 21c is 0.75 μm, the same connection resistance abnormality occurs due to heating for 10 hours or more, and it is necessary to shorten the heat treatment time to less than 10 hours. is there.

(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 100 shown in FIG. 1, a heat sink made of Al is further attached to the substrate (component mounting board), the heat sink and the case are bonded, and then sealed with silicone gel. It is good also as a structure. 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.

It is a schematic sectional drawing of the mounting structure of the electronic component which concerns on embodiment of this invention. It is a schematic sectional drawing for demonstrating the mounting method of the electronic component of embodiment. It is a figure which shows the change of the connection resistance by a thermal cycle test about a comparative example. It is a figure which shows the change of the connection resistance by a high temperature leaving test about a comparative example. It is a figure which shows the change of the connection resistance by a thermal cycle test about embodiment. It is a figure which shows the change of the connection resistance by a high temperature leaving test about embodiment. It is a figure which shows the change of the connection strength by a thermal cycle test about a comparative example. It is a figure which shows the change of the connection strength by a high temperature leaving test about a comparative example. It is a figure which shows the change of the connection strength by a thermal cycle test about embodiment. It is a figure which shows the change of the connection strength by a high temperature leaving test about embodiment. It is a schematic sectional drawing for demonstrating the mode of formation of the alloy layer 21d in the case of alloying. It is a figure which shows the result of having investigated the electroconductive joining member connection resistance with respect to the average film thickness of a plating layer, and heat processing time.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Circuit board as a board | substrate, 11 ... Electrode of a circuit board, 20 ... Electronic component,
21 ... Electrodes of electronic components, 21a ... Underlying metal plating layer, 21b ... Surface plating layer,
30: Conductive adhesive.

Claims (10)

An electronic component (20) is mounted on a substrate (10), and an electrode (11) of the substrate and an electrode (21) of the electronic component are connected via a conductive adhesive (30). In the mounting structure,
The surface layer of the electrode (21) of the electronic component is formed by plating a Sn-based metal, and is composed of a surface plating layer (21b) in which the plated Sn-based metal is modified by heat treatment. Mounting structure for electronic components. The electronic component mounting structure according to claim 1, wherein the surface plating layer (21b) is obtained by recrystallizing the plated Sn-based metal. The said surface layer plating layer (21b) is alloyed by diffusing the metal under the surface layer plating layer (21b) into the surface layer plating layer (21b). Mounting structure of the electronic component described. Of the surface plating layer (21b), an average film thickness of a portion excluding a portion alloyed by diffusion of the base metal into the surface plating layer (21b) is 1.5 μm or less. The electronic component mounting structure according to claim 3. The average film thickness of a portion of the surface plating layer (21b) alloyed by diffusing the underlying metal into the surface plating layer (21b) is 0.5 µm or more. Item 5. The electronic component mounting structure according to Item 3 or 4. 6. The electrode (21) of the electronic component (20), wherein a base of the surface plating layer (21b) is a Ni plating layer (21a) formed by Ni plating. The electronic component mounting structure according to claim 1. An electronic component (20) is mounted on a substrate (10), and an electrode (11) of the substrate and an electrode (21) of the electronic component are connected via a conductive adhesive (30). In the implementation method,
As the electronic component (20), a surface layer of the electrode (21) is prepared by a plating layer (21c) formed by plating Sn-based metal,
The plated layer (21c) is modified by heat treatment,
Subsequently, the electronic component mounting method is characterized in that the electrode (11) of the substrate and the electrode (21) of the electronic component are connected via the conductive adhesive (30). The heating temperature in the heat treatment is set to a range not less than the heating temperature in the mounting step after the heat treatment and not more than the melting point of the plating material of the plating layer (21c). Electronic component mounting method. The method of mounting an electronic component according to claim 8, wherein the heating temperature in the mounting step after the heat treatment is a curing temperature of the conductive adhesive (30). The electrode (21) of the electronic component (20) is characterized in that the base of the plating layer (21c) is a Ni plating layer (21a) formed by Ni plating. The electronic component mounting method according to any one of the above.

Images