JP4365068B2 - Conductive adhesive, component bonding structure, and component bonding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an electrically-conductive adhesive obtained at a low cost by using a particulate filler which is obtained by forming electrically-conductive coating layers on surfaces of a thermal expansion control material, to provide a structure for joining parts by using the same, and to provide a method for joining the parts. <P>SOLUTION: The electrically-conductive adhesive 10 contains a resin component and the particulate filler 6, wherein the filler 6 is composed of particles of the thermal expansion control material 4 and the electrically-conductive coating layers 5 for coating the surfaces of the particles. The particulate filler 6 has a thermal expansion control function inherent in the thermal expansion control material 4, and further has electrical conductivity, because the electrical conductivity thereof is achieved by contacting the electrically-conductive coating layers 5 of the filler 6 with each other. Therefore, electrically-conductive particles which are mixed into conventional adhesives for the purpose of giving the electrical conductivity to the conventional adhesives are not required when the filler 6 is used, so that the electrically-conductive adhesive 10 is produced at the low cost. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a conductive adhesive including a particulate filler having a conductive coating layer, and a component joining structure and method using the same.
[0002]
[Prior art]
Conventionally, when electronic components such as surface mount components are bonded to a substrate, a method of bonding by solder is generally employed. However, in recent years, for the reasons described later, a joining method using an adhesive composed of a resin composition instead of a solder material has been increasingly desired. In particular, when a surface mount component is mounted on a substrate, a conductive adhesive is used in order to achieve electrical connection between the electrode of the mount component and the electrode of the substrate. As such a conductive adhesive, for example, as disclosed in Japanese Patent Application Laid-Open No. 10-265748 or Japanese Patent Application Laid-Open No. 11-45618, silver which is conductive particles in a thermosetting resin and / or a thermoplastic resin. Those in which metal fillers such as copper and copper are dispersed are widely used.
[0003]
The reason for using an adhesive, particularly a conductive adhesive, in place of solder is as follows. Since the melting point of the solder is 183 ° C., it is necessary to join the joint by heating the joint to 183 ° C. or higher. For this reason, a method of passing through a furnace having a high temperature of 200 ° C. or higher is common, and the electronic component and the substrate are subjected to a large thermal stress. In addition, the electrodes of electronic parts are often made of aluminum, but since the bondability between solder and aluminum is poor, when joining electronic parts whose electrodes are made of aluminum with solder, It is necessary to form a metal (barrier metal) excellent in bondability on an electrode made of aluminum in advance, which is troublesome and disadvantageous in terms of cost. In addition, the solder contains lead, which is not preferable from the viewpoint of environmental friendliness.
[0004]
Therefore, in order to solve the above-mentioned problems in solder, joining using a conductive adhesive has been performed. However, conventional conductive adhesives have the following problems.
[0005]
A resin constituting the adhesive, for example, a thermosetting resin such as epoxy, has a large difference in thermal expansion coefficient from the electronic component or the substrate. Therefore, when heat is applied to the resin, thermal stress is applied and damages electronic components and the like. Therefore, in order to alleviate the difference in thermal expansion coefficient, thermal expansion adjusting material particles such as silica particles and alumina particles are generally added to the adhesive. Moreover, in order to provide electroconductivity to an adhesive agent, since the electroconductive particle is further added, the manufacturing cost of an electroconductive adhesive agent becomes high. In particular, when Ag preferable as the conductive particles is used, it becomes expensive.
[0006]
In addition, when bonding is performed with solder, mounting can be performed by melting and solidifying the solder in a lump after mounting a plurality of electronic components (solder paste reflow bonding). When using an adhesive, it is necessary to cure the conductive adhesive each time an individual electronic component is mounted on the board. In addition, the time required for this curing is usually several tens of seconds, which increases productivity. Is bad. In addition, in the continuity inspection after mounting electronic components, if good continuity is not confirmed, solder can be easily reworked simply by melting, while conductive adhesive containing a thermosetting resin When joining by means of reworking is difficult due to the high joining strength. Moreover, in the conductive adhesive containing a thermoplastic resin, although rework is possible by heating, since the tolerance with respect to a heat | fever and a solvent becomes weak, required joint strength may not be obtained. Here, reworking refers to, for example, removing an electronic component bonded to a substrate from the substrate and attaching it again to the same location, or attaching a new electronic component to the removed location.
[0007]
[Problems to be solved by the invention]
The present invention has been conceived under such circumstances, and in the conventional adhesive, in place of the conductive particles necessary for imparting conductivity, a thermal expansion adjusting material is used. To provide a conductive adhesive that achieves cost reduction of a conductive adhesive by omitting conductive particles while ensuring conductivity by using a particulate filler having a conductive coating layer formed on the surface. It is an issue.
[0008]
Another object of the present invention is to provide a conductive adhesive that is superior in terms of reworkability by enabling continuity inspection without curing the adhesive.
[0009]
DISCLOSURE OF THE INVENTION
In the present invention, the following technical means are taken in order to solve the above-described problems.
[0010]
That is, the conductive adhesive provided by the first aspect of the present invention includes a resin component and a particulate filler, and the filler covers the thermal expansion adjusting material particles and the surface of the thermal expansion adjusting material particles. It is characterized by having a conductive coating layer.
[0011]
Since the filler which is the composition of the conductive adhesive of the present invention has the thermal expansion adjusting material particles and the conductive coating layer covering the surface of the thermal expansion adjusting material particles, the thermal expansion adjusting material In addition to the inherent thermal expansion adjustment function, electrical conductivity can be achieved by bringing the filler conductive coating layers into contact with each other. Therefore, the conductive particles that have been mixed for imparting conductivity to the conventional adhesive are not necessary, and the cost of the conductive adhesive can be reduced. Conventionally, it has been necessary to mix two types of thermal expansion adjusting material and conductive particles. However, in the present invention, only the filler need be mixed, and work efficiency in the manufacturing process of the conductive adhesive is reduced. Will be better.
[0012]
Preferably, the thermal expansion adjusting material is silica particles and / or alumina particles. The conductive coating layer can be formed of a metal including one or more selected from In, Sn, Zn, Pb, Sb, and Bi, but is preferably formed of In in consideration of imparting reworkability. . The mixing ratio of the particulate filler is preferably in the range of 20 to 60% by volume of the entire adhesive.
[0013]
The fillers are brought into contact with each other by pressurization to the conductive adhesive, but in particular, since In is soft, the conductive coating layer is easily deformed. Therefore, simply pressurizing the adhesive increases the mutual contact area of the conductive coating layer between the filler particles, and can establish good electrical conduction. In addition, since good electrical continuity can be established simply by applying pressure, for example, continuity inspection performed when an IC chip is mounted on a substrate can be performed without curing the resin component, and rework can be performed even when continuity is poor. It can be done easily.
[0014]
The resin component is preferably a thermosetting resin, which comprises a main agent and a curing agent. Examples of the main agent include epoxy. Examples of the curing agent include imidazole-based curing agents. The addition amount of the curing agent is determined in consideration of various factors such as a curing speed to be achieved or a pot life (a usable period after preparation of the adhesive). It is in the range of 20 to 60 parts by weight.
[0015]
Preferably, the conductive adhesive further contains a coupling agent. By mixing the coupling agent, the affinity between the resin component constituting the conductive adhesive and the filler is increased, and the filler can be dispersed stably and uniformly in the resin component. As the coupling agent, a silicone-based coupling agent is preferable, and the content thereof is, for example, in the range of 0.5 to 2.0 parts by weight with respect to 100 parts by weight of the main agent.
[0016]
The electronic component bonding structure using the conductive adhesive provided by the second aspect of the present invention is a structure in which the first bonding target component and the second bonding target component are bonded using the conductive adhesive. In addition, the conductive adhesive is interposed between the first joining target part and the second joining target part to join the two joining target parts, and the filler between the joining target parts of both the joining target parts. It is characterized by having a structure in which the parts to be joined are made conductive by bringing the conductive coating layers into contact with each other.
[0017]
The above-mentioned conductive adhesive contained in the conductive adhesive interposed between the first bonding target component and the second bonding target component by crimping the first bonding target component and the second bonding target component using the conductive adhesive. The fillers are brought into contact with each other, and the first joining target part and the second joining target part are electrically connected through the conductive coating layer of filler particles. Therefore, it is not necessary to separately add conductive particles only for the purpose of imparting conductivity in addition to the filler that mainly adjusts the thermal expansion as in the prior art, and the cost can be reduced.
[0018]
The electronic component bonding method using the conductive adhesive provided by the third aspect of the present invention is a method of bonding and fixing the first bonding target component and the second bonding target component. It is assumed that the coating layer is made of In. Specifically, in the method, the conductive adhesive is applied to the first joining target part and / or the second joining target part, and the first joining target part and the second joining target part are aligned. In addition, both the parts to be joined are temporarily joined by interposing the conductive adhesive therebetween, and a continuity test is performed between the first part to be joined and the second part to be joined, and the continuity test is performed. In the case where good conduction is not confirmed, the first joining target part and the second joining target part are separated and repeated from the adhesive application to the conduction inspection again. When it is confirmed, the conductive adhesive is cured, whereby the first joining target component and the second joining target component are finally joined.
[0019]
When the conductive adhesive of the present invention is interposed between the first bonding target component and the second bonding target component and the temporary bonding of both the bonding target components is performed by pressure bonding, the conductivity interposed between both the bonding target components. In the conductive adhesive, the conductive coating layers of the filler are in contact with each other. However, since In constituting the conductive coating layer is soft and easily deforms by pressurization, a larger contact area can be secured and good electrical properties can be secured. Continuity can be established. For this reason, conventional adhesives do not provide electrical continuity necessary for conducting a continuity test only by crimping, and also require a shrinkage force of the resin applied by curing the adhesive. However, in the conductive adhesive of the present invention, there is no need to cure before the continuity test, and reworkability is improved. In addition to being advantageous in terms of work efficiency, unlike conventional solder bonding, there is no need to apply heat to rework, and it is possible to suppress damage to parts due to heat at the stage of rework. Furthermore, since the reworked part can be easily reused, it is not always necessary to replace it with a new part, which is advantageous in terms of cost.
[0020]
Other advantages and features of the present invention will become more apparent from the following description of embodiments of the invention.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the drawings.
[0022]
FIG. 1 is a schematic diagram showing a process of bonding an electronic component 1 (for example, a semiconductor chip) configured as a surface mount component to a substrate 2 using the conductive adhesive 10 of the present invention. a) represents a coating process, and FIG. 1B represents a bonding process.
[0023]
In the coating step of FIG. 1A, a bonding surface 1A on which a plurality of electrode portions 1a are formed in the electronic component 1, and a bonding surface 2A on which a wiring pattern including a plurality of electrode portions 2a is formed on the substrate 2. A conductive adhesive 10 is applied to the substrate. Note that the conductive adhesive 10 may be applied to only one of the joint surfaces.
[0024]
After performing the application step of FIG. 1A with the conductive adhesive 10 as described above, the electronic component 1 and the substrate 2 are joined as shown in FIG. 1B. This joining process is performed at room temperature. At this time, the electronic component 1 is pressed against the substrate 2 while positioning the electronic component 1 and the substrate 2 so that the electrode portion 1 a of the electronic component 1 faces the electrode portion 2 a of the substrate 2. The electrode portions 1a and 2a slightly protrude from the respective joint surfaces 1A and 2A, and the interval between the positions where the electrode portions 1a and 2a face each other is reduced accordingly. Therefore, a high compression portion 20 and a low compression portion 21 of the conductive adhesive 10 are formed between the electronic component 1 and the substrate 2 by pressing the electronic component 1.
[0025]
As shown in FIG. 2, in the present embodiment, the conductive adhesive 10 includes the resin component 3 and the particulate filler 6 in which the conductive coating layer 5 is formed on the surface of the thermal expansion adjusting material 4. Yes. Therefore, as clearly shown in FIG. 2, in the high compression portion 20, the particulate filler 6 is in an overcrowded state, and the conductive coating layer 5 of the particulate filler 6 is in contact with each other. The electrode part 1 a and the electrode part 2 a on the substrate 2 are electrically connected via the conductive coating layer 5. On the other hand, in the low compression part 21, the particulate filler 6 is not so dense that the conductive coating layer 5 of the particulate filler 6 can contact each other, and does not conduct in the low compression part 21.
[0026]
Examples of the resin component 3 include a thermosetting resin and a thermoplastic resin. In particular, a thermosetting resin is preferably used. The thermosetting resin includes a main agent and a curing agent. Examples of the main agent include epoxy resin, polyimide resin, polyurethane resin, urea resin, and phenol resin. In particular, an epoxy resin is preferably used. Examples of the curing agent include imidazole curing agents, acid anhydride curing agents, and amine curing agents. The addition amount of the curing agent should be appropriately set in consideration of various factors such as the type of curing agent to be used, the curing speed to be achieved, or the pot life of the adhesive, and is based on 100 parts by weight of the main agent. The range is 20 to 60 parts by weight.
[0027]
Examples of the thermal expansion adjusting material 4 include silica particles and alumina particles. Since these coefficients of thermal expansion are small, they have the effect of reducing the coefficient of thermal expansion of the conductive adhesive 10 in the cured state and increasing the Young's modulus. Moreover, as a material which comprises the electroconductive coating layer 5, the metal containing the 1 type (s) or 2 or more types selected from In, Sn, Zn, Pb, Sb, Bi is mentioned. In particular, In is preferably used.
[0028]
The conductive adhesive 10 may further contain a coupling agent. Examples of the coupling agent include silicone coupling agents. By adding a silicone-based coupling agent to the conductive adhesive 10, it is possible to improve the adhesion between the conductive adhesive 10 and the bonding target in the cured state of the conductive adhesive 10. Preferably, the addition amount of the silicone coupling agent is in the range of 0.5 to 2.0 parts by weight with respect to 100 parts by weight of the main agent.
[0029]
Next, examples of the present invention will be described.
[0030]
[Example 1]
In this example, 100 parts by weight of an epoxy resin (trade name: 830 LVP, manufactured by Dainippon Ink) as a main agent, 50 parts by weight of an imidazole-based curing agent (trade name: HX3921, manufactured by Asahi Ciba) as a curing agent, and a conductive filler As a thermal expansion modifier, 100 parts by weight of a particulate filler having a conductive coating layer in which the surface of silica particles having an average particle size of 3 μm (trade name: SO-E5, manufactured by Admatex) is coated with In, and as an additive A conductive adhesive of this example was prepared by uniformly stirring and mixing 1 part by weight of a silicone coupling agent (trade name: MAC2101, manufactured by Nihon Unicar).
[0031]
<Bonding of electronic parts>
The bonding surface of the Si chip (12.5 × 12.5 mm) as an electronic component provided with 352 bumps, that is, electrode portions (125 μm pitch), and the corresponding adhesive adhesive prepared as described above, and corresponding It apply | coated as shown to Fig.1 (a) with respect to the board | substrate which has a joining surface in which the electrode part is provided by the pitch and number which do. Next, as shown in FIG. 1B, the Si chip was pressure-bonded to the substrate with 10 kgf while the electrode part of the Si chip was aligned with the electrode part of the substrate. This joining process is performed at room temperature. In this way, 30 good quality samples of this example were produced. In addition, 30 samples of defective products in which the electrode portion of the Si chip was crimped by shifting the position relative to the electrode portion of the substrate were produced in the same manner.
[0032]
<Immobilization of electronic parts or immobilization after rework>
About the produced non-defective sample, the conductive adhesive was cured under conditions of 150 ° C. and 5 min in a thermostatic chamber after the continuity test. For the defective sample, the pressure-bonded Si chip was removed, and the residue of the conductive adhesive on the substrate was wiped off with acetone. A conductive adhesive was again applied to the substrate after wiping, and a new Si chip was again pressure-bonded thereto by the same method as described above. After crimping, a continuity test was performed, and the conductive adhesive was cured in a constant temperature bath at 150 ° C. for 5 minutes to prepare a re-mounted sample.
[0033]
<Evaluation of bonding reliability>
30 non-defective samples and re-mounted samples prepared as described above were prepared for a total of 60 samples, and the bonding stability of these samples was examined. Specifically, after measuring the initial conduction resistance of 352 electrical connection points where the Si chip electrode and the substrate electrode were connected in each sample, a temperature cycle test was performed in the range of −65 to 125 ° C., and again The conduction resistance was measured. In the temperature cycle test, the sample is first cooled at −65 ° C. for 15 minutes, then the temperature is raised to room temperature, left for 10 minutes, and further heated to 125 ° C. and heated for 15 minutes as one cycle. This cycle was repeated a predetermined number of times. In this example, the number of cycles was 500. As a result, the increase in resistance after the cycle test is as good as 10% or less with respect to the resistance before the cycle test at the electrical connection points of all 30 good products and 30 reloaded samples. It was not confirmed. As described above, it was confirmed that the Si chip and the substrate bonded by the conductive adhesive and the bonding method of this example were stably bonded even when the temperature was changed.
[0034]
[Example 2]
In the remounting of Example 1, in the same manner as in Example 1, except that the conductive adhesive adhering to the removed Si chip was washed with acetone instead of the new Si chip, and remounted. Thus, 30 non-defective samples and 30 reloaded samples were produced. When the reliability of these samples was examined by the same temperature cycle test as in Example 1, the increase in resistance after the cycle test was compared to the resistance before the cycle test at the electrical connection points of all 30 samples. It was as good as 10% or less, and no conduction failure was confirmed. As described above, it was confirmed that the Si chip and the substrate were stably bonded even when the Si chip was reused as in this example.
[0035]
[Example 3]
In the same manner as in Example 1 except that alumina particles having an average particle diameter of 1 μm (trade name: A0902, manufactured by Admatex) were used instead of the silica particles used in preparing the conductive adhesive in Example 1, 30 non-defective samples and 30 reloaded samples were produced. When the reliability of these samples was examined by the same temperature cycle test as in Example 1, the increase in resistance after the cycle test was compared to the resistance before the cycle test at the electrical connection points of all 30 samples. It was as good as 10% or less, and no conduction failure was confirmed. As described above, it was confirmed that the Si chip and the substrate were stably bonded regardless of whether the thermal expansion modifier of this example was silica or alumina.
[0036]
As a summary of the above, the configurations of the present invention and variations thereof are listed below as supplementary notes.
[0037]
(Appendix 1) Including resin component and particulate filler,
The filler has a thermal expansion adjusting material particle and a conductive coating layer that covers the surface of the thermal expansion adjusting material particle.
(Appendix 2) The conductive adhesive according to Appendix 1, wherein the thermal expansion adjusting material particles are silica particles and / or alumina particles.
(Supplementary note 3) The conductive adhesive according to Supplementary note 1 or 2, wherein the conductive coating layer is made of In.
(Supplementary note 4) The conductive adhesive according to any one of supplementary notes 1 to 3, wherein the resin component is a thermosetting resin composed of a main agent and a curing agent.
(Additional remark 5) The said main ingredient is a conductive adhesive of Additional remark 4 selected from an epoxy resin, a polyimide resin, a polyurethane resin, a urea resin, and a phenol resin.
(Additional remark 6) The said hardening | curing agent is a conductive adhesive of Additional remark 4 or 5 which is an imidazole series hardening | curing agent.
(Additional remark 7) Content of the imidazole type hardening | curing agent in the whole said conductive adhesive is a conductive adhesive of Additional remark 6 which is 20-60 weight part with respect to 100 weight part of main agents.
(Appendix 8) The conductive adhesive according to any one of appendices 1 to 7, wherein the conductive adhesive further contains a coupling agent.
(Additional remark 9) The said coupling agent is a conductive adhesive of Additional remark 8 which is a silicone type coupling agent.
(Supplementary note 10) The conductive adhesive according to supplementary note 9, wherein the content of the silicone coupling agent in the whole of the conductive adhesive is 0.5 to 2.0 parts by weight with respect to 100 parts by weight of the main agent. .
(Appendix 11) A structure in which the first bonding target component and the second bonding target component are bonded using the conductive adhesive according to any one of the additional notes 1 to 10,
The conductive adhesive is interposed between the first part to be joined and the second part to be joined to join the parts to be joined, and the conductivity of the filler between the parts to be joined of both parts to be joined. A component joining structure characterized by having a structure in which the parts to be joined are brought into conduction by bringing the covering layers into mutual contact.
(Supplementary Note 12) Using the conductive adhesive according to Supplementary Note 3, the first joining target component and the second joining target component are joined and fixed.
Applying the conductive adhesive to the first joining target part and / or the second joining target part;
While aligning the position of the first joining target part and the second joining target part, by interposing the conductive adhesive between them, both joining target parts are temporarily joined,
Conducting a continuity test between the first part to be joined and the second part to be joined,
In the continuity test, when good continuity is not confirmed, the first part to be joined and the second part to be joined are separated and repeated from the adhesive application to the continuity test again.
In the continuity inspection, when good continuity is confirmed, the first bonding target component and the second bonding target component are finally bonded by curing the conductive adhesive, and the component bonding method .
[0038]
【The invention's effect】
As described above, according to the present invention, as the particulate filler 6 contained in the conductive adhesive 10, by using the one in which the conductive coating layer 5 is formed on the surface of the thermal expansion adjusting material 4, The conductive particles, which are necessary particles such as silver and copper, are no longer necessary, and the cost of the conductive adhesive 10 can be reduced.
[0039]
In addition, when the electronic component 1 and the substrate 2 are temporarily joined by interposing the conductive adhesive 10 of the present invention between the electronic component 1 and the substrate 2 and press-bonding them, the conductivity interposed therebetween. In the adhesive 10, the conductive coating layers 5 of the particulate filler 6 are in contact with each other. However, when the conductive coating layer 5 is In, the material is soft and easily deforms by pressurization. A contact surface can be secured and good electrical continuity can be established. Therefore, conventionally, the electrical continuity necessary for conducting the continuity test cannot be obtained only by crimping, and the shrinkage force of the resin applied by curing the adhesive is also necessary. Although it was necessary to make it harden | cure, in the conductive adhesive 10 of this invention, since there is no need to harden | cure before a conduction inspection, rework property improves. Therefore, in addition to being advantageous in terms of work efficiency, unlike conventional solder bonding, there is no need to apply heat to rework, and it is possible to suppress damage to the electronic component 1 or the substrate 2 due to heat at the rework stage. it can. Furthermore, since the reworked parts 1 and 2 can be easily reused, it is not always necessary to replace them with the new parts 1 and 2, which is advantageous in terms of cost.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory diagram illustrating a method for bonding an electronic component to a substrate using a conductive adhesive according to the present invention.
FIG. 2 is an enlarged view of a main part of a schematic explanatory diagram showing a method for joining an electronic component to a substrate using the conductive adhesive according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electronic component 1a Electrode part 2 Board | substrate 2a Electrode part 3 Resin component 4 Thermal expansion regulator 5 Conductive coating layer 6 Particulate filler 10 Conductive adhesive

Claims (1)

An application step of applying a conductive adhesive to at least one of the first bonding target component and the second bonding target component;
A temporary bonding step of temporarily bonding the first and second bonding target components at room temperature by interposing the conductive adhesive between the first bonding target component and the second bonding target component;
A continuity test step for performing a continuity test between the first part to be joined and the second part to be joined,
In the continuity test, when good continuity is not confirmed, the first bonding target component and the second bonding target component are separated, and the application step, the temporary bonding step, and the continuity checking step are performed.
In the continuity test, when good continuity is confirmed, by curing the conductive adhesive, performing a step of main joining the first joining target component and the second joining target component,
The conductive adhesive includes a resin component and a particulate filler,
The above-mentioned filler has a particle which is at least one of silica particles and alumina particles, and a layer which consists of In which coats the surface of this particle, The component joining method characterized by things.

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