JP4479475B2 - Conductive paste, wiring board using the same, manufacturing method thereof, and electronic equipment using the same - Google Patents

Description

  The present invention relates to a conductive paste for forming a wiring pattern on a substrate, a wiring substrate using the same, a manufacturing method thereof, and an electronic apparatus using the same.

  Conventionally, connection of semiconductor elements such as IC and LSI and other electronic components, mounting on these circuit boards, and wiring on the circuit boards, etc., in order to ensure reliability such as high conductivity and adhesive strength, Soldering and solder paste have been used.

  However, in recent years, environmental pollution problems have been picked up in which harmful lead in solder is eluted from electronic devices left outdoors due to acid rain. As a countermeasure, lead-free solder alloys containing no lead have been developed. However, another problem arises that lead-free solder has a higher melting point than conventional solder and cannot be used for substrates with low heat resistance.

  For this reason, a coating-type conductive paste that does not melt the metal powder (conductive filler) and bonds it to a binder to form a conductor is used for the connection of electronic components with low heat resistance and the wiring of flexible wiring boards. It has been. Thereby, since the connection and wiring can be formed at a curing temperature of the binder, that is, a temperature lower than that of the solder, it has become possible to avoid a decrease in reliability due to a thermal influence.

  However, since the coating type conductive paste is mainly composed of a binder made of an organic material and a conductive filler, the conductivity is lower than that of a conventional solder. In order to improve this, a conductive paste having a high conductive filler content has also been developed. However, for example, when the conductive filler is silver or the like, since silver is expensive, there is a problem that the cost increases due to an increase in the content.

In addition, in a conductive paste composed of a resin such as an epoxy resin, a melamine resin, and an acrylic resin and a conductive filler, an example is disclosed in which the conductivity is improved by using a resin having a large volume shrinkage effect upon curing. (For example, patent document 1). Furthermore, an example in which a conductive filler and a hollow filler are introduced into a binder and the hollow filler is shrunk by volume shrinkage at the time of curing, thereby bringing the conductive fillers close to each other to improve conductivity (for example, patents) is also disclosed. Reference 2).
JP 2002-184236 A JP 2000-349406 A

  However, since the conductive paste shown in Patent Document 1 uses the large volume shrinkage action of the resin constituting the binder, when used for a flexible substrate, the flexible substrate warp or wiring pattern due to the difference in thermal expansion coefficient. There is a problem in reliability because it easily peels off from the substrate. Moreover, in the electrically conductive paste of patent document 2, although the space | interval of an electrically conductive filler is closely approached by the deformation | transformation by crushing of a hollow filler, the method of extracting the air etc. in a hollow filler is unknown. Also, if the air does not escape, the volume does not change and the conductivity is not improved. Furthermore, when air escapes, air holes are generated in the binder resin, so the conductive fillers are not in close proximity. Furthermore, if the deformation of the hollow filler is an elastic deformation, a crack or the like is generated because the hollow filler tends to return to its original shape during use.

  The present invention has been made to solve the problems of such conductive pastes, and provides a conductive paste with improved conductivity, a wiring board using the same, a method of manufacturing the same, and an electronic device using them. The purpose is to do.

In order to solve the problems as described above, the conductive paste of the present invention has a conductive filler component and a binder component, and the binder component includes a thermosetting resin, a biodegradable material, and a biodegradable material. And a microorganism for decomposing the microorganism.

  According to this configuration, it is possible to realize a conductive paste with improved conductivity by reducing the distance between the conductive fillers during curing without reducing the dispersibility of the conductive fillers.

  Moreover, the conductive paste of the present invention may contain a solvent.

  In the conductive paste of the present invention, the biodegradable material may be a biodegradable polymer.

  According to this structure, the absolute amount of the thermosetting resin component in the binder which becomes a resistance increasing component of the conductive paste can be reduced.

  In addition, the conductive paste of the present invention is configured such that microorganisms die at a temperature higher than the curing temperature of the thermosetting resin.

  According to this configuration, it is possible to prevent changes in characteristics over time after the wiring pattern is formed by microorganisms.

  The wiring board of the present invention has a wiring pattern formed using the conductive paste of the present invention.

  According to this configuration, a wiring board having a low wiring resistance of the wiring pattern can be realized.

  The electronic device of the present invention is configured using the wiring board of the present invention.

  According to this configuration, since the wiring resistance is low, an electronic device having excellent power efficiency can be realized.

The method for manufacturing a wiring board according to the present invention includes a conductive filler component and a binder component on a substrate, and the binder component is a microorganism that decomposes a thermosetting resin, a biodegradable material, and a biodegradable material. A wiring pattern forming step for forming a wiring pattern made of a conductive paste, a decomposition step for leaving the substrate on which the wiring pattern is formed for a predetermined time and decomposing the biodegradable material by microorganisms, and a substrate on which the wiring pattern is formed And heating the substrate to kill microorganisms and curing the wiring pattern.

  According to this manufacturing method, the amount of the binder can be reduced by decomposing the biodegradable material in the binder with microorganisms after forming the wiring pattern. Thereby, since the conductive fillers are close to each other at the time of curing, a wiring substrate having a highly conductive wiring pattern can be realized.

The method for manufacturing a wiring board according to the present invention comprises a wiring pattern comprising a conductive filler component and a binder component on a substrate, wherein the binder component comprises a conductive paste containing a thermosetting resin and a biodegradable material. The wiring pattern formation process to be formed, the process of spraying microorganisms that decompose the biodegradable material on the wiring pattern formed on the substrate, and the substrate on which the microorganisms are dispersed are allowed to stand for a predetermined time, and the biodegradable material is decomposed by the microorganisms. And a step of heating the substrate on which the wiring pattern is formed, killing microorganisms and curing the wiring pattern.

  According to this manufacturing method, the amount of the binder can be reduced by decomposing the biodegradable material in the binder with microorganisms after forming the wiring pattern. Thereby, since the conductive fillers are close to each other at the time of curing, a wiring substrate having a highly conductive wiring pattern can be realized. Furthermore, since the microorganisms are not contained in the binder in advance, the biodegradable material is not decomposed by the microorganisms, and the storage characteristics of the conductive paste can be improved.

  In the method for manufacturing a wiring board of the present invention, the conductive paste may contain a solvent.

  ADVANTAGE OF THE INVENTION According to this invention, it has the big effect that the electrically conductive paste which can make between electroconductive fillers close and can improve electroconductivity is realizable.

(Embodiment)
Hereinafter, an embodiment of the present invention will be described with reference to FIG.

  FIG. 1A is a perspective view of a wiring board according to an embodiment of the present invention, and FIG. 1B is a cross-sectional view of a main part as viewed from line AA in FIG. Note that the cross-sectional view is arbitrarily enlarged for easy understanding.

  In FIG. 1A, a wiring substrate 100 is made of a conductive paste on an insulating substrate 110 made of glass epoxy resin obtained by impregnating a glass cloth with resin, PET (polyethylene terephthalate) resin or polyimide, for example. A wiring pattern 120 having a predetermined shape printed by screen printing or the like and cured by heating is provided. As shown in FIG. 1B, the wiring pattern 120 includes a conductive filler 130 containing silver particles, copper particles, and the like, and a binder 140 for binding the conductive filler 130.

  In addition, the wiring pattern 120 of FIG. 1 has shown the state after heat-hardening the conductive paste.

  Hereinafter, the conductive paste for forming the wiring pattern 120 will be described.

  The conductive paste according to the embodiment of the present invention includes, for example, 80 parts by weight to 95 parts by weight of the conductive filler 130 and 5 parts by weight to 20 parts by weight of the binder 140. The binder 140 contains a thermosetting resin, a biodegradable material, and a microorganism.

  When the binder 140 is 5 parts by weight or less, the viscosity of the conductive paste is high, so that sufficient fluidity cannot be obtained at the time of screen printing, printability is lowered, and handling becomes difficult. In particular, when the binder 140 is 0.1 parts by weight or less, the binding strength of the conductive filler 130 and the adhesion with the substrate 110 are reduced. In addition, since the dispersibility of the conductive filler 130 is deteriorated, a part of the conductive filler 130 is partially agglomerated, for example, a portion having a large amount of the binder 140 component is generated, and the wiring resistance of the wiring pattern 120 is increased.

  On the other hand, when the binder 140 is 20 parts by weight or more, the gap between the conductive fillers 130 is widened, so that the conductivity is lowered and consequently the wiring resistance is increased. Therefore, normally, the optimum blending ratio of the conductive filler 130 and the binder 140 is determined by the above conditions.

  Therefore, in the embodiment of the present invention, the conductive filler 130 and the binder 140 are mixed at a predetermined mixing ratio shown above, and the binder 140 contains a thermally decomposable resin, a biodegradable material, and a microorganism. After the wiring pattern 120 is formed on the insulating substrate 110 with the conductive paste, the biodegradable material is decomposed by microorganisms before the heat curing treatment, and finally the binder 140 is converted into carbon dioxide and water. It is something that will be lost. Then, after a predetermined time has elapsed, the microorganisms are killed by heat curing, and the amount of the binder 140 is reduced by decomposing and removing the biodegradable material. The wiring pattern 120 can be formed.

  Moreover, you may add a solvent, a hardening accelerator, a leveling agent, an anti-settling agent, a coupling agent, and an antifoamer as needed. In particular, a volatile or non-volatile solvent can change the viscosity of the conductive paste arbitrarily, so that it is highly effective in forming the fine wiring pattern 120.

  Moreover, what contains saccharides, such as oligosaccharide, biodegradable materials, such as an amino acid, and microorganisms as a solvent can also be used. In this case, viscosity adjustment is easy and the fine wiring pattern 120 can be formed. Further, since the biodegradable material does not volatilize, the viscosity of the conductive paste does not change before and after the formation of the wiring pattern 120, and the reliability such as work efficiency and shape stability is improved. Then, after the wiring pattern 120 is formed, the biodegradable material in the binder 140 and the biodegradable material in the solvent are decomposed by microorganisms. Similarly, the wiring pattern 120 with low wiring resistance can be formed.

  As the conductive filler 130, for example, metal particles such as silver, copper, gold, nickel, palladium, and tin, alloy particles thereof, and the like can be used. Further, for example, a metal coated surface of an inorganic material such as alumina or an organic material such as polystyrene resin can be used. The shape of the conductive filler 130 is not particularly limited, but is preferably spherical or scaly. In the case of a spherical shape, an average particle size of about 0.1 μm to several tens of μm is used, and a size of 0.1 μm to 5 μm is particularly preferable.

  Moreover, as a thermosetting resin, an epoxy resin, a phenol resin, a polyimide resin, a polyurethane resin, a melamine resin, a urea resin etc. are used, for example. Furthermore, it can also be used by 1 type, or 2 or more types of these mixed systems. In particular, the epoxy resin is preferable from the viewpoint of the viscosity of the conductive paste, curing reactivity, and adhesion to the substrate.

  Biodegradable materials include biodegradable plastics made of polysaccharides such as fatty acid polyesters and oligosaccharides produced by microbial synthesis, starch composites produced by natural product induction methods, and starch. The molecular weight of biodegradable plastics, biodegradable polymers such as aliphatic polyesters produced by chemical synthesis, polyesteramides, polycaprolactones, polylactic acids and cellulose acetates A viscous liquid of 100 to several thousand or a solid substance having a molecular weight higher than that can be used. In particular, in the case of a biodegradable polymer composed of a solid substance, the same effect as that of an inorganic filler composed of, for example, silica, which is blended for controlling the conventional fluidity is exhibited. Furthermore, in the case of a biodegradable polymer, it does not remain in the wiring pattern 120 like an inorganic filler in the end, so that the conductivity is not lowered and the effect is great.

  Examples of microorganisms that can be used include bacteria and bacteria such as actinomycetes, green-concentrated fungi, aspergillus, basidiomycetes, and filamentous fungi. In addition, the microorganisms whose activity becomes active near normal temperature (for example, 20 ° C. to 60 ° C.) are preferable, and microorganisms that die at 100 ° C. or higher are desirable. More preferably, microorganisms whose activity ceases or whose degradation rate extremely decreases at a temperature of 0 ° C. or lower are preferable. This is intended to prevent the biodegradable material from being decomposed during storage of the conductive paste containing microorganisms, but is not particularly necessary when the microorganisms are mixed with the binder immediately before screen printing.

  Further, as the volatile or non-volatile solvent, methanol, ethanol, propanol, toluene, butanol, xylene, ethyl acetate, butyl acetate, cyclohexane, ethylene glycol, ether, or the like can be used.

  Below, the manufacturing method of the wiring board 100 which has the wiring pattern 120 formed using the electrically conductive paste of this invention is demonstrated using FIG.

  FIG. 2 is a cross-sectional view of relevant parts for explaining an example of a method for manufacturing the wiring board 100.

  First, as shown in FIG. 2A, a conductive paste is printed in a predetermined wiring pattern 120 shape by screen printing or the like on an insulating substrate 110 such as an epoxy resin. At this time, the conductive paste is 80 parts by weight of conductive filler 130 made of silver particles having an average particle size of 0.3 μm, 20 parts by weight of binder 140 made of epoxy resin, polylactic acid-based biodegradable material, and actinomycetes. It is a mixture of

  Next, the wiring pattern 120 formed by the above method is left at a room temperature of, for example, about 20 ° C. to 30 ° C. for a predetermined time. At this time, the predetermined time is a time required for microorganisms such as actinomycetes to decompose the biodegradable material mixed in the binder 140.

  However, the time required for normal decomposition may be several tens of days to several hundreds of days at room temperature (20 ° C.), for example. Therefore, in order to shorten the decomposition time, it is possible to make it several tens of hours by using a microorganism having a high activity temperature of the mixed microorganism and setting the standing temperature to 40 ° C. to 70 ° C. This is considered to be due to the synergistic effect of the activation and growth of microorganisms due to the temperature rise. Needless to say, this value is not an absolute value, and optimum conditions are determined by factors such as the microorganism used and the environment.

  By the action of the microorganism, the biodegradable material is finally decomposed into water and carbon dioxide through a low-molecular compound as shown in FIG. 2B, and a hole or a cave-shaped hole 150 is formed. .

  Next, the conductive paste in the shape of the wiring pattern 120 in which the holes 150 of FIG. 2B are formed is heat-treated at a temperature equal to or higher than the curing temperature of the thermosetting resin in the binder 140. For example, when the thermosetting resin is an epoxy resin, the heat treatment conditions are 130 ° C. and 60 minutes. By this processing step, the epoxy resin is cured while flowing so as to fill the hole 150, and accordingly, the space between the conductive fillers 130 becomes dense. As a result, the contact area between the conductive fillers 130 is increased, and the conductivity is increased.

  In addition, since the microorganisms in the binder 140 can be completely killed by this heat treatment, the microorganisms remaining after the formation of the wiring pattern 120 shown in FIG. Therefore, a microorganism that does not die at a curing temperature of the thermosetting resin, for example, 130 ° C. or more in the case of an epoxy resin cannot be used.

  In the above-described method for manufacturing the wiring substrate 100, the method of previously mixing microorganisms in the conductive paste has been described, but the present invention is not limited to this. For example, after forming the wiring pattern 120 on the insulating substrate 110 with the conductive paste made of the conductive filler 130 and the binder 140 containing a thermosetting resin and a biodegradable material, at least the wiring pattern 120 covers the microorganisms. Spread like so. Then, after spraying microorganisms and leaving for a predetermined time, a curing process may be performed to form the wiring pattern 120. According to this, the same effect as that of the above embodiment can be obtained, and since the conductive paste is not decomposed by microorganisms during storage, a conductive paste having excellent storage stability can be obtained. In addition, since the microorganisms decompose the biodegradable material from the surface of the wiring pattern 120, the conductive filler 130 is easily exposed, and the contact resistance when connecting to an external device or the like can be reduced.

  Furthermore, the conductive paste used for the wiring substrate 100 may be a conductive paste containing a volatile or non-volatile solvent, a biodegradable material, and a solvent composed of microorganisms. In this case, as the biodegradable material, a viscous liquid material having a molecular weight of about several hundred to several thousand is used. For example, sugars such as oligosaccharides and amino acids. Thereby, the adjustment range of the viscosity of the conductive paste is expanded, and the formation of the fine wiring pattern 120 or the like is facilitated. In particular, a solvent composed of a biodegradable material and a microorganism has a small change in viscosity due to volatilization of the solvent in the manufacturing process. Therefore, the management of the conductive paste is simplified and the shape stability of the wiring pattern 120 is excellent and highly reliable. The wiring board 100 can be realized.

  In addition, by using the wiring substrate 100 using the conductive paste of the embodiment of the present invention for, for example, a portable device or a portable terminal, an electronic device with low power consumption can be realized because of low wiring resistance.

  Hereinafter, the production of the wiring substrate 100 using the conductive paste according to the embodiment of the present invention will be specifically described based on examples.

  In this example, the wiring pattern 120 was printed on the insulating substrate 110 with a conductive paste containing silver particles as the conductive filler 130 under the following conditions, for example. As the insulating substrate 110, a film sheet made of polyimide resin having a thickness of 200 μm was used. The conductive paste is thermosetting made of an epoxy resin having 85 parts by weight of mixed particles of spherical silver particles and scale-like silver particles having a particle size of 0.5 μm to 10 μm as the conductive filler 130 and a curing temperature of 120 ° C. Binder 140 containing 10 parts by weight of a resin, about 5 parts by weight of a biodegradable material composed of oligosaccharides or polylactic acid having a degree of polymerization of about 15 and a microscopic amount of 0.01 parts by weight or less of microorganisms composed of actinomycetes. Used in combination. A wiring pattern 120 shape was printed on the insulating substrate 110 by using a screen printing method with this conductive paste. At that time, the screen mesh had a wire diameter of 25 μm, a photosensitive emulsion layer thickness of 10 μm, and a designed line width of the wiring pattern 120 of 150 μm. After printing the wiring pattern 120 shape with a conductive paste, it was left in an environmental temperature of 35 ° C. for 48 hours in order to allow the microorganisms to decompose the biodegradable material. Thereafter, the wiring pattern 120 was formed by heat treatment for 60 minutes at a curing temperature of 130 ° C. of the thermosetting resin of the binder 140. At this time, the film thickness of the wiring pattern 120 was 20 μm to 30 μm, and the line width was 140 μm to 150 μm. This is smaller than the wiring pattern using the conventional conductive paste, and the cause is considered to be due to the volume shrinkage due to the decomposition of the biodegradable material. Moreover, it was confirmed by culturing the wiring pattern 120 after the treatment that the microorganisms in the binder 140 were killed by this heat treatment.

  The conductivity of the wiring pattern 120 of the wiring board 100 manufactured in this way was evaluated. The results are shown in Table 1.

  From Table 1, the biodegradable material and the microorganism were not contained, and the biodegradable material was contained in comparison with the specific resistance of the wiring pattern 120 using the conventional conductive paste (sample name A) having the same blending ratio. The specific resistance of the conductive paste (sample names B and C) was reduced from 1/2 to 1/3. That is, it was found that the wiring substrate 100 having a low wiring resistance of the wiring pattern 120 can be realized by using the conductive paste.

  According to the conductive paste of the present invention, sufficient conductivity can be obtained, which is useful in realizing a wiring board with low wiring resistance and an electronic device with low power loss.

(A) Perspective view of the wiring board according to the embodiment of the present invention (b) Cross-sectional view of the main part as viewed from the line AA in FIG. Cross-sectional view of relevant parts for explaining an example of a method of manufacturing a wiring board according to an embodiment of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Wiring board 110 Board | substrate 120 Wiring pattern 130 Conductive filler 140 Binder 150 Hole

Claims (9)

A conductive filler component;
A binder component,
The conductive paste, wherein the binder component includes a thermosetting resin, a biodegradable material, and a microorganism that decomposes the biodegradable material . The conductive paste according to claim 1, wherein the conductive paste contains a solvent. The conductive paste according to claim 1, wherein the biodegradable material is made of a biodegradable polymer. The conductive paste according to claim 1, wherein the microorganisms are killed at a temperature equal to or higher than a curing temperature of the thermosetting resin. The wiring board which has a wiring pattern formed using the electrically conductive paste in any one of Claim 1- Claim 4 . An electronic apparatus using the wiring board according to claim 5 . A conductive filler component and a binder component are formed on a substrate, and the binder component forms a wiring pattern made of a thermosetting resin, a biodegradable material, and a conductive paste containing microorganisms that decompose the biodegradable material. A wiring pattern forming process,
Leaving the substrate on which the wiring pattern is formed for a predetermined time, and decomposing the biodegradable material by the microorganisms;
And heating the substrate on which the wiring pattern is formed to kill the microorganisms and curing the wiring pattern. A wiring pattern forming step of forming a wiring pattern comprising a conductive paste including a conductive filler component and a binder component on the substrate, wherein the binder component includes a thermosetting resin and a biodegradable material;
Spraying microorganisms that decompose the biodegradable material on the wiring pattern formed on the substrate;
A decomposition step in which the substrate on which the microorganisms are dispersed is left for a predetermined time, and the biodegradable material is decomposed by the microorganisms;
And heating the substrate on which the wiring pattern is formed to kill the microorganisms and curing the wiring pattern. A method for manufacturing a wiring board according to claim 7 or claim 8 wherein the conductive paste is characterized in that it comprises a solvent.

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