JP2015028869A - Conductive paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive paste containing a phenolic resin to be used for conducting a through-hole in a printed wiring board, which suppresses thickening during storage, improves workability in use, can decrease a product defective percentage caused by thickening, and can extend a quality maintenance period.SOLUTION: The conductive paste comprises a conductive filler, a chelate-forming substance, a boron compound, and a resin including a phenolic resin. The phenolic resin is a resol type phenolic resin; and the proportion of the phenolic resin with respect to the total amount of the resin included in the conductive paste is 60 mass% or more. The chelate-forming substance is one compound or a plurality of compounds selected from a group consisting of pyridine derivatives and 1,10-phenanthroline, and is included by 0.1 to 2.0 pts.mass per 100 pts.mass of the conductive filler. The conductive paste contains, as the conductive filler, copper powder, silver powder, or silver-coated copper powder.

Description

  The present invention relates to a conductive paste that can be suitably used for, for example, forming through-hole conduction in a printed wiring board.

  As a means for conducting conduction of the through hole of the printed wiring board, there is a method of forming a conductive coating layer by applying a conductive paste to the through hole portion using screen printing and curing by heating to ensure conduction. .

  Patent Documents 1 and 2 disclose a conductive paste containing copper powder, a thermosetting resin, a chelate-forming substance, and a specific alkoxy group-containing modified silicone resin.

  On the other hand, in Patent Document 3, as an epoxy resin composition having good storage stability and curing performance, an epoxy resin, an epoxy compound having one or more epoxy groups in one molecule as an essential component, a nitrogen-containing heterocyclic compound, An epoxy resin composition characterized by containing an epoxy adduct obtained by reacting either an aliphatic amine or an aromatic amine, boric acid or a specific borate ester compound, and a phenolic compound is disclosed. Patent Document 4 discloses a low-temperature fast-curing one-part thermosetting epoxy resin composition having a storage stability of one month at room temperature or one week at 40 ° C., epoxy resin, and thiopropionic acid as a curing agent. Disclosed is a thermosetting epoxy resin composition comprising an ester and / or a thioglycolic acid ester, a tertiary amine adduct-based latent curing accelerator as a curing accelerator, and a boric acid ester and a phenol resin as a storage stabilizer. Is done.

JP 2000-219811 A JP 2002-33018 A JP-A-6-172495 JP 2001-316451 A

  The conductive paste described in Patent Document 1 is excellent in the through-hole embedding shape after curing and has a good conduction performance. The conductive paste described in Patent Document 2 can maintain the performance immediately after preparation for a long period of time near room temperature while achieving stabilization of the cured shape.

  However, the conductive paste tends to increase in viscosity during storage. Due to this thickening, the workability when using the conductive paste may deteriorate, and the product defect rate may increase.

  Phenolic resins have a high shrinkage rate when cured. Therefore, when a phenol resin is used for the conductive paste, it is considered that there is an advantage that the particles of the conductive filler are strongly pressure-bonded by the shrinkage of the phenol resin due to the curing reaction, and the conductivity of the cured conductive paste is increased.

  For conductive pastes that use phenolic resins, it is desirable to improve workability during use and reduce the product defect rate after long-term storage, and a phenolic resin-containing conductive paste that can maintain quality over a longer period is desired. It is.

  The object of the present invention is to suppress the thickening of the phenol resin-containing conductive paste during storage, to improve workability during use, to reduce the product defect rate due to thickening, and to extend the quality maintenance period. It is to provide a phenolic resin-containing conductive paste.

  The present invention provides a conductive paste comprising a conductive filler, a chelate-forming substance, a boron compound, and a resin containing a phenol resin.

  The phenol resin is preferably a resol type phenol resin.

  The ratio of the phenol resin to the total amount of the resin contained in the conductive paste is preferably 60% by mass or more.

  The chelate-forming substance is one or more compounds selected from the group consisting of a pyridine derivative represented by the formula I (wherein n represents an integer of 2 or more and 8 or less) and 1,10-phenanthroline. Is preferred.

  The conductive paste preferably contains the chelate-forming substance in a range of 0.1 parts by weight or more and 2.0 parts by weight or less per 100 parts by weight of the conductive filler.

  It is preferable that the conductive paste contains the boron compound in a range of 0.1 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the total amount of resins contained in the conductive paste.

  It is preferable that the boron compound is a boric acid ester compound.

  The boric acid ester compound is preferably a boric acid triester compound.

  The boric acid triester compound preferably has 3 to 54 carbon atoms.

  The conductive paste preferably contains copper powder as the conductive filler.

  The conductive paste preferably contains silver powder as the conductive filler.

  The conductive paste preferably contains silver-coated copper powder as the conductive filler.

  According to the present invention, it is possible to suppress thickening of the phenol resin-containing conductive paste during storage, improve workability during use, reduce the product defect rate due to thickening, and extend the quality maintenance period. A phenolic resin-containing conductive paste is provided.

  The electrically conductive paste of this invention can be used for the printed wiring board in which the conductor pattern for mounting an electronic component was formed. In particular, as a means for conducting the through-hole of the printed wiring board, a conductive paste is applied to the through-hole portion using screen printing and cured by heating, thereby forming a conductive coating layer to ensure conduction. be able to.

The conductive paste includes at least the following components:
・ Conductive filler,
・ Phenolic resin,
A chelating agent, and
-Boron compounds.

[Conductive filler]
As the conductive filler, a known conductive paste, in particular, a conductive filler used in a known conductive paste used for conducting a through hole of a printed wiring board can be appropriately used.

  As the conductive filler, metal powder can be used, particularly copper powder, silver powder, or a kind of powder coated with silver (silver coated copper powder) or a mixture of two or more of these powders. Is preferred.

  The electrical resistivity of copper and silver is low among metals, and good conductivity of the cured conductive paste can be obtained.

  Moreover, the surface of the metal powder may be covered with an oxide film. For example, the surface of normally available copper powder is covered with an oxide film. In such a case, it is difficult to obtain good electrical conductivity only by bringing metal powder particles, particularly copper powder particles, into contact with each other. According to the present invention, since the phenol resin having a high shrinkage rate at the time of curing is used, even in such a case, the particles of the conductive filler can be strongly bonded to each other. Therefore, good conductivity of the cured conductive paste can be obtained. Moreover, even in the case of a metal powder not covered with an oxide film, such as silver powder, the contact resistance between the metal powders can be reduced and the conductivity can be improved by strong pressure bonding.

〔resin〕
The conductive paste includes a resin. A phenol resin is used for a part or all of the resin.

  As described above, the phenolic resin has a high shrinkage rate at the time of curing (thus increasing the conductivity of the cured paste), and also has high adhesion to the substrate material of the printed wiring board, copper foil, and the like.

  As the phenol resin, a resol type phenol resin is preferable. Since the resol type phenol resin has a self-reactive functional group, it has an advantage that it can be cured only by heating.

  The resol type phenol resin can be obtained by reacting phenol or a phenol derivative with formaldehyde in the presence of an alkali catalyst.

  Examples of the phenol derivative include alkylphenols such as cresol, xylenol, and t-butylphenol, and phenylphenol and resorcinol.

  As a phenol resin, Gunei Chemical Industry Co., Ltd. resin top PL-4348 (brand name) can be illustrated.

  The ratio of the phenol resin (particularly, resol type phenol resin) to the total amount of resin contained in the conductive paste is preferably 60% by mass or more, more preferably 70% by mass, from the viewpoint of conductivity of the cured conductive paste. As mentioned above, More preferably, it is 80 mass% or more.

  Examples of resins other than phenolic resins that can be included in the conductive paste include resins used in known conductive pastes, particularly known conductive pastes used to conduct through holes in printed wiring boards. The resin used in the above can be used as appropriate. As the resin other than phenol, a resin having curing shrinkage, that is, a thermosetting resin is preferable. For example, an epoxy resin or a silicone resin can be used.

[Chelating substance]
As a chelate-forming substance, a ligand compound capable of chelate bonding to a conductive filler (especially a metal) can be used. In particular, in the process of acting on a metal powder in the preparation of a conductive paste, It is desirable that it can be dissolved. Chelating substances that satisfy this requirement include diamines capable of bidentate coordination, such as ethylenediamine, N- (2-hydroxyethyl) ethylenediamine, trimethylenediamine, 1,2-diaminocyclohexane, and triethylenetetramine. Bidentate ligands utilizing ring nitrogen and amino nitrogen, for example, 2-aminomethylpyridine, purine, adenine, histamine, etc., and 1,3-diones that produce acetylacetonato type bidentate ligands And similar compounds such as acetylacetone, 4,4,4-trifluoro-1-phenyl-1,3-butanedione, hexafluoroacetylacetone, benzoylacetone, dibenzoylmethane, 5,5-dimethyl-1,3- Cyclohexanedione, oxine, 2-methyloxine, oxine 5-sulfonic acid, dimethylglyoxime, 1-nitroso-2-naphthol, 2-nitroso-1-naphthol, can also be mentioned and salicylaldehyde. The 1,3-diones that generate the acetylacetonato-type bidentate ligands and similar compounds are keto-enol tautomeric, although the keto body itself is not a chelating agent. As a result of the body functioning as an acid, the anion species generated by releasing protons can function as bidentate ligands of the acetylacetonate type.

  The chelate-forming substance is one or two selected from the group consisting of a pyridine derivative represented by the formula I (wherein n represents an integer of 2 or more and 8 or less) and 1,10-phenanthroline. It is preferable that it is a polydentate ligand compound of a seed | species or more. The pyridine derivative represented by Formula I and 1,10-phenanthroline can efficiently chelate metal ions such as copper ions, and the resulting chelate complex is relatively stable near room temperature.

  An example of a method for synthesizing the polypyridine represented by the formula I is shown below. The ortho position is azinated with respect to the nitrogen of the pyridine skeleton by heat mixing the starting material with sodium azide. Subsequently, this is treated with sodium nitrite in oxygen bromide to give diazonium bromide, which is subsequently brominated by adding bromine. When this brominated pyridine is subjected to dehalogenation condensation polymerization with a zerovalent nickel complex at 60 ° C. in DMF (N, N-dimethylformamide), for example, a yellow to yellow-orange precipitate is obtained. The precipitate is washed with hot toluene, water and hot toluene in this order and dried to obtain the desired polypyridine. The degree of polymerization n is adjusted by the choice of starting materials and the degree of bromination of the brominated pyridine contained. For the zerovalent nickel complex, an equimolar mixture of nickel-1,5-octadiene complex and 1,5-octadiene and triallylphosphine is used. When n is 2 or 3, a purified simple compound is commercially available as a reagent. For compounds where n is 4 or more, it is also possible to synthesize compounds having n of 2 or 3 as starting materials.

  In general, the synthesized polypyridine represented by the formula I has a slight distribution of the number of repetitions n of the pyridine skeleton when purified to the extent of recrystallization, and shows an average value obtained from the molecular weight distribution. However, according to the above synthesis method, n = 1 pyridine itself is rarely mixed during precipitation, and only contains those having n of 2 or more. When n is 2 or more, sufficient chelate forming ability is exhibited. On the other hand, as n increases, the solubility in a solvent decreases. When n exceeds 8, the solubility in a solvent becomes poor, and the preparation of a solution required for forming a desired chelate tends to become increasingly difficult. Therefore, when the polypyridine represented by the formula I is used as the chelate-forming substance added to the conductive paste of the present invention, the repeating number n of the pyridine skeleton is preferably selected in the range of 2 to 8, More preferably, n is in the range of 2 to 3.

[Boron compounds]
It is preferable that the boron compound is a boric acid ester compound, particularly a boric acid triester compound. The carbon number of the boric acid triester compound is preferably 3 to 54, more preferably 6 to 30, and still more preferably 6 to 12.

  As the boric acid ester compound, alkyl or aryl esters of boric acid can be used, and specifically, trimethyl borate, triethyl borate, tributyl borate, tridecyl borate, trioctadecyl borate, triphenyl borate and the like can be used.

  Specific examples of the boric acid triester compound having 6 to 12 carbon atoms include triethyl borate, 2-methoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, 2-isopropoxy-4,4, 5,5-tetramethyl-1,3,2-dioxaborolane, 2-isopropoxy-4,4,6-trimethyl-1,3,2-dioxaborinane, tripropyl borate, isopropyl borate, tris (trimethylsilyl) borate, boric acid Mention may be made of tributyl.

[Other ingredients]
If necessary, a solvent, an antifoaming agent, an antisettling agent, a dispersing agent, a coupling agent, and the like can be added to the conductive paste. Zinc powder as an antioxidant and resin curing agents can also be used as appropriate.

  As the solvent, a solvent that does not react with the resin (particularly thermosetting resin) and can dissolve the chelate-forming substance can be selected. For example, ethyl cellosolve, methyl cellosolve, butyl cellosolve, ethyl cellosolve acetate, methyl cellosolve acetate, butyl cellosolve acetate, ethyl carbitol, methyl carbitol, butyl carbitol, ethyl carbitol acetate, methyl carbitol acetate, butyl carbitol acetate, etc. It is done.

  As a coupling agent, a coupling agent effective for conductive fillers (especially metal powders such as copper), for example, a silane coupling agent, is added as appropriate as long as the pot life of the conductive paste is not deteriorated. can do. Preferred coupling agent types are, for example, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane, N- ( β-aminoethyl) -γ-aminopropylmethyldimethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, and the like. be able to. These have low volatility and low reactivity with resins (especially thermosetting resins).

[Composition of conductive paste]
The amount of the chelate-forming substance is preferably 0.1 parts by mass or more and 2.0 parts by mass or less per 100 parts by mass of the conductive filler. When this amount is 0.1 parts by mass or more, it is easy to obtain a good through-hole resistance when used for conducting through-holes. When this amount is 2.0 parts by mass or less, it is easy to obtain good storage stability.

  The amount of the boron compound is preferably 0.1 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the resin (all resins contained in the conductive paste). When this amount is 0.1 parts by mass or more, it is easy to obtain good storage stability. When this amount is 50 parts by mass or less, it is easy to obtain a good through-hole resistance when used for conducting through-holes.

  The amount of resin (all resins contained in the conductive paste) is preferably in the range of 15 to 25 parts by mass with respect to 100 parts by mass of the conductive filler. When the amount is 15 parts by mass or more, it is easy to obtain excellent conductivity of the cured paste by the curing shrinkage force of the resin. When it is 25 parts by mass or less, it is easy to secure a contact area between the fillers, and it is easy to obtain excellent conductivity of the paste cured product.

  The content in the conductive paste may be selected so that the ratio of the conductive filler in the cured product after curing of the conductive paste is 70 to 86.9% by mass, preferably 75 to 83% by mass. preferable. In the conductive paste, a solvent is contained if necessary, but the cured product after curing essentially does not contain such a solvent. Therefore, it is desirable that the content of the conductive filler in the conductive paste is blended at the above ratio with respect to the total constituent components of the conductive paste excluding the solvent contained.

  When using a coupling agent, the addition amount can be suitably selected according to the quantity of the conductive filler contained in a conductive paste, for example, 1-10 mass parts with respect to 100 mass parts of conductive fillers. It can be determined in consideration of adhesion and the like within the range.

  According to the present invention, a conductive paste having excellent storage stability can be obtained without blending a latent curing agent as described in Patent Documents 3 and 4. The conductive paste of the present invention is stable even if it contains a chelating agent that is not a latent curing agent, for example, amines such as pyridine derivatives (for example, compounds represented by Formula I) and 1,10-phenanthroline. Excellent in properties.

  According to the present invention, even when silver powder or silver-coated copper powder is used as the conductive filler, storage stability equivalent to that when copper powder is used can be obtained.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited by this. Tables 1 and 2 summarize the composition and evaluation results of the conductive filler in each example.

[Example 1]
The following components were charged to the reaction vessel:
Resin: Resol-type phenol resin having a weight average molecular weight of about 20,000 obtained by reacting phenol and formaldehyde in the presence of an alkali catalyst (manufactured by Gunei Chemical Industry Co., Ltd., trade name: Resitop PL-4348), 20 parts by mass,
-Chelate-forming substance: 2,2'-bipyridyl, 1 part by mass,
Boron compound: triethyl borate, 0.5 parts by mass,
Solvent: butyl cellosolve, 20 parts by mass.

  These were stirred using a rotation-revolution stirrer (manufactured by Kurashiki Boseki Co., Ltd.) to prepare a uniform liquid resin. Next, 100 parts by mass of copper powder (trade name: T-22, manufactured by Mitsui Mining & Smelting Co., Ltd.) is added as a conductive filler to the prepared resin, and a rotation-revolution stirrer (manufactured by Kurashiki Boseki Co., Ltd.) is used. Stirring was performed to obtain a conductive paste.

[Example 2]
A conductive paste was obtained in the same manner as in Example 1 except that the chelate-forming substance was changed to 1 part by mass of 1,10-phenanthroline.

Example 3
A conductive paste was obtained in the same manner as in Example 1 except that the chelate-forming substance was changed to 1 part by mass of the pyridine compound (compound of formula I: n = 4).

Example 4
A conductive paste was obtained in the same manner as in Example 1 except that the chelate-forming substance was changed to 1 part by mass of the pyridine compound (the compound of n = 8 in Formula I).

Example 5
A conductive paste was obtained in the same manner as in Example 1 except that the chelate-forming substance was changed to 0.1 part by mass of 2,2′-bipyridyl.

Example 6
A conductive paste was obtained in the same manner as in Example 1 except that the chelate-forming substance was changed to 2 parts by mass of 2,2′-bipyridyl.

Example 7
A conductive paste was obtained in the same manner as in Example 1 except that the resin was changed to 12 parts by mass of the resol type phenol resin and 8 parts by mass of epoxy resin (trade name: Adeka Resin EP-4100E, manufactured by ADEKA Corporation). It was.

Example 8
A conductive paste was obtained in the same manner as in Example 1 except that the resin was changed to 14 parts by mass of the resol type phenol resin and 6 parts by mass of the epoxy resin.

Example 9
A conductive paste was obtained in the same manner as in Example 1 except that the resin was changed to 16 parts by mass of the resol type phenol resin and 4 parts by mass of the epoxy resin.

Example 10
A conductive paste was obtained in the same manner as in Example 1 except that the resin was changed to 12 parts by mass of the resol type phenol resin and 8 parts by mass of a silicone resin (trade name: KR-213, manufactured by Shin-Etsu Chemical Co., Ltd.). Obtained.

Example 11
A conductive paste was obtained in the same manner as in Example 1 except that the resin was changed to 14 parts by mass of the resol type phenol resin and 6 parts by mass of the silicone resin.

Example 12
A conductive paste was obtained in the same manner as in Example 1 except that the resin was changed to 16 parts by mass of the resol type phenol resin and 4 parts by mass of the silicone resin.

Example 13
A conductive paste was obtained in the same manner as in Example 1 except that the boron compound was changed to 0.5 parts by mass of trimethyl borate.

Example 14
A conductive paste was obtained in the same manner as in Example 1 except that the boron compound was changed to 0.5 parts by mass of tributyl borate.

Example 15
A conductive paste was obtained in the same manner as in Example 1 except that the boron compound was changed to 0.5 parts by mass of tridecyl borate.

Example 16
A conductive paste was obtained in the same manner as in Example 1 except that the boron compound was changed to 0.5 parts by mass of trioctadecyl borate.

Example 17
A conductive paste was obtained in the same manner as in Example 1 except that the boron compound was changed to 0.02 parts by mass of triethyl borate.

Example 18
A conductive paste was obtained in the same manner as in Example 1 except that the boron compound was changed to 10 parts by mass of triethyl borate.

Example 19
A conductive paste was obtained in the same manner as in Example 1 except that the conductive filler was changed to 100 parts by mass of silver powder (Fukuda Metal Foil Powder Co., Ltd., trade name: AgC-B).

Example 20
A conductive paste was obtained in the same manner as in Example 1 except that the conductive filler was changed to 100 parts by mass of silver-coated copper powder (Fukuda Metal Foil Powder Co., Ltd., trade name: Ag-coated Cu-HWQ). It was.

Example 21
A conductive paste was obtained in the same manner as in Example 1 except that the phenol resin was changed to 15 parts by mass of the resol-type phenol resin and the amount of triethyl borate was changed to 0.375 parts by mass.

[Example 22]
A conductive paste was obtained in the same manner as in Example 1 except that the phenol resin was changed to 25 parts by mass of the resol-type phenol resin and the amount of triethyl borate was changed to 0.625 parts by mass.

[Comparative Example 1]
A conductive paste was obtained in the same manner as in Example 1 except that no boron compound was blended.

[Comparative Example 2]
A conductive paste was obtained in the same manner as in Comparative Example 1 except that the chelate-forming substance was changed to 0.1 part by mass of 2,2′-bipyridyl.

[Comparative Example 3]
A conductive paste was obtained in the same manner as in Comparative Example 1 except that the chelate-forming substance was changed to 0.05 part by mass of 2,2′-bipyridyl.

[Comparative Example 4]
A conductive paste was obtained in the same manner as in Comparative Example 1 except that the phenol resin was changed to 15 parts by mass of a resol type phenol resin.

[Comparative Example 5]
A conductive paste was obtained in the same manner as in Comparative Example 1 except that the phenol resin was changed to 10 parts by mass of the resol type phenol resin.

〔Evaluation test〕
About the electrically conductive paste of said each example, through-hole resistance was evaluated immediately after preparation. In addition, the through-hole resistance and storage stability after leaving at 25 ° C. for 7 days were evaluated for the conductive pastes of the above examples. Separately from this, the through-hole resistance and storage stability after leaving at a high temperature of 40 ° C. for 7 days, which are extremely severe conditions, were also evaluated for the conductive pastes of the above examples.

  The through hole resistance was evaluated by drilling 100 mm holes with a diameter of 0.5 mm (diameter) in a 1.6 mm thick paper phenol substrate for through holes, and embedding a conductive paste by screen printing. . After preheating at 50 ° C. for 2 hours, curing was performed at 150 ° C. for 1 hour. In this board, through holes with 100 holes are connected in series by circuits on the front and back of the board. By measuring the conduction resistance between the terminal through holes, it is possible to measure the through hole resistance of 100 holes in series. It is. The resistance value of the 100-hole through hole was converted to one per hole and was defined as the through-hole resistance.

The evaluation criteria were as follows.
○: Through-hole resistance per hole is 30mΩ or less,
Δ: Through-hole resistance per hole exceeds 30 mΩ and 50 mΩ or less,
X: Through-hole resistance per hole exceeds 50 mΩ.

  Regarding the storage stability evaluation method, the viscometer (trade name: VISCOMETER TV-25, manufactured by Toki Sangyo Co., Ltd.) is used to measure the viscosity immediately after preparation of the conductive paste and the viscosity after storage for a predetermined temperature condition / period. Measured and calculated the rate of increase in viscosity that occurred during storage. Viscosity measurements were made at 25 ° C.

The evaluation criteria were as follows.
○: Increase rate of viscosity is 30% or less,
Δ: Viscosity increase rate exceeds 30% and 50% or less,
X: The increase rate of a viscosity exceeds 50% and is 100% or less.

Claims (12)

  A conductive paste comprising a conductive filler, a chelate-forming substance, a boron compound, and a resin containing a phenol resin.   The conductive paste according to claim 1, wherein the phenol resin is a resol type phenol resin.   The conductive paste according to claim 1 or 2, wherein a ratio of the phenol resin to a total amount of the resin contained in the conductive paste is 60% by mass or more. The chelate-forming substance is one or more compounds selected from the group consisting of a pyridine derivative represented by the formula I (wherein n represents an integer of 2 or more and 8 or less) and 1,10-phenanthroline. The electrically conductive paste in any one of Claims 1-3 characterized by these.

  5. The conductive paste according to claim 1, comprising the chelate-forming substance in a range of 0.1 parts by mass or more and 2.0 parts by mass or less per 100 parts by mass of the conductive filler. .   The boron compound is contained in a range of 0.1 parts by weight or more and 50 parts by weight or less per 100 parts by weight of the total amount of the resin contained in the conductive paste. Conductive paste.   The conductive paste according to claim 1, wherein the boron compound is a boric acid ester compound.   The conductive paste according to claim 7, wherein the boric acid ester compound is a boric acid triester compound.   The conductive paste according to claim 8, wherein the boric acid triester compound has 3 to 54 carbon atoms.   The conductive paste according to claim 1, wherein the conductive filler contains copper powder.   The conductive paste according to claim 1, wherein the conductive filler contains silver powder.   The conductive paste according to claim 1, wherein the conductive filler contains silver-coated copper powder.