JP4539644B2 - Circuit connection material and circuit connection method using the connection material - Google Patents

Description

  The present invention provides a circuit connecting material capable of electrically connecting two mutually facing conductors of two circuit boards without bonding two circuit boards to each other and short-circuiting adjacent circuits on the same circuit board. The present invention relates to a connection method using the connection material.

  Circuit connection materials that can bond two circuit boards to each other and electrically connect the two circuit boards facing each other without short-circuiting the circuit are urethane, polyester, and acrylic. A material in which conductive particles are dispersed in an adhesive component containing a thermoplastic material such as epoxy, or a thermosetting material such as epoxy or silicone is known (see, for example, Patent Documents 1 and 2).

  When the adhesive component is a thermosetting substance, as the curing agent or catalyst for curing the thermosetting substance, tertiary amines and imidazoles which are anionic polymerization type curing agents are mainly used for epoxy resins. . Epoxy resins containing tertiary amines and imidazoles are cured at a medium temperature of about 160 ° C. to 200 ° C. by heating for about several tens of seconds to several hours, so that the pot life is relatively long. Further, it is known that the pot life can be extended by microcapsuling a tertiary amine or imidazole (see, for example, Patent Document 3).

In addition to the above anionic polymerization type curing agent, there is a cationic polymerization type curing agent. As the cationic polymerization type curing agent, a photosensitive onium salt that cures a resin by energy ray irradiation, for example, an aromatic diazonium salt, an aromatic sulfonium salt, or the like is known. In addition to energy ray irradiation, aliphatic sulfonium salts are known as those that are activated by heating to cure the epoxy resin (see, for example, Patent Documents 4 and 5).
JP 52-59889 A JP 55-164007 A JP-A-4-314724 JP-A-57-102922 JP 58-198532 A

  When electrically connecting between conductors on a circuit board with a circuit connecting material using an adhesive component such as imidazole as a curing agent, the connection time is limited to, for example, 15 seconds. The reliability of the part was insufficient. When the temperature is 140 ° C. or higher, there is a problem of causing thermal damage to a substrate using a thermoplastic material having a low softening point such as polycarbonate.

  Furthermore, if the connection time is limited to 5 seconds, the reliability of the connection portion is insufficient at a connection temperature of 200 ° C. or less, and if the connection temperature is 200 ° C. or more, the connection portion may be displaced due to thermal expansion of the circuit board. There was a problem that occurred.

  In addition, in order to electrically connect between conductors on the circuit board with the circuit connecting material, the thickness of the connecting portion needs to be equal to or smaller than the diameter of the conductive particles in the connecting material. It is important to adjust the reactivity with the composition containing the active substance and the fluidity of the composition. Poor fluidity results in poor connection.

  An adhesive component having an aromatic diazonium salt as a curing agent cannot be used because the circuit board does not transmit energy rays. Also, those using aliphatic sulfonium salts as curing agents have the same problems as those using imidazoles as curing agents.

  In the present invention, when connecting between conductors of circuit boards facing each other, even if the connection time is limited to 10 seconds to 20 seconds, thermal damage is not caused even to a substrate having poor heat resistance. It can be cured under relatively low temperature heating conditions of 140 ° C. or lower, and the connection time is limited to a short time. An object of the present invention is to provide a circuit connecting material having a pot life of 10 hours or more and having a good connectivity by allowing the adhesive component to flow sufficiently during connection.

  The present inventors can connect the circuit conductors facing each other on two circuit boards within 60 seconds when heated at 140 ° C. or less, within 30 seconds when heated at 140 to 200 ° C., and inactive at room temperature. As a result of intensive studies on the materials, the inventors have found that the above object can be achieved by using a heat-sensitive sulfonium salt selected from an aromatic sulfonium salt having a benzyl group, and have completed the present invention.

The present invention is an aromatic sulfonium salt of the following with respect to 100 parts by weight of the composition containing the mosquito thione polymerizable substance and polymers in adhesive component blended with 0.5 to 10 parts by weight of that, by dispersing conductive particles A circuit connection material characterized by the following.

Aromatic sulfonium salts of the present invention is a sulfonium salt represented by Formula 1, Formula 1 wherein R ¹ is Ru high group Der electron withdrawing than R ² and R ^3.

化１中、Ｒ^１、Ｒ^２及びＲ^３は、置換又は非置換の基であり、互いに同じでも異なっていてもよく、Ｙ⁻は、非求核性陰イオンである。

In Formula 1, R ¹ , R ² and R ³ are substituted or unsubstituted groups, which may be the same or different from each other, and Y ⁻ is a non-nucleophilic anion.

  The connecting member of the present invention can connect between circuit conductors facing each other even in a relatively low temperature range that does not cause thermal damage to a substrate that is easily damaged by heat, and can be reliably connected in a short time in the middle temperature range. Can do.

化２中、Ｒ^１、Ｒ^２及びＲ^３は、置換又は非置換の基であり、互いに同じでも異なっていてもよく、Ｙ⁻は、非求核性陰イオンである。 The present invention is characterized in that conductive particles are dispersed in an adhesive component containing 0.5 to 10 parts by weight of a sulfonium salt represented by Chemical Formula 2 with respect to 100 parts by weight of a composition containing a cationic polymerizable substance. It is a circuit connection material.

In Chemical Formula 2, R ¹ , R ² and R ³ are substituted or unsubstituted groups, which may be the same or different from each other, and Y ⁻ is a non-nucleophilic anion.

R ¹ is an electron-withdrawing group such as a nitroso group, a carbonyl group, a carboxyl group, a cyano group, a trialkylammonium group, a fluoromethyl group, in order to generate a benzyl cation presumed as an initiator for cationic polymerization. R ² and R ³ are preferably electron donating groups such as an amino group, a hydroxyl group, and a methyl group. Y ⁻ may be a non-nucleophilic anion, for example, hexafluoroarsenate (AsF ₆ ), hexachloroantimonate (SbCl ₆ ), hexafluorophosphate (PF ₆ ), tetrafluoroborate (BF ₄ ). Can be mentioned.

  These sulfonium salts are activated at a temperature of 140 ° C. or lower, can cause cationic polymerization, and the viscosity of the reactive adhesive after 10 hours or more in the presence of a cationic polymerizable substance at room temperature (25 ° C.). Is not more than twice the initial viscosity. Further, these sulfonium salts can be used by dissolving them in various solvents (for example, ethyl acetate) which can be dissolved if necessary. The compounding quantity of a sulfonium salt shall be 0.05-10 weight part with respect to 100 weight part of adhesive components. The amount is particularly preferably 1.5 to 5 parts by weight with respect to 100 parts by weight of the adhesive component. A large amount is undesirable because it tends to cause electrolytic corrosion, and the curing reaction proceeds explosively.

  The conductive particles dispersed in the adhesive component are preferably those that are deformed by heating or pressing or simply pressing. The deformation of the conductive particles increases the contact area with the circuit at the time of connection, improving the connection reliability, variation in the thickness and flatness of the circuit, and a mixture of protrusions and those that are not. Sometimes a good connection can be made. This deformation may be either one in which the conductive particles themselves are deformed or one in which the conductive particles form an aggregate and change the aggregated state at the time of connection.

  Examples of the conductive particles include metal particles such as Au, Ag, Ni, Cu, Sb, Sn, and solder, particles of a conductive material such as carbon, these particles, or non-conductive glass, ceramics, and plastic particles. Some cores have a surface coated with another conductive material. Furthermore, it is also effective to use conductive particles as nuclei and coat the surface of these nuclei with an insulating layer so that when pressed, the inner nuclei break the insulating layer and come into contact. When such conductive particles are used, insulation in a direction perpendicular to the pressurizing direction is secured, and it is extremely effective for connecting narrow thin circuit between circuits. If the particle size of the conductive particles is not smaller than the distance between adjacent lines in the circuit, the adjacent circuits are short-circuited. Moreover, it is preferable that the particle diameter of electroconductive particle is 1-18 micrometers considering that it deform | transforms by the pressurization at the time of a connection and spreads sideways. If necessary, insulating particles may be used in combination so as not to prevent contact between the conductive particles.

  The blending amount of the conductive particles is preferably set so as to produce conductivity only in the pressing direction at the time of bonding. In the circuit, although it varies depending on the distance between adjacent lines and the diameter of the conductive particles, it is in the range of 0.05 to 20% by volume, preferably 0.1 to 15% by volume, more preferably, with respect to the adhesive component. 0.2 to 10% by volume. If it exceeds 20% by volume, the transparency deteriorates and it becomes difficult to align the circuits to be connected. If it is less than 0.05% by volume, conductivity cannot be obtained.

  When the melt viscosity of the adhesive component at 100 ° C. is 1 to 1,000 Pa · s, particularly 10 to 1,000 Pa · s, the adhesive component flows well and the connection thickness is smaller than the diameter of the conductive particles. Become. If it is 1,000 Pa · s or more, the fluidity is poor and the connection thickness is thicker than the diameter of the conductive particles, resulting in poor connectivity. When the pressure is in the range of 1 to 10 Pa · s, it is necessary to take care such that the pressure is initially reduced and the pressure is increased after the adhesive component is cured to some extent. If it is 1 Pa · s or less, it flows too much and the deposition component flows out of the connecting portion and is difficult to be held in the connecting portion, resulting in poor reliability. The adjustment of the melt viscosity will be described later.

  When the sulfonium salt in the adhesive component is microencapsulated, the storage stability of the adhesive component is improved. This is because the cationically polymerizable substance and the sulfonium salt do not come into contact with each other during storage. The method for microencapsulation is not particularly limited, such as solvent evaporation, spray drying, coacervation, and interfacial polymerization. The microcapsules should have a small particle size, and the sulfonium salt is hydrophobic, so that the interfacial polymerization method is preferred.

  Among the adhesive components, examples of the cationically polymerizable substance include an epoxy resin, polyvinyl ether, and polystyrene. These may be used alone or in combination. Moreover, it can also be used by mixing with other polymers or solid resins having a weight average molecular weight of 3000 or less.

  Of the cationically polymerizable substances, an epoxy resin is most preferable. The epoxy resin is a compound having two or more epoxy groups in one molecule. For example, a bisphenol type epoxy resin derived from epichlorohydrin and bisphenol A or bisphenol F, polyglycidyl ether, polyglycidyl ester, fat reductant. An epoxy resin etc. are mentioned.

  Examples of the polymer that can be mixed with the cationic polymerizable substance include polyvinyl acetal, phenoxy resin, polyethylene terephthalate, polyurethane, and polymers such as vinyl chloride, olefin, ethylene ionomer, and polyamide. In consideration of film formability, fluidity at the time of melting, and solubility between resins, the molecular weight of these polymers is preferably 10,000 or more and 80,000 or less. In addition, when having a polar group such as a hydroxyl group (OH group) or a carboxyl group (COOH group), compatibility with the epoxy resin is improved, and a film having a uniform appearance and characteristics can be obtained, and reaction with the epoxy group. It is preferable because of its properties.

  Examples of solid resins having a weight average molecular weight of 3000 or less include natural resins such as rosin and terpene, aliphatic, alicyclic, aromatic, polymer resins such as coumarone, indene and styrene, phenol resins and xylene resins. There are condensed resins, etc., and modified products and derivatives thereof. The solid resin having a weight average molecular weight of 3000 or less is used alone or in combination when it is necessary to adjust the tackiness or adhesiveness.

  The sulfonium salt represented by Chemical Formula 2 is stable at room temperature, and the cationic polymerizable substance is activated and cured by heating at 110 ° C. to 140 ° C. for 10 to 60 seconds and 130 ° C. to 200 ° C. for 1 to 30 seconds. To do. Furthermore, by setting the melt viscosity of the adhesive component to 1 to 1,000 Pa · s at 100 ° C., a suitable flow of the adhesive component is obtained by pressurization of 0.5 to 5 MPa, and between the circuit conductors via the conductive particles Connection is obtained. Therefore, the adhesive component has good storage stability at room temperature, can be cured by adhesion without thermally damaging the substrate material, and circuit connection can be obtained.

  Hereinafter, although an Example demonstrates in detail, this invention is not limited to this.

Example 1
50 g of bisphenol A type liquid epoxy resin (Oka Shell Co., Ltd., using trade name Epicoat 828), 50 g of phenoxy resin (Union Carbide Co., Ltd., using trade name PKHA) having an average molecular weight of 25,000 and a hydroxyl group content of 6% Was dissolved in a mixed solvent of toluene and ethyl acetate in a weight ratio of 1: 1 to obtain a solution having a solid content of 40%.

  A nickel layer having a thickness of 0.2 μm is provided on the surface of particles having polystyrene as a core, and a gold layer having a thickness of 0.02 μm is provided outside the nickel layer, and conductive particles having an average particle diameter of 10 μm and a specific gravity of 2.0. Manufactured.

  p-Acetoxyphenylbenzylmethylsulfonium salt was dissolved in ethyl acetate to give a 50% by weight solution.

The resin component 100 in solid weight ratio, and blended so that p- acetoxy-phenylene behenate emissions Gilles methyl sulfonium salt 2, further conductive particles is 2 vol% blend dispersion was applied to the fluororesin film having a thickness of 80 [mu] m, at room temperature The circuit connection material having a thickness of 25 μm was obtained.

Example 2
A circuit connecting material was obtained in the same manner as in Example 1 except that p-methoxycarbonyloxyphenylbenzylethylsulfonium salt was used instead of p-acetoxyphenylbenzylmethylsulfonium salt.

Example 3
A circuit connecting material was obtained in the same manner as in Example 1 except that p-hydroxyphenylbenzylmethylsulfonium salt was used instead of p-acetoxyphenylbenzylmethylsulfonium salt.

Example 4
A circuit connection material was obtained in the same manner as in Example 1 except that p-hydroxyphenyl-p-nitrobenzylmethylsulfonium salt was used instead of p-acetoxyphenylbenzylmethylsulfonium salt.

Example 5
A circuit connecting material was obtained in the same manner as in Example 1 except that the amount of p-acetoxyphenylbenzylmethylsulfonium salt was 0.2 parts by weight.

Example 6
A circuit connecting material was obtained in the same manner as in Example 1 except that the amount of p-acetoxyphenylbenzylmethylsulfonium salt was 10 parts by weight.

Example 7
A connection material for a circuit was obtained in the same manner as in Example 1 except that an alicyclic epoxy resin (using Daicel Chemical Industries, Ltd., trade name Celoxide 2021) was used instead of the bisphenol A liquid epoxy resin.

Example 8
A circuit connection material was obtained in the same manner as in Example 1 except that bisphenol A type solid epoxy resin (Oilized Shell Epoxy Co., Ltd., using trade name Epicoat 1001) was used instead of bisphenol A type liquid epoxy resin. It was.

Reference Example 9
A circuit connection material was obtained in the same manner as in Example 1 except that an acrylic resin (Showa Polymer Co., Ltd., trade name Lipoxy SD-1509 was used) was used instead of the bisphenol A liquid epoxy resin.

Example 10
A circuit connection material was obtained in the same manner as in Example 1 except that the amount of conductive particles was changed to 0.5% by volume.

Example 11
A circuit connection material was obtained in the same manner as in Example 1 except that the amount of the conductive particles was changed to 5% by volume.

Example 12
A circuit connecting material was obtained in the same manner as in Example 1 except that the diameter of the conductive particles was 3 μm.

Example 13
A circuit connecting material was obtained in the same manner as in Example 1 except that the conductive particles were replaced with nickel particles having an average single particle size of 2 μm and an aggregate particle size of 10 μm.

Example 14
Circuit connection was made in the same manner as in Example 1 except that conductive particles were 0.5% by volume of nickel particles having an average single particle size of 2 μm and an aggregated particle size of 10 μm, and 0.5% by volume of silica particles having a particle size of 2 μm were added. Obtained material.

Example 15
Circuit connection material as in Example 1, except that 70 g of bisphenol A type liquid epoxy resin (Epicoat 828) was used instead of phenoxy resin (Union Carbide Co., Ltd., trade name PKHA was used) and the blending amount was 30 g. Got.

Example 16
10 parts by weight of p-acetoxyphenylbenzylmethylsulfonium salt, 16 parts by weight of methyl methacrylate, 16 parts by weight of styrene, 8 parts by weight of ethylene glycol dimethacrylate, 0.05 parts by weight of azo compound (V-60 manufactured by Wako Pure Chemical Industries, Ltd. V-40 each 0.025 part by weight) as component A, water 200 parts by weight, sodium dodecylbenzenesulfonate 0.2 part by weight, polyvinyl alcohol 0.125 part by weight as component B, in a nitrogen atmosphere sealed container The mixture was stirred at 60 ° C. for 4 hours and dried to microencapsulate the sulfonium salt. Thereafter, a circuit connecting material was obtained in the same manner as in Example 1.

Reference Example 17
A circuit connecting material was obtained in the same manner as in Example 1 except that p-hydroxyphenyldimethylsulfonium salt (sulfonium salt having no benzyl group) was used instead of p-acetoxyphenylbenzylmethylsulfonium salt.

Comparative Example 1
A circuit connecting material was obtained in the same manner as in Example 1 except that 1-cyanoethyl-2-methylimidazole was used in place of the p-acetoxyphenylbenzylmethylsulfonium salt.

Comparative Example 2
A circuit connection material was obtained in the same manner as in Example 1 except that the conductive particles were not blended.

Example 18
A circuit connection material was obtained in the same manner as in Example 1 except that the diameter of the conductive particles was 20 μm.

Example 19
A circuit connecting material was obtained in the same manner as in Example 1 except that 20 g of bisphenol A type liquid epoxy resin (Epicoat 828) and 80 g of phenoxy resin (PKHA) were used.

Measurement of DSC 3 mg (± 0.1 mg) of the circuit connection material obtained above was weighed, and DSC was measured in a sealed aluminum pan at a heating rate of 10 ° C./min. The analyzer used is TA2000 manufactured by DuPont.

Measurement of Melt Viscosity In Examples 1, 15 and 19, bisphenol A type liquid epoxy resin (Epicoat 828) and phenoxy resin (PKHA) were not dissolved in a solvent but were melted around 250 ° C. and mixed uniformly, and about 10 g. Was collected, cooled gradually, and the viscosity at 100 ° C. was measured. At this time, a curing agent and conductive particles were not blended. The apparatus used for the measurement is a digital viscometer HU-8 manufactured by Resuka Co., Ltd.

Circuit connection A flexible circuit board (FPC) having 250 copper circuits having a line width of 100 μm, a pitch of 200 μm, and a thickness of 35 μm using the circuit connection materials of Examples 1 to 19 and Comparative Examples 1 and 2, and indium oxide ( A 0.5 mm thick polycarbonate plate (ASTM D648, heat distortion temperature 140 ° C. at 1.86 MPa) having a thin layer of ITO (surface resistance 40 Ω / □) was formed at 130 ° C. and 1.5 MPa for 20 seconds. It was heated and pressed to connect over a width of 3 mm. At this time, after pasting the adhesive surface of the circuit connection material on the polycarbonate plate in advance, 70 ° C., 0.5 MPa, heating and pressurizing for 5 seconds to temporarily connect, and then peeling the fluororesin film and bonding to the FPC did. In addition, FPC having 250 copper circuits with a line width of 100 μm, a pitch of 200 μm and a thickness of 35 μm and glass with a thin layer of ITO (surface resistance 20 Ω / □) were heated and pressed at 160 ° C. and 1.5 MPa for 10 seconds. Connected over 3 mm. At this time, temporary connection was made on the ITO glass in the same manner as described above.

Measurement of connection resistance After connection of the circuit, the resistance value between adjacent circuits of the FPC including the connection portion was measured with a multimeter after being initially held at a high temperature and high humidity of 85 ° C. and 85% RH for 500 hours.

Storage stability The circuit connection material was kept as a compound solution, sealed so that the solvent would not evaporate, and allowed to stand at 25 ° C., and the time when the solution viscosity doubled was examined.

Measurement of connection thickness The thickness of the substrate on which the ITO thin layer was formed and the FPC were measured in advance with a micrometer, the thickness after connection was measured with a circuit connection material, and the connection thickness was calculated.

  These measurement results are shown in Tables 1 and 2. From this result, the following can be understood.

About each Example, the peak temperature of DSC is 100-120 degreeC, and it is 10-20 degreeC lower than that of the reference example 17 and the comparative example 1. FIG. In particular, the adhesive of Example 7 has a DSC peak temperature that is 10 ° C. lower than that of Example 1 and does not show an increase in connection resistance, thus providing good connection. Further, for each example, the initial resistance value is significantly lower than that of Reference Example 17 and Comparative Example 1, and the increase in connection resistance after holding under high temperature and high humidity is not observed or is a small value. . It is considered that Reference Example 17 and Comparative Example 1 were insufficient in reaction. In the connection material of Example 8, the peak temperature of DSC is as high as 120 ° C., and the increase in connection resistance is slightly large. The reason for this is considered to be that the reactivity was slightly lowered because a solid epoxy resin was used. Since Comparative Example 2 has no conductive particles, the initial resistance is high and the connection resistance is remarkably increased. In Example 18, since the conductive particles were as large as 20 μm, the number of conductive particles in the connection portion was reduced at 2% by volume, and thus the resistance value was slightly high. Similar to the connection material of Example 1, the connection material of Example 10 using nickel particles having an average single particle diameter of 2 μm and an aggregation particle size of 10 μm as the conductive particles is also excellent in connection. The adhesive of Example 11 in which nickel particles and silica particles having a particle diameter of 2 μm are mixed at a volume ratio of 1: 1 can also provide good connection as in Example 1, and in particular, between the nickel particles. It was found that silica particles were present in the surface to improve the insulation from the adjacent circuit. In the connection materials of Example 1 and Example 15, the melt viscosity at 100 ° C. is in the range of 1 to 1,000 Pa · s, and the connection thickness is not more than the particle diameter of the conductive particles. The connection material had a high melt viscosity and was cured before the adhesive component sufficiently flowed, and the connection thickness was larger than the particle diameter of the conductive particles. As a result, the connection resistance increased and the rise was significant. The adhesive solutions of Examples 1, 5, 6 and 16 were allowed to stand at 25 ° C. for a long time. The solution of Example 1 was after 3 months, the solution of Example 5 was after 6 months, and the solution of Example 6 was After one month, the viscosity doubled respectively. In Example 16, the preservability is extended by microencapsulation, which is 3 to 6 months.

Claims (9)

A circuit connection material in which conductive particles are dispersed in an adhesive component containing 0.05 to 10 parts by weight of an aromatic sulfonium salt with respect to 100 parts by weight of a composition containing a cationic polymerizable substance and polymers,
The cationically polymerizable substance is an epoxy resin;
The polymers are phenoxy resins;
A circuit connecting material, wherein the aromatic sulfonium salt is a sulfonium salt represented by the following general formula (1).

Wherein (1), ^{R 1} is water atom, ^{R 2} is methyl group, ^{R 3} represents a hydroxyl group, an -OCOCH ₃ or -OCOOCH _3, Y ^- is a non-nucleophilic Anion, hexafluoroarsenate (AsF ₆ ), hexachloroantimonate (SbCl ₆ ), hexafluorophosphate (PF ₆ ) or tetrafluoroborate (BF ₄ ). ]   The circuit connection material according to claim 1, wherein the aromatic sulfonium salt is a heat-sensitive sulfonium salt.   The conductive particles are selected from particles of a substance exhibiting conductivity, particles having a non-conductive substance coated with a conductive material, and particles having a conductive particle surface coated with an insulating substance. The circuit connection material according to claim 1 or 2, wherein   The circuit connection material according to claim 1, wherein 0.05 to 20% by volume of the conductive particles are contained in the adhesive component.   The circuit connection material according to any one of claims 1 to 4, wherein a particle diameter of the conductive particles is in a range of 1 to 18 µm.   The circuit connection material according to claim 1, wherein the adhesive component has a melt viscosity at 100 ° C. of 1 to 1,000 Pa · s. A circuit connection material in which conductive particles are dispersed in an adhesive component in which 0.05 to 10 parts by weight of an aromatic sulfonium salt is blended with 100 parts by weight of a composition containing a cationic polymerizable substance and polymers faces each other 2 A circuit connection method that is sandwiched between two circuit conductors and is laminated and integrated by heating and pressing from the back of the wiring board having each circuit conductor,
The cationically polymerizable substance is an epoxy resin;
The polymers are phenoxy resins;
The circuit connection method, wherein the aromatic sulfonium salt is a sulfonium salt represented by the following general formula (1).

Wherein (1), ^{R 1} is water atom, ^{R 2} is methyl group, ^{R 3} represents a hydroxyl group, an -OCOCH ₃ or -OCOOCH _3, Y ^- is a non-nucleophilic Anion, hexafluoroarsenate (AsF ₆ ), hexachloroantimonate (SbCl ₆ ), hexafluorophosphate (PF ₆ ) or tetrafluoroborate (BF ₄ ). ] The circuit connection method according to claim 7 , wherein the aromatic sulfonium salt is a heat-sensitive sulfonium salt. The circuit connection method according to claim 7 or 8 , wherein the heating and pressurizing conditions are a temperature of 110 to 140 ° C, a pressure of 0.5 MPa to 5 MPa, and a time of 10 to 60 seconds.