TW201318995A - Lead-free glass composition for conductor formation - Google Patents

Abstract

The subject of the present invention is to provide a lead-free glass composition which can suppress or prevent the problem of warpage at a relatively low cost. The solution relates to a lead-free glass composition for forming a conductor, which comprises B2O3: 5.0 to 25.0% by weight, SiO2: 10.0 to 35.0% by weight, and R2O: 5.0 to 20.0% by weight (however, R represents Li, Na). And at least one element of K), ZnO: 25.0 to 45.0% by weight, and Bi2O3: 10.0 to 35.0% by weight.

Description

Lead-free glass composition for conductor formation Field of invention

This invention relates to lead-free glass compositions. More specifically, it relates to a lead-free glass composition and a conductor-forming composition comprising the same, which is incorporated in a conductive paste for forming a conductor. In particular, it relates to a lead-free glass composition for blending with a conductive paste for forming an electrode, which is formed on a semiconductor substrate used for a solar cell.

Background of the invention

In recent years, in addition to environmental problems such as global warming, depletion of energy resources has been magnified, and the need for clean and renewable energy has increased. As a means for this requirement, interest in solar cells has increased.

Generally, a solar cell is composed of a semiconductor substrate, a light-receiving surface electrode, and a back surface electrode. As far as the method of forming such electrodes is concerned, a low-cost printing method is used now. According to the printing method, after the paste containing the metal powder for electrode formation is printed on the semiconductor substrate, the printed layer is fired at a high temperature to form an electrode.

When the electrode is formed by a printing method, in order to increase the adhesion strength between the electrode and the semiconductor substrate, it is preferable to add a glass frit or an alternative inorganic substance to the conductive paste. Conventionally, in general, PbO-based glass is used as the aforementioned glass glass.

However, the electrode formed by using such a conductive paste may be due to The difference in thermal expansion coefficient between the semiconductor substrate and the metal electrode causes a problem that warpage occurs in the substrate. If warpage occurs in the substrate, cracking or chipping of the semiconductor element is likely to occur in the subsequent step, which is a main cause of deterioration of the yield ratio. This problem becomes more pronounced when forming a back electrode having a large electrode area. Further, in the current state of progress of thinning of the substrate, problems due to warpage of the substrate may become more serious.

In order to solve the above problems, a glass composition for adjusting the thermal expansion coefficient to be added to the conductive paste has been disclosed (Patent Document 1). However, the glass composition shown in Patent Document 1 contains harmful PbO as a main component. From the point of view of environmental protection, even in the case of electronic components, the need for lead-free is also high, and in such a situation, this may become a problem. For glass frits used for conductor formation, the need to switch to lead-free materials that do not contain harmful lead is also high.

For this reason, B ₂ O ₃ -Bi ₂ O ₃ -based glass is disclosed as a glass composition for conductive paste containing no PbO (Patent Documents 2 to 4). However, the glass composition shown in the above Patent Documents 2 to 4 has a problem in production cost because a large amount of Bi ₂ O _{3 is} contained in a large amount. Further, if Bi ₂ O _{3 is} contained in a large amount, the softening point is excessively lowered, and in this case, there is a tendency to flow excessively during firing.

Further, SiO ₂ -B ₂ O ₃ -based glass is disclosed as a glass composition used for a light-receiving surface electrode of a solar cell (Patent Document 5). However, the glass composition shown in Patent Document 5 is used for a light-receiving surface electrode whose electrode area is narrower than that of the back surface electrode, and the light-receiving surface electrode is relatively less likely to warp. The necessity of considering defects in the semiconductor substrate caused by warpage.

Advanced technical literature Patent literature

Patent Document 1: Japanese Special Open 2009-99781

Patent Document 2: Japanese Patent Laid-Open No. 11-329072

Patent Document 3: Japanese Special Open 2010-173904

Patent Document 4: Japanese Special Open 2010-222238

Patent Document 5: WO2007/102287.

Summary of invention

Accordingly, the main object of the present invention is to provide a lead-free glass composition which can suppress or prevent the problem of warpage at a relatively low cost.

The present inventors have found that the above object can be attained by using a specific glass composition in view of the problems of the prior art, and the present invention has been completed.

That is, the present invention relates to the lead-free glass composition described below.

A lead-free glass composition for forming a conductor, which comprises B ₂ O ₃ : 5.0 to 25.0% by weight, SiO ₂ : 9.0 to 35.0% by weight, and R ₂ O: 5.0 to 20.0% by weight (however, R system) It represents at least one element of Li, Na, and K), ZnO: 16.0 to 45.0% by weight, and Bi ₂ O ₃ : 10.0 to 50.0% by weight.

2. The lead-free glass composition for conductor formation according to the above item 1, which further contains Al ₂ O ₃ : 5.0% by weight or less.

3. The lead-free glass composition for conductor formation according to the above-mentioned item 1 or 2, further comprising at least one of MgO, CaO, SrO and BaO: 5.0% by weight or less.

4. The lead-free glass composition for conductor formation according to any one of the above-mentioned items 1 to 3, wherein, as R ₂ O, Li ₂ O: 10.0% by weight or less, Na ₂ O: 20.0% by weight or less, and K ₂ O: 20.0% by weight or less.

5. The lead-free glass composition for conductor formation according to any one of the items 1 to 4 above, wherein the thermal expansion coefficient (α _50-350 ) at 50 ° C to 350 ° C is (70 to 100) × 10 ^{-7 .} / ° C, and the softening point (Ts) is in the range of 500 ~ 650 ° C.

A conductor-forming composition comprising the lead-free glass composition for conductor formation and the conductive particles according to any one of the items 1 to 5 above.

7. The conductor-forming composition according to Item 6, further comprising at least one of a solvent and a binder.

8. The conductor forming composition according to the above item 6 or 7, which is for forming a conductor of a solar cell.

According to the present invention, since a specific glass composition is employed, a lead-free glass composition which can suppress or prevent the problem of warpage can be provided at a relatively low cost. More specifically, for example, when a conductive paste containing the lead-free glass composition of the present invention is used to form an electrode on a semiconductor substrate, it is possible to effectively suppress or prevent a situation in which warpage occurs on the substrate. Further, since the content of expensive bismuth is relatively small (particularly 50% by weight or less, preferably 35% by weight or less, more preferably 30% by weight or less), it becomes a cost in terms of cost alone. Knowing the technology is beneficial. and, By reducing the strontium content, problems that may occur when a large number of sputum-containing conditions are present may also be avoided.

The lead-free glass composition of the present invention having such a feature is useful, for example, in the formation of a conductor, a sintering aid, etc., and can be suitably used for forming a conductor (for forming an electric conductor). Specifically, it can be suitably used as a conductor-forming composition containing a powdery lead-free glass composition and conductive particles (conductive powder).

The conductor forming composition described above can be suitably used, for example, to form a conductor of a solar cell. In particular, by using a conductor forming composition containing the lead-free glass composition and aluminum conductive particles as the back surface electrode on the semiconductor substrate of the solar cell, warpage of the semiconductor substrate can be suppressed.

Simple illustration

Fig. 1 is a view showing a method of measuring warpage in the examples.

Form for implementing the invention

1. Lead-free glass composition

The lead-free glass composition for conductor formation of the present invention (hereinafter also referred to simply as "lead-free glass composition") is characterized by containing B ₂ O ₃ : 5.0 to 25.0% by weight, and SiO ₂ : 9.0 to 35.0% by weight. R ₂ O (however, R represents at least one of Li, Na, and K): 5.0 to 20.0% by weight, ZnO: 16.0 to 45.0% by weight, and Bi ₂ O ₃ : 10.0 to 50.0% by weight. Hereinafter, the main component and the like of the lead-free glass composition of the present invention and the content thereof will be described.

(1) Main ingredients

As described above, the lead-free glass composition of the present invention contains B ₂ O ₃ , SiO ₂ , and R ₂ O (however, R represents at least one of Li, Na, and K), and ZnO and Bi ₂ O ₃ are main components. .

B ₂ O ₃

The component B ₂ O _{3 is} mainly a constituent component of the lattice structure of the glass, and is a main component for imparting stability to the manufacture of the glass. It is made to contain 5.0 to 25.0% by weight of B ₂ O ₃ . When it is less than 5.0% by weight, the glass stability is impaired. On the other hand, when it exceeds 25.0% by weight, the softening point becomes high and the sinterability is lowered. When the glass stability, the softening point, and the like are considered, the content of B ₂ O ₃ is preferably from 10.0 to 20.0% by weight, more preferably from 10.0 to 17.0% by weight.

SiO ₂

Similarly to B ₂ O ₃ , the component SiO ₂ mainly forms a lattice structure of glass and is a main component for making the glass stable. 9.0 to 35.0% by weight of SiO _{2 is} contained. When it is less than 9.0% by weight, the glass stability is impaired. On the other hand, when it exceeds 35.0% by weight, the softening point becomes high and the sinterability is lowered. When the glass stability, the softening point, and the like are considered, the content of SiO ₂ is preferably from 10.0 to 35.0% by weight, particularly preferably from 13.0 to 33.0% by weight, more preferably from 17.0 to 33.0% by weight.

R ₂ O

The component R ₂ O (however, R represents at least one of Li, Na, and K) is mainly a component that lowers the glass transition point, and particularly considers that it is necessary to contain Li ₂ O, Na ₂ O, and K ₂ O. At least 1 element. In total, 5.0 to 20.0% by weight of these oxides are contained. When it is less than 5.0% by weight, the softening point is not effectively lowered. Moreover, if it exceeds 20.0% by weight, the thermal expansion coefficient will increase in addition to the glass stability. In view of softening point, glass stability, thermal expansion coefficient, etc., the content of such oxides is preferably 5.0 to 15.0% by weight, and in particular, 6.0 to 15.0% by weight in total. good.

Further, it is preferred that the components of Li ₂ O, Na ₂ O and K ₂ O are blended in an amount as described below. It is possible to contain 10.0% by weight or less of Li ₂ O. When the softening point, the glass stability, the thermal expansion coefficient, and the like are considered, the content of Li ₂ O is preferably 5.0% by weight or less. It is possible to contain 20.0% by weight or less of Na ₂ O. When the softening point, the glass stability, the coefficient of thermal expansion, and the like are considered, the content of Na ₂ O is preferably 15.0% by weight or less. It is possible to contain 20.0% by weight or less of K ₂ O. In consideration of the softening point, the glass stability, the coefficient of thermal expansion, and the like, the content of K ₂ O is preferably 15.0% by weight or less.

ZnO

The component ZnO is mainly used to suppress the devitrification of the glass during molding and to lower the softening point. It is made to contain 16.0 to 45.0% by weight of ZnO. When it is less than 16.0% by weight, the effect of lowering the softening point is insufficient. Moreover, if it exceeds 45.0% by weight, it may be inferior to the glass stability. When the softening point, the glass stability, etc. are considered, the content of ZnO is preferably 25.0 to 45.0%, more preferably 30.0 to 45.0% by weight, and most preferably 30.0 to 40.0% by weight.

i2O3

The component Bi ₂ O _{3 is} mainly used to lower the softening point and to enhance the bonding property between the electrode and the semiconductor substrate. It is made to contain 10.0 to 50.0% by weight of Bi ₂ O ₃ . When it is less than 10.0% by weight, the effect of lowering the softening point is insufficient. Moreover, if it exceeds 50.0% by weight, in addition to the cost problem, it is not preferable because the glass stability is impaired. In view of softening point, glass stability, etc., the content of Bi ₂ O ₃ is preferably from 10.0 to 35.0% by weight, particularly preferably from 15.0 to 30.0% by weight, further preferably from 15.0 to 25.0% by weight. optimal.

(2) optional ingredients

In the lead-free glass composition of the present invention, in addition to the above-mentioned main components, other components may be included as needed (except for Pb). For example, Al ₂ O ₃ , an alkaline earth metal oxide, or the like can be mentioned. Further, in the case of Pb (PbO), although the effect of lowering the softening point and improving the sinterability is obtained, the necessity of switching to a lead-free material is high, and it is preferable that Pb is not contained.

Al ₂ O ₃

The composition Al ₂ O _{3 is} mainly effective for improving the glass stability. It may be contained in an amount of 5.0% by weight or less, although it is an optional component. When it exceeds 5.0% by weight, the softening point becomes high, and the sinterability is not preferable. In view of the softening point or the like, the content of Al ₂ O ₃ is preferably 3.0% by weight or less, and particularly preferably 1.0% by weight or less. Further, the lower limit value is not limited, and may be, for example, about 0.01% by weight.

Alkaline earth metal oxide

The alkaline earth metal oxide (particularly at least one of MgO, CaO, SrO, and BaO) is mainly effective for improving the glass stability while lowering the softening point. The alkaline earth metal oxide may be contained in an amount of 5.0% by weight or less, although it is an optional component. When it exceeds 5.0% by weight, it is not preferable because the glass stability is impaired. Considering the stability, softening point, etc. of glass, alkaline earth metal The content of the oxide is preferably 3.0% by weight or less, and more preferably 1.0% by weight or less. Further, the lower limit value is not limited, and may be, for example, about 0.01% by weight.

Other ingredients

The glass composition of the present invention may further contain other components as long as it does not impair the effects of the present invention. For example, it may contain a rare earth oxide such as La ₂ O ₃ or at least one of ZrO ₂ , TiO ₂ , V ₂ O ₅ and Sb ₂ O ₃ . The content ratio of these components is preferably 5% by weight or less in total.

(3) Physical properties of lead-free glass compositions

In the present invention, from the viewpoint of use as a lead-free glass composition for reducing warpage of a semiconductor substrate, the coefficient of thermal expansion (α _50-350 ) at 50 to 350 ° C is (70 to 100) × 10 ^{-7 .} The /°C system is ideal. Further considering the influence on the warpage of the semiconductor substrate, it is preferable that the coefficient of thermal expansion (α _50-350 ) is (70 to 90) × 10 ^-7 /°C.

Also, in the lead-free glass composition of the present invention, in order to improve the electrode The sinterability at the time of formation is preferably such that the softening point (Ts) is 500 to 650 °C. Further, the sinterability at the time of electrode formation is considered, and the softening point (Ts) is preferably in the range of 520 to 620 °C.

2. Method for producing lead-free glass composition

For the raw material for producing the lead-free glass composition in the embodiment, for example, H ₃ BO ₃ , B ₂ O ₃ or the like can be used for the component B ₂ O ₃ . As the other component, a raw material compound which is usually used, such as various oxides, carbonates, and nitrates, can be suitably used as a glass raw material.

As a method for producing the lead-free glass composition of the present invention, the lead-free glass composition of the present invention can be obtained, for example, by a production method comprising the steps of: 1) a first step of obtaining a mixture by mixing a raw material compound, and 2) The second step of obtaining the melt by melting the obtained mixture.

In the first step, the raw material compound is weighed and mixed with the composition and ratio of the lead-free glass composition of the present invention, thereby preparing a mixture. In this case, the order of mixing the raw materials of the respective components and the like is not particularly limited, and may be blended simultaneously or sequentially from a predetermined compound. Further, the raw materials are usually supplied in the form of a powder. Such a raw material powder can be obtained by pulverizing, mixing, or the like by a known method using a raw material containing each component.

In the second step, the melt is obtained by melting the mixture. When the melting is performed, the glass melting temperature may be set depending on the composition of the raw material, etc., and it may be carried out usually at about 1000 to 1300 °C. The obtained melt may be supplied directly from the state of the melt to the powder production step as needed. For example, a flaky powder can be obtained while cooling the melt by a cooling roll. Further, for example, after the melt is cooled, the powder may be obtained by pulverization, classification, or the like as necessary. As such, the lead-free glass composition of the present invention can be suitably provided in the form of a powder (powdered glass composition).

Further, as another production method, a method comprising the steps of preparing at least two kinds of melts containing one or two or more kinds of raw material compounds, and then preparing the glass powder from each of the melts may be employed. Mixing each glass powder with the composition of the lead-free glass composition for forming a conductor of the invention and ratio. The method of preparing the glass powder from the melt may be carried out in the same manner as described above.

The composition of each of the above-mentioned melts is not particularly limited, and a) examples thereof include a) B ₂ O ₅ : 36 ± 5 wt%, SiO ₂ : 12 ± 3 wt%, ZnO: 37 ± 5 wt%, and R ₂ O. : 13±3 wt%, Al ₂ O ₃ : 1 wt% or less glass composition, b) Bi ₂ O ₃ : 66±7 wt%, B ₂ O ₅ : 8±3 wt%, SiO ₂ : 11 ±3 wt%, ZnO: 12±3 wt%, Al ₂ O ₃ : 4 wt% or less, BaO: 1 wt% or less, a glass composition or the like. By mixing two or more kinds of melts having such a composition as the composition shown in the invention, a lead-free glass composition for conductor formation can be suitably obtained.

In each of the above production methods, the average particle diameter (D ₅₀ ) in the case of being in a powder form is not limited, and is usually in the range of 50 μm or less, and can be appropriately adjusted depending on the form, use, and the like. Further, the fine particle powder (for example, having a diameter of less than 1 μm) is reduced or removed by classification or the like, whereby warpage of the semiconductor substrate at the time of electrode formation can be effectively suppressed.

3. Lead-free composition for conductor formation

The present invention includes a lead-free composition for forming a conductor, and the lead-free composition for forming a conductor comprises the lead-free glass composition of the present invention and conductive particles.

As the lead-free glass composition of the present invention, for example, the aforementioned powdery glass composition can be suitably used.

The conductive particles are not particularly limited, and for example, a metal or the like can be used. As the metal, an alloy containing these or an intermetallic compound can be used in addition to, for example, silver, copper, gold, nickel, iron, or the like. These can be selected according to the purpose of use. For example, a semiconductor (particularly a germanium) of a solar cell is laminated or In the case of the connected conductor, at least one of silver and aluminum can be suitably used, and more preferably aluminum.

The average particle diameter of the conductive particles (conductive powder) can be changed depending on the shape of the conductor to be formed, etc., and usually it is about 0.1 to 10 μm. Further, the shape of the conductive particles is not limited, and may be any shape such as a spherical shape or a sheet shape.

In the solid content of the lead-free composition for forming a conductor of the present invention, the content of the conductive particles (powder) may be appropriately set depending on the desired conductivity, use, and the like, and may be usually about 70 to 99% by weight.

In addition, the ratio between the conductive particles and the powdery glass composition can be appropriately set in accordance with the desired conductivity, and the powdery glass composition is usually 1 to 30 parts by weight based on 100 parts by weight of the conductive particles. In particular, it is preferably 1 to 10 parts by weight.

The composition for forming a conductor of the present invention may be in the form of a powder, and in particular, it may be suitably used in the form of a paste (conductive paste). In other words, it can be suitably used by including at least one of 1) a solvent and a binder, 2) a powdery glass composition of the present invention, and 3) a paste of conductive particles (powder). For example, as the paste, a conductive paste using ethyl cellulose can be suitably prepared. In this case, the powdery glass composition and the conductive particles (powder) of the present invention are uniformly dispersed in a vehicle liquid obtained by dissolving ethyl cellulose in a solvent such as terpineol, or uniformly dispersed. In the vehicle liquid in which the other additives are contained in the solution, the powdery glass composition and the conductive particles (powder) of the present invention may be uniformly dispersed in the vehicle liquid, and the vehicle liquid is a solution obtained by dissolving ethyl cellulose in a solvent such as terpineol, or It is made up of other additives in the aforementioned solution as needed. When the conductor forming composition is used in the form of a paste, the solid content is usually about 60 to 90% by weight. Further, the conductor forming composition of the present invention can also be applied to a photosensitive glass paste or the like.

In this way, since the conductor forming composition of the present invention can also be used as a conductive paste, it is suitable for formation of various conductors (particularly at least one type of electrode and wiring). For example, it can be suitably used for formation of a conductor (particularly at least one type of electrode and wiring) of a solar cell. As a semiconductor used in a solar cell, there are various kinds of polycrystalline germanium, single crystal germanium, amorphous germanium, compound semiconductor, and the like, among which a polycrystalline germanium solar cell or a single crystal germanium solar cell (particularly a back surface (electrode surface) of a solar cell) It is suitable for the formation of electrodes or wirings connected to the crucible. That is, the conductor-forming composition of the present invention can be joined to the lanthanide system with higher adhesive strength.

The method of forming a conductor using a conductive paste can be carried out, for example, by a method comprising the steps of forming a coating film by a conductive paste and baking the coating film. The method of forming the coating film itself may be carried out according to a known method. For example, in addition to various printing methods such as screen printing, it may be carried out by a method such as coating or spraying. After the coating film is formed, it may be dried as needed before firing. The firing temperature at the time of firing is usually 600 to 800 °C. In addition, the firing gas atmosphere may be appropriately selected, for example, from the atmosphere, an inert gas atmosphere, or a regenerative gas atmosphere depending on the type of the conductive particles.

Example

The embodiments are shown below to more specifically describe the features of the present invention. Sign. However, the scope of the invention is not limited to the embodiments.

Examples 1 to 15 and Comparative Examples 1 to 3

The blended and mixed raw materials were formed into the compositions shown in Tables 1 to 3, placed in a platinum crucible, and melted in an electric furnace, and thereafter, a chill roll was used to obtain a glass flake. Further, a glass block for measuring the coefficient of thermal expansion was obtained by pouring a part into a metal mold and slowly cooling it. The flaky glass was pulverized by a ball mill, and thereafter, glass frit was obtained by classification. Further, in the present invention, the glass frit may be blended and mixed, placed in a platinum crucible, and melted in an electric furnace, after which a flake-shaped glass obtained by using a cooling roll is used. It was pulverized by a ball mill, and then classified, and the glass frit obtained thereby was mixed to have a predetermined composition shown in Tables 1 and 2 to prepare. The coefficient of thermal expansion (α _50-350 ) and the softening point (Ts) were measured for the obtained glass block and glass glass. Further, Comparative Example 3 is the same as the glass described in Example 2 of Patent Document 5. The results of these are shown in Tables 1-3.

The _TCA device (model name "TMA-8310") manufactured by Rigaku Co., Ltd. was used for the measurement of the coefficient of thermal expansion (α _50-350 ). A rod-shaped sample having a length of 15 to 20 mm and a diameter of 3 to 5 mm was heated and heated at a fixed rate of 10 ° C per minute, and the elongation and temperature of the rod-shaped sample were measured and obtained from the obtained thermal expansion curve. .

For the measurement of the softening point (Ts), a TG-DTA apparatus (model name "TG-8120") manufactured by Rigaku Corporation was used. Approximately 30 mg of the glass frit sample was placed in a platinum chamber, using alumina powder as a standard sample, at a fixed rate of 20 ° C per minute from room temperature in an atmospheric atmosphere. The temperature difference between the glass glass sample and the standard sample was measured by heating, and the DTA (differential thermal analysis) curve of the investigation was obtained. Specifically, the temperature at the local maximum point of the exothermic peak seen after the initial endothermic peak of the DTA curve is taken as the softening point.

Test example 1

The evaluation of warpage was performed on the glass compositions obtained in the respective examples and comparative examples. The evaluation of warpage was carried out as follows. First, 3% by weight of a glass frit is added to a conductive paste made of an Al powder and a vehicle, and then coated on a ruthenium substrate (50 mm × 50 mm × 200 μm) by screen printing, and dried. The electrode having a thickness of about 30 μm after firing was formed by sintering at 400 ° C for 1 minute and at 800 ° C for 5 seconds. Thereafter, the sintered crucible substrate was measured by a contact type surface roughness meter, and the average value of the difference between the lowest point and the highest point was obtained as shown in FIG. The case where the average value is less than 150 μm is "○", and the case where the average value is 150 μm or more is "X". The measurement results and evaluation results of these are shown in Tables 1 to 3.

As is clear from the results of Tables 1 to 3, in the glass composition of the example, warpage of the ruthenium substrate was suppressed, and the composition for conductor formation had sufficient performance. On the other hand, it was found that the glass composition of the comparative example shown in Table 3 could not suppress the warpage of the ruthenium substrate.

Thus, it is understood that the glass of the present invention is a suitable glass composition as a material for forming an electrode on a semiconductor substrate, particularly as a material for forming a back surface electrode of a solar cell which is prone to warpage.

Industrial availability

The conductor-forming composition containing the lead-free glass composition of the present invention suppresses warpage of the semiconductor substrate at the time of electrode formation, and causes cracking or chipping of the semiconductor element to occur in a subsequent step. Further, since the warpage of the semiconductor substrate can be suppressed, there is no obstacle to the thinning of the substrate, and therefore there is industrial applicability.

Fig. 1 is a view showing a method of measuring warpage in the examples.

Claims (9)

A lead-free glass composition for forming a conductor, comprising B ₂ O ₃ : 5.0 to 25.0% by weight, SiO ₂ : 9.0 to 35.0% by weight, and R ₂ O: 5.0 to 20.0% by weight (however, R represents Li, At least one of Na and K), ZnO: 16.0 to 45.0% by weight, and Bi ₂ O ₃ : 10.0 to 50.0% by weight. The lead-free glass composition for conductor formation according to the first aspect of the invention, further comprising Al ₂ O ₃ : 5.0% by weight or less. The lead-free glass composition for conductor formation according to the first aspect of the invention, further comprising at least one of MgO, CaO, SrO and BaO: 5.0% by weight or less. The lead-free glass composition for conductor formation according to the first aspect of the invention, wherein R ₂ O includes Li ₂ O: 10.0% by weight or less, Na ₂ O: 20.0% by weight or less, and K ₂ O: 20.0% by weight or less. . For example, the lead-free glass composition for conductor formation according to the first application of the patent scope has a coefficient of thermal expansion (α _50-350 ) at 50 ° C to 350 ° C of (70 to 100) × 10 ^-7 / ° C, and a softening point ( Ts) is in the range of 500 to 650 °C. A conductor-forming composition comprising the lead-free glass composition for conductor formation and the conductive particles according to any one of claims 1 to 5. The composition for forming a conductor according to claim 6, further comprising at least one of a solvent and a binder. A conductor forming composition according to claim 6 of the patent application, which is used to form a conductor of a solar cell. A method for forming a conductor, comprising the steps of: forming a composition for conductor formation according to item 6 of the patent application; a step of forming a coating film; and a step of firing the coating film.