JP5935001B2 - Low softening point glass powder - Google Patents

Description

The present invention relates to a low softening point lead-free powder glass for glass pastes used for sealing of electronic parts, and can be used as a component of metal pastes for electrodes formed on solar cell panels and the like. The present invention relates to a low softening point lead-free powder glass.

Low softening point glass powder is used in the electronics field as a glass paste for sealing various packages by adding fillers, binders and solvents, mainly for the purpose of preventing the entry of corrosive gases and moisture. Sealing is an important process for ensuring the stable operation of electronic components. At present, glass powder containing lead oxide can be sealed at low temperatures and damage to electronic components is low. It is used.

  In recent years, however, the toxicity of lead has become a problem. This is because lead is difficult to be discharged when ingested by the human body and tends to accumulate in the body. And when ingested in large quantities, it is said that there is a high possibility of causing lead poisoning. Furthermore, there is a concern that lead penetrates underground from the discarded electronic components by acid rain and causes soil contamination and groundwater contamination. For this reason, environmental regulations are applied, and in Europe, the use of lead in electronic components is regulated.

  Against this background, there is a strong demand for the development of a low softening point glass powder that can be sealed at a low temperature even with a lead-free composition. So far, bismuth-based glass (Patent Document 1) has been proposed as a practical lead-free low softening point glass powder. However, bismuth is mined and refined as a by-product such as lead and tungsten, but because of its small reserves, it is currently designated as a controlled substance that needs to be recycled. Vanadium-based glass has also been proposed (Non-patent Document 1). In order to achieve a low softening point and chemical durability (water resistance), heavy metal elements such as antimony oxide, tellurium dioxide, and bismuth oxide are used. Need to be added. And these substances are also toxic substances that are suspected of being toxic (tellurium dioxide) or specified as controlled substances because of their small abundance (antimony oxide and bismuth oxide). Was not obtained (patent documents 2 to 4).

In addition to sealing, these glass powders are often kneaded with metal powders and organic vehicles and used as electrodes for metal pastes. In particular, glass powder used as a metal paste for an electrode of a solar panel softens and flows in the baking temperature range of 700 to 800 ° C., breaks through the non-reflective coating layer or the back surface passivation layer, and generates solar power. There is a need for so-called fire-through performance that couples to the cell. In addition, after fire-through, it is required to be in close contact with the photovoltaic power generation cell and form an electrically stable ohmic connection. Since a series of these firing steps are processed in a short time of several tens of seconds to a few minutes at the longest, the glass powder is required to have a capability of responding to a fast firing step.

Japanese Patent Laid-Open No. 10-139478 JP 2004-250276 A JP 2006-342044 A Japanese Unexamined Patent Publication No. 2007-320822

Lead-free vanadium-based low melting glass paste, Shinichi Tachibana, Satoshi Yoshimura, Takashi Naito, Hitachi Chemical Technical Report No. 52 (2009-1)

Glass is a material with poor thermal conductivity, and the temperature of the glass powder cannot reach the set firing temperature with the firing time of several tens of seconds. Therefore, a glass powder that softens at a temperature considerably lower than the set firing temperature must be used. In many cases, the preferred softening point of glass powder used for electrodes applied to sealing of various packages and firing processes of solar panels is 450 ° C., more preferably 425 ° C. or less.

Furthermore, the glass powder has a very large surface area per unit mass compared to general glass such as window glass and tableware, and when measured with a differential thermal analyzer (DTA), the glass softens due to the heating rate. Inventor's research has revealed that the endotherm and exotherm corresponding to crystallization and crystallization change significantly. That is, when the particle size is finer, especially below 5 μm, when the rate of temperature rise is fast, both peaks due to endothermic and exothermic reactions appear greatly, and crystallization is not seen when the rate of temperature rise is slow. The accompanying exothermic peak appears clearly. This exothermic peak is not due to crystallization inside the particle, but has a feature that it is based on crystallization at the outermost surface of the particle, that is, surface crystallization.

In glass powders used for electrode materials, particularly for solar panel electrodes, this surface crystallization hinders softening and fluidity of the electrode material metal paste containing glass powder, and provides fire-through performance and ohmic connectivity. It will cause a decline. As described above, since the firing process of the solar panel electrode is performed in a short time, a glass powder that can achieve fire-through performance and ohmic connectivity without crystallization even at a high rate of temperature rise is necessary. At present, the glass powder satisfying such characteristics has only a composition containing lead, and there is an urgent need for lead-free glass powder.

In addition, the glass powder used for the electrode material may be exposed to severe environments such as high temperature and high humidity, and high chemical durability is required to prevent deterioration of electrical characteristics. Moreover, in order to reduce the environmental load at the time of disposal, it is necessary to minimize elution of materials, and high water resistance is also required.

The purpose of the present invention is to replace the conventional lead glass powder with substantially no lead and bismuth, a softening point of 425 ° C. or less, various package sealing processes for electronic components, and electrodes for solar cell panels The present invention provides a low softening point glass powder that does not precipitate crystals in the temperature raising process of the firing step in the formation. A further object of the present invention is to provide a low softening point glass powder having a chemical durability (water resistance) of 0.5% or less in weight loss when immersed in distilled water at 70 ° C. for 1 hour in an immersion test described later. Is to provide.

In order to solve the problems and achieve the object, the present invention is a glass powder having the following configuration. That is, it consists of four components of V ₂ O ₅ , BaO, P ₂ O ₅ and WO ₃ , and when the content is expressed by weight%, V ₂ O ₅ is 45 to 55%, BaO is 27 to 31%, It is a low softening point glass powder having an average particle size of 0.5 to 5 μm, containing 15 to 18% of P ₂ O ₅ and 1 to 12% of WO ₃ and substantially not containing lead or bismuth oxide. .

The second aspect of the present _invention, V ₂ O _{5, BaO,} consists of four components of P 2 _{O 5} and MoO _3, when expressed the content by _weight%, V 2 _{O 5} of 45% to 55% BaO 27-31%, P ₂ O ₅ 15-18%, MoO ₃ 1-8%, substantially free of lead and bismuth oxides, average particle size 0.5-5 μm The low softening point glass powder.

Further, as the third aspect of the present _invention, V ₂ O 5, _BaO, consists of 5 components of _{P 2} O 5, WO ₃ and MoO _3, the _V 2 _{O 5} the content is in weight percent 45 to 55 %, BaO 27-31%, P ₂ O ₅ 15-18%, the sum of the contents of WO ₃ and MoO ₃ (WO ₃ + MoO ₃ ) is 1-12% (provided that MoO ₃ 8% or less), and a low softening point glass powder having an average particle size of 0.5 to 5 μm and substantially free of lead and bismuth oxides.

In these glass powder compositions, V ₂ O ₅ is a component that forms a glass skeleton, and is an important component for achieving a low melting point, water resistance, and thermal stability. It is important that the content of V ₂ O ₅ is 45 to 55 wt%. If the content is less than 45 wt%, the softening point cannot be 425 ° C. or less, and if it exceeds 55 wt%, the water resistance deteriorates. is there.

In the present invention, BaO is an essential component for realizing a low softening point and water resistance, and it is necessary to contain 27 to 31 wt%. This is because if it is less than 27 wt%, water resistance cannot be realized, and if it exceeds 31 wt%, the glass powder will be crystallized in the firing step.

P ₂ O ₅ is a component that suppresses the crystallization tendency of glass and is an essential component. Content needs to be in the range of 15-18 wt%. When P ₂ O ₅ is less than 15 wt%, crystals are likely to precipitate in the step of firing the glass powder, and the water resistance is deteriorated. If it exceeds 18 wt%, the effect of suppressing crystallization is reduced, and if the addition amount is further increased, it is difficult to achieve a low softening point.

WO ₃ and MoO ₃ are components that stabilize the glass state and prevent crystallization in the firing step, and are essential components. When WO ₃ is contained, the content needs to be 1 to 12 wt%. When MoO ₃ is contained, the content needs to be 1 to 8 wt%. The sum of both contents (WO ₃ + MoO ₃ ) is 1 to 12%, and the content of MoO ₃ needs to be 8% or less. If WO ₃ is less than 1 wt%, the glass will not be sufficiently stabilized and will cause crystallization. Even if it exceeds 12 wt%, crystallization tends to occur. If the MoO ₃ content is less than 1 wt%, the glass is not sufficiently stabilized to cause crystallization, and if it exceeds 8 wt%, the water resistance is significantly deteriorated. When both WO ₃ and MoO ₃ are mixed and used, if the content exceeds 12%, the crystallization inhibiting effect is not exhibited. Further, the MoO ₃ content needs to be 8 wt% or less for the same reason as described above.

Here, the softening point of the glass powder also depends on the particle size of the glass powder. That is, since the time required for heat conduction increases as the particle size increases, the softening point increases. On the other hand, even if the particle size is too small, the particles aggregate due to an increase in surface area, resulting in an increase in softening point. For this reason, the range of a preferable particle size is 0.5-5 micrometers.

  According to the present invention, in the predetermined composition range and the predetermined average particle diameter range of the present invention, even a composition substantially free of lead and bismuth is thermally stable and does not precipitate crystals, and is water resistant. It is possible to provide a glass powder that is excellent in properties and suitable for sealing semiconductor packages and forming electrodes. That is, since the softening point of the glass powder according to the present invention is as low as 425 ° C. or less, it can be expected that the component and the member will not be damaged in the sealing of the package of the electronic component and the firing process of the electrode. Moreover, since the softening point is low and crystallization is difficult, good fire-through property can be expected in the electrode firing step of the solar cell.

  Although the form for implementing this invention is as above-mentioned, an Example and a comparative example are given and demonstrated concretely below.

As a raw material oxide, a raw material batch in which V ₂ O ₅ , BaCO ₃ , metaphosphoric acid and WO ₃ or / and MoO ₃ were mixed so as to have a ratio (% by weight) shown in Table 1 was filled in a platinum crucible, and an electric furnace After melting at 1000 ° C. to 1200 ° C. for 60 to 120 minutes, the melt was poured onto a stainless steel plate and cooled to obtain glasses having the compositions shown in Table 1, respectively. The obtained glass was pulverized by a hammer mill and classified using a sieve having an opening of 100 μm. The glass powder that passed through the sieve was finely pulverized for 48 hours with a pot mill, and further classified using a sieve to obtain glass powders having an average particle diameter shown in Table 1, respectively. The particle size distribution was measured by a laser diffraction method using a commercially available particle size distribution measuring device. The glass powder obtained was measured for glass transition temperature, softening point, and crystallization temperature, and ΔT indicating thermal stability was calculated. Moreover, water resistance was evaluated. The evaluation results are shown in Table 1.

Here, the evaluation methods of glass transition temperature, softening point, crystallization temperature and thermal stability are as follows. Using a differential thermal analyzer (DTA), α-alumina was used as a reference, and the measurement was performed at a heating rate of 10 K / min. The first endothermic peak of the differential curve of the obtained DAT curve was determined as the glass transition temperature, the second endothermic peak as the softening point, and the first exothermic peak as the crystallization temperature. ΔT indicating thermal stability was calculated as the difference between the crystallization temperature and the glass transition temperature.

The evaluation method of water resistance is as follows. The glass piece obtained after melting was gradually cooled to completely remove the strain. Thereafter, the glass piece was processed to 1000 mm ³ (1 cm × 1 cm × 1 cm) and immersed in a container containing 500 mL of distilled water. Before dipping, the surface of the glass piece was polished with sandpaper # 320. The distilled water in the container was heated to 70 ° C. and left for 1 hour. After one hour, the moisture was dried in a thermostat set at 120 ° C., and the weight reduction rate relative to the initial weight was calculated.

As shown in Table 1, when the present invention is within the predetermined composition range and particle size range, a glass powder having no crystallization peak in DTA measurement, that is, no surface crystallization could be obtained. . Moreover, when it was in the predetermined composition range of the present invention, it showed good water resistance with a weight loss of 0.5% or less in the water resistance test. As a result, when the present invention is within the predetermined composition range and particle size range, a glass powder having a softening point of 425 ° C. or less, hardly causing crystallization, and having excellent water resistance can be obtained.

Comparative example

On the other hand, the comparative example shown in Table 2 showed the result about the glass powder in which the composition of the glass powder deviated from the predetermined range of the present invention or the average particle size of the glass powder deviated from the predetermined range of the present invention. Is. In Comparative Examples 1, 2, 6-8, and 10-12, the effect of suppressing crystallization is not sufficient, and crystallization is caused in the firing step. In Comparative Examples 9 and 13, crystallization did not occur, but the softening point was considerably higher than 425 ° C. Moreover, in Comparative Examples 3-5, although it did not crystallize and the softening point was a structure lower than 425 degreeC, the outstanding water resistance was not able to be obtained. Moreover, even if it was the glass powder which exists in this invention predetermined composition range, when the average particle diameter was too small (comparative example 12), the crystallization tendency was expressed by the increase in the surface area. On the other hand, when the average particle size was large (Comparative Example 13), the softening point was increased.

Claims (3)

It consists of 4 components of V ₂ O ₅ , BaO, P ₂ O ₅ and WO ₃ , the content of which is by weight, V ₂ O ₅ is 45 to 55%, BaO is 27 to 31%, P ₂ O ₅ is 15 Low softening point glass powder having an average particle size of 0.5 to 5 μm, containing ˜18%, WO ₃ in 1 to 12%, and substantially free of lead and bismuth oxides. It consists of 4 components of V ₂ O ₅ , BaO, P ₂ O ₅ and MoO ₃ , the content of which is wt%, V ₂ O ₅ is 45 to 55%, BaO is 27 to 31%, P ₂ O ₅ is 15 Low softening point glass powder having an average particle size of 0.5 to 5 μm, containing ˜18%, MoO ₃ ˜1-8%, and substantially free of lead and bismuth oxides. It consists of 5 components of V ₂ O ₅ , BaO, P ₂ O ₅ , WO ₃ and MoO ₃ , the content of which is by weight, V ₂ O ₅ is 45 to 55%, BaO is 27 to 31%, P ₂ O ₅ to 15 to 18%, (WO ₃ + MoO ₃ ) to 1 to 12% (provided that MoO ₃ is 8% or less), and contains substantially no lead or bismuth oxide. Is a glass powder having a low softening point of 0.5 to 5 μm.