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Lead Free Glass Frits and Ceramics

#A-1591


New Lead & Alkali Free Low Melting Sealing Glass Frits & Ceramic Fillers

Tech Area / Field

  • MAT-CER/Ceramics/Materials
  • MAT-SYN/Materials Synthesis and Processing/Materials

Status
8 Project completed

Registration date
15.11.2007

Completion date
27.09.2012

Senior Project Manager
Ryzhova T B

Leading Institute
Institute of Electronic Materials, Armenia, Yerevan

Collaborators

  • Engineering Glass-Ceramic-QM, Germany, Jena\nUniversity of Oulu / Microelectronics and Materials Physics Laboratories, Finland, Oulu\nFriedrich-Schiller-Universität Jena / Otto-Schott-Institute für Glaschemie, Germany, Jena\nUniversität Rostock, Germany, Rostock\nCNRS / Science des Procédés Céramiques et de Traitements de Surface, France, Limoges\nInstitut für Fügetechnik und Werkstoffprüfung GmbH, Germany, Jena\nKorea Institute of Ceramic Engneering & Technology, Korea, Seoul\nHermsdorfer Institut fur Technische Keramik e.V., Germany, Hermsdorf\nMinisterio de Ciencia Y Tecnologia / Instituto de Céramica y Vidrio, Spain, Madrid

Project summary

The objective of the project is to study the phase and glass forming diagrams in ternary lead and alkali free molybdenum(wolfram)tellurium, alkaline-earth bismuth borates systems and development of low melting non-crystallized and crystallized glass frits and glass composite frits with usage of new ceramic fillers for various functional applications and low temperature titanate ceramics sintering.

The electronics development was accompanied with intensive studies of sealing glasses and glass composites having wide temperature of sealing or sintering intervals for various functional applications. Oxide glasses are intensively applied in some devises such as CRT (cathode-ray tubes), FPD (flat panel display), PDP (plasma display panel), thick film hybrid IC, magnetic heads or the like. The most widespread industrial sealing glasses and glass composites were developed basically in 60-80 years of the last century on the basis of well known low melting (497 oC) eutectic in the PbO-B2O3 system. Low firing crystallized frits were developed on the basis of PbO-B2O3-ZnO(SiO2) system glasses. The lead titanate is widely used as ceramic filler for the glass frits’ thermal expansion coefficient (TEC) reduction. These materials provide low temperature hermetic sealing at 390-440 oC and transparent dielectric coverings at 550 oC. They possess excellent physical chemical properties, operational and technological characteristics and remain unsurpassed till now.

Hardening of ecological requirements have led to restriction or interdiction on toxic materials (included PbO) usage in electronics products. Therefore, the substitution of known lead content frits in the industry for new low melting lead free glasses with similar characteristics are strongly needed today. Intensive studies of lead free low melting systems have begun at the beginning of 90th of last century. However, the developed practical frit compositions do not meet these requirements so far. From our point of view, the main problem is the absence of new lead and alkali free low melting eutectics for low temperature hermetic sealing and the lack of investigated phase diagrams. The same actual problem is the revealing of new stoichiometric compositions which may serve as a basis for the development of low melting crystallized frits and ceramic fillers for glass frits TEC reduction. Studies of phase diagrams are connected to significant manpower and time expenses therefore they are not popular now. We hope, that constructing new phase diagrams at present will save us and our colleagues much more time and resources in the future for the development of new practical glass compositions.

Detailed studying of references in conjunction with our preliminary experiments has led to original decisions:

It is known, that a number of eutectics with melting points (m.p.) 500-600oC are available in the RxOy-TeO2, MoO3 (WO3)-TeO2 systems. Besides, these eutectics compositions will have possibility to move from binary to ternary deeper eutectics with m.p. 400-500oC in the RxOy-MoO3 (WO3)-TeO2 ternary systems. However, these glasses have high TEC value ~ (140-150)·10-7, K-1. We determined that the investigated ternary compounds have lower TEC value equal to (120-130)·10-7, K-1 both in glass and the crystallized conditions. It is revealed also, that some compounds have super low TEC value equal to (2-6)·10-7, K-1 in an interval 20-300oC and low dielectric losses (Tan δ=(4-8)·10-4) and have also dielectric constant (ε)=10-50. The crystallization areas of compounds with low TEC (CLTEC) cover an extensive part of the ternary phase diagram coming nearer to ternary eutectics with m.p. below 500oC. Glasses of these compositions have low Tg (~310oC) and enough flowability at 440-540oC depending on compositions. It is possible to regulate TEC of crystallized frits and to reach values up to (80-90) ·10-7, K-1 by the controlled crystallization with CLTEC formation in crystalline phase.

There is no data on transparent dielectric coverings fired at 550oC on lead and alkali free glass frits’ basis. The absence of the phase diagrams in BaO(SrO,CaO)-B2O3-Bi2O3 systems hinders to make the effective decision of these problems. Preliminary studies allow to be confident, that in the given systems it is really possible to develop compositions with necessary flowability at 550oC on the basis of revealed ternary eutectics. Glasses in various areas of these system, depending on bismuth, barium and boron oxides ratio, have TEC values changing from 80 to130•10-7, K-1.

It is known, that bismuth borate glass forming melts have higher surface tension in comparison with lead borates analogues. Therefore, for decreasing surface tension and increasing flowability the influence of oxides additives on bismuth borates melts’ surface tension will be studied. It is known also, that bismuth borates glass coverings are critical to operating conditions. Therefore, influence of oxides additives on stabilization of bismuth oxide valent state will be investigated to increase light transmittance and stability of dielectric coverings in real operating conditions.

Creation and study of lead free ceramic fillers is one of the basic parts of the project. Synthesized CLTEC is perfectly compatible with betta-eucryptite glass ceramics (BEGC) and in various ratios effectively reduces low melting crystallized and not crystallized glass frits’ TEC with vacuum-tight sealing. We strongly believe that within the framework of the project it is possible to develop both low melting composites with TEC=(80-90)·10-7, K-7 for window glass and TEC=(60-132)·10-7, K-1 for packaging and magnetic heads sealing at temperatures starting from 450oC on the basis of tellirite glass frits with TEC=(130-140)·10-7, K-1 using effective mix of CLTEC + BEGC as ceramic filler. It is really possible to develop wide range of sealing composite both crystallized and non-crystallized frits with TEC (33-60)·10-7, K-1 and firing temperatures 550-700oC on the bismuth borate glass frits basis with use of CLTEC + BEGC mix as ceramic filler. These glass frits can be used for the various practical purposes including fiber optics and optical fiber displays hermetic sealing.

CLTEC have low TEC = (2-6)•10-7, K-1, ε =10-50, Tan δ =0,0004-0.0008. CLTEC having low shrinkage and excellent sinterability at 850-900oC is a good candidate for application in LTCC technologies. It can be used both independently and together with other ceramic materials. It is possible to modify CLTEC and increase its TEC up to (30-45)·10-7, K-1 and decrease it sintering temperature up to 750-850oC. In our opinion, the developed new ceramics additives will be very effective for aluminum nitride and other nitride ceramics’ low temperature sintering. It will also be possible to develop both crystallized glass frits with TEC (30-35)·10-7, K-1 and non crystallized glass frits with TEC (40-45)·10-7, K-1 on the CLTEC basis for aluminum nitride ceramic coverings at 700-850oC.

During preliminary studies the several group of perspective lead free ceramic materials was revealed. Some of them have perovskite-like structure and are excellent candidates for use in LTCC technologies for barium titanates (BT) sintering temperature reduction up to 850-900oC. These compositions have low m.p. (850-1000oC) and their small additives favorably influence of BT and other titanates sintering with guarantee zero shrinkage.

The wide range of crystallized and non crystallized lead and alkali free glass frits and glass composites for zinc, aluminum, silver – palladium pastes firing on alumina, aluminum nitride and silicon substrates in thick-film technology at 580-600, 650-700 and 800-850oC will be also developed under project.

To sum up, developed lead and alkali free glass frits with wide interval of TEC changes (30-132)·10-7, K-1 and firing temperatures 450-850oC can be used for various practical purposes and technologies and solve presence problems.

The great volume of academic researches will be carried out in the project framework. The obtained results will make a basis for scientific and practical achievements of the project.

The aim of the project is as follows:

  • Study of phase and glass forming diagrams in ternary RxOy-MoO3 (WO3)-TeO2 systems, DTA and dilatometric analysis of glasses. Study of glass crystallizations regimes and dilatometric, resistive and dielectric characteristics of crystallized glasses, X-ray identification of crystallization products.
  • Study of phase and glass forming diagrams in ternary BaO(SrO,CaO)-B2O3-Bi2O3 systems, DTA and dilatometric analysis of glasses. Study of glass crystallizations regimes and dilatometric, resistive and dielectric characteristics of crystallized glasses, X-ray identification of crystallization products.
  • Characterization of glasses and crystallized glasses of known and newly revealed stoichiometric compositions in studied systems.
  • Study of pseudo-ternary and more complex bismuth, zinc, barium, strontium and calcium borates systems for revealing deeper eutectics with increased flowability and frits’ TEC regulations.
  • Study of oxides additives’ influence on bismuth borates melts both surface tension and wetting angel reduction and flowability increase on various substrates.
  • Study of oxides additives’ influence on bismuth valent state stabilization and achievement of dielectric coverings’ light transmittance stability in real operating conditions
  • Study of CLTEC synthesis regimes on thermal, resistive and dielectric characteristics of ceramics on their basis.
  • Study of CLTEC influence, separately and together with betta – euctiptite glass ceramic, on developed tellurite and bismuth borates glass frits TEC reduction and their flowability and wettability on various substrates.
  • Study of new compounds influence on low temperature sinterability and properties of titanate ceramics.
  • Study of melting technological characteristics and batch formulation on tellurite and bismuth borates glass frits properties.

The following problems will be solved as a practical result:
  • New compositions of crystallized and non-crystallized glass frits and glass composites frits practical compositions with TEC(80-90)•10-7,K-1 for window glass sealing at 440-450oC; with TEC (66-69)•10-7,K-1 for alumina sealing at 450-520oC and TEC (30- 44)•10-7,K-1 for nitride ceramics sealing at 700-800oC will be developed.
  • New compositions of non-crystallized glass frits practical compositions for transparent dielectric window glass coverings with 80-85% transparency and TEC (80-90)•10-7, K-1 and firing temperature 550oC will be developed.
  • Wide range of new compositions of crystallized and non-crystallized glass frits and glass composites for zinc, aluminum, silver – palladium pastes firing on alumina, aluminum nitride and silicon substrates in thick-film technology at 580-600, 650-700 and 800-850oC will be developed
  • New glass frits practical compositions with TEC (60-132)•10-7,K-1 will be developed for magnetic heads sealing at 550-600oC.
  • New glass frits practical compositions with TEC (50-60)•10-7,K-1 will be developed for fiber-optics displays sealing at 550-600oC.
  • New low sintering ceramic (850oC) with low TEC(2-6)•10-7,K-1, dielectric constant (10-50) and low losses (0,0004-0.0008) will be developed.
  • New low temperature sintering (900oC) barium titanate ceramic composition with zero shrinkage will be developed for LTCC application.

The SPEMS laboratories are well equipped and have highly qualified staff. Taking into account our long-term experience in area of technical glasses and glass-ceramics development we are confident that the project goals will be achieved.


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