Low Melting Phosphate Sealing Glass Development

Phosphate glass is suitable for sealing electronic components because of its low sealing temperature and wide range of adjustable thermal expansion coefficient. As a kind of ideal sealing material,phosphate glass has been used to instead of PbO matrix sealing glass. However, the disadvantages of complex preparation technology and low chemical stability limit its usage in electronic industry. The development of new lead-free phosphate sealing glass is conducive to break through the technical barrier of overseas sealing products, which is of great economic value and social significance.In this paper, lead-free low temperature phosphate sealing glasses were prepared by conventional melt-quenching method and improved by adjusting and optimizing glass composition. The relationship among composition, structure and properties was investigated. The effects of chemical composition on the density, characteristic temperatures, thermal expansion, chemical stability and sintering properties of the glass were discussed. The main conclusions as following.In ZnO-B2O3-P2O5-Al2O3-Na2O-Li2O sealing glasses with higher ZnO content, Zn2+ existed in the discontinuities of network structure in the formation of [ZnO6].The connection of network structure was weakened and glass forming ability was decreased. The thermal stability of glass was decreased and cracks occured easily as introducing ZnO too little. The proper content of ZnO was about 30 mol%. Glass forming ability increased with the increasing of P2O5 content, The proper content of P2O5 was about 50～55 mol%.Chemical composition of glass was adjusted and optimized by substituting Bi2O3 and SrO for Al2O3,Na2O and Li2O.As a result, glass forming ability and chemical stability were improved. With the increasing of SrO content, Sr2+ could connect two adjacent [PO4], the network structure was strengthened.. The introduction of excessive Bi2O3 will lead to surface crystallization.With the increasing of Zn/P radio, the thermal expansion coefficient of the glasses decreased firstly then became flat and the characteristic temperatures of the glass increased in a small range. With the increasing of SrO content, the thermal expansion coefficient increased and the characteristic temperatures decreased.With the increasing of Bi2O3 content, the density increased, the thermal expansion coefficient increased firstly then became flat, the characteristic temperatures decreasd firstly then became flat and the chemical stability of the glass increased firstly then decreased.The chemical stability reached the maximum when Bi2O3 content was 7 mol. The introduction of Bi3+ is conducive to incrasing the troque of bending vibration of B-O-B and P-O-P bond, so bending vibration of B-O-B and P-O-P bond shifted to higher wave number. Meanwhile, P=O double-bonds were transformed into B-O-B and P-O-P bond with Bi3+ entering into network structure of glass.The sealing glass of ZnO-B2O3-P2O5-SrO-Bi2O3 system has the best fluxion property at 540℃, which indicated low sealing temperature. Compared with Polyvinyl Alcohol(PVA) binder, the bending strength of sintered sample by using Polyvinyl Butyral(PVB) as binder improved apparently.