Investigation of the possibility of replacing high-lead glasses in fusible glass solders by less toxic glasses

Abstract

The possibility of partial or complete replacement of PbO in fusible glass solders by less toxic components is investigated. It is found that it is impossible to find a full-fledged replacement for glasses in the lead-borate eutectic, used as the glass base in glass soldering compositions for sealing glass ceramic packages of integrated microcircuits at temperatures 390 -420°C, within the systems PbO -P 2 O 5 -ZnO -B 2 O 3 , V 2 O 5 -P 2 O 5 -ZnO -B 2 O 3 , and TeO 2 -PbO -V 2 O 5 -Bi 2 O 3 with different additives and total mass content of class-I hazard components not exceeding 70%.Integrated microcircuits are ordinarily assembled in metal, plastic, cermet, or glass ceramic packages. The latter have a number of advantages: manufacturability and low cost as compared with cermet packages and mechanical and dielectric properties as compared with plastics and, in part, metal packages. In addition, microcircuits assembled in cermet packages are hermetic, reliable, and long-lasting.The technical-operational characteristics of the cermet packages of integrated microcircuits are largely determined by the properties of the glass solders used to glue the ceramic parts and the metal leads of the microcircuits in a hermetic case. In this connection the glass solder must form a mechanically strong and chemically stable vacuum-tight dielectric layer between the parts of the package and the leads of the microcircuits at a prescribed temperature.The main characteristics of the glass solders are the volume resistivity r, permittivity e, CLTE, and sealing temperature. The higher r and the lower e of the glass solder, the more the leads can be placed per unit surface area of a package and therefore the size and mass of a device can be decreased to the maximum extent possible for its prescribed functional possibilities. Modern electronic devices often operate with sharp temperature differentials, so that the microcircuits must possess a high heat resistance. This condition can be satisfied if the CLTE of the glass solder, the ceramic base of the package, and metal leads of the microcircuits are all compatible with one another. Microcircuit indicators such as the maximum working temperature and the operational stability and service life are temperature dependent, and these dependences are largely contradictory. Thus, to increase the working temperature it is best to use refractory glass solders, but high sealing temperatures are a source of thermionic emission of electrons, which greatly decreases reliability, stability and service life of microcircuits. In this connection a sealing temperature of 390 -420°C is considered to be optimal.The most suitable glass bases meeting the indicated requirements are obtained with a lead-borate eutectic (85% 3 PbO, 15% B 2 O 3 ) base [1 -3]. The deformation onset temperature of the glasses synthesized in this system are t d.o = 305 -350°C, CLTE -(100 -115)´10 -7 K -1 , surface crystallization near the sealing temperature (400 -450°C) -1 -15%, r at 150°C -to 10 11 W × cm and e -18 -19. With cryst...

Review of Bi2O3 based glasses for electronics and related applications

“…Low process temperatureOptical propertiesRadiation shieldingGood chemical durability 'Crystal' glass (see Table 1 1); (f) critical to avoid degradation; 45 (g) difficult combination of low process temperature and low thermal expansion, especially directly on chip, achieved through fillers; 18 (h) surface states in semiconductors also important 29,30 -reduce/avoid alkalis, which are mobile under electric field; (i) important on sensitive substrates/other layers, e.g. glass, metals, prefired TFRs; (j) critical for underwater applications 27 or for automotive.…”

“…[224][225][226][227][228] One interesting open point relevant for this work is the possible substitution of Pb by Bi as an additive to achieve water durable ultra low melting tin fluorophosphate glasses, 153,220 i.e. 45,73,113,120,123,126,[229][230][231][232][233][234][235][236][237][238][239][240][241] Although toxicity of V 2 O 5 is a cause of concern (the section on 'Toxicity of elements in glasses' in Supplementary Material 1 http:// dx.doi.org/10.1179/1743280412Y.0000000010.S1), these oxides are useful as additives in small amounts, to improve adhesion, wetting and durability, suppress crystallisation in glasses and reduce working temperatures. 35,[56][57][58]146,198,207,216,222,242 …”

“…(i) hermetic sealing of packages, lamps, electrical feedthroughs and semiconductor devices 13,14,16,17,19,44,45 (ii) hermetic sealing and mechanical attachment of sensors 23,27 ( Fig. 1) (iii) encapsulation of semiconductor devices 29,30 (iv) overglazing of automotive, packaging and architectural glass 33,34,[46][47][48] (v) photovoltaic (PV) solar cell technology -conductors and contacts 42,43,[49][50][51][52][53] (vi) enamelling of aluminium in architecture and home appliances 35,[54][55][56][57][58] (vii) thick film (TF) electronics and other devices 21,22,24,25,27,59 on various substrates: 60 glasses for TF resistor (TFR), 61,62 conductor, 63,64 overglaze, dielectric 65 and sealing [15][16][17][18][19] m...…”

The use of regression models to describe the temperature coefficient values of linear expansion and technological temperatures of CaSO4-KPO3-Na2B4O7 low-melting glass system

“…Considerable experimental material concerning low-melting glasses in numerous glass-forming systems has already obtained [2][3][4][5][6]. The data about the properties such as TCLE, the softening temperature (Ts) and the glass transition temperature (Tg) for various glass systems is not generalized.…”

Effect of the melting conditions on the properties of glasses in the system PbO–ZnO–B2O3–SiO2

“…Glass frits with softening temperatures below 420-450 0 Ñ are currently used for sealing of semiconductor micro-electronic devices. The oxide system PbO-ZnO-B 2 O 3 -SiO 2 with the content of ÐbÎ of more than 45 mol.% is the basis of compositions of such low-melting glasses [1,2]. It should be noted that high-lead glasses melts are characterized by increased aggressivity towards the material of crucible where they are synthesized.…”