High-temperature creep of low-dielectric-constant glass composites
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High-temperature creep of low-dielectric-constant glass composites Jau-Ho Jean Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan, Republic of China (Received 18 December 1995; accepted 21 March 1996)
The constant-stress compressive creep behavior of a low-dielectric constant (low-k) glass composite, containing a low-softening-point borosilicate glass (BSG) and a high-softening-point high silica glass (HSG), has been investigated at 800–950 ±C. For all stages of creep, the deformation behavior exhibits linear viscoelasticity, and is controlled by viscous flow of the low-softening-point borosilicate glass. An analytical expression is proposed to describe mathematically the creep behavior of the glass composite, and the results show a fairly good agreement with experimental observations.
I. INTRODUCTION
In previous investigations,1–3 a low-dielectricconstant (low-k) silica composite containing a low-softening-point borosilicate glass (BSG) and a highsoftening-point high silica glass (HSG) was developed. The glass system identified had desirable properties for applications in the area of electronic packaging, such as a relative sintered density grater than 95% at temperatures less than 1000 ±C, a low dielectric constant of 3.9–4.2 at 1 MHz, and a thermal expansion coefficient matched to silicon. The glass compositions developed to manufacture thin, flat ceramic substrates by tape casting and firing were not always successful, because camber resulted from differential shrinkage between top and bottom surfaces. Similar phenomena were also observed in manufacturing thin alumina substrates. One of the industrial solutions to these problems is to flatten the cambered substrate by pressing at a temperature lower than that of sintering. To have better control of the processing parameters such as pressure, temperature, and time, knowledge of high-temperature creep behavior of the glass composite is required. This work is thus initiated to investigate the creep behavior of a low-k silica dielectric containing a low-softening-point BSG and a high-softening-point HSG in three-point fixture at temperatures between 800 and 950 ±C. II. EXPERIMENTAL
Samples used in this study were prepared by tapecasting process. The inorganic and organic compositions used for tape casting were typical of those reported previously.4,5 The organic vehicle contained polyvinyl butyral (PVB), dibutyl phthalate (DBP), toluene, and ethanol. The total organic content (PVB 1 DBP) was approximately 15 –25 wt. % of the inorganic powders. The inorganic composition contained 40 vol % low2098
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J. Mater. Res., Vol. 11, No. 8, Aug 1996
Downloaded: 27 Mar 2015
softening-point borosilicate glass (BSG) and 60 vol % high-softening-point high silica glass (HSG). The lowsoftening-point BSG had a composition of approximately .70 wt. % SiO2 , .25 wt. % B2 O3 , and a trace amount of alkali oxides, such as Na2 O and K2 O, and HSG contained .95 wt. %
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