Properties of Porous AlN Multilayered Ceramic Sandwich Substrates
- PDF / 712,473 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 69 Downloads / 231 Views
The development of denser and higher powered integrated circuits has led to a corresponding demand on the performance of dielectric substrates. This paper reports on the fabrication and properties of an AlN multilayered sandwich substrate comprising porous tape-cast layers sandwiched between nonporous layers. Tapes were produced by nonaqueous tape casting, with the porous tapes produced using polymer microspheres as sacrificial molds. Starting from initially Al2O3-rich tapes, the multilayered sandwich substrates were reaction sintered to produce AlN substrates. No interface cracking or delamination was observed in the substrates as a result of the processing. The added porosity resulted in a decrease in the substrate dielectric constant in correspondence to porosity volume. Mechanical strength of the sandwich substrates was improved over that of nonsandwich porous substrates, while substrates having noninterconnected pores showing higher mechanical strength than substrates with connected pores. Substrates with more than 2% porosity showed porosity-dependent thermal conductivity values, while thermal conductivity of substrates with less than 2% porosity was dependent on grain boundary effects. Thermal expansion coefficient of the substrates was unaffected by porosity levels.
I. INTRODUCTION
Rapid progress made in the miniaturization of integrated circuit devices has led to the evolution of microelectronic circuitry with high device density. This trend of increasing device density has demanded stringent requirements on dielectric substrates. As predicted by the Semiconductor Industry Associate,1 board-to-die frequency is expected to reach 1 GHz speed by the year 2007, while producing 200 W of power (Table I). As such, ceramic substrates have gained popularity in this area due to their good electrical insulation, high thermal conductivity, good mechanical support, and ability to operate at high temperatures without hazardous degradation in chemical, mechanical, or dielectric properties.2,3 Currently, aluminum oxide (Al2O3), glass, and glass– ceramics are utilized as substrate materials.4 Although these materials generally provide adequate dielectric properties for current applications, they all possess the common disadvantage of a low thermal conductivity, about 15–37 W/mK for Al2O3. Recent attention has focused on aluminum nitride (AlN), as it does not have the inherent toxicity problems associated with BeO processing.5,8 In addition to having a high thermal conductivity of about 320 W/mK, AlN has a relatively lower dielectric constant of 8, as compared to Al2O3 (10.5).9,10 AlN also offers an excellent thermal expansion J. Mater. Res., Vol. 17, No. 5, May 2002
http://journals.cambridge.org
Downloaded: 24 Mar 2015
coefficient (4.3 × 10−6/°C) match to that of silicon (3.9 × 10−6/°C). Although the use of AlN offers superior thermal expansion coefficient and thermal properties, its material synthesis and production costs are very high.11 AlN does not occur naturally and has to be synthesized from another starting ma
Data Loading...
