Multichip Module Technologies:LTCC Substrates and Aluminum Nitride

By -
LTCC Substrates

The use of glass and glass-ceramics in electronic packaging goes back to the invention of semiconductors. Glasses are used for sealing T-O type packages and CERDIPs, as crossover and inter-level dielectrics in hybrid substrates. The success of co-fired alumina substrates spurred the development of the multilayer glass-ceramic substrates. These advantages derive from the higher electrical conductivity lines of copper, silver, or gold; the lower dielectric constant of the glass ceramic; and the closer CTE match of the substrate to silicon.

Multichip Module Technologies-0131

Two approaches have been used to obtain glass-ceramic compositions suitable for fabricating self- supporting substrates [6–8]. In the first approach, fine powder of a suitable glass-composition is used that has the ability to sinter well in the glassy state and simultaneously crystallize to become a glass- ceramic. More commonly, mixtures of ceramic powders are used, such as alumna and a suitable glass in nearly equal proportions, to obtain densely sintered substrates [9,10]. Because many glass and ceramic powders can be used to obtain densely sintered glass-ceramic, the actual choice is often made on the basis of other desirable attributes in the resulting glass-ceramic—such as low dielectric constant for lowering the signal propagation delay and coefficient of thermal expansion (CTE) closely matched to the CTE of silicon to improve the reliability of solder interconnections. Unlike the case of a crystallizing glass, the mixed glass and ceramic approach allows for a much wider choice of materials.

Aluminum Nitride

Aluminum nitride products are used in a variety of commercial and military applications.

Thermal management with solutions such as AlN can provide superior cooling to ensure reliable system operation. AlN packages typically offer a thermal conductivity of 150 to 200 W/mK, a level which can be compared with many metals or other high thermal conductive materials such as berillia (BeO) or silicon carbide (SiC). AlN has a thermal coefficient of expansion of 4.4 ppm, which is better matched to silicon than to alumina or plastics. Table 9.2 provides a comparison of AlN properties.

Comments

Post a Comment

Popular posts from this blog

SRAM:Decoder and Word-Line Decoding Circuit [10–13].

By -
Image
Decoder and Word-Line Decoding Circuit [10–13] Two kinds of decoders are used in SRAM: the row decoder and the column decoder. Row decoders are needed to select one row of word-lines out of a set of rows in the array. A fast decoder can be implemented by using AND/NAND and OR/NOR gates. Figure 52.7 shows the schematic diagrams of static and dynamic AND gate decoders. The static NAND-type structure is chosen due to its low power consumption, that is, only the decoded row transitions. The dynamic structure is chosen due to its speed and power improvement over conventional static NAND gates. From a low-voltage operation standpoint, a dynamic NOR-base decoding would provide lower delay times through the decoder due to the limited amount of stacking of devices. Figure 52.8 shows circuit diagrams of dynamic NOR gates. The dynamic CMOS gate as shown in Figure 52.8(a) consists of input- NMOSs whose drain nodes are precharged to a high level by a PMOS when a clock signal Φ is at a low lev...
Read more

ASIC and Custom IC Cell Information Representation:GDS2

By -
Image
GDS2 The Graphical Design System (GDS) format is a binary format developed by Calma Company in 1971 to convey IC layout information between IC designers and fabricators. Calma presented GDS2 format, the improved version of GDS, in 1978. Finally in 1991, when Cadence acquired Calma, GDS2 rights were transferred to it. In the design process, after the completion of routing and placement, design rule check (DRC) and layout versus schematic (LVS) are performed to verify the final layout. Then the verified layout, dumped in a GDS2 file, is transferred to IC foundries for fabrication. GDS2 File Format GDS2 is a standard mask layout intermediate format containing a single cell or a library of cells each of which includes a number of geometrical objects such as boundaries, paths, boxes, etc. These objects correspond to different layers of a cell where each layer is specified by a layer number and data type [3]. The file format of GDS2 is in binary. A GDS2 file contains a number of variable...
Read more

Timing Description Languages:SDF

By -
Image
SDF Standard Delay Format (SDF) is an ASCII format used to convey timing information between EDA tools. SDF was first developed by Cadence in 1990. Open Verilog International (OVI) approved SDF version 2 in 1993 and SDF version 2.1 and 3 in the following years. Improving SDF version 3 features, resulted in IEEE Standard 1497 [1]. Role of SDF in Design Process SDF can be used in different levels of a design process to annotate timing specifications, including timing data and constraints. Timing constraints are used during the forward-annotation process while timing data are applied during the back-annotation process. Forward-annotation process deals with porting timing constraints to synthesis, floorplanner, layout, and routing tools to meet the required constraints. During the design process, timing data can be back-annotated to analysis tools (including simulators, static timing analysis tools, etc.) to provide more accurate timing representations. SDF Structure An SDF f...
Read more