MCM Architecture

 

The basic idea behind developing MCM technology is to decrease the average spacing between ICs in an electronic system. Therefore, the fundamental aspect of MCM technology is chip interconnection, which includes connecting I/O conductors on a chip to an MCM substrate. The goals are higher performance resulting from reduced signal delays between chips, improved signal quality between chips, reduced overall size and reduced number of external components [7, 8].

An MCM substrate can be composed of different layers and their number depends on the MCM technology used. These layers provide all the interconnections between the different mounted ICs in addition to the interconnections needed to interface for ``Level - 2'' packaging using any of the interconnection technologies discussed in section .

  
Figure: A generic schematic diagram of an MCM which shows how bare dice are interconnected to an MCM substrate using different interconnection technologies.

  
Figure: The basic architecture of MCMs.

The basic architecture of an MCM is composed of:

• Integrated circuits: Packaged and bare chips, and mounted on/in the surface of the substrate.
• ``Level - 1'' Interconnections: Involves mounting integrated circuits using any of the interconnection methods discussed in section , as shown in Figure .
• Substrate: The common base that provides all the signal interconnections and the mechanical support for all chips
• MCM Seal: Provides a degree of protection to the circuits in addition to heat removal and interconnections.
• ``Level - 2'' Interconnections: Provides the necessary interface to the second level of interconnection.

A schematic diagram which illustrates the above described MCM basic architecture is shown in Figure . Moreover, Table  shows the relationships between architectural components and the corresponding technologies.

   

LEVEL FUNCTIONS TECHNOLOGIES

Chips Digital Si: CMOS, bipolar

Analog GaAs, CGaAs Mixed Analog-Digital

1st level interconnections Conductor connection Peripheral: Wire bond,

from chips to common TAB, flip TAB

circuit base Area: flip chip, solder bump, area TAB

Common circuit base Signal interconnection Hybrid circuits

Power and Ground MCM-L, MCM-C, MCM-D

conductors MCM-D/C

MCM Seal Hermeticity Peripheral Conductors:

Heat removal DIP, QFP

Physical protection Area array conductors:

conductors PGA

2nd level connection Conductor connection Plated through-hole vias

to PWB surface mount

There is a long list of specifications that are used to describe an MCM technology. Some of the main specifications are (see also Figure ) line pitch; which is defined as the nominal distance from centre to centre of adjacent wires, via pitch; which is the nominal distance from centre to centre of adjacent vias, and the number of layers used in the implementation of an MCM. These parameters will be used in the next section to compare between the different MCM technologies.

  
Figure: A schematic diagram illustrating some of the MCM basic parameters.