A multi-chip module (MCM) is generically an electronic assembly (such as a package with a number of conductor terminals or "pins") where multiple integrated circuits (ICs or "chips"), semiconductor dies and/or other discrete components are integrated, usually onto a unifying substrate, so that in use it can be treated as if it were a larger IC. Other terms for MCM packaging include "heterogeneous integration" or "hybrid integrated circuit". The advantage of using MCM packaging is it allows a manufacturer to use multiple components for modularity and/or to improve yields over a conventional monolithic IC approach.
Multi-chip modules come in a variety of forms depending on the complexity and development philosophies of their designers. These can range from using pre-packaged ICs on a small printed circuit board (PCB) meant to mimic the package footprint of an existing chip package to fully custom chip packages integrating many chip dies on a high density interconnection (HDI) substrate. The final assembled MCM substrate may be done in one of the following ways:
The ICs that make up the MCM package may be:
The PCB that interconnects the ICs is known as an interposer. This is often either organic (a laminated circuit board, which contains carbon, hence organic) or is made of silicon (as in High Bandwidth Memory) Both have their advantages and limitations. Using interposers to connect several ICs instead of connecting several monolithic ICs in separate packages reduces the power needed to transmit signals between ICs, increases the amount of transmission channels, and reduces delays caused by resistance/capacitance (RC delays). However, communication between chiplets consumes more power and has higher latency than components within monolithic ICs.
A relatively new development in MCM technology is the so-called "chip-stack" package. Certain ICs, memories in particular, have very similar or identical pinouts when used multiple times within systems. A carefully designed substrate can allow these dies to be stacked in a vertical configuration making the resultant MCM's footprint much smaller (albeit at the cost of a thicker or taller chip). Since area is more often at a premium in miniature electronics designs, the chip-stack is an attractive option in many applications such as cell phones and personal digital assistants (PDAs). With the use of a 3D integrated circuit and a thinning process, as many as ten dies can be stacked to create a high capacity SD memory card. This technique can also be used for High Bandwidth Memory.
The possible way to increasing the performance of data transfer in the Chip stack is use Wireless Networks on Chip (WiNoC).