A multi-chip module (MCM) is a specialized electronic package where multiple integrated circuits (ICs), semiconductor dies or other discrete components are packaged onto a unifying substrate, facilitating their use as a single component (as though a larger IC). The MCM itself will often be referred to as a "chip" in designs, thus illustrating its integrated nature.
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.
Multi-Chip Module packaging is an important facet of modern electronic miniaturization and micro-electronic systems. MCMs are classified according to the technology used to create the HDI (High Density Interconnection) substrate.
- MCM-L - laminated MCM. The substrate is a multi-layer laminated PCB (Printed circuit board).
- MCM-D - deposited MCM. The modules are deposited on the base substrate using thin film technology.
- MCM-C - ceramic substrate MCMs, such as LTCC.
Chip stack MCMs 
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). After a thinning process, as many as ten dies can be stacked to create a high capacity SD memory card.
Examples of MCM technologies 
- IBM Bubble memory MCMs (1970s)
- IBM 3081 mainframe's thermal conduction module (1980s)
- Intel Pentium Pro, Pentium D Presler , Xeon Dempsey and Clovertown, Core 2 Quad (Kentsfield and Yorkfield) and Clarkdale
- Sony memory sticks
- Xenos, a GPU designed by ATI Technologies for the Xbox 360, with eDRAM
- POWER2, POWER4 and POWER5 from IBM
- z196 from IBM
- AMD processors for Socket G34
- Nintendo's Wii U has its CPU, GPU, and onboard VRAM (integrated into the GPU) on one MCM.
See also 
- System in package (SIP)
- Hybrid integrated circuit
- Chip carrier Chip packaging and package types list
- "Iwata Asks". Iwataasks.nintendo.com. Retrieved 2012-10-11.
- Multi-Chip Modules C-MAC MicroTechnology
- Multichip Module Technology (MCM) or System on a Package (SoP)
- AMD aims to stay in the race with Magny-Cours 12-core CPU
- MCM Design in AutoCAD - CDS Master MCM Designer Suite