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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, such as "hybrid" or "hybrid integrated circuit", also refer to MCMs. The individual ICs that make up an MCM are known as chiplets. Intel and AMD are using MCMs to improve performance and reduce costs, as splitting a large monolithic IC into smaller chiplets allows for easy performance improvements (easily allows for more transistors split across multiple chiplets), more ICs per wafer, and improved yield, as smaller dies have a reduced risk of getting destroyed by process variations during semiconductor fabrication. This approach also allows for chiplets to be reused in several products, reduces the amount of time required to design a module compared to designing a monolithic IC, and also reduces the number of bugs that have to be solved during design. However, communication between chiplets consumes more power and has higher latency than components in monolithic ICs. Each chiplet is physically smaller than a conventional monolithic IC die, (A monolithic IC is an IC package with a single die that performs all functions). An example of MCMs in use for mainstream CPUs is AMD's Zen 2 design.
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 substrate.
- MCM-L – laminated MCM. The substrate is a multi-layer laminated printed circuit board (PCB, used in AMD's Zen 2 processors).
- MCM-D – deposited MCM. The modules are deposited on the base substrate using thin film technology.
- MCM-C – ceramic substrate MCMs, such as low temperature co-fired ceramic (LTCC)
The PCB that interconnects the chiplets is known as an interposer. This is often either organic or is made of silicon (as in High Bandwidth Memory) Both have their advantages and limitations. Using interposers to connect several chiplets instead of connecting several monolithic ICs in separate packages reduces the power needed to transmit signals between chiplets, increases the amount of transmission channels, and reduces delays caused by resistance/capacitance (RC delays).
Chiplets are often attached to interposers using flip chip.
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). 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.
Examples of multi-chip packages
- IBM Bubble memory MCMs (1970s)
- IBM 3081 mainframe's thermal conduction module (1980s)
- Superconducting Multichip modules (1990s)
- Intel Pentium Pro, Pentium D Presler, Xeon Dempsey and Clovertown, Core 2 Quad (Kentsfield, Penryn-QC and Yorkfield), Clarkdale, Arrandale, and Haswell-H
- Micro-SD cards and Sony memory sticks
- Xenos, a GPU designed by ATI Technologies for the Xbox 360, with eDRAM
- POWER2, POWER4, POWER5 and POWER7 from IBM
- IBM z196
- Nintendo's Wii U Espresso (microprocessor) has its CPU, GPU, and onboard VRAM (integrated into the GPU) on one MCM.
- VIA Nano QuadCore
- Flash and RAM memory combined on a PoP by Micron
- Samsung MCP solutions combining mobile DRAM and NAND storage.
- AMD Ryzen Threadripper and Epyc CPUs based on Zen or Zen+ architecture are MCMs of two or four chips (Ryzen based on Zen or Zen+ is not MCM and consist of one chip)
- AMD Ryzen, Ryzen Threadripper and Epyc CPUs based on the Zen 2 or Zen 3 architecture are MCMs of one, two, four or eight chips containing CPU cores and one bigger I/O chip
3D multi-chip modules
- System in package (SIP)
- Hybrid integrated circuit
- Chip carrier Chip packaging and package types list
- Single Chip Module (SCM)
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