A Multichip Module (MCM) or package is defined as a single unit (“package”) containing two or more chips and an interconnection substrate which function together as a system building block. The MCM, or Multichip Package (MCP), provides signal interconnect and input / output (I/O) management for the chips contained within the module, thermal management (typically cooling), mechanical support, and environmental protection. MCMs or MCPs are an important technique for the packaging of integrated circuits (ICs) and associated subsystem and system elements. The MCM was developed in the early 1980s and is an evolution of the traditional hybrid package that appeared soon after the birth of the IC.
Today’s high-performance supercomputers and mainframes require many, many chips to form one central processing unit (CPU), in contrast to today’s personal computers (PCs) that typically use one chip for each processor. MCM technology allows chips to be spaced more closely with less overall volume and weight than individually (single chip package) packaged parts. Since MCM packages are very dense with minimum volume and weight, they have widespread application in aerospace, medical, consumer, and all portable products in addition to supercomputers and mainframe computers (circa 1980s), compared to a single chip PC processor from Intel.
Clearly, the MCM, by its very nature-multiple chips on a substrate or carrier-is different from its individually packaged counterpart. But what sets it apart from its precursor, the hybrid? It is the chip density. It is commonly held that for a package containing multiple chips to be classified as an MCM, 50% or greater of the substrate (carrier) or packaging area must be covered with active semiconductor devices. This can be represented by the simple formula:
AC = ≥0.5AS
Where Ac equals the area of the semiconductor (or chip) and AS equals the area of the substrate (package or carrier).
The substrate or carrier is the key element in any MCP and especially in the MCM. The substrate provides the mechanical attachment for the chips, handles the interchip signals, provides power and ground for all chips, and interfaces the module with the next level system elements. In addition, the substrate can play a major role in module thermal management, as well as help protect the chips from environmental impact.
As a rule of thumb, a packaged electronic circuit is considered to be an MCM if more than half of its area is covered with active devices, although some circuits adapt more readily to this definition than others. MCMs come in three basic styles:
- MCM-Ls, based on organic laminate technology (similar to standard printed wiring boards (PWBs), but with denser component placement and greater wiring densities.)
- MCM-Cs, thick film or cofired ceramic technology
- MCM-Ds, deposited thin film multilayers
Multi-Chip Module (MCM) is a chip package within which more than one bare semiconductor die is bonded directly to a substrate by flip-chip, TAB or wire bonding. MCM is generally an electronic assembly, such as a package with a number of conductor terminals or “pins“, where multiple 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 most complex are really encapsulated PCBs.