Definition: MCM

(MultiChip Module or MicroChip Module) A chip package that contains several bare die mounted close together on a substrate (base). The short tracks between the chips increase performance and eliminate much of the noise that external tracks between individual chip packages can pick up. MCM also allows CMOS and bipolar technologies to be used in the same package.

Chiplets Rather than One Large Chip
An MCM is an option for fabricating large chips such as a system-on-chip (SoC), which has several specialized processing circuits. After being manufactured and tested, larger die tend to fail more than small ones. By combining several small bare die, known as "chiplets" on the same substrate, a comprehensive system can be manufactured at less cost. See SoC.

More Flexible for the Future
In addition to the fabrication issues, individual components on an MCM can be enhanced for the next generation of the product without redesigning the entire chip. For example, the CPU may be upgraded while retaining the graphics and AI processor circuits. This is an extremely valuable benefit.

Substrate Classes (MCM-C, D, S and L)
Multichip modules are classified by substrate: an MCM-C uses a ceramic substrate with wire bonding between the chips. MCM-D uses a dielectric layer over a ceramic, glass or metal substrate, and thin film interconnects are created on the dielectric layer. MCM-S uses a silicon substrate with tracks created in the silicon like regular ICs. Transistors can also be formed in the substrate. MCM-L uses a laminated circuit board with up to 25 tracking layers. MCM-L evolved into the multichip module (see MCP).

MCMs followed "hybrid microcircuits," which used a ceramic base, but MCMs typically have higher component and tracking densities. See system in package, chip package and Trilogy.