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 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. Larger die tend to fail more when tested in the semiconductor fab than small chips. By combining several smaller bare die, known as "chiplets" on the same substrate, a comprehensive system can be manufactured at less cost. See SoC.

Substrate Classes
MCMs 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.