Multi Chip Module: Architecture, Substrates, Packaging, and PCB Design

August 29, 2026

Multi Chip Module: Architecture, Substrates, Packaging, and PCB Design

“A multi chip module is just several chips in one package” is a definition, not a design guide. The difficult part is deciding which functions belong on which die, how those dies communicate, how power and heat move through the module, how known-good die are selected, and how the final package connects to a buildable PCB.

A multi chip module can shorten interconnects, combine different semiconductor processes, and reduce system size. It can also multiply yield, thermal, warpage, test, repair, and supply-chain problems if integration is treated as a packaging afterthought.

Multi chip module with multiple semiconductor dies on a shared substrate

Direct Answer: What Is a Multi Chip Module?

A multi chip module (MCM) integrates two or more semiconductor dies or chiplets on a shared substrate or interconnect structure within one module or package. The dies may be connected by wire bonds, flip-chip bumps, redistribution layers, bridges, or interposers. MCM performance depends on substrate technology, die interfaces, power delivery, thermal paths, assembly yield, test strategy, and the host PCB.

1. Do Not Confuse an MCM with a Normal Multi-IC PCB

Structure	Where the dies/components are integrated	Typical system boundary
Multi chip module	Multiple dies share a package/module substrate	Appears to the PCB as one complex component
Conventional PCBA	Individually packaged ICs mount on a PCB	Board-level interconnect joins separate packages
System in package (SiP)	Multiple functions/components integrated in one package	Often broader than dies alone; terminology overlaps MCM
Chiplet package	Functionally partitioned dies connected through a defined in-package fabric	Modern heterogeneous MCM/advanced-package implementation
2.5D package	Dies connect through an interposer or bridge-like structure	High-density lateral die-to-die links
3D package	Dies are vertically stacked with dense vertical interconnect	Very short links but demanding thermal/test integration

MCM and SiP are often used loosely. Do not approve an architecture based on the label; ask for the actual die, substrate, interconnect, package and external-I/O structure.

2. Understand the Traditional MCM-L, MCM-C, and MCM-D Classes

IPC-MC-790 documented traditional multichip-module classifications and design considerations including materials, substrate, thermal issues, wire bonding and flip-chip attachment. The document is historical, so use its vocabulary for orientation rather than as an automatically current procurement standard.

Class	Traditional substrate concept	Common strength	Common tradeoff
MCM-L	Laminated organic substrate	PCB-like processing, larger formats and cost familiarity	Feature density and dimensional behavior depend on build-up technology
MCM-C	Cofired ceramic substrate	Thermal stability, hermetic/high-temperature options and multilayer conductors	Cost, shrinkage/process constraints and material stiffness
MCM-D	Deposited thin-film dielectric/conductor layers	Very fine interconnect and controlled high-density routing	Process complexity, area and cost
Hybrid/advanced variants	Organic, silicon/glass interposer, bridge or redistribution combinations	Technology can be placed only where density is needed	More interfaces, suppliers and co-design work

Modern chiplet packaging does not always fit neatly into one legacy box. Describe the physical stack rather than relying only on an MCM class.

3. Partition the System Before Selecting the Package

Intel describes current advanced packaging as a move from a monolithic system-on-chip toward “systems of chips,” mixing IP, architectures, memory and I/O. Partitioning can put each function on a suitable process node, but every split creates an interface.

Partition question	Why it matters	Failure if ignored
Which die owns each function?	Controls process node, IP and verification boundaries	Duplicate/missing functions or unclear responsibility
What bandwidth crosses the boundary?	Drives bump count, protocol, power and routing density	Interface cannot meet throughput
What latency is acceptable?	Package links are not identical to on-die wires	System timing target is missed
How is clock/reset distributed?	Multiple dies need deterministic startup and synchronization	Intermittent boot or state mismatch
How are faults contained?	One die failure can affect the whole module	No graceful degradation or diagnosis
Can dies evolve independently?	Chiplets promise reuse, but interfaces must remain stable	Every upgrade forces full redesign

An open or proprietary die-to-die interface is an architectural decision, not merely a routing rule.

Multi chip module package showing chiplets and high-density interconnects

4. Choose the Substrate from Interconnect and Reliability Needs

Substrate option	Best reason to consider it	Critical checks
Organic laminate/build-up	Cost, package size, multilayer routing and board-like supply base	Warpage, fine-line capability, moisture and CTE mismatch
LTCC/HTCC ceramic	Temperature stability, embedded passive options or harsh environment	Shrinkage control, metallization, thermal path and brittleness
Silicon interposer	Very fine routing, TSV options and close die integration	Cost, area, stress and test flow
Glass interposer	Dimensional/electrical opportunities for fine interconnect	Process maturity, vias, metallization and supply chain
Embedded bridge	Dense local die-to-die routing without a full large interposer	Bridge placement, alignment and package co-design
Redistribution/fan-out	Thin package and high-density redistribution	Mold/warpage, die shift, RDL yield and package size

The lowest-loss or finest-pitch substrate is not automatically best. Select the least complex structure that meets bandwidth, power, thermal, mechanical, reliability and volume needs.

5. Select the Die-Attach and Interconnect Method

Interconnect	Strength	Design/manufacturing risk
Wire bond	Mature, flexible and accessible for many I/O patterns	Loop inductance, pad placement, wire sweep and keepouts
Flip chip	High I/O density, short electrical path and distributed power/ground	Bump alignment, underfill, warpage and hidden-joint inspection
Thermocompression bonding	Fine-pitch bonding with controlled force/heat	Coplanarity, throughput and thermal budget
Hybrid bonding	Very fine direct dielectric/metal connection potential	Surface preparation, alignment, particles and yield
Bridge/interposer link	High-density die-to-die interface	Multiple assembly interfaces and known-good-die requirement

Interconnect choice changes the die pad map, substrate escape, underfill, inspection, rework and thermal sequence. It cannot be finalized after die tape-out.

6. Treat Power Delivery as a Hierarchy

A module may expose only a few external rails while distributing large transient currents internally. Package and PCB power integrity must be solved together.

PDN level	Main design variable	Verification need
On-die	Grid, local capacitance and current distribution	Die power model and droop analysis
Die-to-substrate	Bump/ball allocation and current density	Electromigration and connection limits
Package substrate	Planes, vias, embedded/discrete decoupling	Impedance vs frequency and anti-resonance review
Package-to-PCB	BGA map, return paths and spreading inductance	Package/board co-simulation
PCB/regulator	VRM placement, planes, bulk/high-frequency decoupling	Load-step and stability validation

Do not place every decoupling capacitor on the host PCB and assume it can correct a high-inductance in-package path.

7. Build a Thermal Path for Every Die

Multiple dies can have different junction limits, power maps and workload timing. A single package-top temperature does not describe them all.

Thermal issue	MCM consequence	Engineering action
Unequal die power	Local hot spot under a shared lid	Map die-level power and interface resistance
Die height variation	Uneven TIM bond line or lid contact	Control coplanarity and interface stack
Stacked dies	Inner die has a longer heat path	Model vertical heat flow and workload
Neighbor heating	One chiplet raises another’s junction temperature	Run coupled transient analysis
Substrate/PCB spreading	Heat also leaves through balls and board copper	Coordinate thermal vias, planes and heatsink path
CTE mismatch	Thermal cycles stress bumps, die attach and substrate	Validate materials and reliability profile

Thermal simulation should use package geometry and material properties that manufacturing can actually hold.

8. Use Known-Good Die and a Layered Test Strategy

Adding dies multiplies the cost of discovering one bad element late. Intel notes that advanced multi-stage testing and die sort prevent faulty dies from advancing into packaging.

Test stage	Main purpose	Coverage gap
Wafer probe/die sort	Screen die before module assembly	Probe conditions may not reproduce packaged performance
Incoming die inspection	Verify identity, damage and handling	Does not prove electrical function
Substrate test	Verify fine interconnect before die attach	Cannot test final bonded interfaces
Mid-process test	Catch faults before expensive later operations	Requires temporary access and test design
Final package test	Verify module interfaces and functions	Internal fault localization can be difficult
Burn-in/reliability test	Screen/characterize defined failure mechanisms	Adds cost and must be justified/validated
Board/system test	Verify interaction with PCB, firmware and cooling	Late failures are expensive to diagnose

Test access, scan, BIST, die IDs, telemetry and fault isolation belong in the architecture—not in a fixture request after packaging.

9. Model Yield at Module Level

Yield driver	Why it compounds	Mitigation
Individual die yield	One bad die can scrap an expensive assembly	Known-good-die screening and partition strategy
Substrate yield	Large/fine substrates accumulate defect opportunity	Design rules, test structures and supplier capability
Each attach step	Every bond adds process loss	Reduce steps and control critical parameters
Reworkability	Some die/underfill structures cannot be repaired	Decide rework strategy before material selection
Final test coverage	Escapes consume all previous value	Layered test and diagnosability
Supply matching	One unavailable die blocks the whole module	Lifecycle, buffer and alternate architecture planning

Chiplets can improve reuse and allow different process nodes, but a multi-die package is not guaranteed to be cheaper than a monolithic solution. Yield, substrate area, test, assembly and volume decide the economics.

10. Design the Host PCB Around the Actual Package

The module still needs power, signals, mechanical support, cooling and assembly on a PCB. A complex MCM often appears as a dense BGA with demanding breakout and power requirements.

PCB interface	Required input from package team	PCB action
Ball map	Signal, power, ground, NC and reserved balls	Verify symbol/footprint and escape strategy
Package dimensions	Body, ball pitch, tolerances, warpage and keepouts	Land pattern, courtyard and assembly review
Channel models	Package S-parameters/IBIS models and reference design	Co-design launches, vias and stackup
PDN model	Rail currents, transient targets and package parasitics	Plan planes, vias, regulators and decoupling
Thermal model	Power map and package resistance/network	Design board copper, heatsink and airflow
Assembly limits	Reflow, MSL, coplanarity, support and inspection	Panel support, stencil, profile and X-ray strategy

Request a PCB manufacturing and package-interface review before the MCM footprint and stackup are frozen.

11. Control Assembly, Underfill, and Warpage

Process variable	Failure mode	Control evidence
Substrate/die coplanarity	Opens, nonuniform joints and bond-line variation	Incoming/process metrology
Bond force/temperature	Weak or damaged interconnect	Qualified process window and monitoring
Flux/cleanliness	Leakage, corrosion or underfill adhesion problem	Material compatibility and cleanliness validation
Underfill flow/cure	Voids, delamination and stress	Dispense, capillary/cure and inspection controls
Mold/lid/TIM	Warpage, die stress or thermal resistance	Material/process characterization
Package reflow to PCB	Joint failure from package/board warpage	Profile, support, paste and X-ray evidence

Inspection methods should match hidden structures. A top-side visual check cannot validate flip-chip bumps, interposer interfaces, underfill voids or bottom BGA joints.

12. Multi Chip Module Decision Checklist

Gate	Pass condition	Blocker
Architecture	Partition, interfaces, latency and fault boundaries are defined	“Use chiplets for flexibility” only
Die readiness	Models, pad maps, known-good-die and lifecycle plans exist	Unproven die supply/test flow
Substrate	Technology, stack, routing, materials and supplier capability align	Finest pitch selected without yield evidence
Interconnect	Attach method, pitch, underfill and inspection are co-designed	Die/package decisions are separated
Power/thermal	Die-level models close package and PCB budgets	Only total package power is known
Test	Wafer, mid-process, final and system coverage map exists	First meaningful test occurs after full assembly
Reliability	Use environment maps to materials and stress tests	Generic qualification copied from another product
PCB integration	Footprint, breakout, PDN, channel and cooling are reviewed	Package is thrown over the wall to PCB layout
Change control	Die, substrate, process and firmware revisions are traceable	Mixed configurations cannot be reconstructed

For production planning, coordinate PCB fabrication and assembly support with the module’s ball map, stackup, channel/PDN models, thermal requirements and inspection plan. Complete a final CAM, DFM, and BGA assembly review before PCB tooling release.

Multi chip module mounted on PCB with BGA package and thermal design

Frequently Asked Questions

What is the difference between an MCM and a SiP?

The terms overlap. MCM traditionally emphasizes multiple semiconductor dies on a shared substrate, while SiP often describes a broader functional system that may include dies, packaged components and passives. The physical construction matters more than the label.

Is a chiplet package a multi chip module?

It can be considered a modern multi-die or MCM-style implementation when multiple chiplets share a package and interconnect. “Chiplet” also implies intentional functional partitioning and a die-to-die interface ecosystem.

What are MCM-L, MCM-C, and MCM-D?

They are traditional classifications based mainly on substrate/interconnect technology: laminated organic, cofired ceramic, and deposited thin-film structures. Modern packages may combine several approaches.

Why use multiple dies instead of one SoC?

Potential reasons include mixing process nodes, reusing IP, integrating memory/I/O, exceeding reticle-scale limits, improving development flexibility, or separating analog/RF from advanced logic. Benefits must be weighed against packaging, test, power, thermal and yield cost.

Can a multi chip module be repaired?

Sometimes, but reworkability depends on die attach, underfill, molding, access and process sequence. Many dense or underfilled structures are difficult or uneconomic to repair, so known-good-die and mid-process test become important.

Final Takeaway

A multi chip module is a system integration project, not simply a larger component. Partition functions carefully, choose the least complex substrate and interconnect that meet requirements, design power and thermal paths across die/package/PCB boundaries, test before value accumulates, and control the as-built configuration. The package only succeeds when the host PCB and manufacturing flow succeed with it.