IPC-6015 Explained: MCM-L Organic Substrate Specification for Multichip Modules

When AMD released its Zen 2 processors with multiple chiplets on an organic substrate, they were using technology that IPC-6015 was written to address over two decades ago. Most PCB engineers are familiar with IPC-6012 for rigid boards and IPC-6013 for flex, but few have encountered IPC-6015—the specification that covers organic substrates for multichip modules.

IPC-6015, the Qualification and Performance Specification for Organic Multichip Module (MCM-L) Mounting and Interconnecting Structures, establishes requirements for the specialized substrates that interconnect bare semiconductor dies. As chiplet architectures become mainstream in processors, GPUs, and system-in-package designs, understanding this specification becomes increasingly relevant for advanced packaging engineers.

What Is IPC-6015?

IPC-6015 is the IPC specification that defines qualification and performance requirements for organic laminate substrates used in multichip modules (MCM-L) and single-chip modules (SCM-L). Unlike standard PCBs that mount packaged components, MCM-L substrates directly interconnect bare semiconductor dies using wire bonding or flip chip attachment.

IPC-6015 Standard Overview

Attribute	Details
Full title	Qualification and Performance Specification for Organic Multichip Module (MCM-L) Mounting and Interconnecting Structures
Release date	February 1998
Pages	25 pages
Parent document	IPC-6011 (Generic Performance Specification)
Design companion	IPC-2225 (Sectional Design Standard for MCM-L)
Coverage	SCM-L and MCM-L organic substrates

The specification addresses electrical, mechanical, and environmental properties specific to MCM-L mounting structures, supplementing the generic requirements in IPC-6011.

Where IPC-6015 Fits in the IPC-6010 Family

IPC-6015 is part of the IPC-6010 document family that covers all printed board types:

Specification	Coverage
IPC-6011	Generic requirements for all printed boards
IPC-6012	Rigid printed boards
IPC-6013	Flexible and rigid-flex printed boards
IPC-6015	Organic multichip module (MCM-L) substrates
IPC-6017	Printed boards with embedded passive devices
IPC-6018	High frequency (microwave) printed boards

Understanding MCM-L Technology

Before diving into IPC-6015 requirements, it’s essential to understand what MCM-L technology actually is and how it differs from conventional PCBs.

What Is a Multichip Module?

A multichip module (MCM) is an electronic assembly that integrates multiple integrated circuits (ICs) or semiconductor dies onto a single substrate, allowing them to function as a cohesive unit. The key distinction from traditional PCB assembly is that MCMs typically mount bare (unpackaged) dies rather than packaged components.

MCM-L Defined

MCM-L specifically refers to multichip modules built on organic Laminate substrates—hence the “L” designation. These substrates use advanced PCB technology with enhanced materials, tighter tolerances, and finer features than standard printed boards.

MCM-L Characteristic	Description
Substrate material	Organic laminate (similar to advanced PCB)
Die attachment	Wire bonding, flip chip, or TAB
Feature size	Finer than standard PCB (lines/spaces down to 25-50 µm)
Via technology	Blind, buried, and microvias common
Surface finish	Selective plating for different attachment methods
Chip density	≥50% substrate area covered by active devices

MCM-L Substrate Process

The MCM-L substrate fabrication process follows five basic steps:

Step	Process	Description
1	Core selection	Choose appropriate core and prepreg layers for electrical and mechanical requirements
2	Patterning	Photolithographic patterning and etching of copper conductors
3	Via formation	Drilling of blind, buried, and through-hole vias
4	Lamination	Multiple lamination cycles for complex via structures
5	Surface finish	Selective plating of gold (wire bond), solder (flip chip), or other finishes

MCM Types Comparison: MCM-L vs MCM-C vs MCM-D

Understanding the differences between MCM substrate types helps clarify when IPC-6015 applies versus other specifications.

MCM Substrate Technology Comparison

Attribute	MCM-L (Laminate)	MCM-C (Ceramic)	MCM-D (Deposited)
Substrate	Organic laminate	Ceramic (LTCC/HTCC)	Silicon, ceramic, or metal base
Conductor formation	Subtractive etch	Thick film printing	Thin film deposition
Dielectric	Reinforced organic	Co-fired ceramic	Spun-on or deposited polymer
Minimum line/space	25-75 µm	75-125 µm	10-25 µm
Layer count	High (20+ possible)	Moderate (10-15)	Moderate (5-10)
Cost	Low to moderate	Moderate to high	High
Thermal performance	Moderate	Excellent	Good
Dielectric constant	3.5-4.5	5-9	2.5-3.5
IPC specification	IPC-6015	Not covered by IPC-6010 series	Not covered by IPC-6010 series

When to Use Each MCM Type

MCM Type	Best Applications
MCM-L	High volume, cost-sensitive, high layer count, moderate performance
MCM-C	High temperature, hermetic requirements, RF/microwave
MCM-D	Highest density, fastest signals, lowest dielectric loss

MCM-L is the most common choice for commercial applications because it leverages existing PCB manufacturing infrastructure while achieving the density and performance needed for advanced packaging.

IPC-6015 Scope and Requirements

IPC-6015 establishes requirements across several key areas that distinguish MCM-L substrates from standard PCBs.

Materials Requirements

Material Category	IPC-6015 Requirement
Base laminate	Per IPC-4101 or equivalent
Prepreg	Per IPC-4101 or equivalent
Copper foil	Per IPC-4562
Metallic plating	Per applicable specifications
Solder resist	Per IPC-SM-840
Hole fill insulation	As specified in procurement documentation

Structural Integrity Requirements

IPC-6015 defines acceptance criteria for structural features both before and after thermal stress testing.

Before Thermal Stress

Feature	Requirement
Lifted lands	Not acceptable if affects function
Lifted conductors	Not acceptable if affects function
Delamination	Not acceptable
Measling	Acceptable if limited and not affecting function
Crazing	Acceptable if limited
Weave exposure	Not acceptable on bondable surfaces

After Thermal Stress

Feature	Requirement
Blistering	Not acceptable
Delamination	Not acceptable
Crazing propagation	Limited acceptable
Lifted lands/conductors	Not acceptable

Conductor Requirements

Requirement	Specification
Width reduction	Per class requirements (similar to IPC-6012)
Thickness	Per design and class
Edge definition	Smooth, well-defined edges required
Undercut	Controlled to maintain conductor integrity

Performance Classes for MCM-L Substrates

Like other IPC-6010 series specifications, IPC-6015 applies the three-class system defined in IPC-6011.

IPC-6015 Class Definitions

Class	Name	Description	MCM-L Applications
Class 1	General Electronic Products	Function is primary requirement	Consumer MCMs, cost-driven applications
Class 2	Dedicated Service Electronic Products	Extended life, reliable performance	Industrial, commercial computing
Class 3	High Reliability Electronic Products	Continued performance critical	Aerospace, military, medical

Class Requirements Comparison

Requirement	Class 1	Class 2	Class 3
Inspection level	Reduced	Standard	Enhanced
Conductor tolerance	Relaxed	Moderate	Tight
Plating uniformity	Basic	Controlled	Strict
Documentation	Minimal	Standard	Full traceability
Testing frequency	Sample	Lot sample	Per lot/100%

Surface Finish Requirements for Die Attachment

MCM-L substrates require specialized surface finishes to support bare die attachment methods. This is a major differentiator from standard PCBs.

Surface Finish by Attachment Method

Attachment Method	Required Finish	Typical Specification
Wire bonding (Au)	Gold over nickel	0.75-1.25 µm Au over 2.5-5 µm Ni
Wire bonding (Al)	Aluminum or gold	Application dependent
Flip chip (solder)	Solder or ENIG	Per J-STD-006 or IPC-4552
TAB bonding	Gold or tin-lead	Per design requirements
Edge connectors	Hard gold	0.75-2.5 µm hard Au

Selective Plating Requirements

Unlike standard PCBs that typically have uniform surface finish, MCM-L substrates often require selective plating:

Area	Finish	Purpose
Wire bond pads	Soft gold over nickel	Reliable wire bonding
Flip chip pads	Solder or OSP	Solder joint formation
Edge connectors	Hard gold	Wear resistance
Test pads	Per test requirements	Probe contact

This selective plating adds complexity and cost compared to standard PCB fabrication.

Solder Resist Requirements

Solder resist (solder mask) on MCM-L substrates must meet specific requirements for the demanding environment of chip-level packaging.

Solder Resist Criteria

Requirement	Specification
Coverage	Complete coverage of specified areas
Registration	±50 µm typical for fine-pitch applications
Adhesion	Per IPC-SM-840 testing
Cure	Complete cure, no tackiness
Thickness	Uniform, per design specification
Voids	Not acceptable over conductors

Solder Resist Openings

Feature	Requirement
Wire bond pads	Clean opening, no resist on bondable surface
Flip chip pads	Defined openings for solder paste/bump
Via tenting	As specified in design

Quality Assurance and Testing

IPC-6015 Section 4 defines quality assurance provisions specific to MCM-L substrates.

Required Testing

Test Category	Tests Included
Visual inspection	External features, workmanship
Dimensional	Feature sizes, registration, flatness
Electrical	Continuity, isolation, insulation resistance
Environmental	Thermal stress, moisture resistance
Mechanical	Bond pull strength, adhesion
Microsection	Internal structure, plating quality

Wire Bond Pull Strength Testing

For substrates intended for wire bonding, IPC-6015 references IPC-TM-650 Method 2.4.42.3 for bond pull testing:

Parameter	Typical Requirement
Gold wire (25 µm)	≥3.0 grams minimum
Aluminum wire (25 µm)	≥2.5 grams minimum
Test method	Vertical pull, 90° to substrate
Sample size	Per class and lot requirements

Insulation Resistance

Condition	Requirement
As received	≥500 MΩ minimum
After moisture exposure	≥100 MΩ minimum
Test voltage	100V DC typical

IPC-6015 vs IPC-6012: Key Differences

Understanding when to apply IPC-6015 versus IPC-6012 is critical for proper specification.

Specification Selection Guide

Application	Correct Specification
Standard rigid PCB	IPC-6012
HDI rigid PCB	IPC-6012 (with HDI requirements)
Substrate for packaged components	IPC-6012
Substrate for bare die (wire bond)	IPC-6015
Substrate for bare die (flip chip)	IPC-6015
MCM organic substrate	IPC-6015
SiP organic substrate	IPC-6015

Key Differences Between Specifications

Aspect	IPC-6012	IPC-6015
Primary focus	PCB for packaged components	Substrate for bare die
Surface finish	Uniform finish typical	Selective plating common
Wire bond requirements	Not addressed	Detailed requirements
Feature size	Standard to HDI	Fine pitch, HDI typical
Chip density criteria	Not applicable	≥50% coverage defined
Die attach requirements	Not addressed	Addressed

Modern Relevance: MCM-L in the Chiplet Era

While IPC-6015 dates from 1998, its relevance has increased with the industry’s shift toward chiplet and heterogeneous integration architectures.

Contemporary MCM-L Applications

Application	Examples
Processor chiplets	AMD Ryzen (Zen 2/3/4), Intel Alder Lake
GPU chiplets	AMD RDNA 3 (Radeon RX 7000 series)
High bandwidth memory	HBM stacks on organic interposers
System-in-Package	Apple Watch S-series, smartphone SiPs
Automotive	ADAS processors, infotainment SoCs
Networking	Switch ASICs, network processors

MCM-L vs Modern SiP Terminology

Term	Definition	Relationship to IPC-6015
MCM-L	Multichip module on organic laminate	Directly covered
SiP	System-in-Package	Often uses MCM-L substrates
2.5D packaging	Side-by-side dies on interposer	May use organic (MCM-L) interposer
FOWLP	Fan-out wafer level packaging	Different technology, not MCM-L
Chiplet	Modular die in multi-die package	Often assembled on MCM-L substrate

Most SiPs that have achieved high-volume manufacturing are essentially MCM-L assemblies—multiple dies on organic laminate substrates, falling under IPC-6015’s scope.

Related Standards and Design Guidelines

IPC-6015 works in conjunction with several other standards for complete MCM-L design and fabrication.

Design Standards

Standard	Coverage
IPC-2225	Sectional Design Standard for Organic Multichip Modules (MCM-L) and MCM-L Assemblies
IPC-2221	Generic Standard on Printed Board Design
IPC-2226	Sectional Design Standard for HDI Printed Boards

Material Standards

Standard	Coverage
IPC-4101	Specification for Base Materials for Rigid and Multilayer Printed Boards
IPC-4562	Metal Foil for Printed Board Applications
IPC-SM-840	Qualification and Performance of Permanent Solder Mask

Test Methods

Standard	Coverage
IPC-TM-650	Test Methods Manual
IPC-TM-650 2.4.42.3	Wire Bond Pull Strength
IPC-TM-650 2.6.3	Moisture and Insulation Resistance

Frequently Asked Questions About IPC-6015

What is the difference between IPC-6015 and IPC-6012?

IPC-6012 covers standard rigid printed circuit boards designed for mounting packaged components through soldering. IPC-6015 covers organic substrates specifically designed for mounting bare semiconductor dies using wire bonding, flip chip, or TAB attachment. The key differences include surface finish requirements (IPC-6015 addresses selective plating for wire bonding), wire bond pull strength testing, and die attachment considerations. If your substrate will have bare dies attached directly to it, use IPC-6015. If you’re mounting packaged components, use IPC-6012.

Is IPC-6015 still relevant with newer packaging technologies?

Yes, IPC-6015 remains highly relevant. While the specification dates from 1998, the fundamental technology it covers—organic laminate substrates for bare die attachment—is the basis for most modern System-in-Package (SiP) and chiplet assemblies. AMD’s Zen processors, many smartphone SiPs, and numerous automotive modules use MCM-L technology that falls under IPC-6015’s scope. The shift toward heterogeneous integration and chiplet architectures has actually increased the relevance of organic substrate specifications.

What does MCM-L mean and how does it differ from MCM-C and MCM-D?

MCM-L refers to Multichip Modules built on organic Laminate substrates using advanced PCB technology. MCM-C uses Ceramic substrates (like LTCC) with thick-film conductors, offering excellent thermal performance but at higher cost. MCM-D uses thin-film Deposited metals on silicon or ceramic bases, achieving the finest features but at the highest cost. MCM-L offers the best balance of cost, density, and manufacturing scalability, which is why it dominates commercial applications. IPC-6015 specifically covers MCM-L; ceramic and deposited thin-film substrates are not covered by the IPC-6010 series.

What surface finish does IPC-6015 require for wire bonding?

IPC-6015 requires gold over nickel plating for gold wire bonding applications. Typical specifications call for 0.75-1.25 µm of soft gold over 2.5-5 µm of nickel as a barrier layer. The gold must be high purity and the surface must be free of contamination to ensure reliable wire bonds. Unlike standard PCB finishes like HASL or OSP, wire bond finishes require electroless or electrolytic gold plating with careful control of thickness, purity, and surface roughness. This selective plating requirement is one of the key differentiators between MCM-L and standard PCB fabrication.

Can a standard PCB fabricator manufacture to IPC-6015?

Most standard PCB fabricators cannot manufacture to IPC-6015 requirements without specialized capabilities. MCM-L fabrication requires fine-line imaging (25-50 µm lines/spaces), selective plating equipment for wire bond gold, cleaner processing environments, and testing capabilities for wire bond pull strength. Fabricators serving the semiconductor packaging industry or those with advanced HDI capabilities are more likely to offer IPC-6015 compliant substrates. When sourcing MCM-L substrates, verify that your supplier has experience with bare die substrates and the specific attachment method you require.

Useful Resources

Official IPC Standards:

• IPC Store (IPC-6015): shop.ipc.org/ipc-6015
• ANSI Store: webstore.ansi.org
• GlobalSpec: standards.globalspec.com

Related IPC Standards:

• IPC-6011: Generic Performance Specification for Printed Boards
• IPC-2225: Sectional Design Standard for Organic Multichip Modules (MCM-L)
• IPC-6012: Qualification and Performance Specification for Rigid Printed Boards
• IPC-4101: Specification for Base Materials
• IPC-SM-840: Qualification and Performance of Permanent Solder Mask
• IPC-TM-650: Test Methods Manual

Industry Resources:

• IPC Training and Certification: ipc.org
• IMAPS (International Microelectronics Assembly and Packaging Society): imaps.org
• SEMI Standards (Semiconductor Equipment and Materials International): semi.org

IPC-6010 Family Bundle:

• IPC-6010-FAM: Complete family of board performance specifications

Conclusion

IPC-6015 fills a critical niche in the IPC-6010 specification family, addressing organic substrates for bare die mounting that standard PCB specifications don’t cover. As the electronics industry increasingly adopts chiplet architectures and heterogeneous integration, understanding this specification becomes essential for packaging engineers.

Key takeaways:

1. IPC-6015 covers MCM-L substrates – Organic laminates for bare die attachment, not packaged components
2. Different from standard PCBs – Selective plating, wire bond requirements, finer features
3. MCM-L dominates commercial SiP – Most cost-effective approach for high-volume multichip packaging
4. Surface finish is critical – Gold for wire bonding, solder for flip chip, often on the same substrate
5. Still highly relevant – Chiplet architectures use MCM-L technology extensively

Whether you’re designing next-generation processors or specifying substrates for automotive SiPs, IPC-6015 provides the framework for ensuring your organic multichip module substrates meet their reliability and performance requirements.