Inquire: Call 0086-755-23203480, or reach out via the form below/your sales contact to discuss our design, manufacturing, and assembly capabilities.
Quote: Email your PCB files to Sales@pcbsync.com (Preferred for large files) or submit online. We will contact you promptly. Please ensure your email is correct.
Notes: For PCB fabrication, we require PCB design file in Gerber RS-274X format (most preferred), *.PCB/DDB (Protel, inform your program version) format or *.BRD (Eagle) format. For PCB assembly, we require PCB design file in above mentioned format, drilling file and BOM. Click to download BOM template To avoid file missing, please include all files into one folder and compress it into .zip or .rar format.
IPC-6012 Complete Guide: Rigid PCB Qualification, Class 2 vs Class 3 & Acceptance Criteria
Meta:IPC-6012 complete guide covering Class 2 vs Class 3 requirements, copper thickness, annular ring, and acceptance criteria for rigid PCB qualification.
Every PCB fabrication drawing I’ve reviewed in the past decade includes some variation of “Fabricate per IPC-6012 Class 2” or “IPC-6012 Class 3 required.” Yet when I ask designers what specific requirements that callout invokes, many can’t answer beyond “Class 3 is stricter.” Understanding IPC-6012 isn’t optional for anyone serious about PCB quality—it’s the specification that defines whether your boards pass or fail inspection.
IPC-6012, the Qualification and Performance Specification for Rigid Printed Boards, establishes the requirements that fabricators must meet and inspectors use to accept or reject your boards. From copper thickness and annular ring dimensions to plating voids and thermal stress testing, this specification covers every measurable aspect of rigid PCB quality. This guide breaks down what you need to know to properly specify, manufacture, and inspect rigid printed boards.
What Is IPC-6012?
IPC-6012 is the industry standard that defines qualification and performance requirements for rigid printed circuit boards. Developed by the IPC Rigid Printed Board Performance Specifications Task Group (D-33a), it covers everything from single-sided boards to complex HDI multilayers with embedded components.
IPC-6012 Standard Overview
Attribute
Details
Full title
Qualification and Performance Specification for Rigid Printed Boards
Current revision
IPC-6012F (October 2023)
Previous revisions
IPC-6012E (2020), D (2015), C (2010), B (2004), A (1999)
Pages
~80 pages
Parent document
IPC-6011 (Generic Performance Specification)
Visual companion
IPC-A-600 (Acceptability of Printed Boards)
Supersedes
IPC-RB-276
The specification works in conjunction with IPC-6011, which defines the performance classes (Class 1, 2, 3), and IPC-A-600, which provides photographs and illustrations of acceptable and nonconforming conditions.
IPC-6012F: What’s New in the 2023 Revision
IPC released Revision F in October 2023, incorporating significant updates based on evolving manufacturing technologies and reliability concerns.
Key Changes in IPC-6012F
Area
Update
Printed board cavities
New section with requirements for cavity construction
Copper wrap plating
Expanded requirements for filled via cap plating
Back drill requirements
Clarified measurement methods and depth specifications
Microvia reliability
New test coupon designs for interconnected via structures
Internal plated layers
Additional requirements for buried structures
Dielectric spacing
Updated minimum spacing requirements
Intermediate target lands
New category between capture and target lands
Solderability testing
Updated requirements and methods
The microvia reliability updates are particularly significant, addressing industry concerns about stacked microvia failures in high-layer-count HDI boards.
Board Types Covered by IPC-6012
IPC-6012 covers six types of rigid printed board constructions:
IPC-6012 Board Type Classifications
Type
Description
Construction
Type 1
Single-sided
With or without plated-through holes
Type 2
Double-sided
With or without plated-through holes
Type 3
Multilayer
Without blind and/or buried vias
Type 4
Multilayer
With blind and/or buried vias (may include microvias)
Type 5
Metal core
Without blind and/or buried vias
Type 6
Metal core
With blind and/or buried vias (may include microvias)
Additionally, IPC-6012 addresses:
Active/passive embedded circuitry with capacitive or resistive components
Metal core boards with or without external heat frames
High Density Interconnect (HDI) structures
Understanding IPC-6012 Performance Classes
The three performance classes defined in IPC-6011 and applied throughout IPC-6012 represent progressive levels of quality requirements.
Performance Class Definitions
Class
Name
Description
Applications
Class 1
General Electronic Products
Cosmetic imperfections acceptable; function is primary requirement
Consumer electronics, toys, basic appliances
Class 2
Dedicated Service Electronic Products
Extended life and continued performance required; uninterrupted service not critical
Industrial equipment, communications, computers
Class 3
High Reliability Electronic Products
Continued performance critical; downtime cannot be tolerated
Medical devices, military, aerospace, life support
The user must specify the performance class in procurement documentation. A board cannot be “upgraded” from Class 2 to Class 3 after fabrication—it must be manufactured to Class 3 requirements from the start.
IPC-6012 Class 2 vs Class 3: Key Differences
The Class 2 vs Class 3 comparison is the most frequently searched topic related to IPC-6012. Here are the critical differences:
Plating Thickness Requirements
Location
Class 2 Minimum
Class 3 Minimum
Hole wall (average)
20 µm (0.8 mil)
25 µm (1.0 mil)
Surface copper
20 µm (0.8 mil)
25 µm (1.0 mil)
Wrap plating (cap)
Per Table 3-11
Per Table 3-11 (stricter)
Through-Hole Barrel Fill
Requirement
Class 2
Class 3
Minimum vertical fill
50%
75%
Solder wetting
Required on surfaces
Required on surfaces
This difference significantly impacts assembly process time. Achieving 75% barrel fill requires slower wave soldering or additional solder paste, adding cost and cycle time.
Annular Ring Requirements
Condition
Class 2
Class 3
External layers
90° breakout acceptable
No breakout allowed
Internal layers
90° breakout acceptable
90° breakout acceptable
Minimum ring (external)
50 µm (2 mil)
50 µm (2 mil)
Lifted/fractured ring
Acceptable if functional
Not acceptable
Conductor Width Reduction
Requirement
Class 2
Class 3
Maximum reduction
30%
20%
Junction area reduction
20% maximum
10% maximum
Plating Voids in Holes
Void Type
Class 2
Class 3
Single void (max)
5% of hole length
5% of hole length
Total voids
5% cumulative
No multiple voids
Location restrictions
Not at interface
Not at interface
Complete Class 2 vs Class 3 Comparison
Requirement
Class 2
Class 3
Hole wall plating
20 µm minimum
25 µm minimum
Surface plating
20 µm minimum
25 µm minimum
Barrel fill
50%
75%
Annular ring breakout
90° external allowed
No external breakout
Conductor reduction
30% max
20% max
Plating voids
5% single/cumulative
5% single only
Lifted pads
Acceptable if functional
Not acceptable
Measling
Allowed in limited areas
More restricted
Inspection level
Standard
Enhanced
Documentation
Standard
Full traceability
Cost impact
Baseline
15-30% higher
Copper Thickness Requirements
One of the most misunderstood aspects of IPC-6012 is copper thickness specification. Tables 3-13 (internal) and 3-14 (external) define requirements, but the left column indicates starting copper weight, not finished.
Internal Copper Thickness (Table 3-13 Concept)
Starting Copper
Minimum Finished (All Classes)
1/2 oz (17 µm)
12 µm
1 oz (35 µm)
25 µm
2 oz (70 µm)
56 µm
Internal layers undergo only subtractive (etching) processes, so finished copper is always less than starting copper.
External Copper Thickness (Table 3-14 Concept)
Starting Copper
Minimum Finished (Class 2)
Minimum Finished (Class 3)
1/2 oz (17 µm)
35 µm
40 µm
1 oz (35 µm)
53 µm
58 µm
2 oz (70 µm)
88 µm
93 µm
External layers gain copper through electroplating, so finished thickness exceeds starting thickness.
Common Copper Specification Mistakes
Mistake
Problem
Solution
Specifying “1 oz finished”
Ambiguous
Specify “1 oz starting” or actual finished thickness
Using internal tables for external
Wrong requirements applied
Reference correct table
Measuring average vs minimum
May accept underplated boards
Understand IPC measurement method
When specifying copper weight on fabrication drawings, clearly state whether requirements are “starting” or “finished” to avoid disputes.
Annular Ring and Hole Requirements
Annular ring is measured differently for internal and external layers, creating another common source of confusion.
Annular Ring Measurement
Layer Type
Measurement Point
External layers
From edge of plating to land edge
Internal layers
From edge of drilled hole to land edge
Minimum Annular Ring by Class
Layer
Class 1
Class 2
Class 3
External
0 µm (tangent)
50 µm
50 µm
Internal
0 µm (tangent)
25 µm
25 µm
Breakout Acceptance
Breakout Degree
Class 1
Class 2
Class 3
90°
Acceptable
Acceptable external
Internal only
180°
Acceptable
Not acceptable
Not acceptable
The pad size calculation formula per IPC-6012 and IPC-2221:
Thermal stress testing per Section 3.6.1 validates that boards will survive assembly without delamination or barrel cracking.
Microsection Evaluation Requirements
Microsection analysis reveals internal quality that can’t be assessed by visual inspection.
Key Microsection Measurements
Feature
Class 2 Requirement
Class 3 Requirement
Hole wall copper
20 µm average
25 µm average
Inner layer copper
Per Table 3-13
Per Table 3-13
Plating voids
5% max
5% max, single only
Etchback/smear
Per specification
Per specification
Dielectric thickness
As specified
As specified
Registration
Annular ring met
Annular ring met
Frequently Asked Questions About IPC-6012
What is the difference between IPC-6012 and IPC-A-600?
IPC-6012 is the performance specification that defines what requirements a rigid PCB must meet—it tells fabricators how to make boards and provides numerical acceptance criteria. IPC-A-600 is the visual acceptance standard that provides photographs and illustrations showing what acceptable and nonconforming conditions look like. Inspectors use IPC-A-600 to determine whether boards meet IPC-6012 requirements. The two documents are designed to work together: IPC-6012 says “annular ring must be 50 µm minimum,” and IPC-A-600 shows you what acceptable and unacceptable annular rings look like under magnification.
Can a Class 2 board be upgraded to Class 3 after fabrication?
No. A printed board must be manufactured to the specified class requirements from the beginning. You cannot take a board fabricated to Class 2 tolerances and “certify” it as Class 3 after the fact, even if it happens to meet Class 3 criteria upon inspection. The class designation affects process controls, inspection frequency, and documentation throughout manufacturing, not just final acceptance criteria. If you need Class 3 boards, you must specify Class 3 in your procurement documentation before fabrication begins.
How do I specify copper weight correctly on my fabrication drawing?
The most common IPC-6012 misinterpretation involves copper thickness. Tables 3-13 and 3-14 reference “starting” copper weight, not finished. To avoid confusion, explicitly state whether your requirement is for starting copper (what goes into production) or finished copper (what you measure on the completed board). For example, write “1 oz starting copper” or “35 µm minimum finished copper.” External layers gain copper through plating, so finished will exceed starting. Internal layers lose copper through etching, so finished will be less than starting.
When should I specify IPC-6012ES, EM, or EA addenda?
Specify the appropriate addendum when your application requires reliability beyond standard Class 3. Use IPC-6012ES for space, satellite, military aviation, and missile systems. Use IPC-6012EM for medical devices, especially implantables and life-critical equipment. Use IPC-6012EA for automotive electronics exposed to vibration and thermal cycling. These addenda impose additional testing, tighter tolerances, and enhanced documentation requirements. They also typically increase cost and lead time, so only specify them when your application genuinely requires that reliability level.
What changed in IPC-6012F that I need to know about?
IPC-6012F (October 2023) includes significant updates in several areas. The most impactful changes address microvia reliability with new test coupon designs for evaluating stacked and staggered microvia structures—critical for HDI boards. New requirements cover printed board cavities, copper wrap plating specifications, and back drill measurement methods. Clarifications on internal plated layers and dielectric spacing help resolve previous interpretation issues. If you’re manufacturing HDI boards with microvias, the Rev F reliability requirements deserve careful attention.
IPC-6012 is the definitive specification for rigid printed board quality, establishing the requirements that separate acceptable boards from rejects. Whether you’re specifying Class 2 for commercial products or Class 3 with ES addendum for satellite systems, understanding this standard is essential for successful PCB procurement.
Key points to remember:
Class selection matters – Specify the right class in procurement documentation before fabrication
Copper thickness is confusing – Clarify starting vs. finished requirements on drawings
Class 2 vs Class 3 – Know the specific differences in plating, annular ring, and acceptance criteria
Addenda exist for a reason – Use ES, EM, or EA when your application demands it
IPC-6012F is current – Ensure your fabricator works to the latest revision
The investment in understanding IPC-6012 pays dividends through fewer rejected lots, clearer communication with fabricators, and boards that reliably meet your application requirements.
Inquire: Call 0086-755-23203480, or reach out via the form below/your sales contact to discuss our design, manufacturing, and assembly capabilities.
Quote: Email your PCB files to Sales@pcbsync.com (Preferred for large files) or submit online. We will contact you promptly. Please ensure your email is correct.
Notes: For PCB fabrication, we require PCB design file in Gerber RS-274X format (most preferred), *.PCB/DDB (Protel, inform your program version) format or *.BRD (Eagle) format. For PCB assembly, we require PCB design file in above mentioned format, drilling file and BOM. Click to download BOM template To avoid file missing, please include all files into one folder and compress it into .zip or .rar format.
