Understanding IPC Class 2 vs. Class 3 classifications is crucial for ensuring the right level of reliability and performance in your electronic devices.
IPC Class 2 and Class 3 are two of the most commonly referred to standards for PCB (Printed Circuit Board) assembly and manufacturing.
In addition to establishing standards and offering training and certification programs for the electronics manufacturing industry, the IPC (Association Connecting Electronics Industries) is a global trade association.
This blog will explore the distinctions between IPC Class 2 and Class 3. We’ll be expounding on their significance and applications in PCB manufacturing, especially flexible and rigid-flex PCB manufacturing.
Overview of IPC Class 2 vs. Class 3
These respected standards are crucial in the flex PCB industry by providing guidelines and requirements for manufacturing processes, materials, and product quality. These standards ensure consistency, reliability, and performance in flex PCBs. This section will briefly explore the significance of IPC Class 2 vs. Class 3 standards and their impact on the industry.
This short video will introduce you to the topic:
Main Differences between Class 2 and Class 3 for Flex PBCs
These are—
Acceptable Defects
Class 2 allows for a higher number of acceptable defects than Class 3, which has stricter criteria for defect tolerance.
Reliability
Class 3 emphasizes higher reliability and extended lifespan, making it suitable for critical applications where failure is not an option.
Environmental Conditions
Class 3 requirements regarding harsh ecological conditions are more stringent, ensuring the PCB’s durability in challenging operating environments.
Manufacturing Processes
Class 3 often requires more rigorous manufacturing processes, such as tighter tolerances, advanced testing methods, and additional quality control measures.
End-Use Applications
Class 2 is commonly used in consumer electronics and applications with less stringent requirements, while Class 3 is prevalent in high-reliability sectors like aerospace, medical, and military applications.
Testing and Inspection
Class 3 mandates more extensive testing and inspection procedures, including cross-section analysis, to ensure compliance with rigorous quality standards.
You can make informed decisions for your flex PCB project if you understand the difference between IPC Class 2 vs. Class 3.
Main Requirements
What are the Distinct Requirements for IPC Class 2 Vs. Class 3 in Flex PBCs?
Here’s a clear and concise breakdown of the IPC standards applicable to Class 2 and Class 3 requirements in the flex PCB industry:
Class 2 Requirements
- IPC-6012: Qualification and Performance Specification for Rigid Printed Boards
- IPC-6013: Qualification and Performance Specification for Flexible Printed Boards
Class 3 Requirements
- IPC-6012: Qualification and Performance Specification for Rigid Printed Boards
- IPC-6013: Qualification and Performance Specification for Flexible Printed Boards
- IPC-6012 and IPC-6013 standards cover the requirements for both Class 2 and Class 3 applications. The distinction between Class 2 and Class 3 lies in the PCBs’ specific performance and reliability requirements rather than the different standards for IPC Class 2 vs. Class 3.
Now, let’s get into the main blog, where we expound on the differences individually.
Rules for Through-Hole Rules for Flex and Rigid-Flex PCBs: IPC Class 2 vs. Class 3
To elaborate—
Diameter requirements for holes
Plated Through Holes (PTH)
In Class 2 PCBs, the diameter of plated through holes typically ranges from 0.2 mm to 0.5 mm. This size ensures sufficient space for component leads or pins to pass through, maintaining a stable electrical connection.
With Class 3 PCBs, the diameter requirements for plated through holes are more stringent. They must adhere to tighter tolerances, typically ranging from 0.15 mm to 0.35 mm. These stricter specifications ensure higher reliability and performance in demanding applications.
Non-Plated Through Holes (NPTH)
For IPC Class 2: For mechanical support or positioning purposes in Class 2 PCBs, non-plated through holes have larger diameters ranging from 0.5 mm to 1.0 mm. This size allows for secure mounting and alignment of components.
IPC Class 3: Similarly, in Class 3 PCBs, non-plated through holes have similar diameter requirements, typically ranging from 0.5 mm to 1.0 mm. The focus on precision and reliability remains consistent across both IPC classes.
Tolerance considerations for hole size and position
Hole Tolerance
In IPC Class 2 PCBs, the hole diameter tolerance is typically around ±0.05 mm. This tight tolerance ensures the hole size remains within the specified range, allowing for precise component insertion and safe connections.
For Class 3 PCBs demand even stricter tolerances. The hole diameter tolerance in Class 3 PCBs is usually around ±0.025 mm, ensuring extremely precise hole sizes for high-reliability applications.
Hole Position
With IPC Class 2the hole position tolerance is typically around ±0.1 mm. This tolerance ensures the holes are aligned accurately with the circuit pattern, enabling proper component alignment during assembly.
IPC Class 3 PCBs maintain the same ±0.1 mm hole position tolerance, emphasizing precise alignment in critical applications requiring maximum performance and reliability.
Copper Plating
For Copper Plating Thickness and Quality Standards IPC Class 2 vs. Class 3
Copper Plating Thickness Specifics
In IPC Class 2, the copper plating thickness for through holes typically ranges between 25 µm and 35 µm. This thickness ensures sufficient conductivity and establishes reliable electrical connections between layers.
Meanwhile, Class 3 PCBs demand higher performance; the copper plating thickness is also stringent. In Class 3 PCBs, the copper plating thickness is usually between 30 µm and 50 µm, enhancing conductivity and reliability for critical applications.
Copper Plating Quality Standards
IPC Class 2: Class 2 PCBs stick to industry standards so that the plating meets specified criteria for thickness, adhesion, and uniformity. These quality IPC Class 2 vs. Class 3 help maintain proper conductivity and prevent voids or uneven plating issues.
Class 3 PCBs maintain the same plating quality standards as Class 2, emphasizing the need for exceptional plating quality to ensure reliable conductivity in high-performance and high-reliability applications.
Case illustration
To help you grasp the concepts, let’s use a hypothetical case. Imagine we’re designing a medical device requiring precise signal transmission and reliable connections. Our example emphasizes the significance of distinguishing between IPC Class 2 and Class 3 standards in your product’s design considerations.
Now, this device you’re designing has strict quality and reliability requirements. One critical component is an integrated circuit (IC) that needs to be securely attached to the flex PCB. Here’s why proper hole size, aspect ratio, and alignment are essential, considering the IPC Class 2 vs. Class 3 classification:
Sufficient Hole Size for Component Leads or Pins
For IPC Class 2 PCBs, selecting an appropriate hole size, typically ranging between 0.2 mm and 0.5 mm, ensures that the fine-pitch leads of the IC fit through the holes without any issues during assembly.
However, for IPC Class 3 PCBs, even tighter tolerances may be required due to higher performance demands.
The Right Aspect Ratios
Adhering to IPC Class 2 or 3 standards is critical for aspect ratio guidelines. High aspect ratios can lead to barrel cracking or plating problems, compromising the connection’s reliability.
Following the recommended guidelines helps maintain acceptable aspect ratios. It minimizes the risk of issues with stricter requirements for Class 3 PCBs.
Correct Hole Alignment
Precise alignment of the holes with the circuit pattern is crucial for Class 2 and Class 3 PCBs. Misaligned holes can result in poor electrical connections or misalignment with other components, impacting the device’s overall functionality and reliability.
We hope that the illustration helps. Now, let’s move on to other differences between IPC Class 2 vs. Class 3 for flex and rigid-flex circuits.
Dielectrics & Materials
Rules for Dielectric Rules and Material Considerations: IPC Class 2 vs. Class 3
Selecting the appropriate class will determine the specific characteristics needed for optimal performance. Let’s discuss the key factors and how they differ between these classes. We’ll continue using our medical device as an example for IPC Class 2 vs. Class 3 comparison:
Dielectric constant (Dk) IPC Class 2
In Class 2, flex PCBs for general-purpose electronic products allow for a wider range of dielectric materials, including standard FR-4 with varying Dk values.
When designing a medical device with a flex PCB for signal transmission, you can select dielectric materials with a Dk of, let’s say, 3.5 ± 0.1. This ensures proper maintenance of signal propagation and impedance across the circuit.
Dielectric constant (Dk) IPC Class 3
Class 3 flex PCBs for high-performance electronics require more stringent dielectric constant requirements.
In the case of a medical device used for monitoring purposes, precise impedance control is crucial. To ensure accurate and reliable signal transmission, you’ll need dielectric materials with a specific Dk, such as 3.5 ± 0.05.
Dissipation factor (Df) IPC Class 2
Class 2 allows for slightly higher dissipation factors, which may result in some signal loss. However, this meets the requirements for general-purpose electronic products.
Dissipation factor (Df) IPC Class 3
Class 3 demands lower dissipation to minimize signal degradation and ensure accurate measurements.
For a medical device focused on monitoring, where accurate and sensitive readings are vital, you would select flex PCB dielectric materials with low Df values, such as 0.02 or below.
Thermal properties IPC Class 2
Class 2 flex PCBs typically have more relaxed thermal requirements, allowing for a broader range of dielectric materials with moderate thermal properties.
For our medical device example, the flex PCB would require dielectric materials with good thermal conductivity and moderate thermal expansion coefficients to ensure stable performance without extensive thermal demands.
Thermal properties IPC Class 3
Class 3 flex PCBs demand dielectric materials with excellent thermal properties to withstand varying temperatures and maintain reliable performance.
It is essential to choose materials with superior thermal conductivity and low thermal expansion coefficients when constructing a high-performance medical equipment. This ensures effective heat dissipation, preventing adverse effects on the device’s performance.
Annular Rings
Rules for Annular Rings: IPC Class 2 vs. Class 3
Annular rings refer to the copper ring around a drilled hole on a PCB. They are crucial for establishing electrical connections and providing mechanical support. Different classes of PCBs have specific requirements for annular rings in IPC Class 2 vs. Class 3.
Minimum requirement IPC Class 2
For Class 2 PCBs, which are commonly used in general-purpose electronic products, the minimum annular ring requirement is typically larger compared to Class 3 PCBs. This provides a margin of safety and ensures reliable connections.
Minimum requirement IPC Class 3
In Class 3 PCBs designed for high-performance applications, such as aeronautic or healthcare devices, more stringent requirements for annular rings are necessary. The minimum annular ring size is smaller, allowing for higher-density designs and more precise connections.
Rules for Annular Rings: IPC Class 2 vs. Class 3
Trace widths determine the width of the conductive paths on a PCB, carrying electrical signals between components. Choosing the appropriate trace width is crucial to prevent signal degradation and ensure proper functionality.
IPC Class 2: Class 2 PCBs generally allow wider trace widths than Class 3 PCBs. This provides flexibility and allows for higher currents or lower manufacturing costs in general-purpose electronic products.
IPC Class 3: Class 3 PCBs demand narrower trace widths for higher density and precision. This ensures precise signal transmission, especially in high-frequency applications or when dealing with high-speed signals.
Rules for Clearances IPC Class 2 vs. Class 3
Proper clearance between annular rings and adjacent traces prevents signal crosstalk, reducing the risk of noise and interference. Clearances also contain short circuits or unintended electrical connections between neighboring components.
To illustrate, let’s consider our medical monitoring device again. If we use IPC 3, the clearances would be more tightly controlled than those using IPC 2.
For example, the recommended clearance between annular rings and adjacent traces in IPC Class 3 will be as low as 0.15 mm (6 mil).
Using IPC Class 2 standards with a larger clearance, e.g., 0.25 mm (10 mil), between annular rings and adjacent traces is problematic. The larger clearance in IPC Class 2 allows for more tolerance and potentially looser spacing between the annular rings and traces.
While this may not pose significant issues in general-purpose electronic products, it can have implications in more demanding applications like our example medical monitoring device.
Drill Breakout & Pad Measurements
Rules for Drill Breakout and Pad Size
Specifically, these are—
Drill Breakout
This refers to the distance between the drilled hole and the edge of the pad. Adhering to specific IPC 2 and 3 guidelines, you can prevent breakout-related issues and maintain reliable connections.
IPC Class 2: Adhering to specific IPC Class 2 guidelines for drill breakout is essential to prevent breakout-related issues and maintain reliable connections.
IPC Class 3: Similar to Class 2, IPC Class 3 sets more stringent requirements for drill breakout to ensure robust connections in high-performance applications.
Breakout Distance
IPC Class 2: For Class 2, aim for a minimum breakout distance of at least 0.25 mm (10 mil) to prevent potential electrical and mechanical issues.
IPC Class 3: In Class 3, the breakout distance requirements are more demanding and typically stricter than the Class 2 standards.
Breakout-related Issues
IPC Class 2 and Class 3: Insufficient breakout distance can lead to problems such as pad lifting, pad cracking, or poor solderability. These issues can result in unreliable connections, signal degradation, or complete circuit failure. By following the recommended breakout distance, you assure optimum performance of your PCB.
Pad Size
The size of the pads on your PCB is crucial for effective soldering and component attachment. This applies to both IPC Class 2 and Class 3.
Through-Hole Components: For through-hole components, typical pad sizes range from 1.5 mm to 2.5 mm (60 mil to 100 mil) in diameter, allowing for a good solder fillet and reliable joint formation.
Surface-Mount Components: The pad sizes for surface-mount components vary based on the component size and lead configuration. Generally, pad sizes ranging from 0.5 mm to 1.5 mm (20 mil to 60 mil) in diameter are commonly used.
Testing and Inspection
Testing and Inspection Guidelines
The last major difference in IPC Class 2 vs. Class 3 lies in testing and inspection guidelines.
Here’s a breakdown of the main differences:
Acceptance Criteria
IPC Class 3 has stricter acceptance criteria compared to IPC Class 2. Class 3 requirements typically demand higher reliability, performance, and quality levels. This means that the acceptance criteria for electrical testing, visual inspection, or solderability testing are more stringent for Class 3.
Test Frequency
The testing and inspection frequency may differ between IPC Class 2 vs. Class 3. Class 3 flex PCBs often require more extensive testing and inspection procedures due to their higher reliability demands.
Environmental Testing
Class 3 flex PCBs typically undergo more comprehensive and challenging environmental tests to ensure their suitability for demanding applications.
Documentation and Traceability
IPC Class 3 requires detailed record-keeping of manufacturing processes, materials used, test results, and any modifications or revisions made during production. The goal is to provide a complete history and traceability of the Class 3 flex PCBs for quality control.
MV Circuits is Your Best Bet
End Notes of Today’s Blog
Congratulations! You now understand the critical factors in flex PCB manufacturing, from design considerations to material selection and adherence to IPC standards.
Today, we explored the advantages of Laser Direct Imaging (LDI) over traditional photolithography and how it specifically benefits flex and rigid-flex PCBs.
We also discussed important considerations such as dielectric rules, annular rings, trace widths, drill breakouts, pad sizes, and clearances. By following these guidelines and IPC Class 2 vs. Class 3, you can ensure your flex PCBs’ reliability, performance, and signal integrity.
Now, when it comes to turning your design into reality, you need a reputable manufacturer specializing in flex PCBs and competent in utilizing advanced technologies like Laser Direct Imaging (LDI). That’s where MV Flex Circuits comes in.
MV Circuit: World-Class Producer of IPC Class & IPC Class 3 Flex Circuit Boards
Our company is based in Shenzhen. It’s a city known as the silicon valley of China, where we clearly differentiate IPC Class 2 vs. Class 3 standards in production.
MV Flex Circuit is dedicated to delivering high-quality flex and rigid-flex PCBs using cutting-edge techniques and stringent quality control measures. With our commitment to your success, we always use innovative solutions for flex PCBs.
If you require any help with your flex circuit boards, please get in touch with us. We’re here to help!
