IPC-A-600 is a standard set-out by the Institute of Printed Circuits (IPC). It is meant to spell-out the different requirements for making a Printed Circuit Board (PCB) acceptable or ideal for usage.
IPC-A-600 houses a total of 3 classes, which are the categories of the guidelines for different kinds of circuit boards. In this article, you will find out what these standards are and the different applicable cases.
What is the IPC 600 Standard?
It is the set of guidelines meant to be followed when manufacturing Printed Circuit Boards (PCBs). The Institute of Printed Circuits (IPC) intended these guidelines to serve the following purposes:
- Different Levels of Acceptance: the IPC600 standard sets-out the different levels of classes of maintaining the reliability of circuit boards.
- Observation: the standard also sets-out the internal and external observations of the admissibility and non-negotiations of the circuit boards.
- The Benchmark: at the core of how the IPC-A-600 works is the setting up of benchmarks or minimum standards. These, in turn, serve as the minimum criteria expected of PCB manufacturers when making the boards.
How to Avoid “PCB Imperfections” with the IPC-A-600 Standard
The primary goal of these guidelines is to reduce the chances of having an “imperfect” PCB – a circuit board that doesn’t satisfy the basic requirements.
By using the guidelines spelt out in the IPC-A-600 standard, it is possible to avoid both the internal and external imperfections.
Here is a breakdown of the observable conditions:
Internally Observable Conditions
These refer to the “imperfections” or design-related flaws that can be found inside the PCB. It is common to have these flaws projected as either blisters or voids.
A microscopic evaluation of the specimen is often used to determine the internal observable conditions in the circuit board.
Externally Observable Conditions
These are the imperfections that you could notice on the PCB’s surface.
Note: whether the circuit board suffers the internal or external observable conditions – it is always advised to evaluate the extent of the imperfections. That way, a logical approach can be used to address the issue.
Introducing the IPC-A-600 Classes
The classifications of the IPC-A-600 guidelines are due to the following reasons:
- These classes are used to differentiate the quality of one circuit board from another.
- The differences in the circuit boards’ quality are based on the requirements and quality of the electronic device the PCB is meant for.
With that being said, let us dive into the different categories of the IPC-A-600 standards.
1. Class 1
This category is dedicated to the General Electronic Products. It is meant for the typical everyday electronic products we use. Worthy of mention is that the IPC-A-600 Class 1 is used for the electronics with a limited product life.
Here are additional pieces of information on what the class covers:
- This class covers the electronic products that have both a limited product life and which use inexpensive circuit boards.
- Examples of these electronic products are kids’ toys and Light-Emitting Diodes (LEDs).
- Certain defects can be allowed. For example, the Class 1 PCBs might allow for defects that don’t negatively affect the board’s performance.
2. Class 2 IPC-A-600 Boards
The dedicated service electronic products fall under the IPC-A-600 Class 2. Unlike the Class 1 boards, they have higher product life and are more reliable.
Communication gadgets, laptops, tablets and smartphones are examples of the Class 2 PCBs.
Here are some of the additional details of what the IPC-A-600 Class 2 standard covers:
- Supports Cosmetic Imperfections: despite the higher reliability, this class also makes room for some superficial shortcomings in the electronic products.
- These electronic products are not exposed to extreme environmental conditions.
- The supported appliances require a mix of longer shelf life and higher performance.
- Uninterrupted service of the products is required, but it is not a critical factor.
3. Class 3 PCBs
This IPC-A-600 Class is used to describe the Printed Circuit Boards (PCBs) designed for use with electronic products requiring optimum performance.
Due to the maximum expectations of the IPC-A-600 Class 3 PCBs, it is not a surprise that circuit board manufactures are expected to follow stringent standards.
Here are some of the facts worth noting about this standard:
- The circuit boards are required to keep performing at the optimum paces, even when in use in harsh environments.
- The Class covers the PCBs designed for use in technical and high-risk pieces of equipment. Examples of the use cases are electronic monitoring systems, life support systems, military equipment and automotive devices.
- Class 3 PCBs are also subjected to a lot of testing and inspection processes.
Class 3 PCB Extension
Due to the peculiarities of the applications, the Class 3 PCBs are subject to further compliances. These boards are also required to follow the laid-down guidelines in the IPC-6012E document.
Here are some of the specifications of the IPC-6012ES document:
- Certain changes can be made to the PCB’s acceptance testing. Examples of such changes are variations to the testing frequency, the criteria for deeming the PCB “accepted” and the size of the sample.
- The document also specifies the specifications for the Class 3 PCBs meant for use in the military avionics and space industries.
- The document also specifies the guidelines for the PCB to withstand the following: thermal cycling, vibration and ground testing.
The second addendum is in the IPC-6012EM document. It specifies the following:
- It creates a set of stringent guidelines for devices or applications meant for use in the healthcare industry.
- These additional measures are particularly for the rigid circuit boards for the medical industry.
IPC-A-600 Class 2 vs Class 3
These two classes are the most important, because of the applications. While the Class 2 PCBs are becoming the main standards; the Class 3 circuits also have a place in the market.
Here is a comparison of the two:
Manufacturing Considerations
How these boards are produced makes them different. The differences here are almost based on the costs, drilling pattern and the dielectric requirements.
While the Class 2 PCBs can accept certain defects, such as a 90-degree breakage out of the hole; the constraints for the Class 3 circuits are higher. For the Class 3 PCBs, it is expected that the entire process is error-free.
In terms of the costs of production, the Class 2 PCBs are affordable. They are advantaged due to the mass production, which saves time and money. On the other hand, the Class 3 boards are not always massively-produced, and the use of the THT process also increases the costs by up to 20%.
The Class 2 and Class 3 PCBs also differ by the dielectrics whereby the latter uses 3.5 mils and the former uses the same. However, the difference in the dielectrics can be when the users decide to go above the minimum dielectric requirements.
Differences in the Inspection Methods
There are also noticeable differences in the methods of inspecting and testing the performances of these boards.
For the Class 3 boards, the inspection process is usually tedious and could lead to additional costs. The following testing and inspecting methods apply:
- Vibration testing
- Environmental stress testing and;
- Thermal cycling
To ensure that the boards are fully-tested, microscopes are commonly used for the inspection. The engineer watches out for internal defects in the PCB during the tests.
On the other hand, the Class 2 PCBs require less processes and are cost-effective when compared to the Class 3 PCBs.
The engineer checks for the board’s compliance with the basic performance requirements. The inspector also checks the board’s surface for physical defects, such as broken electronic components and cracks on the board’s surface.
Class 2 and Class 3 PCBs Differ by Design Rules
Design rules refer to the guidelines for manufacturing circuit boards, as per the initial designs. As to be expected, the design rules and specifications are more lenient for the Class 3 circuit boards than for the Class 3.
While Class 2 boards’ design rules focus on the via, plating and other desired functional specifications, that of Class 3 boards focus on:
- Circuit board component placements and;
- The layout designs.
Differences in Assembly Processes
Another IPC-A-600 Class 2 vs Class 3 difference is in the processes of assembling the circuit boards. Although they both use the Surface-Mount Technology (SMT) process, their difference lies in the methods of placing the Surface Mount Devices (SMDs)/components.
Here are some of the key points:
- A slight placement of the electronic components off the pad can be tolerated on Class 2 boards, but cannot be accepted for the Class 3 boards.
- A good reason why a visual defect on the Class 2 PCB is not always considered is because it doesn’t impact the board’s electrical and mechanical performance. The reversal is the case with the Class 3 boards, where the visual defects tend to trigger the board’s failure during inspection.
Conclusion
Both the IPC-A-600 Class 2 and Class 3 standards help you to stick to the guidelines for producing and ensuring the reliability of circuit boards. Your favorite circuit board manufacturer will help you understand the differences between the two so you would make informed decisions on which is ideal for your electronic products.
