Learn why reliability standards for electronics are important in PCB design.
Find out what IPC standards are relevant for PCB designers.
Explore how to determine a design’s reliability requirements.
Designing with reliability standards for electronics in mind can prevent issues like this burnt PCB
Reliability issues can strike almost any mechanism or structure, including electronic systems that contain a PCB. Depending upon the system, the failure of a circuit board can result in a loss of time, money, or even life. Fortunately, you can reduce the probability of these failures with a good plan, design, manufacturing process, and effective stress testing. Let’s see how to create a design that will facilitate the development of PCBs that meet reliability standards for electronics.
Why Are Reliability Standards for Electronics Important?
PCB design is both an objective and subjective process. While there are basic rules that dictate how a product should be designed, hardware engineers are left to decide what constitutes best practices. This causes different interpretations that might lead to varying and inconsistent product quality. For example, engineers might ponder these questions when designing a PCB:
- What’s the optimal drilling aspect ratio that facilitates a smooth plating process?
- What is the permissible temperature increase for a single copper trace?
- How do you define the minimum spacing between conductors?
Left to subjective interpretations, PCB designers can not ensure that the outputs are consistently reliable. You might produce an electrically functional PCB but face potential assembly issues, such as component misalignment, or one that is optimized for fabrication but fails the EMC compliance test.
The first step in devising a good plan for PCB mechanical reliability is to qualify our objective, which is as follows:
Electronics reliability may be defined as the degree of certainty or probability that a circuit board will not suffer a structural, operational, or electrical failure over its expected lifetime.
It is important for PCB designers to be guided by specific reliability standards for electronics. The IPC standards serve as an excellent reference for developing reliable electronics products. These standards leave nothing to assumption or guesswork when designing a PCB.
IPC Standards for PCB Design
IPC Standards for PCB Design, Manufacturing and Testing
The IPC, formerly known as the Institute of Printed Circuits, is associated with thousands of electronics companies. The association is responsible for developing and publishing standards that manufacturers must meet. Today, electronics engineers and PCB manufacturers alike use IPC standards to ensure consistency, quality, and reliability across the PCB design chain.
While IPC standards encompass design, material, inspection, performance, and other aspects of PCB manufacturing, there are a few standards that relate to the work of a PCB designer. Here are just a few examples of some design standards that manufacturers must adhere to:
- IPC - 2221 - This is a generic IPC standard that serves as guidance for almost every area of PCB design. You’ll find specific guidelines for via size, thermal dissipation land patterns, transmission line geometries, component placement, and more in the IPC-2221.
- IPC - 2222 - This standard serves as a guideline for cross-sectional rigid PCB design. It offers guidelines for structural elements like hole aspect ratio, dielectric clearance, and board thickness.
- IPC - 2223 - This standard provides guidelines for flex PCB design, including structural considerations like bending radius, shield pattern, material selection, and impedance control.
Board Reliability Requirements
Now that we have qualified what PCB reliability is, we need to quantify it. This means that specific criteria must be established that we can use in the design and manufacturing process.
To do this, we must be able to answer the following questions:
What are the regulatory requirements for your board’s operation?
The minimum reliability requirements for your board are to meet all applicable regulatory standards. Therefore, you should be aware of how your IPC classification impacts the manufacturing of your design.
Will the board undergo vibration?
Suppose your board will be installed as part of an automotive, industrial, or aerospace system. In that case, it is likely to be subjected to vibration, which can have immediate adverse effects on the mechanical structure of your PCB. In such cases, shock testing is vital to ensure the PCB’s mechanical reliability.
- Will the board be in continuous or intermittent motion?
A single motion may not be felt immediately; however, continuous or intermittent movement may result in structural breakdown or failure.
- What is the temperature range of the environment where the board will be installed?
Another significant threat to PCB integrity is temperature variation or excessive heat or cold.
- What are the ranges of voltage and current present during normal operation?
Excessive voltages and currents can cause arcs and shorts that, if severe enough, damage the PCB and components.
- What is the operational lifecycle for the PCB?
No board is expected to last forever; however, it should be designed to operate reliably for its projected lifetime in its nominal environment.
Once these metrics are determined, they must be incorporated into your design to ensure PCB reliability.
Designing Boards to Meet Reliability Standards
Designing a board to ensure that it meets or exceeds reliability requirements and objectives extends into virtually every design stage. And, the ability to achieve the best design effectively and efficiently depends on what PCB design tool is used.
For example, a good PCB design tool allows you to set solder resist clearance as specified by IPC-2221 and generate the appropriate manufacturing files. You can also define clearance rules and run thermal analysis to identify potential hotspots that may compromise board reliability.
OrCAD PCB Editor is comprehensive and helps engineers meet industry reliability standards for electronics. This is but one of the capabilities that are standard as part of Cadence’s PCB Design and Analysis package. Additional advanced functionalities, such as real-time DFM checks, 3-D visual integration, and new product integration (NPI), make front-to-back design integration faster and simpler.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.