What is failure mode and effects analysis (FMEA)?
How to build an effective FMEA process.
How and why to apply FMEA to PCBA design and manufacturing.
How FMEA implementation minimizes the probability of PCBA failure.
Quantifying failure mode and effects analysis
As a former gym rat, one of my favorite motivational sayings is “no pain, no gain.” It is indisputable that if you want to gain more strength and endurance you must endure the pain of hitting the weights and doing cardio training. Closely related to this saying is “no risk, no reward.” The lesson here is that the size of the harvest you reap is proportional to the amount of seed you are willing to sacrifice. Certainly, there are times when taking a great risk can be justified; however, there are also situations where the objective should be to minimize risk to the lowest level possible.
PCBA development and production are situations where mitigating risk is a primary concern. When designing circuit boards, the first concern is, of course, that the board functions as intended. However, achieving that goal is all but irrelevant if the PCBA is not reliable enough for its intended lifecycle. This includes operational consistency, as well as mechanical reliability. Whether your company employs a dedicated reliability engineer(s) or not, contributing to optimal manufacturing process flow must also be a design priority to effectively minimize the risk of premature board failure.
The process of taking an idea and transforming it into a functioning, reliable PCBA is a complex endeavor consisting of several key stages. The major stages are design, manufacturing, and testing. Although these stages are performed separately, they are interdependent. And the best circuit board development and production occur when this integration is maximized. For development, this requires that your board design incorporates your contract manufacturer’s (CM) DFM rules and guidelines. Typically, PCBA production is guided by balancing cost versus value and yield rate, or the ratio of usable boards to the number built. To optimize reliability, a means of risk management, such as an effective and quantifiable failure mode and effects analysis (FMEA) strategy, must be instituted.
Let’s define failure mode and effects analysis and see how its effective usage can help us achieve the most reliable PCBAs.
What is Failure Mode and Effects Analysis?
Reliability, in most connotations, is one of those words that is hard to accurately describe, yet everyone knows what it means. Unfortunately, this more abstract interpretation is insufficient in the realm of PCBA development. When speaking of circuit board reliability, a more consistently applicable description is required. Failure mode and effects analysis provides a means of doing this by establishing quantifiable metrics that can be used to ascertain not only how often, but also the root cause of board failures.
Virtually all aspects of PCB design present options that must be weighed to minimize the possibility of board failure once deployed. For example, risk-benefit analysis should be employed to determine the best placement of your components. Managing risk is at the heart of FMEA, which can be defined as follows:
FMEA can be applied to a single process, multiple processes, or the operation of a complex system. In either case, there are commonalities to ensure the algorithm is effective, as discussed below.
What is Effective FMEA?
The FMEA algorithm
As stated above, the goal of FMEA is to quantify reliability. This is aptly illustrated by the FMEA algorithm shown in the figure above and summarized below.
FMEA Algorithm Steps:
The team includes all personnel that impact the process.
List Failure Modes and Effects
All types of failures and their causes should be listed.
All failure modes should be ranked according to the severity of their effect on the process.
List Potential Causes
All potential causes for the failure modes should be listed.
The likelihood of a failure mode being caused by a specific cause should be ranked against other potential causes.
List Process Controls
For each failure mode, a control or mitigation action should be listed, which often depends upon its severity and/or cause.
Probability of detection should be assigned a rank. This value will likely continue to change as failures occur.
The Risk Priority Number (RPN) is calculated by multiplying the severity by the occurrence by the detection. RPN = (S x O x R).
Take Action on High Priority RPNs
High RPNs typically have controls that require an action to interfere with or stop the process. In the event of a failure mode that requires it, these controls must be instituted.
RPNs should be recalculated any time there is a significant occurrence.
At almost every stage it is necessary to define a parameter for the FMEA algorithm. This is one of its greatest strengths, and its effectiveness lies in the accuracy of the definitions, many of which are numbers.
FMEA was originally developed in the aerospace industry to improve root-cause-analysis (RCA), which is still a popular method of trying to figure out the cause of a failure after it happens. FMEA, on the other hand, is intended to prevent failures by predicting how often and to what severity they will occur. Moreover, there is no particular process size that limits its application, as demonstrated by the many ways FMEA may be applied to PCBA development. Some of these applications include FMEA risk assessment, supply chain FMEA, and PCBA development process FMEA, each of which is discussed in the next section.
Applying FMEA to PCBA Design and Manufacturing
In the sections below, examples of how FMEA can be applied to individual stages of the PCBA development process are summarized. Prior to delving into these, let’s discuss an invaluable tool for instituting this algorithm—the FMEA chart.
The FMEA Chart
FMEA chart example
In the figure above, an example of a chart used to analyze risks is shown. Sometimes referred to as a risk analysis matrix, this chart is used to list failure modes, causes and controls, and to rank their occurrence, severity, and detection. Additionally, it also shows the RPN for each event. This FMEA chart is a dynamic instrument to illustrate the current state of risk, or conversely, the reliability of the process under evaluation.
This blog instructs when and how to use an FMEA chart for electronics design.
FMEA of Component Selection
The PCBA development process consists of dozens of individual tasks and decisions that could potentially lead to board failure. Achieving a well-built, high quality, and reliable board begins with the design stage. And the most critical step of design is the selection of components. Components failing to meet their performance objectives of functionality and longevity will ultimately result in premature PCBA failure. Therefore, an FMEA risk assessment of component selection is one of the best uses for this risk analysis and prevention algorithm.
Here is greater detail about FMEA risk assessment for component selection.
Extending FMEA to the PCB Supply Chain
As mentioned above, component selection is a critical design task in preventing PCBA failure. However, even the best selection procedures can still allow inferior or counterfeit components to slip through the cracks. Therefore, it is also important to incorporate supply chain FMEA, which consists of the following essential steps:
PCBA Supply Chain FMEA Steps
Step #1: Identify risk types
Step #2: Identify potential risks
Step #3: Rate each risk
Step #4: Quantify each risk
Step #5: Analyze risks
Step #6: Develop controls
Step #7: Apply control and reassess
Employing the above steps adds robustness to your risk management of components and FMEA regimen.
Here is more information on using FMEA to secure the supply chain.
FMEA of the PCBA Development Process
The first applications of FMEA were almost exclusively manufacturing processes. Therefore, it is only fitting that FMEA can be applied to the entire PCBA development process, which is primarily an iterative cycle consisting of board design, manufacture and testing. In fact, utilizing the development or prototyping stage to reduce the potential of risk occurrence has many benefits including cost-effectiveness as it is done pre-production.
This details more information about PFMEA.
Using FMEA for Lean Manufacturing
Not only can FMEA be used for PCBA development or pre-production, but it can be used for production as well. During production, FMEA is implemented as a real-time analysis method as it utilizes actual board failures in the field to refine the manufacturing process and improve reliability. One implementation that can significantly improve board yield rates and reduce costs is FMEA lean manufacturing.
This blog details how to realize the advantages of FMEA lean manufacturing for your PCBA production.
How to Achieve PCBA Reliability Through Comprehensive FMEA
Should FMEA be used for all PCBA or electronics design projects? You can certainly make a convincing case that for all but the simplest and smallest of projects, making an investment into optimizing the reliability of your boards is worthwhile. Practically, investments into your board design, development, and production processes must be guided by considerations such as manufacturing overhead and production volume variance, as they greatly impact your overall cost and PCBA reliability. For reasonably-sized low volume, and certainly for high-volume projects, the use of effective FMEA is usually justifiable. However, as with all methodologies and technologies, the benefit of their usage is directly correlated with the functionality and capabilities of the tools used to implement them.
Risk management with Allegro Pulse
The flagship PCB Design and Analysis program from Cadence, Allegro, which includes Pulse, is shown in the figure above. Its robust risk-analysis features can help make efficient improvements in optimizing your PCBA reliability to ultimately save you time and money. Pulse is just one of the multiple advanced Library, Design Data, and Process Management tools that can aid you in implementing a comprehensive FMEA strategy.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.
About the AuthorFollow on Linkedin Visit Website More Content by Cadence PCB Solutions