Effective Process Failure Mode and Effects Analysis of PCBA Development

May 6, 2020

Cadence PCB Solutions

Key Takeaways

How PFMEA can be used for PCBA development.
Common PCBA development risks.
How to make PFMEA most effective for PCBA development.

PCB assembly process equipment

It has been said and reiterated that “fear is only in our minds, but it is taking over all the time.” Probably even more famous is a response to this sentiment put forth by US President Franklin D. Roosevelt, when he stated: “The only thing we have to fear is fear itself.” Although, most would agree that these are indeed truisms; nevertheless, fear can be quite incapacitating. However for some, fear, especially of failure, can have the opposite effect. And serve as a catalyst to push for better results.

Embracing the fact that failure is a real possibility and using this to devise ways to avoid failing is at the heart of failure mode and effects analysis (FMEA) for PCBAs. Although FMEA can be utilized to the advantage of various procedures, supply chain reliability for PCBAs as an example, it is most commonly used to analyze and improve a manufacturing or production process. Thus, let’s see how process failure mode and effects analysis can be applied most effectively to PCBA development; including the fabrication and assembly manufacturing stages.

What is Process Failure Mode and Effects Analysis for PCBA Development?

Failure mode and effects analysis is a well-known well-structured procedure-based method of evaluating a design or process. For design FMEA or DFMEA, which originated in the aerospace industry as a means to prevent failures for which root cause analysis (RCA) proved inadequate, the objective is to identify risks and devise actions that could be taken to reduce the probability of failures occurring for the system being designed. This method is typically applied to new designs or previous designs that are undergoing modification(s).

Similarly, process failure mode and effects analysis (PFMEA), is an algorithm that seeks to avoid failure events that may halt a process or reduce the quality of the results. Any such event constitutes a risk and PFMEA is performed to identify, classify and mitigate risks. The steps that comprise a PFMEA are as follows:

Process Failure Mode and Effects Analysis Steps

Step 1: Perform a process review

The purpose here is to partition the process into smaller sections or units.

Step 2: Identify the failure modes for each unit

Any and all of the ways that the units can fail should be listed.

NOTE: Units may have multiple failure modes.

Step 3: For each failure mode, attach an effect

The effect is the impact on the overall process, subsequent units or the product being made. These may be quantitative or qualitative; however,nqualitative may be more useful.

Step 4: Rank the failure modes severity

Establish a severity scale based upon defined criteria (e.g. employee injury may be the highest and equipment reset required may be the lowest). The rankings should be quantitative (numbers will make scaling and comparisons easier).

Step 5: Rank the failure modes occurrence

Assign a severity ranking to each failure mode.

Step 6: Rank the failure modes probably of detection

This is the probability of detection prior to occurrence and should also be quantitative.

Step 7: Calculate risk probability numbers (RPNs)

Calculate an RPN (severity X occurrence X detection) for each failure mode. It may be a good idea to create a risk analysis matrix, especiallynfor complex processes.

Step 8: Develop a risk analysis plan

This is determining what action should be taken for each failure mode, if necessary, and by whom.

Step 9: Implement the risk analysis plan

Apply the advice, recommendations and/or guidelines of the plan to your Process.

Step 10: Reassessment

Recalculate the RPNs and evaluate the effectiveness of the devised plan.

It may be necessary to repeat steps 8-10 until RPNs meet defined acceptability levels individually or an overall criterion is reached.

To develop a PFMEA for your PCBA development you should include all aspects of board design, fabrication, assembly and subassembly that pose a risk to the overall process or the quality of your boards. Some of the more common risks are presented below.

What Are The Most Common Risks to My PCBA Development Process?

Designing and building circuit boards in most cases is a complicated process. It is possible for the entire process to span weeks, months or even years and involve several companies and many professionals. Obviously, developing PCBAs includes many risks and comprehensive PFMEA can be quite challenging.

Nevertheless, this type of analysis is necessary to ensure that your boards meet design objectives, are manufacturable and most of all function reliably in the field over their entire lifecycle. Additionally, it is important to you as the developer that these goals are met as efficiently as possible. Therefore, it is very important that you are aware of the most common risks to the development process, some of which are listed below.

COMMON RISKS FOR PCBA DEVELOPMENT
Design	Fabrication	Assembly
Selected component(s) unavailable	Trace width violations	Solder bridge(s)
Unconnected nets in your layout	Copper weight violations	Unclear reference indicators
Missing drill holes	Solder mask clearance violations	Component to component clearance violations
Wrong material chosen	Minimum spacing violations	Board edge clearance violations

Although the list above is not exhaustive, it does include risks that will interrupt the development process and should; therefore, be included in the PFMEA. Failure to do so may result in minor failures that may cost you time and frustration and more serious ones that may show up in the field, as shown below, and necessitate recalls, replacements or redesigns and the associated costs.

Premature board failure due to water exposure

How To Make PFMEA Most Effective for PCBA Development

The establishment and utilization of process failure mode and effects analysis for your PCBA development can be beneficial in a number of ways. For example, a detailed evaluation of your process can lead to designs optimized for sustainable manufacturing and/or that deliver the best ROI based on your design-to-cost vs design-to-value intent.

PCBA design with Realtime DFM

However, your PFMEA needs to be as effective as possible in discovering risks during the process where they can be mitigated. To meet this requirement you need the best design tools and capabilities, one of which is the ability to perform realtime DFM analysis during design as shown in the figure above. Advanced PCB Design and Analysis functionality such as this is a standard of Cadence’s Allegro suite of design tools.

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.