FMEA - Failure Modes and Effects Analysis

Failure Modes and Effects Analysis (FMEA)

Failure Modes and Effects Analysis, or FMEA, is a methodology for identifying the potential failure modes that a product or process may encounter, assessing the risks associated with these failure modes, prioritization of these failure modes according to their urgency, and prevention of the more urgent failure modes, i.e., the ones that are most likely to cause serious harm to the company.

The output of an FMEA cycle is the FMEA Table, which documents how vulnerable a product or process is to its potential failure modes. The FMEA table also shows the level of risk attached to each potential failure mode, and the corrective actions needed (or already completed) to make the product or process more robust. The FMEA Table generally consists of 16 to 17 columns, with each column corresponding to a piece of information required by FMEA.

The FMEA is a proactive analysis tool, allowing engineers to anticipate failure modes even before they happen, or even before a new product or process is released. It also helps the engineer to prevent the negative effects of these failure modes from reaching the customer, primarily by eliminating their causes and increasing the chances of detecting them before they can do any damage. The actions generated by a good FMEA cycle will also translate to better yield, quality, reliability, and of course, greater customer satisfaction.

There are many types of FMEA, but the most widely used are probably the following: 1) System FMEA, which is used for global systems; 2) Design or Product FMEA, which is used for components or subsystems; 3) Process FMEA, which is used for manufacturing and assembly processes; 4) Service FMEA, which is used for services; and 5) Software FMEA, which is used for software. In the semiconductor industry, the Design or Product FMEA and the Process FMEA are the most frequently-encountered FMEA versions.

Despite the existence of many types of FMEA today, the basic structure and process for executing them remains the same. Any FMEA process must include the following steps, information details of which are documented in the FMEA Table:

1) Assembly of the team;

2) Understanding of the Product or Process to be subjected to FMEA;

3) Breaking down of the product or process into its components or steps (components and steps are also known as items);

4) Identification and assessment of the following for every item listed: function(s), potential failure mode(s), failure mode effect(s), failure mode cause(s), and controls for detecting or preventing the failure mode(s);

5) Evaluation of the risks associated with the failures modes and prioritizing them according to importance;

6) Implementation of corrective actions to minimize the occurrence of the more significant failure modes;

7) Reassessment of the product or process by another cycle of FMEA after the actions have been completed; and

8) Regular updating of the FMEA Table.

Please refer to the FMEA Procedural Guide for more details on how FMEA is usually performed.

The most critical information on the FMEA Table is the Risk Priority Number (RPN), which is the numerical rating given to the level of risk associated with a failure mode, and therefore denotes the urgency of addressing that failure mode.

The RPN is actually the product of three (3) factors, namely, the severity of the effect of the failure mode (SEV), the probability of the occurrence of the cause of the failure mode (PF, for probability factor), and the effectiveness of the controls for detecting and preventing the failure mode (DET). Thus, RPN = SEV x PF x DET. The SEV, PF, and DET are also documented in the FMEA Table.

The FMEA Table is a living document, constantly changing from the time of its first release when the product or process is still being designed until its archiving after the product or process has been obsoleted.

Critical times or events that require an update to the FMEA Table include the following:

1) when a new product or process is being designed or introduced;

2) when a critical change in the operating conditions of the product or process occurs;

3) when the product or process itself undergoes a change;

4) when a new regulation that affects the product or process is instituted;

5) when customer complaints about the product or process are received; and

6) when an error in the FMEA Table is discovered or new information that affects its contents come to light.

Many published standards on FMEA procedures and reporting formats now exist. Among them are the SAE J1739, the AIAG FMEA-3, and the Mil-Std-1629A.

See also: FMEA Process Guide; Failure Analysis

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