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FMEA is a systematic analysis of potential failure modes aimed at preventing failures. This is intended to be a preventative action process carried out before implementing new or changes in products or processes. An effective FMEA identifies corrective actions required to prevent failures from reaching the customer and to assure the highest possible yield, quality and reliability.
In semiconductor device design and manufacturing, it is common to perform different types of FMEA. These can be divided into two primary categories: product related and process related. These are often called Design FMEA and Process FMEA and they are often further subdivided to focus on specific areas of product or process development. The main purpose of an FMEA is: To identify possible failure modes that could occur in the design or manufacturing of a product.
- To identify corrective actions that could reduce or eliminate the potential for failures to occur.
- To provide documentation of the process.
- To quantify the risk level associated with each potential failure mode.
An FMEA is a two-phase process. First the potential failure modes and corrective actions are identified. Then after the corrective actions are implemented, the product or process is re-evaluated to determine if the result is acceptable. This is best accomplished with a cross-functional team with members from all affected work groups (e.g. Marketing, Engineering, Manufacturing, Test, QRA, etc.)
Benefits of FMEA
An FMEA provides benefits to both the manufacturer and the customer. Some of these benefits include:
- Assists in determining the best possible design and development options to provide high reliability and manufacturability potential.
- Assists in considering the possible failure modes and their effect on the reliability and manufacturability of the product.
- Provides a well-documented record of improvements from corrective actions implemented.
- Provides information useful in developing test programs and in-line monitoring criteria.
- Provides historical information useful in analyzing potential product failures during the manufacturing process.
- Provide new ideas for improvements in similar designs or processes.
Documenting an FMEA
This preventative action process provides a methodical approach to study the cause and effect of potential failures. The form below (Fig. 1) is used to document the process.
| Product or Process: |
FMEA Type: |
FMEA Date: |
| FMEA Team Members: |
|
Rev __ / Rev Date: |
| Process/Product Description or Purpose |
Potential Failure Modes |
Potential Effect(s) of Failure |
S
E
V
|
C
L
A
S
S
|
Potential Causes/
Mechanisms
Of Failures |
O
C
C |
Current
Design/
Process
Control
Prevention
Detection |
D
E
T
|
R
P
N |
Recommended
Actions |
Who
When |
Actions
Taken |
S
E
V |
O
C
C |
D
E
T |
R
P
N |
Fig. 1: Typical FMEA Form
The Process/Product Description or Purpose should be clearly defined. This may be broken down into sub-processes with each being considered separately. Potential Failure Modes lists the different ways the process might fail to meet the process requirements or design intent. The Potential Effect(s) of Failure is how the customer perceives the failure. The "customer" includes subsequent design or manufacturing operations and/or the end customer. Each of the Failure Modes and Effects is assigned a Severity (SEV) value and Classification (CLASS). How a failure could occur should be described in terms of something that can be corrected or controlled and listed under Potential Causes/Mechanisms of Failures. The probability that a given cause or mechanism that might occur is assigned a numeric value in OCC. Current Design/Process Control Prevention/Detection describes any controls that can prevent or detect each of the failure mechanisms. The probability that each control will effectively detect the failure is assigned a numeric value in DET.
The Risk Priority Number (RPN) is the product of Severity, Occurrence and Detection. These are assessed and engineering judgment is used to determine if the risk is acceptable. Recommended Actions are developed to reduce the RPN with priority given to the highest RPN values and customer defined specific characteristics. Once the actions are implemented, the Severity, Occurrence and Detection values are reassessed, and a new RPN is calculated. This process continues until the risk level is acceptable.
An FMEA is a living document that should be reviewed and updated periodically. Any change in design, process or use of the product should be updated in the FMEA.
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