最坏分析其实就是极端值分析

好处很多拉，其实一句话，就是让你知道怎么样才会出问题。

Assure acceptable operation throughout the entire product life cycle under the most unfavorable combination of anticipated conditions
Define Critical Components and Spec. Control Drawing (SCD) Limits
Provide Acceptance Test Procedure (ATP) Limits
Define Need for and Range of Select-At-Test (SAT) components
Improve Reliability through Parts Stress and Derating analysis
Identify design concerns which during test, alignment, and use could result in circuit damage or premature degradation.

WCCA helps ensure increased product reliability. We accomplish this through rigorous mathematical and simulation-based models along with hardware correlation. Correlated models are then used to determine part stress margins, and EOL/BOL product operating specifications. A single over-stressed component can cost your company millions of dollars. A thorough Worst Case Analysis can eliminate this from happening.

Background & Definition

A Worst Case Circuit Analysis is a quantitative assessment of the equipment performance, accounting for manufacturing, environmental and aging effects. In addition to a circuit analysis, a WCCA often includes stress and derating analysis, Failure Modes and Effects Criticality (FMECA) and Reliability Prediction (MTBF).

The specific objective is to verify that the design is robust enough to provide operation which meets the system performance specification over design life under worst case conditions and tolerances (initial, aging, radiation, temperature, etc.).

一般我们做的比较多的就是stress和derating，这个最直观也最明显了。
The Stress and Derating Analysis is intended to increase reliability by providing sufficient margin compared to the allowable stress limits. This reduces overstress conditions that may induce failure, and reduces the rate of stress-induced parameter change over life. It determines the maximum applied stress to each component in the system.

Methodology

• A WCCA follows this general form:
• Generate/Obtain circuit model
• Obtain Correlation to validate model
  
• Determine sensitivity to each component parameter
  
• Determine component tolerances
  
• Calculate the variance of each component parameter as sensitivity times absolute tolerance
  
• Use at least two methods of analysis (eg. hand analysis and SPICE or Saber, SPICE and measured data) to assure the result
  
• Generate a formal report to convey the information produced

自己列公式+Pspice+测试数据，选两个对照一下罗

The design is broken down into the appropriate functional sections. A mathematical model of the circuit is developed and the effects of various part/system tolerances (see below) are applied. The circuit's EVA and RSS results are determined for Beginning-of-Life and End-of-Life states.

Two methods of analysis and/or hardware correlation are always used to confirm results.

These results are used to calculate part stresses and are applied to other analyses. In order for the WCCA to be useful throughout the product’s life cycle, it is extremely important that the analysis be documented in a clear and concise format. This will allow for future updates and review by other than the original designer. A compliance matrix is generated that clearly identifies the results and all issues.

Factors Addressed During WCCA

Analog Circuit Analysis
Some of the factors to be considered during analysis include:

Component Tolerances