7.2.1 Purpose of Reliability Option

The Reliability option identifies the dominant failure mechanisms affecting a package and, through the Attributes command in its Utilities option, enables you to adjust package or environmental parameters in response to the results of failure analysis. In Mission Profile, you loaded environment and stress condition files. Now use the Reliability option to select the failure mechanisms that apply to the package subjected to those environments or stress conditions, measure the package response to the failure mechanisms, and alter package or environment parameters to correct failures.

CADMP-II uses physics-of-failure models to assess package reliability in terms of mean time-to-failure for each package element. The failure mechanisms are ranked in order of increasing time-to-failure. The time-to-failure estimate is the deterministic time estimate for the worst case situation.  

7.2.2 The Reliability Option Screen

• In the CADMP Manager, select the Reliability option from the Analyze menu. A message that the device information is being processed appears.

After material temperature dependencies are evaluated, a window may appear with material warnings. These are due to: use of a material above a temperature (e.g., use of a solder or wire material above its melting point); use of a material above a temperature at which it undergoes a second -order phase transformation which radically alters the values for its material properties; use of a failure mechanism model in a temperature range in which it has not been validated.

When you invoke the Reliability Analysis CADMP-II analyzes the failure models in relation to the package being designed and identifies those that are irrelevant or cannot be used on the package. The eliminated models appear in blue in the Failure Mechanisms list described in Section 7.2.2.2, The Select Command.

Figure 24. The Reliability Option screen  
• The Reliability screen in Figure 24 appears. It contains five options.

• Environment enables you to select the active environment from those in the current Mission Profile.
• Select enables you to select failure models.
• Analyze performs failure model calculations.
• Display enables you to view calculation results.
• Utilities enable you to print reports and adjust parameters

Use this menu option to choose the environment or stress condition, from the current Mission Profile, that you wish to use in the analysis. (See Figure 25) To select an environment or stress simply highlight it and press Enter. Your selection will appear in the upper right of the screen. Mission Profile enables user to analyze the effect of the combination of environments on the package and provides the user with a value for the number of mission cycles the package can endure for each failure mechanism.

7.2.2.2 The Select Option

• Select the Select option. The window in Figure 26 appears.
Figure 26. The list of failure mechanisms  
• Select the failure model category you want to use. If you want to use all the models nested within the category, press Enter. A checkmark appears next to the category entry.

You may want to use only certain models contained in the category. Select the Model hot key to view the individual models nested within each category (see Figure 27). Tag the models in this Models window that you want to use. A check mark appears next to the models. Select the Tag/Untag All hot key to tag or untag all models at once. After you Close the Models window, a check mark appears next to the appropriate failure model category in the first window.

You may not select a failure model colored in blue because they are either not applicable to the package, or attributes required to solve the model have not been assigned a value.

Figure 27. Tagging failure models  
• Close the window when you finish selecting failure models. You return to the Reliability option screen.

Select the Analyze option header in the Reliability option screen. A window appears asking you to wait while the models are evaluated. A second window replaces it and informs you of the actions CADMP-II takes while performing the calculations (see Figure 28). Press Esc to abort the calculations.

Note: You may see a message in the model selection window indicating that results may be inaccurate for this model. This is due to material temperature constraint violation as discussed below.

7.2.2.4 The Display Option

The Display option contains four commands:

Summary enables you to view the results of the failure model calculations.

• Complete enables you to view a complete record of the calculations.
• Error Log enables you to view errors that occurred during the calculations.
• Screen Log records the analysis performed during
• the failure models screening operation.

Select the Summary option in the Display menu. If you have chosen a single environment in section 7.2.2.1, the window in Figure 29 appears. Scroll up and down and from side to side the view the information in it.

• The window has four hot keys in addition to Close. Select Unit Convert at the upper right corner to toggle the time-to-failure measurement unit between hours, thousands of hours, or years.
• Select Log at the lower left corner to view comments about the results connected with a highlighted failure mechanism. The comment for a "Pass" or a "Failure" result informs you which element(s) were evaluated. The comment for an "Error" or an "Undefined" result informs you CADMP-II was unable to evaluate the failure model.
• Press F1 to receive an Analysis Summary for the highlighted model. This contains a listing of the exact function value calculated for each die, see Figure 30. This is useful when the package has more than one die because only the worst case value is displayed in the Reliability Summary.