Temperature Rise Calculation Window
When the 217Plus or PRISM model is selected, multiple temperature rise calculations are supported for calculating the failure rates for some parts such as integrated circuits, semiconductors, and resistors. In the Prediction Data pane for these parts, clicking Temperature Rise opens the Temperature Rise Calculation window.
For Junction Temp Calculation Method, you select the method for calculating the junction temperature for the part from those methods supported for the part. Each method requires the entry of one or more values. Additional information about these methods appears in Junction Temperature Calculation Methods.
• The P variable in a method equation indicates the need for a power dissipation value.
• The X in a Theta-X value indicates the location where thermal resistance is measured.
For integrated circuits, a Theta-JA thermal resistance value is entered to account for the temperature at the assembly.
For semiconductors, a Theta-EJ, Theta-JA, or Theta-JC is entered to account for the temperature at the junction, assembly, or case.
For resistors, a Theta-EA or Theta-EC is entered to account for the temperature at the assembly or case.
If you do not make a method selection and/or enter required parameter values, the built-in default values are used to calculate junction temperature. To view the values, you click Defaults on the right side of the Temperature Rise Calculation window. This button works in the same way as the one in the Prediction Data pane. Clicking Defaults shows and hides the built-in default values that are used for fields that have been left blank (#.#).
Based on the parameter values entered, Computed Junction Temperature shows the junction temperature calculated. This display-only parameter appears at the bottom of the Temperature Rise Calculation window.
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The Prediction Data pane may also show Junction Temp Override and/or Case Temp Override for the part. If values are entered for one or both of these parameters, these override temperature rise values for failure rate calculations are used in place of the calculated value shown for Computed Junction Temperature in the Temperature Rise Calculation window.
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