HTOL Burn-In FIT and Acceleration Factor Calculator
HTOL, or high temperature operating life, is the standard way to estimate how fast a chip wears out in the field. This calculator converts stress hours into equivalent field hours and gives an upper-bound FIT rate for a test with zero failures.
Your numbers
Common default 0.7 eV for general silicon failure mechanisms; use the value for your mechanism.
Junction temperature in the field, not ambient.
Junction temperature during the HTOL.
Total across all lots, for example 77 per lot over 3 lots.
Your results
This is the zero-failure case using the chi-square relationship for a Poisson failure count, in the style of JESD85. If any failures occur, the upper bound is larger and must use the chi-square quantile for the observed failure count. Arrhenius assumes a single temperature-driven mechanism and a chosen activation energy, so treat results as an estimate.
Acceleration factor vs stress temperature
Sweeps Stress junction temperature from 85 to 150, holding your other inputs fixed.
Tie reliability data to lot genealogy
Optional: discuss linking qualification results to lots and parts in your ERP.
Optional. The tool and every export work without this. No spam.
How to use the calculator
Enter the activation energy, the use junction temperature and the stress junction temperature. Then enter the total devices across all lots and the stress duration. Choose a confidence level; 60 percent is common in semiconductor qualification reporting, and 90 percent is more conservative. The tool computes the Arrhenius acceleration factor, total device-hours, equivalent field device-hours and the upper-bound FIT. The chart shows how sensitive acceleration is to stress temperature, which is useful when choosing test conditions or checking that a chamber setpoint was reached.
- Use junction temperature, not chamber temperature
- Add devices across all lots
- State the confidence level in your report
- Check the activation energy for your mechanism
The formulas
The Arrhenius acceleration factor is AF = exp((Ea / k) * (1/Tuse - 1/Tstress)), with temperatures in kelvin and Boltzmann's constant k equal to 8.617e-5 eV per kelvin. Equivalent device-hours equal devices times stress hours times AF. With zero failures, the upper confidence bound on the failure rate is lambda = chi-square(2, C) / (2 times equivalent device-hours), and chi-square with two degrees of freedom at confidence C equals minus two times the natural log of one minus C. FIT is lambda times one billion hours.
Worked example
With Ea of 0.7 eV, use junction temperature of 55 C and stress at 125 C, the acceleration factor is roughly 78. A test of 231 devices for 1,000 hours gives 231,000 device-hours at stress, or about 18 million equivalent field device-hours. At 60 percent confidence with zero failures the upper bound FIT is about 51, which is the figure that would appear on a reliability report. Increase sample size or duration to lower the bound, or accept a higher bound. Doubling both devices and hours roughly quarters it.
Common mistakes
The largest error is using ambient or chamber temperature rather than junction temperature, which includes self-heating from power dissipation and can be many degrees higher. Another is applying one activation energy to every mechanism; oxide wear-out, electromigration and ionic contamination behave differently, and a high stress temperature can also activate mechanisms that do not exist in the field. Never claim a FIT without stating the confidence level, activation energy and temperatures. Combining lots that failed with those that passed requires the failure-count form of the formula.
Frequently Asked Questions
What does FIT mean?
FIT stands for failures in time, defined as one failure per billion device-hours. A FIT of 50 means about 50 failures expected per billion device-hours of operation under the stated use conditions.
Why use 60 percent confidence?
Many semiconductor suppliers report reliability at 60 percent confidence by long-standing convention, while some customers ask for 90 percent. The choice should be stated clearly, since higher confidence gives a larger upper-bound FIT.
What activation energy should I use?
Use the value for the failure mechanism you are accelerating. General use of 0.7 eV is common for silicon, but gate oxide, electromigration and corrosion mechanisms have different values. Your qualification standard or customer may specify one.
How does this change if there are failures?
The formula replaces the zero-failure chi-square value with the chi-square quantile at two times the failure count plus two degrees of freedom. The result is a higher upper-bound FIT, so use a statistics reference or spreadsheet function for that case.
If reliability results need to be tied to lot genealogy and parts data in your ERP, Netray can help build that connection privately.
Related Tools
Wire Bond Pull and Shear Test Report Template
A bond pull and ball shear test report for wire bond process monitoring, with sample table, failure mode codes and approval lines.
Compliance & ContractsSemiconductor Process Change Notification (PCN) Template
A customer-facing PCN document covering the change description, reason, qualification plan, affected part numbers and timeline.
Quality & InspectionWafer Probe Bin Yield Log Worksheet
An editable wafer sort log that totals bin counts per wafer and calculates probe yield and loss percentages, ready for Excel.
Quality & InspectionSemiconductor Lot Hold and Release Form Template
A fill-in lot hold and release record for wafer fabs and assembly and test houses, covering hold reason, affected wafers, disposition and sign-off.
More Quality & Inspection tools
See all- Fab SPC Xbar-R Chart Worksheet
- Wafer Sort Test Yield Pareto Worksheet
- Wafer Excursion OCAP Response Template
- Semiconductor OCAP Out-of-Control Action Plan Template
- OSAT Supplier Qualification Assessment
- SAP QM Process Capability Cp Cpk Calculator
- SAP QM Lot Rejection Rate, PPM and Sigma Level Calculator
- SAP QM Gauge R&R Study Calculator
- SAP QM Cp and Cpk Capability Calculator