# HTOL Burn-In FIT and Acceleration Factor Calculator > Source: https://netray.co/tools/htol-burn-in-fit-and-acceleration-factor-calculator > Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems. > Section: Free Tools ## Short answer Compute the Arrhenius acceleration factor, equivalent field hours and the upper-bound FIT rate for a zero-failure high temperature operating life test. ## Category quality ## Industry Semiconductors ## Audience - Reliability engineer - Product engineer - Qualification engineer ## Tool **Kind:** calculator **Inputs:** #### Activation energy **Key:** ea **Type:** number **Default:** 0.7 **Min:** 0.1 **Max:** 1.5 **Step:** 0.05 **Unit:** eV **Help:** Common default 0.7 eV for general silicon failure mechanisms; use the value for your mechanism. #### Use junction temperature **Key:** t_use **Type:** number **Default:** 55 **Min:** -40 **Max:** 150 **Step:** 1 **Unit:** C **Help:** Junction temperature in the field, not ambient. #### Stress junction temperature **Key:** t_stress **Type:** number **Default:** 125 **Min:** 50 **Max:** 200 **Step:** 1 **Unit:** C **Help:** Junction temperature during the HTOL. #### Devices on test **Key:** n_dev **Type:** number **Default:** 231 **Min:** 1 **Step:** 1 **Unit:** devices **Help:** Total across all lots, for example 77 per lot over 3 lots. #### Stress duration **Key:** hours **Type:** number **Default:** 1000 **Min:** 1 **Step:** 24 **Unit:** hours #### Confidence level **Key:** conf **Type:** select **Default:** 0.6 **Options:** ##### 60% **Value:** 0.6 ##### 90% **Value:** 0.9 ##### 95% **Value:** 0.95 **Outputs:** #### Arrhenius acceleration factor **Key:** af **Expr:** exp(ea / 0.00008617333 * (1 / (t_use + 273.15) - 1 / (t_stress + 273.15))) **Format:** decimal #### Total device-hours at stress **Key:** dev_hours **Expr:** n_dev * hours **Format:** integer #### Equivalent field device-hours **Key:** equiv_hours **Expr:** dev_hours * af **Format:** integer #### Equivalent years per device **Key:** equiv_years **Expr:** hours * af / 8760 **Format:** years **Description:** Stress hours converted to field hours for one device. #### Upper-bound FIT (zero failures) **Key:** fit **Expr:** 0 - ln(1 - conf) / equiv_hours * 1000000000 **Format:** decimal **Primary:** true **Description:** Failures per billion device-hours at the chosen confidence, assuming zero failures observed. #### Equivalent MTTF at that FIT **Key:** mttf_years **Expr:** 1000000000 / fit / 8760 **Format:** years **Chart:** #### Acceleration factor vs stress temperature **Type:** line **X:** t_stress **From:** 85 **To:** 150 **Steps:** 27 **Series:** - af **Disclaimer:** 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. ## Content **Intro:** 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. **Sections:** #### How to use the calculator **Body:** 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. **Bullets:** - 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 **Body:** 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 **Body:** 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 **Body:** 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. **Cta:** If reliability results need to be tied to lot genealogy and parts data in your ERP, Netray can help build that connection privately. **Faq:** #### What does FIT mean? **Answer:** 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? **Answer:** 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? **Answer:** 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? **Answer:** 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. ## Search terms HTOL calculator, burn-in FIT rate calculator, Arrhenius acceleration factor calculator, JESD85 FIT calculation, high temperature operating life test calculator, zero failure FIT estimate, semiconductor reliability calculator, device hours acceleration --- Talk to an engineer: https://netray.co/contact?intent=erp_ai | Machine catalog: https://netray.co/agent/catalog.json