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TL432B-Q1: TL432B-Q1 FIT Estimation Tool Question

Wei-Hao Chen (TW-FAE)
Expert 3260 points

Part Number: TL432B-Q1

Hi Support Team,

My customer is using the FIT estimation tool find the FIT rate for TL432BQDBZRQ1, and they had few questions.

1. Why is the confidence level only 60%? can we provide the confidence level 90% data?

2. What does usage temperature mean? The explanation says the estimated usage temperature, does this mean the ambient temperature for the IC in normal use or the junction temperature?

3. Does the test temperature mean the ambient or junction temperature of IC?

Thank you very much.

Best Regards,

Wei-Hao

  • 0
    TI__Mastermind 19580 points

    Hi Wei-Hao,

    I have answered the questions below.

    Q1. Why is the confidence level only 60%? can we provide the confidence level 90% data?

    A1. TI typically reports 60% confidence because it is the industry standard. There is an equation to calculate the FIT rate at 90% is this app note.

    The FIT rate for TL432BQ 90% confidence, 0.7eV, stress temp of 125C and junction temperature of 55C is 1.39

    Q2. What does usage temperature mean? The explanation says the estimated usage temperature, does this mean the ambient temperature for the IC in normal use or the junction temperature?

    A2. The FIT rate test is performed at high temperatures to accelerate testing time. Due to this, you need to derate the temperature from 125C to the junction temperature in the application. The higher the junction temperature the higher the FIT rate.

    Q3. Does the test temperature mean the ambient or junction temperature of IC?

    A3. Test temperature means the temperature that was used in the HTOL test. Typically these devices are in a high temperature oven to estimate over life time conditions. The testing methods are in JESD85 so it is an industry standard.

    -Marcoo

  • 0 in reply to Marcoo Z
    Prodigy 60 points
    Hello Marcoo

    I have one question.

    Is Equation 2 of the app note correct? And what does X mean in the Equation 2?

    Therefore, I don't know how to use example in app note to calculate the λ.CL with equation 2.

    Thank you

    -Ted
  • 0 in reply to Ted Hsu
    TI__Mastermind 19580 points

    Hi Ted,

    Equation 2 can be a bit confusing. I have re written it below.

    FIT rate = (Chi^2 Distribution, 2f+2 where f = failures, for X confidence level) * 1E9 / (2 * testing hours * sample size * Acceleration Factor )

    The Chi^2 Distribution can be found on a table such as the one below. For TL431, 1 failure at 60% confidence = 4.04. 1 failure at 90% confidence = 7.78.

    The other number that is missing would the AF. AF can be calculated in many ways but a table such as the one below is the easiest way. With a test temp of 125C to 55C with a eV of 0.7 the value is 77.6.

    Testing hours, sample size, and failures can be found in the quality table you provided in the initial post. I used the values above and calculated the 90% confidence level in my first reply. Depending on how much we round, there can be a slight difference in final value but they should be roughly equal.

    I hope this is helpful in clearing up your questions.

    -Marcoo