我们是做消费类电子产品的，最近客户要求我们计算一个新产品（我们只是生产PCBA和外壳，光纤部分由客户组装）的MTBF，如下：

Product FITS value
Worst case junction temperature of 150 Celsius we have:
1 - 10 years: 18.24 FITS
11 -20 years: 9.12 FITS

Fiberxon Transceiver
534.81 40 Celsius

十分迷惑，不知道这些信息是用来做什么的。我们以往计算MTBF（BQR的软件），都是只要测量出产品的最高温度做MTBF计算时的环境温度，按照MIL217计算，要求要达到45000hrs.

FIT: failure in Time
FITS is a more intuitive way of representing MTBF. FITS is nothing but the total number of failures of the module in a billion hours (i.e. 1000,000,000 hours).


Failure Rate, MTBF, and FITs

For this discussion, we will assume that the resulting failure rate is shown in failures per million hours. This is simply the number of failures that you would expect to have in a million hours of operation of your equipment. Failure rates for many basic devices are well below 1 failure per million hours, so these values may seem insignificant. But if you have hundreds of parts in your design and have a thousand systems operating in the field, you can see that the failure rates will quickly add up. MTBF, or Mean Time Between Failures, is the inverse of the failure rate and is the average time between failures. It is calculated from the failure rate as follows:

MTBF = 1,000,000/Failure Rate

You can choose the units in which the failure rate is shown. Another common unit used, besides failures/million hours, is failures per billion hours which is also known as FITs (Failures In Time).

Component failure rates are commonly expressed in FITS (Failures In Time).A FIT is one failure in one billion device-hours.

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