MPXM2102AS datasheet(14/670 Pages) MOTOROLA

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Motorola Sensor Device Data

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The temperature acceleration factor for a particular failure

mechanism can be related by taking the ratio for the reaction

rate of the two different stress levels as expressed by the

Arrhenius type of equation. The mathematical derivation of

the first order chemical reaction rate computes to:

(RT)HS + tHS

(RT)LS

tLS

+ exp Ea

TLS

* 1

THS

Where:

Acceleration Factor

Reaction Rate

time

temperature [

°K]

activation energy of expressed

in electron-volts [eV]

Boltzman’s constant, 8.6171 x 10-5 eV/

°K

Low stress or nominal temperature

High stress or test temperature

The activation energy is dependent on the failure mecha-

nism and typically varies from 0.3 to 1.8 electron-volts. The

activation energy is directly proportional to the degree of

influence that temperature has on the chemical reaction rate.

A listing of typical activation energies is included in reference

[6] and [7].

An example using the Arrenhius equation will be demon-

strated. A 32 device HTB test for 500 hours total and no

failure was performed. The 125

°C, 100% rated voltage test

resulted in no failures. If a customer ’s actual usage

conditions was 55

°C at full rated voltage, an estimate of the

lower one side confidence limit can be calculated. An

assumption is made that the failure rate is constant thus

implying the exponential distribution. The first step is to

calculate the equivalent device hours for the customer’s use

conditions by solving for the acceleration factor.

From the acceleration factor above, if eA is assumed equal

to 1,

+ exp Ea

TLS

* 1

THS

Where:

0.7eV/

°K (assumed)

TLS

=55

°C + 273.16 = 328.16°K

THS

125

°C + 273.16 = 398.16°K

then;

77.64

Therefore, the equivalent cumulative device hours at the

customer’s use condition is:

tLS

AF x tHS = (32

500) 77.64

tLS

1,242,172 device hours

Computing the lower one sided failure rate with a 90% confi-

dence level and no failures:

l +

x2 (

a, d.f.)

1.853E–06 failures per hour

1,853 FITs

The inverse of the failure,

λ, or the Mean Time To Failure

(MTTF) is:

MTTF

+ 1l

MTTF = 540,000 device hours

CONCLUSION

Reliability testing durations and acceptance numbers are

used as a baseline for achieving adequate performance in

the actual use condition that the silicon pressure sensor

might encounter. The baseline for reliability testing can be

related to the current record high jump bar height. Just as

athletes in time achieve a higher level of performance by

improvements in their level of physical and mental fitness,

silicon pressure sensors must also incorporate improve-

ments in the design, materials, and manufacturability to

achieve the reliability growth demands the future market

place will require. This philosophy of never ending improve-

ment will promote consistent conformance to the customer’s

expectation and production of a best in class product.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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