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Reliability Physics and Engineering
Design engineers are continually asked reliability questions such as: (1) how long is your newly designed device/product expected to last and (2) how can you make costeffective design changes to improve the reliability robustness of the device? Often the designer will attempt to answer these questions by stating a safety factor v which was used for a design:
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1.
An IC designer worried about electromigration decides to increase the metal width of an aluminumalloy conductor by 20 %. Assuming J
_{crit} is negligibly small, how much of an increase in lifetime can the designer expect?
2.
If the conductor in Problem 1 is copper, how much lifetime improvement can be expected with an increase in conductor width by 20 %?
3.
If the temperature of the Alalloy conductor in Problem 1 could be reduced from 105 to 95 °C by using a heat sink, how much longer would the conductor be expected to last?
4.
If the temperature of the copper conductor in Problem 2 could be reduced from 105 to 95 °C by using a heat sink, how much longer would the conductor be expected to last?
5.
A 45 Å gate oxide MOSFET operates in inversion with a gate voltage of 2.7 V. How much would the TDDB lifetime increase if gate voltage is reduced to 2.5 V?
6.
If the transistor described in Problem 5 is a pchannel MOSFET, how much would the NBTI lifetime increase if the gate voltage is reduced from 2.7 to 2.5 V?
7.
If the transistor described in Problem 5 is a nchannel MOSFET, how much would the HCI lifetime increase if the device operating voltage is reduced from 2.7 to 2.5 V?
8.
Assuming that a rotor’s arm is made of a strong metal and that the operational stress in the rotor’s arm is much greater than the materials yield point, what is the expected increase in creep lifetime if the length of the rotor’s arm
r is reduced by 20 %?
9.
Assuming that a thinwalled spherical storage vessel is made of a strong metal and that the operational stress is much greater than the materials yield point, what is the expected increase in creep lifetime if the thickness of the wall is increased by 30 %?
10.
Assuming that a leaf spring is made of a strong metal and that the operational stress is much greater than the materials yield point, what is the expected increase in creep lifetime if the thickness of the spring is increased by 30 %?
11.
Assuming that a nut and bolt type clamp is made of a strong metal and that the operational stress in the shaft of the bolt is much greater than the materials yield point, what is the expected increase in stressrelaxation lifetime if the radius of shaft is increased by 30 %?
12.
Assuming that a thinwalled spherical storage vessel is made of a strong metal and that the operational stress is much greater than the materials yield point, what is the expected increase in fatigue lifetime if the allowed pressure range is decreased by 20 %?
13.
Assuming that the elastic range is negligibly small and that a fatigue exponent of
n = 4 can be used for a plastic molded integrated circuit, what is the expected increase in IC thermalcycling lifetime if the operational thermal range is decreased by 20 %?
1
2
3
A REF = 2 means that the improved design should last 2 times longer than the original design, a REF = 3 means the improved design should last 3 times longer than the original design, etc.
Recall that the stresslevel
σ
_{design} must be greater than the yieldstrength
σ
_{yield} for creep to occur.
The value of
n
_{creep} = 5 is used so often in creep analysis that it is generally referred to as the literature as the
five
power
law for creep behavior.
 Titel
 Increasing the Reliability of Device/Product Designs
 DOI
 https://doi.org/10.1007/9783319936833_16
 Autor:

J. W. McPherson
 Sequenznummer
 16
 Kapitelnummer
 Chapter 16