verndewd
05-29-2007, 08:59 PM
Firstly ,let me point out that this is not meant to deter overclocking, As chips are designed for a specific lifespan which they will never see in the hands of enthusiasts. generally the cpu's have roughly 10 to 20 years of life as the rough estimate goes, and there is no rock solid math by wich to arrive accurately at a lifespan.
Toshiba has done some work in this field. This link is very important in understanding how overvoltage affects lifespan.
http://www.semicon.toshiba.co.jp/eng/shared/reliability_pdf/bde0128b_3.pdf
What this is intended to do is inform any new and old users of the inherent dangers and inform them on the topics of every danger so that running overclocks can be done with knowledge of risk and details on affects so you will know if an oc has damaged your cpu.And ultimately that is a guessing game until the chip is actually dead Unless you have an electron microscope laying around or some extremely expensive testing gear.
first we have a whitepaper study of various examples of types of electromigration.
http://www.tycoelectronics.com/documentation/whitepapers/pdf/p313-89.pdf
next we have Blacks equation which to our mathemeticians and scientists is of value. And a quote from the source of the topic.
http://www.siliconfareast.com/emig.htm
Another resource. This is likely the best lamens description there is on this post so far; So if you are new to overclocking and concerned about longevity This link will be your best friend to open the door way of understanding.
Enjoy.
Quote:
Electromigration
Electromigration refers to the gradual displacement of the metal atoms of a conductor as a result of the current flowing through that conductor. The process of electromigration is analogous to the movement of small pebbles in a stream from one point to another as a result of the water gushing through the pebbles.
Because of the mass transport of metal atoms from one point to another during electromigration, this mechanism leads to the formation of voids at some points in the metal line and hillocks or extrusions at other points. It can therefore result in either: 1) an open circuit if the void(s) formed in the metal line become big enough to sever it; or 2) a short circuit if the extrusions become long enough to serve as a bridge between the affected metal and another one adjacent to it.
Electromigration is actually not a function of current, but a function of current density. It is also accelerated by elevated temperature. Thus, electromigration is easily observed in Al metal lines that are subjected to high current densities at high temperature over time.
Blacks equation.
t50 = CJ-ne(Ea/kT)
where:
t50 = the median lifetime of the population of metal lines subjected to electromigration;
C = a constant based on metal line properties;
J = the current density;
n = integer constant from 1 to 7; many experts believe that n = 2;
T = temperature in deg K;
k = the Boltzmann constant; and
Ea = 0.5 - 0.7 eV for pure Al.
Die-related Failure Mechanisms and Attributes
Here is an interesting point of contact migration,I dont know how many folk have witnessed effects of contact migration, but it occurs in many forms outside of chips.
Contact Migration
Quote:
Contact migration refers to the diffusion of the metal atoms of a contact (usually Al or an alloy thereof) into the silicon substrate. This phenomenon is due to the natural occurrence of interdiffusion between two different interdiffusible materials in contact with each other, which are Al and Si in this case. This phenomenon of interdiffusion occurs in both ways, i.e., Al diffuses into Si and Si diffuses into Al. This is not current-related and must not be confused with electromigration, which is a different mechanism.
Dielectric Breakdown
Dielectric breakdown refers to the destruction of a dielectric layer, usually as a result of excessive potential difference or voltage across it. It is usually manifested as a short or leakage at the point of breakdown.
Quote:
and as we all know leakage means heat.
There are many types of dielectric in a typical die circuit, varying not only in purpose but in chemical composition as well. The most commonly used dielectric is SiO2, which is an oxide of silicon. The permanent breakdown of an oxide dielectric is also usually referred to as 'oxide rupture' or 'oxide breakdown.' The most common cause of dielectric breakdown in devices with no wafer fab problem is EOS/ESD, since this can expose the dielectric layer to high voltages.
Non-EOS/ESD-related dielectric breakdowns may be classified into either an early life dielectric breakdown (ELDB) or a time-dependent dielectric breakdown (TDDB), depending on when in the device lifetime it occurs. Early life dielectric breakdown, usually occurring within the device's first year of operation, is just a special case of early life failure (ELF) involving a dielectric layer. A dielectric breakdown is usually classified as a TDDB if the device has been in operation for at least two years already. These are just guidelines, because the point at which a dielectric breakdown occurs is not just related to time, but to other factors as well. ELDB and TDDB failures are usually caused by a defect in the dielectric layer, such as stray particles which decrease the effective thickness of the dielectric making it prone to breakdown.
Since SiO2 is a very common dielectric material, its breakdown mechanism has been understood over the years. SiO2 breakdown is believed to be due to charge injection, and may be broken down into 2 stages. During the first stage, current starts to flow through the oxide as a result of the voltage applied across it. High field/high current regions are then formed as charges are trapped in the oxide. Eventually, these abnormal regions reach stage 2, a critical point wherein the oxide heats up and allows a greater current flow. This results in an electrical and thermal runaway that quickly leads to the physical destruction of the oxide
http://www.xradia.com/Applications/cu_via.html
I found video simulations of damaged via on a chip Courtesy of IBM.
Heres a link from cambridge on the subject.
http://www.msm.cam.ac.uk/doitpoms/tlplib/electromigration/index.php
Toshibas reliability information link
http://www.semicon.toshiba.co.jp/eng/product/reliability/index.html
Tf = Ae(-BV)
where:
Tf = the time to failure;
A = a constant;
V = the voltage applied across the dielectric layer; and
B = a voltage acceleration constant that depends on the properties of the oxide.
I should have put all of this information in quotation and do not make any claims to actually have studied such information outside of finding these links. If you are going to Overclock you should know what the actual effects are.
Links gathered thus far.
http://www.semicon.toshiba.co.jp/eng/shared/reliability_pdf/bde0128b_3.pdf
http://www.tycoelectronics.com/documentation/whitepapers/pdf/p313-89.pdf
http://www.siliconfareast.com/emig.htm
http://www.xradia.com/Applications/cu_via.html
http://www.msm.cam.ac.uk/doitpoms/tlplib/electromigration/index.php
http://www.iupac.org/publications/pac/2004/pdf/7602x0443.pdf
http://en.wikipedia.org/wiki/BCS_theory
http://en.wikipedia.org/wiki/Phonon
http://en.wikipedia.org/wiki/Cooper_pair
http://dcmp.bc.edu/images/APS2007Rowell.pdf
http://hyperphysics.phy-astr.gsu.edu/hbase/solids/bcs.html
http://www.siliconfareast.com/manufacturing.HTM
http://www.fonerbooks.com/cpu_ram.htm
http://www.owlnet.rice.edu/~wakin/vlsi/testing/results.html
http://www.electronics-cooling.com/articles/2007/feb/techdata/
Thanks to jack...
http://www.ece.uwaterloo.ca/~cdr/pubs/vassighi.pdf
http://www.sigda.org/Archives/ProceedingArchives/Compendiums/papers/19...edt97/p
http://www.itcprogramdev.org/35th_anniv/pdfs/2000_2.pdf
thanks to cb62fcni
http://www.dailytech.com/Intel+Goes+LeadFree+for+45nm+Again/article7402.htm
Thanks to Toms
http://www.tomshardware.com/2007/01/18/overclocking-guide-part-1/
http://www.tomshardware.com/2006/12/11/overclocking-guide-part-1/index.html
http://www.tomshardware.com/2004/12/17/cpu_stress_test/index.html
http://forumz.tomshardware.com/hardware/Core-Duo-Temperature-Guide-fto...t221745
Toshiba has done some work in this field. This link is very important in understanding how overvoltage affects lifespan.
http://www.semicon.toshiba.co.jp/eng/shared/reliability_pdf/bde0128b_3.pdf
What this is intended to do is inform any new and old users of the inherent dangers and inform them on the topics of every danger so that running overclocks can be done with knowledge of risk and details on affects so you will know if an oc has damaged your cpu.And ultimately that is a guessing game until the chip is actually dead Unless you have an electron microscope laying around or some extremely expensive testing gear.
first we have a whitepaper study of various examples of types of electromigration.
http://www.tycoelectronics.com/documentation/whitepapers/pdf/p313-89.pdf
next we have Blacks equation which to our mathemeticians and scientists is of value. And a quote from the source of the topic.
http://www.siliconfareast.com/emig.htm
Another resource. This is likely the best lamens description there is on this post so far; So if you are new to overclocking and concerned about longevity This link will be your best friend to open the door way of understanding.
Enjoy.
Quote:
Electromigration
Electromigration refers to the gradual displacement of the metal atoms of a conductor as a result of the current flowing through that conductor. The process of electromigration is analogous to the movement of small pebbles in a stream from one point to another as a result of the water gushing through the pebbles.
Because of the mass transport of metal atoms from one point to another during electromigration, this mechanism leads to the formation of voids at some points in the metal line and hillocks or extrusions at other points. It can therefore result in either: 1) an open circuit if the void(s) formed in the metal line become big enough to sever it; or 2) a short circuit if the extrusions become long enough to serve as a bridge between the affected metal and another one adjacent to it.
Electromigration is actually not a function of current, but a function of current density. It is also accelerated by elevated temperature. Thus, electromigration is easily observed in Al metal lines that are subjected to high current densities at high temperature over time.
Blacks equation.
t50 = CJ-ne(Ea/kT)
where:
t50 = the median lifetime of the population of metal lines subjected to electromigration;
C = a constant based on metal line properties;
J = the current density;
n = integer constant from 1 to 7; many experts believe that n = 2;
T = temperature in deg K;
k = the Boltzmann constant; and
Ea = 0.5 - 0.7 eV for pure Al.
Die-related Failure Mechanisms and Attributes
Here is an interesting point of contact migration,I dont know how many folk have witnessed effects of contact migration, but it occurs in many forms outside of chips.
Contact Migration
Quote:
Contact migration refers to the diffusion of the metal atoms of a contact (usually Al or an alloy thereof) into the silicon substrate. This phenomenon is due to the natural occurrence of interdiffusion between two different interdiffusible materials in contact with each other, which are Al and Si in this case. This phenomenon of interdiffusion occurs in both ways, i.e., Al diffuses into Si and Si diffuses into Al. This is not current-related and must not be confused with electromigration, which is a different mechanism.
Dielectric Breakdown
Dielectric breakdown refers to the destruction of a dielectric layer, usually as a result of excessive potential difference or voltage across it. It is usually manifested as a short or leakage at the point of breakdown.
Quote:
and as we all know leakage means heat.
There are many types of dielectric in a typical die circuit, varying not only in purpose but in chemical composition as well. The most commonly used dielectric is SiO2, which is an oxide of silicon. The permanent breakdown of an oxide dielectric is also usually referred to as 'oxide rupture' or 'oxide breakdown.' The most common cause of dielectric breakdown in devices with no wafer fab problem is EOS/ESD, since this can expose the dielectric layer to high voltages.
Non-EOS/ESD-related dielectric breakdowns may be classified into either an early life dielectric breakdown (ELDB) or a time-dependent dielectric breakdown (TDDB), depending on when in the device lifetime it occurs. Early life dielectric breakdown, usually occurring within the device's first year of operation, is just a special case of early life failure (ELF) involving a dielectric layer. A dielectric breakdown is usually classified as a TDDB if the device has been in operation for at least two years already. These are just guidelines, because the point at which a dielectric breakdown occurs is not just related to time, but to other factors as well. ELDB and TDDB failures are usually caused by a defect in the dielectric layer, such as stray particles which decrease the effective thickness of the dielectric making it prone to breakdown.
Since SiO2 is a very common dielectric material, its breakdown mechanism has been understood over the years. SiO2 breakdown is believed to be due to charge injection, and may be broken down into 2 stages. During the first stage, current starts to flow through the oxide as a result of the voltage applied across it. High field/high current regions are then formed as charges are trapped in the oxide. Eventually, these abnormal regions reach stage 2, a critical point wherein the oxide heats up and allows a greater current flow. This results in an electrical and thermal runaway that quickly leads to the physical destruction of the oxide
http://www.xradia.com/Applications/cu_via.html
I found video simulations of damaged via on a chip Courtesy of IBM.
Heres a link from cambridge on the subject.
http://www.msm.cam.ac.uk/doitpoms/tlplib/electromigration/index.php
Toshibas reliability information link
http://www.semicon.toshiba.co.jp/eng/product/reliability/index.html
Tf = Ae(-BV)
where:
Tf = the time to failure;
A = a constant;
V = the voltage applied across the dielectric layer; and
B = a voltage acceleration constant that depends on the properties of the oxide.
I should have put all of this information in quotation and do not make any claims to actually have studied such information outside of finding these links. If you are going to Overclock you should know what the actual effects are.
Links gathered thus far.
http://www.semicon.toshiba.co.jp/eng/shared/reliability_pdf/bde0128b_3.pdf
http://www.tycoelectronics.com/documentation/whitepapers/pdf/p313-89.pdf
http://www.siliconfareast.com/emig.htm
http://www.xradia.com/Applications/cu_via.html
http://www.msm.cam.ac.uk/doitpoms/tlplib/electromigration/index.php
http://www.iupac.org/publications/pac/2004/pdf/7602x0443.pdf
http://en.wikipedia.org/wiki/BCS_theory
http://en.wikipedia.org/wiki/Phonon
http://en.wikipedia.org/wiki/Cooper_pair
http://dcmp.bc.edu/images/APS2007Rowell.pdf
http://hyperphysics.phy-astr.gsu.edu/hbase/solids/bcs.html
http://www.siliconfareast.com/manufacturing.HTM
http://www.fonerbooks.com/cpu_ram.htm
http://www.owlnet.rice.edu/~wakin/vlsi/testing/results.html
http://www.electronics-cooling.com/articles/2007/feb/techdata/
Thanks to jack...
http://www.ece.uwaterloo.ca/~cdr/pubs/vassighi.pdf
http://www.sigda.org/Archives/ProceedingArchives/Compendiums/papers/19...edt97/p
http://www.itcprogramdev.org/35th_anniv/pdfs/2000_2.pdf
thanks to cb62fcni
http://www.dailytech.com/Intel+Goes+LeadFree+for+45nm+Again/article7402.htm
Thanks to Toms
http://www.tomshardware.com/2007/01/18/overclocking-guide-part-1/
http://www.tomshardware.com/2006/12/11/overclocking-guide-part-1/index.html
http://www.tomshardware.com/2004/12/17/cpu_stress_test/index.html
http://forumz.tomshardware.com/hardware/Core-Duo-Temperature-Guide-fto...t221745