Disclaimer: The following experiment can merely guess the short/midterm voltage induced degradation and

**only** the voltage induced degradation of 14 nm Intel CPUs at room temperature with air cooling. It does

**not** reflect the combined degradation mechanism resulting from electromigration and temperature induced effects.

I'd refrain from dialing in 1.55 V as you'll most likely have to add another 10 mV or so to keep your super tight overclock stable within two weeks. Let me explain the experiment I've been doing for the past weeks before bothering you with numbers and details. I was about to start a dedicated thread to it but when I saw this one on the first page I thought that's the perfect place and timing.

So I had a few dud 7700Ks lying around which I decided to sacrifice for the sake of science

I was really curious about the rate of degradation in new generation CPUs at crazy high voltages. One by one, I tested them to determine the amount of time (under constant high core voltage) it takes to see a noticeable change (which is 5 mV or 0.005 V) in the Vcore one needs to apply to stabilise a mediocre, rather low voltage overclock. My procedure follows as such:

First, I determined a very tight overclock and two corresponding core voltages namely Vcore_max_unstable and Vcore_min_stable. As the names suggest, there happens to be a rather sharp transition point in Vcore, below which I can repeatedly prove the overclock is unstable and above which it can repeatedly pass the stability test (that is the Vcore_min_stable) when using V-Ray benchmark which is a miraculously effective tool to roughly check the stability in a very quick fashion. Since the chips were dud and I intended to isolate the influence of other factors like current and temperature on degradation, I've set the fixed overclock speed for my experiment to 4.6 GHz. Here are the initial voltages for the following CPUs:

CPU1 (batch L709C966):

Vcore_max_unstable = 1.195 V

Vcore_min_stable = 1.200 V

CPU2 (batch L710C662):

Vcore_max_unstable = 1.175 V

Vcore_min_stable = 1.180 V

CPU3 (batch L709C966):

Vcore_max_unstable = 1.190 V

Vcore_min_stable = 1.195 V

Now it's time to apply those crazy voltages. Degrading new generation Intel chips wasn't really a distant concept to me as I'd already played with and completely degraded (complete degradation would mean the required minimum voltage gets shifted so much that it fails to boot even at its stock speed on a fresh motherboard) numerous CPUs before like several G4400s, many i3s and some i5 6400s so I already knew what to expect and that anything between 1.75-1.85 V could bring sudden death. That's why I limited myself to 1.7 V. But first I started with 1.55 V. I dialed it in, got to the Win10 desktop and simply waited. I didn't run any intentional tasks but only some background Windows processes were running. I just interrupted the experiment every 12 hours to check the stability at those low voltages I mentioned above. At first I thought it would take weeks to see any change in my stable min. Vcore but then I was surprised to witness that all 3 chips were unstable at the initially stable voltages after 36 hours. Here are the results of the 1.55 V experiment:

CPU1: new Vcore_min_stable = 1.205 V after 24 hours

CPU2: new Vcore_min_stable = 1.185 V after 36 hours

CPU3: new Vcore_min_stable = 1.200 V after 24 hours

Next up was 1.6 V. I checked the stability every 4 hours during the experiment which yielded:

CPU1: new Vcore_min_stable = 1.210 V after 8 hours

CPU2: new Vcore_min_stable = 1.190 V after 12 hours

CPU3: new Vcore_min_stable = 1.205 V after 12 hours

Then I went on to 1.65 V and checked the stability every half an hour

CPU1: new Vcore_min_stable = 1.215 V after 1 hour

CPU2: new Vcore_min_stable = 1.195 V after 1.5 hours

CPU3: new Vcore_min_stable = 1.210 V after 1 hour

Finally 1.7 V. I guess I didn't check the stability frequent enough but the outcome was still obvious

CPU1: new Vcore_min_stable = 1.220 V after 15 mins

CPU2: new Vcore_min_stable = 1.200 V after 30 mins

CPU3: new Vcore_min_stable = 1.215 V after 15 mins

Well, can we deduce anything from all that? I guess so. Just like the mean time to failure rates of silicon chips vs. temperature follow the Arrhenius curve (failure time decreases exponentially with increasing temperature), the degradation rate vs. core voltage could also be an exponential function as the activation energy for voltage induced degradation/breakdown depends on the electric field strength in the transistor. As a matter of fact, even those very roughly determined degradation rates in my experiment follow a very clear exponential trajectory as you can see below.

So I took the liberty to extrapolate it further into the lower voltages to predict the time it would take for the required min. stable Vcore to degrade by 5 mV. Of course I'm not suggesting that at 1.45 V your CPU will degrade by 5 mV after 1000 hours since there must be significant amount of uncertainty margin in this tiny experiment but at least it gives some abstract picture. Assuming the uncertainty is less than 10x I can pretty much say that you're sure to lose a very tight overclock after a year or so (10000 hours) if you set a 24/7 fixed Vcore of 1.45 but then again, it's only 0.005 Volts. Then if I assume that the amount of voltage shift degradation has also an exponential behaviour, I can predict another trajectory namely the 50 mV degradation curve. What this curve shows at 1.5 V is particularly interesting to me as it would suggest the stable Vcore to shift by 50 mV after about 20000 hours which is 2.5 years. Given that Intel insists on the absolute max. voltage rating of 1.52 V for 3 years of warranty, the prediction doesn't seem too far fetched. And I also think Intel sets the stock VID to around 50-100 mV higher than what the chip can actually remain stable. Considering the 7700K I think every single chip can operate stable below 1.2 V at a stock turbo of 4.5 GHz but the stock voltage for it seems to be around 1.25-1.27 V. Which means even if you push your chip to the limits for 2.5 years with a constant 1.5 V, Intel has to make sure it's still stable at 1.25 V.

Then what's the bottom line? To me, the bottom line is unless you're sure to upgrade your CPU within the current year, going above 1.5 V doesn't seem to be a good idea. And 1.55 V is surely a no go for long term. After all, it only takes 36 hours to lose 5 mV off of your overclock.