Lapping The CPU
As we ran our tests, we realized that this sample was above average. So, we tried to land a record for eight-core processors, including AMD and Intel CPUs. The combat was relentless. On one hand, there were some very good results obtained by overclockers right around the time Ryzen was released, and it isn't hard to imagine that they had access to a sizeable quantity of hand-picked chips. On the other hand, Intel's Core i7-5960X compensates for its age with frequencies beyond 6 GHz under liquid nitrogen cooling.
We therefore decided to concentrate our efforts on two benchmarks: Cinebench R15 and GPUPI. In both cases, we succeeded in taking second place, in front of the -5960X contenders running around 6200 MHz (in the case of GPUPI).
Lapping In Pursuit Of MHz
At that time, our highest clock speed in GPUPI was 5390 MHz. The leader, Der8auer, was at 5440 MHz. First place, while so close, seemed out of reach. Without a better 1800X at our disposal, we decided to lap our sample in the hopes of better thermal transfer.
During our tests, we saw a gain of 2.7 MHz/°C at -196°C. If lapping helped us gain 15°C, which is not impossible given the high voltages we were using, 5430 MHz should be attainable.
The process proved more laborious than we expected. Within the first few minutes, defects began appearing in the CPU lid's shape. A flat processor should be “worn” completely on the surface in a homogeneous manner. However, we were uniquely attacking the edges of the IHS.
There were two possible scenarios: either the processor was not actually flat, or we were lapping incorrectly. To remove any doubt, we took a brand new razor blade and placed it on the CPU's surface. There it was: the blade only touched the borders, allowing a seam of light to shine through in the center.
Our lapping effort resumed. We used emery cloth (comparable to sand paper and intended for use in sanding metals) attached to a piece of glass to guarantee a uniform surface. We started with a course grit to rapidly remove (relatively, of course) the extra material on the edges.
This is the progress we made in one hour. The nickel coating is removed, revealing copper on the sides. Gradually as we eroded the surplus material, our uniform area grew in size. In the end, almost the entire IHS appears to be copper. Two visible spots persist, but the defect is sufficiently small to be ignored. The processor doesn't need to be polished any further. Having a flat surface is top priority. Fine scratches won't affect performance.
At this point, we resumed our trials with liquid nitrogen, confident in our work and hopeful that we'd realize our estimated gains.
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