360° View - Noctua NH-L9i Heatsink Information on Frostytech's test methodology is available here.
Noctua's NH-L9i heatsink ships with a special Noctua NF-A9x14 15x92x92mm PWM fan. The 36mm tall cooler has two 6mm diameter copper heatpipes embedded into the body which help conduct heat from the copper base plate out to the edges of the thick, nickel plated aluminum fins. Each aluminum fin measures 0.4mm thick and is spaced 1.2mm from the next. The bottom of the fins are elevated 7mm above the motherboard.
The two 6mm diameter nickel plated copper heat pipes are set into the 18mm thick fin stack, positioned slightly below the top surface and nearest to the exhaust airflow from the fan. The copper base provides support for the mounting brackets which screw into it.
The nickel plated copper base plate which makes contact with the processor measures 40x40mm. With the fan and steel side plates removed, we can better see how the Noctua NH-L9i is constructed.

Base Finish and Flatness

Flipping a heatsink over to inspect the business end is often a simple indicator of overall cooler quality. More practically speaking, a heatsink is in many ways only as effective as the contact it makes with the processor - the flatter and smoother the better. Base finish is one of the criteria that Frostytech measure in the course of evaluating heatsinks, and it involves two distinct aspects. Surface Finish is the first; this is calculated with the aid of Surface Roughness Comparator that has a cross section of common machine surface finishes and their numerical surface roughness equivalents in microinches. The second is Surface Flatness. This is tested with an engineer's straight edge or proven flat surface, in two axes.

The thick copper base of Noctua's NH-L9i heatsink has been machined perfectly flat, then nickel plated. Surface finish is smooth, surface roughness is approximately ~16 microinches. The base is perfectly flat in both axes.

Up next, heatsink sound level comparisons....