The heatsink can be mounted uniformly using the Heat-Spring as a TIM because the surface alteration in this compressible metal squishes with surface irregularities of the heatsink. Image Courtesy of www.ocztechnologyforum.com
"My perception is that the Heat-Spring does not wet out the interface
surfaces. While there is clamping pressure on the heatsink, is it possible to rock the heatsink, releasing the clamping pressure? What will keep the Heat-Spring in place in this situation?"
I thought that this was a good question and I would pose the answer to it because it points out a unique attribute of the Heat-Spring™ and a question that others have probably considered.
The Heat-Spring does not flow. It is designed to compress into an interface, however. This is an engineered product, unique to each application, so the thickness and surface alteration are designed to compress enough that uniform contact is made along the entire interface, and no single location acts as a shim which will lead to rocking of the heatsink. When engineered correctly for an application, the heatsink will clamp tightly with the Heat-spring filling in all surface irregularities.