AMD Socket AM5 Renders For Zen 4 Highlight A Potential Cooling Advantage Over Alder Lake

hero amd zen 4 ces news
Back at CES 2022, AMD gave an update on the Zen 4 architecture that will first show up with the Ryzen 7000 series processors. Those chips, at least in desktop form, will go into Socket AM5. Where Socket AM4 (and most of AMD's previous mainstream processors) used a Pin Grid Array design, the next-generation Socket AM5 will adopt a Landing Grid Array design similar to the one used on Intel's processors since the venerable LGA 775, first used for later models of the Pentium 4.

igorslab socketam4 backplate diagram
Diagram purportedly picturing the Socket AM5 socket layout. Image: Igor's Lab (click for highres)

We say "similar to" because, despite looking nearly identical at a glance, there's at least one significant departure from the way Intel's CPU sockets work. We'll say it up front: AMD's LGA retention module isn't just attached to the mainboard itself, but in fact screws directly through the board into the heatsink retention plate. That gives the socket four additional loading points over which to distribute mechanical stress, reducing the chance of bending the board, socket, or indeed, the CPU itself.

You might be reading this thinking, "is that really necessary?" Well, yeah, actually. See, this information comes to us by way of Igor's Lab, who broke the story along with sharing a couple of CAD diagrams of the AM5 socket and its retention mechanism. Igor doesn't explain where he came across the information, but remarks that he decided to share it as a follow-up to his other recent story about the Intel LGA 1700 socket slightly bending installed processors, reducing cooling performance.

inline igorslab alderlake bent ihs
Picture clearly showing bent Intel CPU IHS with a significant gap in the middle. Image: Igor's lab

Igor initially wrote about this back in early December, just after the release of the Alder Lake processors. However, at that time, it wasn't completely clear what was at fault: were the CPUs uneven out of the box, or were they being bent by the motherboard? In the latter case, what exactly was at fault—the CPU loading mechanism, or the cooler mounting mechanism?

Thanks to some help from Buildzoid (of the YouTube channel Actually Hardcore Overclocking), it was determined that Intel's "Independent Loading Mechanism" (ILM) was at fault. The ILM is that clamp that locks down over the CPU to hold it in place while you install your heatsink. Because the ILM is secured to the motherboard, and because it places its load entirely in the center of the CPU horizontally, it's able to slightly bend the CPU package—not enough to damage it, or prevent it from working, but just enough to create a gap in the top that worsens cooling performance.

inline igorslab alderlake washer ilm mod
Washers between motherboard and ILM reduce bending and improve temps. Image: Igor's Lab

Igor proved his hypothesis by testing an Alder Lake system exhaustively using washers between the LGA 1700 socket's ILM and the motherboard. Testing with gaps of 0.5mm, 0.8mm, 1.0mm, and 1.3mm, he found that the greatest benefit was realized with 1.0mm-thick washers installed, effectively raising the ILM by 1 millimeter off the mainboard. That gave the Core i9-12900K CPU underneath his Corsair XC7 waterblock a full 5.76° drop in load temperature compared to the stock configuration.

That's a pretty handy tweak for Alder Lake owners, but didn't we start this post talking about AMD CPUs? As we mentioned earlier, according to Igor's information, AMD's Socket AM5 will actually attach its LGA socket's Socket Actuation Mechanism ("SAM," the AMD equivalent of the "ILM") straight through the motherboard to the heatsink backplate. Spreading the tensile stress across eight screws, including the four for the heatsink itself, should help guard against the deformation of the CPU seen in Alder Lake, but it also may improve the stability of heavy coolers attached to the backplate.

igorslab socketam4 SAM diagram
Supposed diagram of the AMD Socket Actuation Mechanism. Image: Igor's Lab (click for big)

The primary downside of this approach is that while Socket AM5 is compatible with legacy heatsinks and waterblocks (as AMD already stated), coolers that use custom back-plates will definitely need new ones to accommodate the SAM attachment points. Likewise, the screw holes for the AM5 backplate differ from those of the Socket AM4 backplate, so again, legacy heatsink backplates will not be compatible. However, heatsinks that attach to the stock dual-clip retention system should be fine. We'll see for ourselves when Zen 4 launches in the second half of this year.
Tags:  AMD, Processors, CPU, zen 4, am5