[SOLVED] Why no fins on VRM heatsinks nowadays?

[Craig C2]

I've been looking at Asus Z390 boards, but other brands are similar. The VRM sinks have no real fins, more like a few grooves. What hapenned to the importance of surface area? (Asus WS Z390 Pro pics below.)

I'm aware that chipsets do not get as hot as they used to, du to their high-speed functions being moved to the CPU, but what a bout VRMs?

Theory: Maybe VRM temps "spike" much more than a CPU's. Then, extra mass & heat capacity of a sink would be more advantageous than heat conductance. The extra mass would smooth out spikes, but convecting it outwards slowly. Yes I'm reading a physics textbook. Sawing more grooves would remove mass. But skiving or extrusion would not, yet still no fins?

 

[CountMike]

Unfortunately looks became more important than functionality, just look at all those lights and different color schemes on essentially identical MBs. On the other hand, digital power/voltage control is much better that raw power/voltage regulators from the past.
At this point, physics get another twist, heat transfer from chips to coolers, chips have small surface, there's many of them so they are not all at same level which makes use of pads instead of paste necessary and they have less of heat conductivity, even giant hat sink wouldn't help much. A fan would help more.

 

[drea.drechsler]

.....
Theory: Maybe VRM temps "spike" much more than a CPU's. Then, extra mass & heat capacity of a sink would be more advantageous than heat conductance. The extra mass would smooth out spikes, but convecting it outwards slowly. Yes I'm reading a physics textbook. Sawing more grooves would remove mass. But skiving or extrusion would not, yet still no fins?

I think you're on to it...

Today's CPU's, with massive processing potential get jobs finished and back to idling as many parts of the CPU as possible to save energy. So what's important is to have a big hunk of metal sitting on the FET's to draw off the thermal energy really quickly during those seconds and milliseconds of heavy processing. Finning is nice to in turn dissipate the thermal energy into the air flow, but considered not as important.

With that in mind designers get to have a field day so the can make awesome looking motherboards that feature crazy things like RGB festooned plastic I/O shields that block airflow over the block of aluminum that acts as the heat sink. I mean, who needs airflow over a heatsink with no fins? right?

You can't really blame them to much for this as people may think they need amazing heatsinking but they really don't (see above) when doing run-of-the-mill like gaming. And those awesome looking designs, they hope, will spur interest in upgrading in a saturated and declining PC market.

So what happens if you are one of the weird ones who want to run an 8 hour rendering on your heavily over-clocked 8 core CPU? In only a few minutes that block of aluminum will thermally saturate (that's why liquid coolers are so nice as water can hold a massive amount of heat before it thermally saturates). But without fins the aluminum can't dissipate the heat into the (usually obstructed) airflow, thermal run-away takes over, the VRM overheats and starts throttling the CPU. Most people don't notice so they think "i got a cool system!".

But you are one who monitors HWinfo and know different... so you have to take off those pretty shrouds and locate a fan blowing across the block of aluminum to help dissipate the heat.

 

[Craig C2]

thermal run-away

Is that an actual term?

 

[drea.drechsler]

Is that an actual term?

Yes it is!

https://en.wikipedia.org/wiki/Thermal_runaway

TL/DR:
"Thermal runaway occurs in situations where an increase in temperature changes the conditions in a way that causes a further increase in temperature, often leading to a destructive result. It is a kind of uncontrolled positive feedback."

 

[Craig C2]

Informative link, thanks!