How much does the motherboard's PCB help dissipate heat?

[Zap]

How much does the motherboard's PCB help dissipate heat? For instance, all else being equal would a CPU run cooler on an ATX board versus say a micro ATX board strictly from the size of the motherboard? If so, how much of a difference?

[WNG]

Re: How much does the motherboard's PCB help dissipate heat?

for cpu heat?
None, the heat has no pathway to the PCB.
How cool a cpu runs is dependent on the cooling solution implemented and the airflow rates and restrictions within the case.
(if all else being equal, ie. same video card, same chipset, same drives)

[gastorgrab]

Re: How much does the motherboard's PCB help dissipate heat?

In general;

The circuit board material is an insulator. If it wasn't, every component would be shorted to every other one.

There are exceptions, but a good electrical conductor is usually a good heat conductor as well.


As for why (and the best example of 'an exception');

http://www.eng.auburn.edu/~wfgale/in...s/section1.htm

The key feature that distinguishes metals from non-metals is their bonding. Metallic materials have free electrons. In the case of pure metals, the outermost layer of electrons is not bound to any given atom, instead these electrons are free to roam from atom to atom. Thus, the structure of metallic material can be thought of a consisting of positive centers (or ions) sitting in a “gas” of free-electrons

The existence of this free electron gas has a number of profound consequences for the properties of metallic materials. For example, one of the most important features of metallic materials is that freely moving electrons can conduct electricity and so metallic materials tend to be good electrical conductors. Some metals more closely resemble the idealized picture of free electrons than others. Consequently, some metals are better conductors of electricity than others (for example, copper is a more efficient electrical conductor than tin).

Electrical conductivity is such an important characteristic of metals that conductivity is sometimes used to distinguish metals from non-metals. The problem with using conductivity to distinguish metals from non-metals is that this approach is somewhat arbitrary. For example, graphite is a form of carbon which has quite a high electrical conductivity, but the bonding of carbon atoms in graphite is very different from that of atoms in a metal. Therefore, it would be quite misleading to describe graphite as a metal. Note: the way in which atoms are arranged in a structure is just as important as the nature of the atoms themselves in determining the extent of electrical conductivity. Both diamond and graphite are made up of pure carbon, but diamond is a very good electrical insulator, rather than an electrical conductor like graphite. The structure of graphite and diamond are discussed in MATL 3200: Engineering Materials II.

http://www.uh.edu/engines/epi273.htm

Diamonds are called ice, but we're also told that you can tell diamonds from glass because diamonds are warm. Actually, diamonds aren't like ice at all. Ice is a good thermal insulator. But diamond is the best natural conductor of heat we know -- three or four times better than copper or silver.

.

[PedroDaGr8]

Re: How much does the motherboard's PCB help dissipate heat?

Believe it or not diamond absorbs the heat in an interesting way too. If I remember correctly they call the heat absorbed phonons (not photons) because of the way they are absorbed. I need to remember more from inorganic where we covered this as an aside.

[Zap]

Re: How much does the motherboard's PCB help dissipate heat?

Thanks guys. The reason I asked was that in another forum I'm having a disagreement (well, I'm trying to be logical, the other guy is IMO borderline insulting) regarding ATX versus micro ATX motherboards. Yes, mundane topic, but this guy's as bad as people who argue over AMD versus Intel, or ATI versus Nvidia. He maintains that the physically larger PCB of ATX keeps the CPU running cooler. Here's how it went:

The small-form factor board is narrower and shorter than a standard ATX MB. That's a 25% reduction in surface area! Surface area is very important for an air-cooled PC. Some MB manufacturers also included heat-pads on the back of the MB to dissipate the heat from the CPU and chipset regions. To achieve the same level of air flow in a smaller case, the fan(s) must work harder to overclock the internal case resistance. Translation...more noise level.

Huh? If a PCB can cool so well, then why are heatsinks still made of copper and aluminum? What does the surface area of a motherboard have to do with cooling?

Do you understand about heat transfer? Have you attempted to de-solder a capacitor from the MB? Care to guess how many watts it would take to do this job? Please don't lecture me about heat sink until you have measured the amount of heat that is absorbed by the MB!

Desoldering caps from a motherboard? I've never done that, so I decided to ask the experts... you guys.

[Per Hansson]

Re: How much does the motherboard's PCB help dissipate heat?

Yea, the mainboard is very very good at absorbing heat, or, more specifically the big ground planes that big components are connected to, like MOSFET's Capacitors etc

However the board needs active cooling (i.e. there needs to be airflow) otherwise it will not help to cool, it will just get warm... Try touching the PCB of a high-end GFX card after a heavy gaming session, it's common for it to be very very hot... That's part of the reason why the Zalman flower coolers work so well, they cool the whole surface of the card, not just the GPU

But about the CPU temp, I think that is not so havily affected by the mainboard, sure, some heat can travel though the processor pins into the mainboard. But I think it's a negliable ammount compared to what goes into the heatsink

And yes, desoldering a capacitor from the ground plane on a mainboard can indeed be very difficult, because you are not heating just the capacitor, but the whole mainboard. With some practice it becomes quite easy though

[shadow]

Re: How much does the motherboard's PCB help dissipate heat?

Motherboards do absorb a fair amount of heat. This can be seen clearly by the MOSFET's on motherboards. The primary heatsink for MOSFET's on a motherboard is the motherboard itself.

Having said this, a CPU does not use the motherboard as a heatsink. It does heat up a bit, however I believe this would be mainly a side effect.

Surface area has alot to do with cooling. If you increase the surface area of a heatsink, then it can be cooled down easier. This is achieved by increasing the number of fins on a heatsink as well as making them thinner.

However I believe the argument about the surface area of a motherboard is flawed.

What is the surface area between the CPU and the copper/aluminium heatsink?
The answer to this is the whole CPU spreader on modern CPU's and the core of the CPU on older CPU's. The heat transfer capabilities between the CPU and the heatsink is very good because of the material (copper and aluminium are very good at heat transfer) and the layer of thermal paste (this helps reduce heat build up by filling in the imperfections of the heatsink with a heat conductive compound).

What is the surface area between the CPU and the motherboard itself?
The answer to this question is simply the pins of the CPU plus the plastic socket.

There is no thermal paste between the CPU and the motherboard or the plastic socket, plastic is clearly a poor conductor of heat in comparison to metals and the surface area is clearly smaller between the CPU and the motherboard in comparison to a heatsink. Add to that that the motherboard is hardly an efficient heat conductive material. Therefore a whole lot more heat gets transferred to the heatsink in comparison to the motherboard.

However I must agree that graphics cards get damn hot. A common measure of how good a graphics cards cooling solution is by feeling the heat along the back of the PCB. If it is very hot, then the cooling solution is poor, if it is reasonable then the cooling solution is effective. This is of course after a benchmark or a solid round of gaming.

[gonzo0815]

Re: How much does the motherboard's PCB help dissipate heat?

Well, on graphics boards the CPU is usually on a BGA package, and soldered to the PCB.
The VRM mosfets usually too.
So i think it is obvious, that on graphic boards the PCB is indeed a part of the colling solution, but nevertheless the HSF does the main job too.

[gastorgrab]

Re: How much does the motherboard's PCB help dissipate heat?

I'm not convinced that fiberglass reinforced epoxy resin circuit board will conduct heat very well at all. One of the materials i use as heat insulation, where i work, is a mylar backed fiberglass fabric.

Heat source is through convection and infared. The mylar is specifically there to reflect the infared since things made of glass (like fiberglass) tend to let most visible wavelengths, and some invisible, pass right through.
.

[Per Hansson]

Re: How much does the motherboard's PCB help dissipate heat?

gastorgrab; it's the copper grounding planes that transfer the heat

[gastorgrab]

Re: How much does the motherboard's PCB help dissipate heat?

I guess we would have to include the metal portions if we spoke about the thermal, or electrical conductivity of the PCB.