“Cantilever cooler” with only 4 mounting points
Let us now turn to a consequence of this thermal concentration on just a few areas. All MSRP cards I’ve seen so far use inexpensive coolers where the heatsink alone is used to connect the cooler to the board. In order to generate a margin of 2 to 5% at all with a card, such a cooler must not cost much more than 20 USD at purchase. Since the prices for coolers have increased significantly in the meantime, you then just get a cheap and RGB-free variant with 2 fans, a maximum of 3 heatpipes, heatsink and the four mounting points on the heatsink. Cost down.
We will now take a look at a cooler as an example, but it has two problems as a result. The first thing you’ll notice is that there are no heatsinks or cooling surfaces for the two voltage converters of the memory and also the cooling option for the single DrMOS on the upper side of the card, which should sit in the center of the upper, bent heat pipe in the picture. Furthermore, the distance between the VRM heatsink on the right (dark gray thermal pad) and the DrMOS is quite large. Yes, thick pads can be made, but then the heatsink would also have to be connected back to the board somehow. But it is not. If the circuit board bends backwards, with a bit of bad luck there is no contact at all.
After all, many of the users will install the cards horizontally. Then the board is firmly connected to the case via slot bracket. The entire cooler hangs on only four screws and pulls the center section down. As a result, the board can bend at high temperatures (bending) and the support of the VRM heatsink becomes significantly weaker because the distance increases and the pressure decreases. So you would have to stabilize the whole thing to at least prevent the board from bending.
This is where the backplate comes into play. So this is not just optical frippery, but first and foremost a purely mechanical safeguard against bending. However, we’re back to the vexed costs again, and the temptation to simply solve this with plastic is unfortunately quite great. The board shown below as an example is unfortunately completely unstable and almost flexible. Nothing is stabilized there, because it is simply far too pliable itself for that.
I will now show you in a short video what happens when you press against it in the right place. The circuit board and backplate bend. And please turn off the sound, because I’m snorting like Darth Vader because of my cold and stuffy nose:
The fact that this no longer offers any real contact on the VRM heatsink is unfortunately the logical consequence. The card was mounted horizontally in the test case for one day and was allowed to sweat diligently. If you unscrew the backplate and measure the card in an upright position (open benchtable), the result doesn’t look very nice anymore. I have created the whole thing as a superposition, so that you can also see the (invisible) front side of the board. For this I pick up the board on the first page with the yellow markings of the hotspots again and what a surprise: unfortunately this matches exactly!
Up to 106 degrees is really horrible here. Well, the PCB material still works without problems up to 140 degrees, the DrMOS do not burn off either, but one must not forget that outgassing of the composites can already occur from around 100 °C onwards. In addition, a multilayer board contains thin tracks, and together with bending, extreme heating and subsequent cooling can cause the tracks to tear. Hairline cracks are not even rare here. Just find them first. Another point is the faster aging of the components located in the immediate vicinity, especially the capacitors. No, it’s not all pretty.
And what happens when you don’t cool a DrMOS for the NVVDD at all is what we see at measurement point VRM #2. We have already discovered on the first exemplary picture that there is no heatsink at all. The almost 96 °C are then only the logical consequence. The third and last page shows that it is also possible to make it more practical. Unfortunately, this card then has another drawback, but more about that after the turn of the page.
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