Mechanical engineering questions concerning computer GPU’s

[Testing123]

Are there any mechanical engineers in the house?

I have a question concerning graphics processing units (GPU).

Here are the questions:

• Was the backplate originally intended as a support item for the printed circuit board (PCB) of the GPU?
  
• Do backplates have any positive effect on GPU sag?
  

(The backplate is the metal plate that covers the PCB.)

Thanks for any insight you can share.

[T3sl4co1l]

"Yes" seems obvious enough to me... so, what did you really want to know?

I mean, FR-4 is pretty flexible stuff, when compared to a steel plate, or the large silicon die of the GPU itself (which is probably the main rigidity in the chip).  Obviously you don't want much flex across that.

FR-4 also cold-flows or creeps slowly over time, which is to say: it's even more flexible over long time scales.  So it is important to design PCB clamping hardware with extra flex range in mind (using springy washers and clamps, for example).

I'm not familiar with the term "GPU sag".

Tim

[senso]

Its pretty common today with 2 and 3 slot gigantic GPU coolers so heavy that the whole card sits croocked and over time some rip the PCIe connector from the board.

The backplate should help, and indeed they help, BUT almost all the cases are thin sheet metal and the threads in card rack/holder wont take any torque, so the card sits there with a massive cooler and even more weight from the backplates not fastened to the case properly, I solved that in a couple friends desktops with some nice stainless M3 screws and nylon spacers, put two m3 screws in place of that crappy kinda self threading screw that the GPU's come bundled with and now the cards dont sag and there is no need to prop something inside the case to hold the back end of the GPU.

[Ian.M]

Back in the day, IBM PCs and other quality leading brand clones had card guides to engage with the far end of full length cards so that the card was supported by two points on the backplate, the opposite end and a significant portion of the bottom edge + all slots were vertical.   Its unfortunate that such sound engineering practice has been discarded as the size of the card edge connector has shrunk with each new bus..

[james_s]

The problem with the card guides is that as parts shrank the need for cards to be full length diminished and most of them got shorter for obvious reasons, a big PCB costs a lot more than a small one. I've had a few old cards that were not quite full length and had a plastic bracket on the end that fit in the card guide though. Seems like we might need a standardized mechanical solution to support heavy graphics cards, maybe a metal bracket that connects to the slot cover and goes all the way to the card guide, which is still present in most PC cases though rarely used.

[senso]

Or just not having a case made of 0.7mm metal with 1.5 turn of thread in a flow drilled hole..

[David Hess]

Graphics card with heavy coolers tend to take two slots which adds a lot to the mechanical rigidity.

[Testing123]

Its pretty common today with 2 and 3 slot gigantic GPU coolers so heavy that the whole card sits croocked and over time some rip the PCIe connector from the board.

Indeed! Here's an example of what you are referring to:

The backplate should help, and indeed they help, BUT almost all the cases are thin sheet metal and the threads in card rack/holder wont take any torque, so the card sits there with a massive cooler and even more weight from the backplates not fastened to the case properly,

This is what I notice as well and why I posed the questions. Allow me to rephrase as a statement:

If the original and primary design, implementation and use of backplates was to keep the GPU from sagging, it seems that the goal was not achieved.

This is why I asked the questions as I did. I'm still unclear as to whether or not the initial implementation and primary goal of backplates was one of support.

I solved that in a couple friends desktops with some nice stainless M3 screws and nylon spacers, put two m3 screws in place of that crappy kinda self threading screw that the GPU's come bundled with and now the cards dont sag and there is no need to prop something inside the case to hold the back end of the GPU.

This sounds promising, but I'm not sure I understand fully. Are you talking about using m3 screws with nylon spacers to screw the GPU into the computer case's PCI expansion slots (see pic)?




Thanks for your thoughts and suggestion!

[Testing123]

Graphics card with heavy coolers tend to take two slots which adds a lot to the mechanical rigidity.

I've seen that, but I've also seen more than a few two slot GPU's sagging (Google 'GPU sag').