Mechanical engineering questions concerning computer GPU’s - Page 1
Forum section: electronics / general

author: Testing123
author_rank: Contributor
timestamp: May 03, 2017, 03:00:57 pm
content: 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.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 03, 2017, 06:32:47 pm
content: "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

author: senso
author_rank: Frequent Contributor
timestamp: May 03, 2017, 06:44:36 pm
content: 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.

author: Ian.M
author_rank: Super Contributor
timestamp: May 03, 2017, 07:04:03 pm
content: 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..

author: james_s
author_rank: Super Contributor
timestamp: May 03, 2017, 08:11:29 pm
content: 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.

author: senso
author_rank: Frequent Contributor
timestamp: May 03, 2017, 08:19:19 pm
content: Or just not having a case made of 0.7mm metal with 1.5 turn of thread in a flow drilled hole..

author: David Hess
author_rank: Super Contributor
timestamp: May 03, 2017, 11:27:23 pm
content: Graphics card with heavy coolers tend to take two slots which adds a lot to the mechanical rigidity.

author: Testing123
author_rank: Contributor
timestamp: May 04, 2017, 01:22:36 am
content: Quote from: senso on May 03, 2017, 06:44:36 pmIndeed! Here's an example of what you are referring to:Quote from: senso on May 03, 2017, 06:44:36 pmThis 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.Quote from: senso on May 03, 2017, 06:44:36 pmThis 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!

author: Testing123
author_rank: Contributor
timestamp: May 04, 2017, 01:30:19 am
content: Quote from: David Hess on May 03, 2017, 11:27:23 pmI've seen that, but I've also seen more than a few two slot GPU's sagging (Google 'GPU sag').