are the under sides of mobos, gpus, hard drives.etc allowed to touch a surface while running?

Question

Hey so im not exactly a "newb" when it comes to PC building, However i recently started building a flat table top PC/"case" , so the current plan is to cover the the areas that the components are on with a rubber mat or some other non slip soft non conductive material, so really im wondering is weather its safe for the bottom of for example the mobo or the gpu to make contact with the rubber surface or weather i should get bumpers for the screw so the components arent directly touching the surface? (and yes ino this may seem like a pretty dumb question, but since this is my first time building a PC like this i just wanna be safe, especially considering im using all new hardware on this lol )

Answer 1

Motherboard

You'll notice that the underside of a motherboard typically has many exposed pins. A conductive surface would short those pins, potentially damaging the board. A non-conductive surface might work, but it's safer to mount the board properly. Directly resting the board on a surface has the potential for physical damage to any pins and under-board components, not to mention unevenness from any heatsink mounts etc. on the underside.

Motherboards are designed to be mounted with standoffs, which elevate the board above the mounting surface. The screw holes on motherboards are reinforced for this purpose. Use those if possible.

GPU

This tends to have more variation, as some modern GPUs are fully enclosed with a flat back. Those are largely safe to leave resting on a surface. The ones with exposed component leads (looking like metal pins) sticking out should not be in contact with anything conductive, and preferably should not be resting at all.

Note that it may be difficult to extend a PCIe slot away from the motherboard. High-bandwidth connections like PCIe are vulnerable to interference. Ideally, you would just insert the GPU directly on the motherboard slot.

Storage

We'll start with the easy case: SSDs are typically fully enclosed. They can be safely left anywhere, though airflow and a thermally-conductive surface will aid cooling.

HDDs are a bit finicky, because they do tend to have an exposed circuit board. Again, avoid contacting that circuit board with metal, and if it has any protruding leads (pins) try not to rest the drive on those leads (elevate it slightly).

Other considerations

Airflow

Many components are designed to operate with some airflow for cooling. In your typical computer case, this airflow is provided by the CPU, GPU and especially PSU fans, not to mention any additional case fans, and helps cool chips and heatsinks without dedicated fans. If you're mounting them flat on a surface, you'll want to check temperatures and make sure you don't end up with areas of hot air and lacking airflow.

Answer 2

I'm somewhat skeptical of elements of @bob answer - and would answer that while it's definitely not a best practice, provided the material they are resting on is suitable - ie non-conductive and has a little give - it should work. Here is why -

1. Hot air rises, and components are typically on top of the board. It's not like there are case fan's blowing air on the underside of a board.

2. When boards are tested on work benches, they are often tested on a non-conductive base - not suspended in air.

3. For things like hard disks, the bottom of the disk case protrudes past the maximum depth of the circuit board so you can stack them touching without risk of shorting.

4. Laptop motherboards don't have standoffs(although the case is often moulded for an air gap)