Now you should lay down the motherboard on the metallic plate again, placing a screw on every motherboard hole that matches a nut that you've installed. There is a very important detail that a lot of people don't know, however. If you pay close attention to the motherboard's holes, you will find two kinds of holes: metalized and non-metalized. As the name implies, the metalized holes have a metallic contact around them. Pay close attention in Figure 6 to see the difference between these two kinds of holes.

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Figure 6: Metalized versus non-metalized hole.

Metalized holes are meant to be directly screwed. So, on these holes go ahead and place a screw on them. But the non-metalized holes you cannot screw them directly. You need to place a cardboard washer between them and the screws. Actually, two washers are needed per hole, one between the nut and the motherboard and another between the motherboard and the screw, like a sandwich where the motherboard is the stuffing.

One of the most common mistakes while installing a motherboard is using these washers on all holes. This cannot be done. The metalized holes were metalized to make the proper grounding with the system case. Actually, you probably won't find any non-metalized holes on motherboards nowadays. And if you do, almost always they don't match any hole on the chassis anyway. So, just leave these cartonboard washers behind! Don't use them!

Another very common – and dangerous – mistake is to use a foam sheet (which is usually pink) that some motherboards come with between the motherboard and the metallic plate. Some people believe that this foam will prevent the motherboard from touching the metallic plate, avoiding a short-circuit. This way thinking is completely wrong. First, if you install all the nuts correctly and install a screw on all motherboard holes possible, the motherboard will never touch the case's metallic plate. In second place, if you install this foam sheet you will simply cut the motherboard ventilation, which will lead to an overheating condition. The space between the motherboard and the metallic plate is used to dissipate the heat generated by the motherboard and nothing should be put there.

For more common mistakes made when installing a motherboard, you should read two tutorials: Typical PC Assembling Problems and Cases: How to Avoid Overheating.

After these explanations, let's go ahead. In Figure 7 you see the motherboard correctly installed to the case's metallic plate.

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Figure 7: Motherboard correctly installed to the metallic plate.

You may think that the next step is to install the metallic plate back to the case, now with the motherboard attached to it. But it is not. Before doing that, we still need to do several things.