How To Build A PC: From Component Selection To Installation

Step 11: Install Motherboard And Power Supply

Most enclosures support a range of motherboard sizes, each with a few different mounting points. These points connect a layer of the motherboard called the ground plane to the case's mounting tray, reducing signal crosstalk due to radio frequency interference (RFI). Thus, the mounting points are usually grounded.

Misaligned mounting points could contact a hot trace on the motherboard's back side, so case manufacturers usually make them removable via metal spacers called standoffs. It's important to observe the exact location of each mounting hole in the motherboard before placing a standoff in the corresponding tray location. A mistake made here could potentially damage the board, though the most likely result of an improperly-placed standoff is a system that simply refuses to power on. Arrows in the photo below illustrate the matching mounting points where standoffs were placed.

The ATX form factors specifies the size and location of a rectangular plate, called an I/O shield, which fills the gaps around the ports and connectors on the back of the motherboard. That is to say, an I/O shield fits a customized port selection to a standardized hole in the chassis. Cases often include an old-fashioned standard plate that must be snapped out before inserting the new, custom replacement.

Note that the upper tabs of this I/O shield hang down because it arrived in a semi-flattened state. These need to be bent approximately ninety-degrees from the surface to prevent them from blocking nearby ports during motherboard installation. The left tab in the photo below has been bent to the proper orientation. Many of today’s most popular boards instead use foil-faced foam to contact the ports.

Recheck standoff positions before inserting the motherboard at a slight angle, aligning ports with cover plate holes while guiding the board until it rests flat against the standoffs. Grounding tabs or foil-faced foam on the I/O shield will typically push the motherboard out of position, but the board should be easy to push into place. Align one hole perfectly with the standoff and affix a screw, then push the board into alignment for a second hole before tightening the second screw. The first two screws should prevent the board from twisting out of position while installing the remaining screws.

The power supply is usually secured with four coarsely-threaded screws, though it’s not always mounted to the back of the case. Some enclosures relocate the power supply and use an extension cable to place power on the back. Variations in design may demand that the power supply is installed before the motherboard, as specified in the case’s manual or installation guide.