microATX Motherboard Interface Specification

Version 1.2

Page 17

2.4 Height Constraints

2.4.1 Primary (Component) Side Height Constraints

One of the major advantages of the microATX form factor is its backward-compatibility with the ATX

specification. The microATX motherboard can be installed in any ATX chassis with the addition of

motherboard mounts. Table 6 lists the status of height constraints for specific areas. Figure 7 shows the

required maximum component height constraints for the components on the PC board. For full compliance

with microATX and to prevent interference with the chassis structure, power supply, or peripherals, the

motherboard components should not exceed the height limit in each zone defined. Similarly, microATX-

compliant power supplies, peripherals, and chassis features should not extend into the motherboard

component area.

Table 6: Height Constraints

Feature Status Comment

microATX motherboard maximum component heights Required See Figure 7.

microATX chassis keepout in Area A Required 3.0 inches (76.20mm) required; 3.5 inches

(88.90mm) is preferred.

The required chassis keepout for Area A is 3.0 inches (76.20mm) to facilitate dynamic considerations of

components in this area on the motherboard. The preferred (recommended) clearance is 3.5 (88.90mm)

inches to facilitate cooling solutions that require ducting. The bottom right corner of the board (as oriented in

Figure 7) is the most constrained because of the presence of 5.25-inch and 3.5-inch peripherals in some

chassis configurations. To maintain strict compliance to the microATX specification, careful placement of

peripherals, power supply, and chassis features is required.

2.4.2 Secondary (Bottom/Solder) Side Height Constraints

Required secondary (bottom) side motherboard height constraints for all areas (A-C, as shown in Figure 7) are

defined as follows (measured from the bottom planar surface of the motherboard PCB):

• ≤0.010” – Mounting hole standoff areas – no components. Restriction applies within 0.400” square area

centered on each required mounting hole location defined in Section 2.2. Nominal allowance is provided

only to accommodate slight reflow solder excess.

• ≤0.098” – All board circuit components (including leads) that are electrically conductive and intolerant of

direct connection to chassis ground (e.g., through-hole leads, surface mount resistors)

• ≤0.120” – Board components that are non-conductive or otherwise tolerant of direct connection to chassis

ground (e.g., connector guide/stake pins)

• ≤0.200” – Devices attached to the motherboard for the sole purpose of structural retention or stiffening

A chassis and its related elements (e.g., stiffening ribs, base pan, structural supports fasteners, etc.) must allow

≥0.250” clearance to the bottom planar surface of the motherboard PCB. This does not including mounting

hole standoffs, which may extend to and contact the PCB at the mounting holes within the prescribed 0.400”-

square areas.