Sensors

Freescale Semiconductor

7

MMA6281QT

MINIMUM RECOMMENDED FOOTPRINT FOR SURFACE MOUNTED APPLICATIONS

Surface mount board layout is a critical portion of the total

design. The footprint for the surface mount packages must be

the correct size to ensure proper solder connection interface

between the board and the package.

With the correct footprint, the packages will self-align when

subjected to a solder reflow process. It is always

recommended to design boards with a solder mask layer to

avoid bridging and shorting between solder pads.

The flag underneath the package is internally connected to

ground. It is not recommended for the flag to be soldered

down.

PCB DESIGN GUIDELINES

The following are the recommended guidelines to follow

for mounting QFN sensors for either automotive or consumer

applications.

1. NSMD (Non Solder Mask Defined) is shown in

Figure 7.

2. Solder mask opening = PCB land pad +0.1 mm.

3. Stencil aperture size = PCB land pad – 0.025mm, as

shown in Figure 8

with a 6 mil stencil.

4. Do not place insertion components or vias at a

distance less than 2mm from the package land area.

5. Signal trace connected to pads should be as

symmetric as possible. Put dummy traces if there is

NC pads, in order to have same length of exposed

trace for all pads. Signal traces with 0.1mm width and

min. 0.5mm length for all PCB land pad near package

are recommended as shown in Figure 7 and

Figure 8. Wider trace can be continued after the

0.5mm zone.

6. Use a standard pick and place process and

equipment (no hand soldering process).

7. It is recommended to use a cleanable solder paste

with an additional cleaning step after SMT mount

8. It is recommended to avoid screwing down the PCB

to fix it into an enclosure since this may cause the

PCB to bend.

9. PC boards should be rated for multiple reflow of lead-

free conditions with 260°C maximum temperature.

\

Figure 7. NSMD Solder Mask Design Guidelines

•

Do not solder down flag for

consumer application

•

Do not place metal pattern or via

structures underneath of package

0.55 mm

0.50 mm

Package Pad

PCB land pattern - NSMD

Cu: 0.55 x 0.50 mm sq.

Solder mask opening =

PCB land pad +0.1mm

=0.65x0.60 mm sq.

Signal trace 0.1mm width

and 0.5mm (min) length near

package. Wider trace can be

continued after these traces.