Sensors
8
Freescale Semiconductor
MMA7260QT
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 8
.
2. Solder mask opening = PCB land pad +0.1 mm.
3. Stencil aperture size = PCB land pad –0.025mm, as
shown in
Figure 9
with a 6mil 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 8
and
Figure 9
. 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 8. NSMD Solder Mask Design Guidelines
Figure 9. Stencil Design Guidelines
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.
Stencil opening (black) for land pad (yellow)
= PCB landing pad -0.025mm
= 0.525mmx0,475mm
Package foot pirnt
Signal trace near package: 0.1mm width and
0.5mm (min) length are recommended near
package. Wider trace can be continued after
these.
