MMA8452Q
Sensors
Freescale Semiconductor, Inc.
43
7
Printed Circuit Board Layout and Device Mounting
Printed Circuit Board (PCB) layout and device mounting are critical portions of the total design. The footprint for the surface
mount packages must be the correct size as a base for a proper solder connection between the PCB and the package. This,
along with the recommended soldering materials and techniques, will optimize assembly and minimize the stress on the package
after board mounting.
Freescale application note AN4530, “QFN (Quad Flat Pack No-Lead)” discusses the QFN package used by the FXAS21000.
7.1
Printed Circuit Board Layout
The following recommendations are a guide to an effective PCB layout. See
for footprint dimensions.
1.
Do not solder down Exposed Pad (EP) under the package to minimize board mounting stress impact to product
performance.
2.
PCB landing pad is 0.813 mm x 0.305 mm as shown in
3.
Solder mask opening = PCB land pad edge + 0.2 mm larger all around.
4.
Stencil opening size is 0.787 mm x 0.280 mm.
5.
Stencil thickness is 100 or 125
μ
m.
6.
The solder mask should not cover any of the PCB landing pads, as shown in
.
7.
No additional via nor metal pattern underneath package on the top of the PCB layer.
8.
Do not place any components or vias within 2 mm of the package land area. This may cause additional package stress
if it is too close to the package land area.
9.
Signal traces connected to pads should be as symmetric as possible. Put dummy traces on NC pads, to have same
length of exposed trace for all pads.
10. Use a standard pick and place process and equipment. Do not use a hand soldering process.
11. Customers are advised to be cautious about the proximity of screw down holes to the sensor, and the location of any
press fit to the assembled PCB when in an enclosure. It is important that the assembled PCB remain flat after
assembly to keep electronic operation of the device optimal.
12. The PCB should be rated for the multiple lead-free reflow condition with max 260°C temperature.
13. Freescale sensors are compliant with Restrictions on Hazardous Substances (RoHS), having halide free molding
compound (green) and lead-free terminations. These terminations are compatible with tin-lead (Sn-Pb) as well as tin-
silver-copper (Sn-Ag-Cu) solder paste soldering processes. Reflow profiles applicable to those processes can be used
successfully for soldering the devices.
