FXLS8471Q Datasheet, PDF (67/75 Pages) Freescale Semiconductor, Inc – Linear Accelerometer

11 Mounting Guidelines for the Quad Flat No-Lead (QFN) Package
Printed Circuit Board (PCB) 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 PCB and the package. With the correct footprint, the
packages will self-align when subjected to a solder reflow process.
These guidelines are for soldering and mounting the Quad Flat No-Lead (QFN) package inertial sensors to PCBs. The purpose
is to minimize the stress on the package after board mounting. The FXLS8471Q uses the QFN package platform. This section
describes suggested methods of soldering these devices to the PCB for consumer applications.
Freescale application note AN1902, “Quad Flat Pack No-Lead (QFN) Micro Dual Flat Pack No-Lead (DFN)” discusses the QFN
package used by the FXLS8471Q, PCB design guidelines for using QFN packages and temperature profiles for reflow soldering.
11.1 Overview of soldering considerations
Information provided here is based on experiments executed on QFN devices. As they cannot represent exact conditions present
at a customer site, the information provided herein should be used for guidance only and further process and design optimizations
are recommended to develop an application specific solution. It should be noted that with the proper PCB footprint and solder
stencil designs, the package will self-align during the solder reflow process.
11.2 Halogen content
This package is designed to be Halogen Free, exceeding most industry and customer standards. Halogen Free means that no
homogeneous material within the assembled package will contain chlorine (Cl) in excess of 700 ppm or 0.07% weight/weight or
bromine (Br) in excess of 900 ppm or 0.09% weight/weight.
11.3 PCB mounting recommendations
1. The PCB land should be designed with Non-Solder Mask Defined (NSMD) as shown in Figure 18 and Figure 19.
2. No additional via pattern underneath package.
3. PCB land pad is 0.8 mm by 0.3 mm as shown in Figure 18 and Figure 19.
4. Solder mask opening = PCB land pad edge + 0.113 mm larger all around.
5. Stencil opening = PCB land pad -0.015 mm smaller all around = 0.77 mm by 0.27 mm.
6. Stencil thickness is 100 or 125 μm.
7. Do not place any components or vias at a distance less than 2 mm from the package land area. This may cause
additional package stress if it is too close to the package land area.
8. Signal traces connected to pads should be as symmetric as possible. Put dummy traces on the NC pads in order to
have same length of exposed trace for all pads.
9. Use a standard pick and place process and equipment. Do not use a hand soldering process.
10. Do not use a screw down or stacking to fix the PCB into an enclosure as this could bend the PCB, putting stress on the
package.
11. The PCB should be rated for the multiple lead-free reflow condition with max 260°C temperature.
12. No copper traces on top layer of PCB under the package. This will cause planarity issues with board mount. Freescale
QFN 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.
Sensors
Freescale Semiconductor, Inc.
FXLS8471Q
67