APPENDIX A – PACKAGE REQUIREMENTS FOR MMA7660FC
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.
Soldering And Mounting Guidelines for the DFN Accelerometer Sensor to a PC Board
These guidelines are for soldering and mounting the Dual Flat No-Lead (DFN) package inertial sensors to printed circuit
boards (PCBs). The purpose is to minimize the stress on the package after board mounting. The MMA7660 digital output
accelerometer uses the DFN package platform. This section describes suggested methods of soldering these devices to the PC
board for consumer applications. Pages 31, 32, and 33 show the package outline drawing for the package.
Overview of Soldering Considerations
Information provided here is based on experiments executed on DFN devices. They do not represent exact conditions present
at a customer site. Hence, information herein should be used as guidance only and 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. The following are the recommended guidelines to follow for
mounting DFN sensors for consumer applications.
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 assembly package shall 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.
Note: Halogen Free is only compliant to the MMA7660FC, not to the packaging material.
PCB Mounting Recommendations
1. The PCB land should be designed with Non Solder Mask Defined (NSMD) as shown in Figure 16 and Figure 17.
2. No additional via pattern underneath package.
3. PCB land pad is 0.825 mm x 0.3 mm as shown in Figure 16 and Figure 17.
4. Do not solder down smaller side tabs on either end of the package.
5. The solder mask opening is equal to the size of the PCB land pad plus 0.15 mm.
6. The stencil aperture size is equal to the PCB land pad – minus 0.03 mm total.
7. Stencil thickness should be 75 μm.
8. 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.
9. Signal traces connected to pads should be as symmetric as possible. Put dummy traces on NC pads in order to have same
length of exposed trace for all pads. Signal traces with 0.15 mm width and minimum 0.5 mm length for all PCB land pads
near the package are recommended as shown in Figure 16 and Figure 17. Wider trace can be continued after the 0.5 mm
zone.
10. Use a standard pick and place process and equipment. Do not use a hand soldering process.
11. It is recommended to use a no clean solder paste.
12. Do not use a screw down or stacking to fix the PCB into an enclosure because this could bend the PCB putting stress on
the package.
13. The PCB should be rated for the multiple lead-free reflow condition with max 260°C temperature.
14. No copper traces on top layer of PCB under the package. This will cause planarity issues with board mount.
Freescale DFN 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.
MMA7660FC
Sensors
Freescale Semiconductor
25
FREESCALE [ Freescale ]
