DocID025635 Rev 6

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SPWF01SA, SPWF01SC

Package mechanical data

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Note:

An antenna area of 217 x 520 mils must be free of any ground metalization or traces under

the unit. The area extending away from the antenna should be free from metal on the PCB

and housing to meet expected performance levels. Pin 25 is the required paddle ground and

is not shown in this diagram.

Figure 7. Wi-Fi footprint

PCB design requires a detailed review of the center exposed pad. This pad requires good

thermal conductivity. Soldering coverage should be maximized and checked via x-ray for

proper design. There is a trade-off between providing enough soldering for conductivity and

applying too much, which allows the module to “float” on the paddle creating reliability

issues. ST recommends two approaches, a large center via that allows excess solder to

flow down into the host PCB with smaller vias around it, or many smaller vias with just

enough space for the viscosity of the chosen solder/flux to allow some solder to flow into the

smaller vias.

Either of these approaches must result in 60% or more full contact solder coverage on the

paddle after reflow. ST strongly encourages PCB layout teams to work with their EMS

providers to ensure vias and solder paste designs that will result in satisfactory

performance.