Mechanical dimensions

SPWF04SA, SPWF04SC

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DocID029757 Rev 5

Figure 8: Module footprint

Note: 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.