Rev 1.2 October 2008
EN5335QI
Design Considerations for Lead-Frame Based Modules
Exposed Metal on Bottom of Package
Lead frame offers many advantages in thermal performance, in reduced electrical lead resistance,
and in overall foot print. However, they do require some special considerations.
In the assembly process lead frame construction requires that, for mechanical support, some of the
lead-frame cantilevers be exposed at the point where wire-bond or internal passives are attached.
This results in several small pads being exposed on the bottom of the package.
Only the large thermal pad and the perimeter pads are to be mechanically or electrically connected to
the PC board. The PCB top layer under the EN5335QI should be clear of any metal except for the
large thermal pad. The “grayed-out” area in Figure 4 represents the area that should be clear of any
metal (traces, vias, or planes), on the top layer of the PCB. Figure 5 shows the recommended PCB
footprint for this device.
Figure 4. Lead-Frame exposed metal. Grey area highlights exposed metal that is not to be mechanically or
electrically connected to the PCB.
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