Datasheet

LM3658
SNVS328E –MAY 2005–REVISED MARCH 2007 www.ti.com
The thermal advantage of the WSON package is fully realized only when the exposed die attach pad is soldered
down to a thermal land on the PCB board with thermal vias planted underneath the thermal land. Based on
thermal analysis of the WSON package, the junction-to-ambient thermal resistance (θ
JA
) can be improved by a
factor of two when the die attach pad of the WSON package is soldered directly onto the PCB with thermal land
and thermal vias, as opposed to an alternative with no direct soldering to a thermal land. Typical pitch and outer
diameter for thermal vias are 1.27 mm and 0.33 mm respectively. Typical copper via barrel plating is 1 oz,
although thicker copper may be used to further improve thermal performance. The LM3658 die attach pad is
connected to the substrate of the IC and therefore, the thermal land and vias on the PCB board need to be
connected to ground (GND pin).
For more information on board layout techniques, refer to Application Note 1187 (SNOA401) “Leadless Lead
Frame Package (LLP).” This application note also discusses package handling, solder stencil and the assembly
process.
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