During the surface-mount solder
operation (when the leads are being soldered), the thermal pad must be soldered to a
copper area underneath the package. Through the use of thermal paths within this
copper area, heat is conducted away from the package into either a ground plane or
other heat-dissipating device. Always solder the thermal pad to the PCB, even with
applications that have low power dissipation. Follow these steps to attach the
device to the PCB:
- Connect the thermal pad to
the most negative supply voltage on the device, V–.
- Prepare the PCB with a
top-side etch pattern. There must be etching for the leads, as well as
etching for the thermal pad.
- Thermal vias improve heat
dissipation, but are not required. The thermal pad can connect to the PCB
using an area equal to the pad size with no vias, but must be externally
connected to V–.
- Place recommended holes in
the area of the thermal pad. Recommended thermal land size and thermal via
patterns for the SON-12 DNT package are shown in the thermal land pattern
mechanical drawing appended at the end of this document. Keep the holes
small, so that solder wicking through the holes is not a problem during
reflow. Use a 0.2-mm size via with a minimum of five connected directly
below the thermal pad.
- Additional vias can be placed
anywhere along the thermal plane outside of the thermal pad area. These vias
help dissipate the heat generated by the OPA593 device. These additional
vias can be larger than the vias directly under the thermal pad because the
additional vias are not in the thermal pad area to be soldered; thus,
wicking is not a problem.
- Connect all holes to the
internal power plane of the correct voltage potential, V–.
- When connecting these holes
to the plane, do not use the typical web or spoke via connection
methodology. Web connections have a high thermal resistance connection that
is useful for slowing the heat transfer during soldering operations, making
the soldering of vias that have plane connections easier. In this
application, however, low thermal resistance is desired for the most
efficient heat transfer. Therefore, the holes under the OPA593 WSON package
must make the connections to the internal plane with a complete connection
around the entire circumference of the plated-through hole.
- The top-side solder mask must
leave the pins of the package and the thermal pad area exposed. The
bottom-side solder mask must cover the holes of the thermal pad area. This
masking prevents solder from being pulled away from the thermal pad area
during the reflow process.
- Apply solder paste to the
exposed thermal pad area and all of the device pins.
- With these preparatory steps
in place, simply place the device in position, and run through the solder
reflow operation as with any standard surface-mount component.