BUF12800 Datasheet, PDF (15/20 Pages) Burr-Brown (TI) – REFERENCE VOLTAGE GENERATOR for LCD GAMMA CORRECTION

BUF12800
www.ti.com
GENERAL PowerPAD DESIGN
CONSIDERATIONS
The BUF12800 is available in the thermally-enhanced
PowerPAD package. This package is constructed using
a downset leadframe upon which the die is mounted, as
shown in Figure 17(a) and (b). This arrangement
results in the lead frame being exposed as a thermal
pad on the underside of the package; see Figure 17(c).
Due to this thermal pad having direct thermal contact
with the die, excellent thermal performance is achieved
by providing a good thermal path away from the thermal
pad.
The PowerPAD package allows for both assembly and
thermal management in one manufacturing operation.
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 can be conducted away from the package
into either a ground plane or other heat-dissipating
device. Soldering the PowerPAD to the PCB is
always required, even with applications that have
low power dissipation. This provides the necessary
thermal and mechanical connection between the lead
frame die pad and the PCB.
The PowerPAD must be connected to the device’s most
negative supply voltage, V−.
1. Prepare the PCB with a top-side etch pattern. There
should be etching for the leads as well as etch for the
thermal pad.
2. Place recommended holes in the area of the thermal
pad. Ideal thermal land size and thermal via patterns
(2x4) can be seen in the technical brief, PowerPAD
Thermally-Enhanced Package (SLMA002), avail-
able for download at www.ti.com. These holes
should be 13 mils in diameter. Keep them small, so
SBOS315 − DECEMBER 2004
that solder wicking through the holes is not a prob-
lem during reflow.
3. Additional vias may be placed anywhere along the
thermal plane outside of the thermal pad area. This
helps dissipate the heat generated by the
BUF12800 IC. These additional vias may be larger
than the 13-mil diameter vias directly under the
thermal pad. They can be larger because they are
not in the thermal pad area to be soldered; thus,
wicking is not a problem.
4. Connect all holes to the internal ground plane.
5. When connecting these holes to the ground 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. This
makes 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
BUF12800 PowerPAD package should make their
connection to the internal ground plane with a
complete connection around the entire
circumference of the plated-through hole.
6. The top-side solder mask should leave the terminals
of the package and the thermal pad area with its
eight holes exposed. The bottom-side solder mask
should cover the holes of the thermal pad area. This
prevents solder from being pulled away from the
thermal pad area during the reflow process.
7. Apply solder paste to the exposed thermal pad area
and all of the IC terminals.
8. With these preparatory steps in place, the
BUF12800 IC is simply placed in position and run
through the solder reflow operation as any standard
surface-mount component. This preparation results
in a properly installed part.
DIE
Side View (a)
Thermal
Pad
DIE
End View (b)
Bottom View (c)
The thermal pad is electrically isolated from all terminals in the package.
Figure 17. Views of Thermally-Enhanced DGN Package
15