BUF11705 Datasheet, PDF (13/17 Pages) Burr-Brown (TI) – 22 - V Supply, 10 + 1 Channel Gamma Correction Buffer

BUF11705
www.ti.com
GENERAL PowerPAD DESIGN
CONSIDERATIONS
The BUF11705 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 27(a) and (b). This arrangement
results in the lead frame being exposed as a thermal
pad on the underside of the package; see Figure 27(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 most
negative supply voltage of the device.
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
can be seen in technical brief, SLMA002 PowerPAD
Thermally-Enhanced Package, available for down-
load at www.ti.com. These holes should be 13 mils
in diameter. Keep them small, so that solder wicking
through the holes is not a problem during reflow.
SBOS349 − DECEMBER 2005
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
BUF11705 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; so that,
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. Web
connections make the soldering of vias easier. In
this application, however, low thermal resistance is
desired for the most efficient heat transfer.
Therefore, the holes under the BUF11705
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 ten
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
BUF11705 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)
DIE
End View (b)
Bottom View (c)
The thermal pad is electrically isolated from all terminals in the package.
Figure 27. Views of Thermally-Enhanced DGN Package
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