BUF20800 Datasheet, PDF (21/27 Pages) Burr-Brown (TI) – 18-Channel GAMMA VOLTAGE GENERATOR with Two Programmable VCOM Channels

BUF20800
www.ti.com
GENERAL POWERPAD DESIGN
CONSIDERATIONS
The BUF20800 is available in a thermally-enhanced
PowerPAD package. This package is constructed using a
downset leadframe upon which the die is mounted, as
shown in Figure 20(a) and Figure 20(b). This arrangement
results in the lead frame being exposed as a thermal pad
on the underside of the package; see Figure 20(c). This
thermal pad has direct thermal contact with the die; thus,
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 printed circuit board
(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 on the device, GND_A and GND_D.
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
(2x5) can be seen in the technical brief, PowerPAD
Thermally-Enhanced Package (SLMA002), available
for download 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 re-
flow.
SBOS329D − JUNE 2005 − REVISED OCTOBER 2006
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 BUF20800
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 plane that is at the
same voltage potential as the GND pins.
5. When connecting these holes to the internal 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 BUF20800
PowerPAD package should make their connection to
the internal 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 masking
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 BUF20800
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.
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