BUF04701 datasheet(19/30 Pages) TI2

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MAX

qJA

(

P =

(a)SideView

(b)EndView

(c)BottomView

DIE

Thermal

Pad

BUF07703

BUF06703

BUF05703

www.ti.com

SBOS269C – MARCH 2003 – REVISED APRIL 2010

GENERAL PowerPAD DESIGN

soldering operations. This makes the soldering of

CONSIDERATIONS

vias that have plane connections easier. In this

application, however, low thermal resistance is

The BUF07703 is available in the thermally enhanced

desired for the most efficient heat transfer.

PowerPAD family of packages. These packages are

Therefore,

the

holes

under

the

BUF07703

constructed using a downset leadframe upon which

PowerPAD package must make their connection

the die is mounted; see Figure 42(a) and (b). This

to the internal ground plane with a complete

arrangement results in the lead frame being exposed

connection around the entire circumference of the

as a thermal pad on the underside of the package;

plated-through hole.

see Figure 42(c). Due to this thermal pad having

6. The

top-side

solder

mask

must

leave

the

direct thermal contact with the die, excellent thermal

terminals of the package and the thermal pad

performance is achieved by providing a good thermal

area with its five holes (dual) or nine holes (quad)

path away from the thermal pad.

exposed. The bottom-side solder mask must

The PowerPAD package allows for both assembly

cover the five or nine holes of the thermal pad

and thermal management in one manufacturing

area. This prevents solder from being pulled

operation. During the surface-mount solder operation

away from the thermal pad area during the reflow

(when the leads are being soldered), the thermal pad

process.

can also be soldered to a copper area underneath the

7. Apply solder paste to the exposed thermal pad

package. Through the use of thermal paths within this

area and all of the IC terminals.

copper area, heat can be conducted away from the

8. With these preparatory steps in place, the

package

into

either

ground

plane

other

BUF07703 IC is simply placed in position and run

heat-dissipating device. Although there are many

through the solder reflow operation as any

ways to properly heatsink the PowerPAD package,

standard surface-mount component. This results

the

following

steps

illustrate

the

recommended

in a part that is properly installed.

approach.

1. Prepare the PCB with a top-side etch pattern,

For a given qJA, the maximum power dissipation is

(see Pin Configurations). There must be etching

calculated by the following formula:

for the leads as well as etch for the thermal pad.

2. Place 18 holes in the area of the thermal pad.

These holes must be 13 mils in diameter. Keep

them small, so that solder wicking through the

Where:

holes is not a problem during reflow.

•

PD = maximum power dissipation (W)

3. Additional vias may be placed anywhere along

•

TMAX = absolute maximum junction temperature

the thermal plane outside of the thermal pad

(+150°C)

area. This helps dissipate the heat generated by

•

TA = free-ambient air temperature (°C)

the BUF07703 IC. These additional vias may be

•

qJA = qJC + qCA

larger than the 13-mil diameter vias directly under

•

qJC = thermal coefficient from junction to case

the thermal pad. They can be larger because

(°C/W)

they are not in the thermal pad area to be

•

qCA = thermal coefficient from case-to-ambient air

soldered, so that wicking is not a problem.

(°C/W)

4. Connect all holes to the internal ground plane.

This lower thermal resistance enables the BUF07703

5. When connecting these holes to the ground

to deliver maximum output currents even at high

plane, do not use the typical web or spoke via

ambient temperatures.

connection methodology. Web connections have

a high thermal resistance connection that is

useful for slowing the heat transfer during

Note:

The thermal pad is electrically isolated from all terminals in the package.

Figure 42. Views of Thermally-Enhanced DGN Package

Product Folder Link(s): BUF07703 BUF06703 BUF05703

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