BUF16821 datasheet(21/29 Pages) EPCOS

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GENERAL POWERPAD DESIGN

BUF16821

www.ti.com ...................................................................................................................................................................................................... SBOS428 – JULY 2008

example thermal land pattern mechanical drawing

CONSIDERATIONS

is attached to the end of this data sheet.

3. Additional vias may be placed anywhere along

The BUF16821 is available in a thermally-enhanced

the thermal plane outside of the thermal pad area

PowerPAD package. This package is constructed

to help dissipate the heat generated by the

using a downset leadframe upon which the die is

BUF16821 IC. These additional vias may be

mounted; see Figure 19(a) and Figure 19(b). This

larger than the 13-mil diameter vias directly under

arrangement results in the lead frame being exposed

the thermal pad. They can be larger because

as a thermal pad on the underside of the package;

they are not in the thermal pad area to be

see Figure 19(c). This thermal pad has direct thermal

soldered; thus, wicking is not a problem.

contact

with

the

die;

thus,

excellent

thermal

performance is achieved by providing a good thermal

4. Connect all holes to the internal plane that is at

path away from the thermal pad.

the same voltage potential as the GND pins.

5. When connecting these holes to the internal

The PowerPAD package allows for both assembly

plane, do not use the typical web or spoke via

and thermal management in one manufacturing

connection methodology. Web connections have

operation. During the surface-mount solder operation

a high thermal resistance connection that is

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

useful for slowing the heat transfer during

must be soldered to a copper area underneath the

soldering operations. This configuration makes

package. Through the use of thermal paths within this

the soldering of vias that have plane connections

copper area, heat can be conducted away from the

easier. In this application, however, low thermal

package

into

either

ground

plane

other

resistance is desired for the most efficient heat

heat-dissipating device. Soldering the PowerPAD to

transfer.

Therefore,

the

holes

under

the

the printed circuit board (PCB) is always required,

BUF16821 PowerPAD package should make

even

with

applications

that

have

low

power

their connection to the internal plane with a

dissipation. This technique provides the necessary

complete

connection

around

the

entire

thermal and mechanical connection between the lead

circumference of the plated-through hole.

frame die pad and the PCB.

6. The top-side solder mask should leave the

The PowerPAD must be connected to the most

terminals of the package and the thermal pad

negative supply voltage on the device, GNDA and

area

with

its

twelve

holes

exposed.

The

GNDD.

bottom-side solder mask should cover the holes

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

of the thermal pad area. This masking prevents

There should be etching for the leads as well as

solder from being pulled away from the thermal

etch for the thermal pad.

pad area during the reflow process.

2. Place recommended holes in the area of the

7. Apply solder paste to the exposed thermal pad

thermal pad. Ideal thermal land size and thermal

area and all of the IC terminals.

via patterns for the HTSSOP-28 PWP package

8. With these preparatory steps in place, simply

can be seen in the technical brief, PowerPAD

place the BUF16821 IC in position and run the

Thermally-Enhanced

Package

(SLMA002),

chip through the solder reflow operation as any

available for download at www.ti.com. These

standard

surface-mount

component.

This

holes should be 13 mils (0,33mm) in diameter.

preparation results in a properly installed part.

Keep them small, so that solder wicking through

the holes is not a problem during reflow. An

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