PowerPAD DESIGN CONSIDERATIONS

PowerPAD PCB LAYOUT CONSIDERATIONS

DIE

Side View (a)

DIE

End View (b)

Thermal

Pad

Bottom View (c)

0.060

0.040

0.075

0.025

0.205

0.010

vias

Pin 1

Top View

0.017

0.035

0.094

0.030

0.013

THS4504

THS4505

www.ti.com ......................................................................................................................................................... SLOS363D – AUGUST 2002 – REVISED MAY 2008

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

The

THS4500

family

is

available

in

a

shown in Figure 90. There should be etch for the

thermally-enhanced PowerPAD family of packages.

leads as well as etch for the thermal pad.

These packages are constructed using a downset

leadframe upon which the die is mounted [see

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

Figure 89(a) and Figure 89(b)]. This arrangement

These holes should be 13 mils in diameter. Keep

results in the lead frame being exposed as a thermal

them small so that solder wicking through the

pad

on

the

underside

of

the

package

[see

holes is not a problem during reflow.

Figure 89(c)]. Because this thermal pad has direct

3. Additional vias may be placed anywhere along

thermal contact with the die, excellent thermal

the thermal plane outside of the thermal pad

performance can be achieved by providing a good

area. This helps dissipate the heat generated by

thermal path away from the thermal pad.

the THS4500 family IC. These additional vias

may be larger than the 13-mil diameter vias

The PowerPAD package allows for both assembly

directly under the thermal pad. They can be

and thermal management in one manufacturing

larger because they are not in the thermal pad

operation. During the surface-mount solder operation

area to be soldered so that wicking is not a

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

problem.

can also be soldered to a copper area underneath the

package. Through the use of thermal paths within this

4. Connect all holes to the internal ground plane.

copper area, heat can be conducted away from the

5. When connecting these holes to the ground

package into either a ground plane or other heat

plane, do not use the typical web or spoke via

dissipating device.

connection methodology. Web connections have

a high thermal resistance connection that is

The PowerPAD package represents a breakthrough

useful for slowing the heat transfer during

in combining the small area and ease of assembly of

soldering operations. This makes the soldering of

surface

mount

with

the,

heretofore,

awkward

vias that have plane connections easier. In this

mechanical methods of heatsinking.

application, however, low thermal resistance is

desired for the most efficient heat transfer.

Therefore, the holes under the THS4500 family

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 five holes exposed. The bottom-side

Figure 89. Views of Thermally Enhanced Package

solder mask should cover the five holes of the

thermal pad area. This prevents solder from

Although there are many ways to properly heatsink

being pulled away from the thermal pad area

the PowerPAD package, the following steps illustrate

during the reflow process.

the recommended approach.

7. Apply solder paste to the exposed thermal pad

area and all of the IC terminals.

8. With these preparatory steps in place, the IC is

simply placed in position and run through the

solder

reflow

operation

as

any

standard

surface-mount component. This results in a part

that is properly installed.

Figure 90. View of Thermally Enhanced Package

Copyright © 2002–2008, Texas Instruments Incorporated

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Product Folder Link(s): THS4504 THS4505