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General Thermal Pad Design Considerations

DIE

SideView(a)

EndView(b)

BottomView(c)

DIE

Thermal

Pad

M0031-01

Thermalpadarea=68mils

70mils(1.73mm 1.78mm)with5vias.

´

´

Viadiameter=13mils(0.33mm).

M0032-02

THS4021

THS4022

SLOS265C – SEPTEMBER 1999 – REVISED JULY 2007

The THS402x is available packaged in a thermally-enhanced DGN package, which is a member of the

PowerPAD family of packages. This package is constructed using a downset leadframe upon which the die is

mounted [see Figure 37(a) and Figure 37(b)]. This arrangement results in the lead frame being exposed as a

thermal pad on the underside of the package [see Figure 37(c)]. Because this thermal pad has direct thermal

contact with the die, excellent thermal performance can be 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 can also 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.

The PowerPAD package represents a design breakthrough, combining the small area and ease of the surface

mount assembly method to eliminate the previously difficult mechanical methods of heatsinking.

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

Figure 37. Views of Thermally Enhanced DGN Package

Although there are many ways to heatsink this device properly, the following steps illustrate the recommended

approach.

Figure 38. Thermal Pad PCB Etch and Via Pattern

1. Prepare the PCB with a top side etch pattern as shown in Figure 38. There should be etch for the leads as

well as etch for the thermal pad.

2. Place five holes in the area of the thermal pad. These holes should be 13 mils (0.33 mm) in diameter. Keep

them small so that solder wicking through the holes is not a problem during reflow.

3. Additional vias may be placed anywhere along the thermal plane outside of the thermal pad area. These vias

help dissipate the heat generated by the THS402xDGN IC. These additional vias may be larger than the

13-mil (0.33-mm) diameter vias directly under the thermal pad. They can be larger because they are not in

the thermal pad area to be soldered, so 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. 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 THS402xDGN package should connect 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 solder mask should cover the five holes of the thermal pad area. This

prevents solder from being pulled away from the thermal pad area during the reflow process.

Copyright © 1999–2007, Texas Instruments Incorporated

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Product Folder Link(s): THS4021 THS4022