THS4271 datasheet(27/41 Pages) TI

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DIE

Side View (a)

DIE

End View (b)

Thermal

Pad

Bottom View (c)

Single or Dual

68 Mils x 70 Mils

(Via Diameter = 13 Mils)

D +

Tmax * TA

where

PD = Maximum power dissipation of THS4211 (watts)

TMAX = Absolute maximum junction temperature (150°C)

TA = Free-ambient temperature (°C)

θJA = θJC + θCA

θJC = Thermal coefficient from junction to the case

θCA = Thermal coefficient from the case to ambient air

(

°C/W).

(6)

PowerPAD PCB LAYOUT CONSIDERATIONS

THS4211

THS4215

SLOS400D – SEPTEMBER 2002 – REVISED NOVEMBER 2004

pad on the underside of the package [see Fig-

directly under the thermal pad. They can be

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

larger because they are not in the thermal pad

thermal contact with the die, excellent thermal per-

area to be soldered, so wicking is not a problem.

formance can be achieved by providing a good

4. Connect all holes to the internal ground plane.

thermal path away from the thermal pad.

5. When connecting these holes to the ground

The PowerPAD package allows both assembly and

plane, do not use the typical web or spoke via

thermal management in one manufacturing operation.

connection methodology. Web connections have

a high thermal resistance connection that is

During the surface-mount solder operation (when the

useful for slowing the heat transfer during

leads are being soldered), the thermal pad can also

soldering operations. This resistance makes the

be soldered to a copper area underneath the pack-

soldering of vias that have plane connections

age. Through the use of thermal paths within this

easier. In this application, however, low thermal

copper area, heat can be conducted away from the

resistance is desired for the most efficient heat

package into either a ground plane or other heat

transfer. Therefore, the holes under the THS4211

dissipating device.

and THS4215 PowerPAD package should make

their connection to the internal ground plane, with

The PowerPAD package represents a breakthrough

a complete connection around the entire circum-

in combining the small area and ease of assembly of

ference of the plated-through hole.

surface mount with the heretofore awkward mechan-

ical methods of heatsinking.

6. The top-side solder mask should leave the ter-

minals 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.

7. Apply solder paste to the exposed thermal pad

area and all of the IC terminals.

Figure 89. Views of Thermally

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

Enhanced Package

simply placed in position and run through the

solder reflow operation as any standard sur-

Although there are many ways to properly heatsink

face-mount component. This results in a part that

the PowerPAD package, the following steps illustrate

is properly installed.

the recommended approach.

For a given

JA , the maximum power dissipation is

shown in Figure 91 and is calculated by Equation 6:

Figure 90. PowerPAD PCB Etch and

Via Pattern

The next consideration is the package constraints.

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

The two sources of heat within an amplifier are

shown in Figure 90. There should be etching for

quiescent power and output power. The designer

the leads as well as etch for the thermal pad.

should never forget about the quiescent heat gener-

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

ated within the device, especially multi-amplifier de-

These holes should be 13 mils in diameter. Keep

vices. Because these devices have linear output

them small so that solder wicking through the

stages (Class AB), most of the heat dissipation is at

holes is not a problem during reflow.

low output voltages with high output currents.

3. Additional vias may be placed anywhere along

The other key factor when dealing with power dissi-

the thermal plane outside of the thermal pad

pation is how the devices are mounted on the PCB.

area. They help dissipate the heat generated by

The PowerPAD devices are extremely useful for heat

the THS4211 and THS4215 IC. These additional

dissipation.

But,

the

device

should

always

vias may be larger than the 13-mil diameter vias

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