OPA445 datasheet(12/25 Pages) TI

12 / 25 page

OPA445

SBOS156B − MARCH 1987 − REVISED APRIL 2008

www.ti.com

PowerPAD THERMALLY-ENHANCED

PACKAGE

In addition to the SO-8, DIP-8, and TO-99 packages, the

OPA445 also comes in an SO-8 PowerPAD. The SO-8

PowerPAD is a standard-size SO-8 package where the

exposed leadframe on the bottom of the package can be

soldered directly to the PCB to create an extremely low

thermal resistance. This architecture enhances the

OPA445’s power dissipation capability significantly and

eliminates the use of bulky heatsinks and slugs

traditionally used in thermal packages. This package can

be easily mounted using standard PCB assembly

techniques. NOTE: Since the SO-8 PowerPAD is

pin-compatible

with

standard

SO-8

packages,

the

OPA445 can directly replace operational amplifiers in

existing sockets. Soldering the PowerPAD to the PCB is

always required, even with applications that have low

power dissipation. Soldering the device to the PCB

provides

the

necessary

thermal

and

mechanical

connection between the leadframe die pad and the PCB.

The PowerPAD package is designed so that the leadframe

die pad (or thermal pad) is exposed on the bottom of the

IC; see Figure 13. This design provides an extremely low

thermal resistance (

qJC) path between the die and the

exterior of the package. The thermal pad on the bottom of

the IC can then be soldered directly to the PCB, using the

PCB as a heatsink. In addition, plated-through holes (vias)

provide a low thermal resistance heat flow path to the back

side of the PCB.

Mold Compound (Plastic)

Leadframe Die Pad

Exposed at Base of the Package

(Copper Alloy)

Leadframe (Copper Alloy)

IC (Silicon)

Die Attach (Epoxy)

Figure 13. Section View of a PowerPAD Package

GENERAL PowerPAD LAYOUT GUIDELINES

The OPA445 is available in a thermally-enhanced

PowerPAD package. This package is constructed using a

downset leadframe upon which the die is mounted. This

arrangement results in the lead frame being exposed as a

thermal pad on the underside of the package. This thermal

pad has direct thermal contact with the die; thus, excellent

thermal performance is 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 must 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. Soldering

the PowerPAD to the PCB is always required, even with

applications that have low power dissipation. Follow these

steps:

The PowerPAD must be connected to the most

negative supply voltage on the device, V−.

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

should be etching for the leads as well as etch for the

thermal pad.

Place recommended holes in the area of the thermal

pad. Recommended thermal land size and thermal via

patterns for the SO-8 DDA package is shown in

Figure 14. These holes should be 13 mils in diameter.

Keep them small, so that solder wicking through the

holes is not a problem during reflow. The minimum

recommended number of holes for the SO-8

PowerPAD package is five.

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 OPA445

IC. These additional vias may be larger than the 13-mil

diameter vias directly under the thermal pad. They can

be larger because they are not in the thermal pad area

to be soldered; thus, wicking is not a problem.

Connect all holes to the internal power plane of the

correct voltage potential (V−).

When connecting these holes to the 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, makeing 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 OPA445 PowerPAD package

should make the connections to the internal plane with

complete

connection

around

the

entire

circumference of the plated-through hole.

The top-side solder mask should leave the terminals

of the package and the thermal pad area exposed.

The bottom-side solder mask should cover the holes

of the thermal pad area. This masking prevents solder

from being pulled away from the thermal pad area

during the reflow process.

Apply solder paste to the exposed thermal pad area

and all of the IC terminals.

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