Oct. 17. 2008 / Rev. 0.0

13/15

* This specifications are subject to be changed without notice

http://www.ad-tech.co.kr

ADT7310

PCB to the bottom layers, thermal VIAs need to be

incorporated into the thermal pad design. The number of

thermal VIAs improve the package thermal performance.

Generally, web-constructed VIA is often used in through-hole

applications to facilitate the soldering of a pin to a large plane.

It has a large thermal resistance to the surrounding layer. For

this reason, do not use web-constructed VIA to the thermal

PAD. It is recommended use completely connected VIA to the

surrounding layer (Figure 2).

If the diameter of the VIAs is too large, solder will be pulled

away from the exposed paddle (solder wicking) during the

reflow process. This will decrease thermal characteristic of the

VIA

3. Recommended PCB patterns

Figure 3 and 4 show adoptive PCB pattern of the ADT7310.

Top and bottom of the thermal PAD patterns are the same and

connected through the thermal VIAs. Also the bottom thermal

PAD must be connected to adjacent ground plane. It is recom-

mended that an array of thermal VIAs should be incorporated

at 1.0 to 1.2mm pitch with VIA diameter of 0.3 to 0.33mm.

PCB design for optimized thermal performance

1. Overview

Temperature characteristic of the ADT7310 is dependant to

power dissipation and heat away of the PCB pattern.

Therefore, in design of the PCB pattern, Consideration of the

heat away characteristic is important.

ADT7310 package is designed to provide enhanced thermal

characteristics through the exposed PAD on the bottom surface

of the package. Exposed PAD effectively decrease the thermal

resistance, which in turn provides excellent heat dissipation

from the die.

In order to take full advantage of exposed PAD, the PCB must

have features to effectively conduct heat away from the

package. This can be achieved by incorporating thermal PAD

and thermal VIAs.

2. PCB Layout considerations

2.1 Heat transfer

For enhanced thermal performance, the exposed PAD on the

package needs to be soldered to thermal PAD on the PCB.

Furthermore, for proper heat conduction through the PCB,

thermal VIAs need to be incorporated in the PCB in the

thermal PAD region. The exposed PAD should be attached to

the ground plane for proper thermal and electrical

performance.

Figure 1 illustrates primary heat away through GND layer of

the PCB. The presence of large metal planes in the PCB can

heat away 90% of the generated heat in the ADT7310

(Reference 1)

2.2 Thermal PAD

To maximize thermal performance, the size of the thermal

PAD should at least match the exposed PAD size. The size of

the thermal PAD on the bottom PCB layer should be at least as

large as the thermal PAD on the top PCB layer. It is

recommended that the bottom thermal PAD be thermally

connected to a GND layer (Reference 2)

2.3 Thermal VIAs

In order to effectively transfer heat from the top layer of the

<Figure 1. Heat transfer>

<Figure 2. Thermal Landing and Thermal VIA>

<Figure 3. PCB land pattern – Top Layer>