IDT82V3285AEQG【PDF 34/149 页】IC PLL WAN SE STRATUM 100TQFP

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IDT82V3285A

WAN PLL

Thermal Management

129

August 7, 2009

8.4

TQFP EPAD THERMAL RELEASE PATH

In order to maximize both the removal of heat from the package and

the electrical performance, a land pattern must be incorporated on the

Printed Circuit Board (PCB) within the footprint of the package corre-

sponding to the exposed metal pad or exposed heat slug on the pack-

age, as shown in Figure 29. The solderable area on the PCB, as defined

by the solder mask, should be at least the same size/shape as the

exposed pad/slug area on the package to maximize the thermal/electri-

cal performance. Sufficient clearance should be designed on the PCB

between the outer edges of the land pattern and the inner edges of pad

pattern for the leads to avoid any shorts.

Figure 29. Assembly for Expose Pad thermal Release Path (Side View)

While the land pattern on the PCB provides a means of heat transfer

and electrical grounding from the package to the board through a solder

joint, thermal vias are necessary to effectively conduct from the surface

of the PCB to the ground plane(s). The land pattern must be connected

to ground through these vias. The vias act as ‘heat pipes’. The number

of vias (i.e. ‘heat pipes’) are application specific and dependent upon the

package power dissipation as well as electrical conductivity require-

ments. Thus, thermal and electrical analysis and/or testing are recom-

mended to determine the minimum number needed. Maximum thermal

and electrical performance is achieved when an array of vias is incorpo-

rated in the land pattern. It is recommended to use as many vias con-

nected to ground as possible. It is also recommended that the via

diameter should be 12 to 13mils (0.30 to 0.33mm) with 1 oz copper via

barrel plating. This is desirable to avoid any solder wicking inside the via

during the soldering process which may result in voids in solder between

the exposed pad/slug and the thermal land. Precautions should be taken

to eliminate any solder voids between the exposed heat slug and the

land pattern. Note: These recommendations are to be used as a guide-

line only. For further information, please refer to the Application Note on

the Surface Mount Assembly of Amkor’s Thermally/Electrically Enhance

Leadfame Base Package, Amkor Technology.

THERMAL

VIA

SOLDER

GROUND

PLANE

LAND

PATTERN

(GROUND PAD)

PAD

SOLDER

EXPOSED HEAT SLUG

PAD

SOLDER

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