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ICS844246BG REV.C NOVEMBER 14, 2007

ICS844246

FEMTOCLOCKS™ CRYSTAL-TO-LVDS FREQUENCY SYNTHESIZER W/INTEGRATED FANOUT BUFFER

PRELIMINARY

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

and the electr ical perfor mance, a land patter n must be

incorporated on the Printed Circuit Board (PCB) within the footprint

of the package corresponding to the exposed metal pad or

exposed heat slug on the package, as shown in Figure 5. 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/electrical 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.

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 requirements. Thus,

thermal and electrical analysis and/or testing are recommended

to determine the minimum number needed. Maximum thermal

and electrical performance is achieved when an array of vias is

incorporated in the land pattern. It is recommended to use as

many vias connected to ground as possible. It is also

recommended that the via diameter should be 12 to 13mils (0.30

to 0.33mm) with 1oz 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 guideline only. For further information, refer to the Application

Note on the Surface Mount Assembly of Amkor’s Thermally/

Electrically Enhance Leadfame Base Package, Amkor Technology.

GROUND PLANE

LAND PATTERN

SOLDER

THERMAL VIA

EXPOSED HEAT SLUG

(GROUND PAD)

PIN

PIN PAD

SOLDER

PIN

PIN PAD

SOLDER