NB100LVEP221

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9

APPLICATIONS INFORMATION

Using the thermally enhanced package of the

NB100LVEP221

The NB100LVEP221 uses a thermally enhanced 52−lead

LQFP package. The package is molded so that a portion of

the leadframe is exposed at the surface of the package

bottom side. This exposed metal pad will provide the low

thermal impedance that supports the power consumption of

the NB100LVEP221 high−speed bipolar integrated circuit

and will ease the power management task for the system

design. In multilayer board designs, a thermal land pattern

on the printed circuit board and thermal vias are

recommended to maximize both the removal of heat from

the

package

and

electrical

performance

of

the

NB100LVEP221. The size of the land pattern can be larger,

smaller, or even take on a different shape than the exposed

pad on the package. However, the solderable area should be

at least the same size and shape as the exposed pad on the

package. Direct soldering of the exposed pad to the thermal

land will provide an efficient thermal conduit. The thermal

vias will connect the exposed pad of the package to internal

copper planes of the board. The number of vias, spacing, via

diameters and land pattern design depend on the application

and the amount of heat to be removed from the package.

Maximum thermal and electrical performance is achieved

when an array of vias is incorporated in the land pattern.

The

recommended

thermal

land

design

for

NB100LVEP221 applications on multi−layer boards

comprises a 4 X 4 thermal via array using a 1.2 mm pitch as

shown in Figure 8 providing an efficient heat removal path.

Figure 8. Recommended Thermal Land Pattern

All Units mm

Thermal Via Array (4 X 4)

1.2 mm Pitch

0.3 mm Diameter

Exposed Pad

Land Pattern

4.6

4.6

The via diameter should be approximately 0.3 mm with

1 oz. copper via barrel plating. Solder wicking inside the via

may result in voiding during the solder process and must be

avoided. If the copper plating does not plug the vias, stencil

print solder paste onto the printed circuit pad. This will

supply enough solder paste to fill those vias and not starve

the solder joints. The attachment process for the exposed pad

package is equivalent to standard surface mount packages.

Figure 9, “Recommended solder mask openings”, shows a

recommended solder mask opening with respect to a 4 X 4

thermal via array. Because a large solder mask opening may

result in a poor rework release, the opening should be

subdivided as shown in Figure 9. For the nominal package

standoff of 0.1 mm, a stencil thickness of 5 to 8 mils should

be considered.

Figure 9. Recommended Solder Mask Openings

All Units mm

Thermal Via Array (4 X 4)

1.2 mm Pitch

0.3 mm Diameter

Exposed Pad

Land Pattern

4.6

4.6

0.2

1.0

1.0

0.2

Proper thermal management is critical for reliable system

operation. This is especially true for high−fanout and high

output drive capability products.

For thermal system analysis and junction temperature

calculation, the thermal resistance parameters of the

package are provided:

Table 10. Thermal Resistance *

lfpm

qJA 5C/W

qJC 5C/W

0

35.6

3.2

100

32.8

4.9

500

30.0

6.4

* Junction to ambient and Junction to board, four−conductor

layer test board (2S2P) per JESD 51−8

These recommendations are to be used as a guideline,

only. It is therefore recommended that users employ

sufficient thermal modeling analysis to assist in applying the

general recommendations to their particular application to

assure adequate thermal performance. The exposed pad of

the NB100LVEP221 package is electrically shorted to the