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
substrate of the integrated circuit and V
EE
. The thermal land
should be electrically connected to V
EE
.
