Package Application Note AN913

VISHAY SILICONIX
Power ICs and Power MOSFETs
Application Note 913
The PowerPAK SO-8L: A Package
with Thermo-Mechanical Resilience
By Kandarp Pandya
Vishay is adding to its package portfolio with the PowerPAK
SO-8L, an AEC Q101 qualified package. Its power cycling
capabilities at rated temperature ensure the product life cycle
in high-power automotive applications where the standard
leadless packages can fail for various reasons. The new
design shares certain characteristics of two previous
packages the high-efficiency, leadless PowerPAK SO-8 and
the industry work-horse DPAK (TO-252) with its heat
dissipating tab. Figures 1, 2, and 3 highlight the
commonalities of these three package types.
1
PowerPAK SO-8 Backside View
Fig. 2 - PowerPAK SO-8
PowerPAK SO-8L Backside View
0.72
Fig. 1 - PowerPAK SO-8L Concept
Document Number: 64721
09-Jan-09
www.vishay.com
1
APPLICATION NOTE
Fig. 3 - DPAK Bottom and side view
Application Note 913
Vishay Siliconix
The PowerPAK SO-8L: A Package
with Thermo-Mechanical Resilience
otherwise lead to failure of the solder joint either during the
product life cycle test, the solder joint reliability test, or the
power cycling test.
The recommended minimum PAD pattern for PowerPAK
SO-8 single is shown in figure 5.
0.260
(6.61)
0.150
(3.81)
0.024
(0.61)
0.3
0.174
(4.42)
Vishay performed a design level solder fatigue analysis and
characterization using Ansys 9.0 on the SO-8, PowerPAK
SO-8 and PowerPAK SO-8L packages using identical
material properties and electrical power/load assumptions.
The 2D modeling used 82 structural elements and Visco108
for solder material. The load power cycle ramped from room
temperature to 125 °C in a minute, stayed at 125 °C for 40
minutes, and then returned back to room temperature. The
PCB was held in the UX and UY directions in the lower left
corner and held in the UY in direction the lower right corner,
allowing the PCB to freely expand in the UX direction during
thermal expansion. A comparison of thermal fatigue
displacement is shown in figure 4.
0.154
(3.91)
0.026
(0.66)
0.050
(1.27)
0.25
0.2
PW/V
0.15
0.050
(1.27)
0.032
(0.82)
0.040
(1.02)
0.1
Fig. 5 - Recommended Minimum PADs for PowerPAK SO-8
Single Dimensions in Inches/(mm)
0.05
Fig. 4 - Thermal Fatigue Displacement Comparisons
APPLICATION NOTE
The thermal fatigue displacement of the PowerPAK SO-8
was 72 % higher than the SO-8, while PowerPAK SO-8L
displacement was only 24 % higher. In other words, the new
package design provides for a significant improvement in
thermo-mechanical resilience.
The gate and source pins in the new package are terminated
like those on the DPAK, while the package's dimensional
profile remains the same as the regular PowerPAK SO-8.
The contoured shape of the pins allows them to expand in
order to relieve the thermo-mechanical stress generated by
the mismatch of coefficient of thermal expansion (CET)
among the different material elements constituting the
device, including the silicon die, die attach epoxy, copper
lead frame, and plastic mold compound. The pin experiences
a spring action in the central portion of its contour as the two
ends are rigidly held in its place, one by the molding
compound and the other by the solder joint on the PC board
assembly. Thus the thermo-mechanical resilience is built into
the package design to eliminate damaging stresses
experienced mainly by the solo gate pin, which could
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0.11
0.10
PowerPAK SO-8
0.29
0.26
0.40
1
0.05
PowerPAK SO-8L
0.05
SO-8
The part overlay over the recommended PAD for single
channel PowerPAK SO-8 is shown in figure 6 and the part
overlay over the same recommended single channel PAD for
PowerPAK SO-8L is shown in figure 7.
0.10
0
Overlap Flipped "PowerPAK SO-8 PCB
Foot Print" onto
"PowerPAK SO-8 Backside View"
Fig. 6 - Single Channel PowerPAK SO-8 on its PAD Layout
Document Number: 64721
09-Jan-09
Application Note 913
Vishay Siliconix
0.52
0.44 0.18
0.37
Figures 8 shows the recommended minimum PAD pattern
for new designs using the single-channel PowerPAK SO-8L.
The four side leaps are part of different drain tab design.
0.24
0.09
0.03
The PowerPAK SO-8L: A Package
with Thermo-Mechanical Resilience
6.7500
(0.266)
5.1300
(0.202)
As figures 6 and 7 indicate, the single-channel PowerPAK
SO-8L serves as a drop-in replacement for the
single-channel PowerPAK SO-8, even though the packages
differ in their physical appearance.
0.5100
(0.020)
0, 0
0.9150
(0.036)
Overlap Flipped "PowerPAK SO-8 PCB
Foot Print" onto "PowerPAK SO-8L
Backside View"
3.0750
(0.121)
2.1100
(0.083)
Fig. 7 - Single Channel PowerPAK SO-8L on Single Channel
PowerPAK SO-8 PAD Layout
3.9900
(0.157)
0.5850
(0.023)
1.9800
(0.078)
0.55
0.03
0.24
0.2550
(0.010)
0.4700
(0.019)
7.7500
(0.305)
2.5650
(0.101)
3.9600
(0.156)
6.1500
(0.242)
0.4100
(0.016)
0.7200
(0.028)
1.2700
(0.050)
0.4100
(0.016)
Fig. 8 - Recommended PAD for Single Channel
Power PAK SO-8L
Dimensions in mm (inches)
Keep-out 6.75 (0.266) x 7.75 (0.305)
SUMMARY
The single channel PowerPAK SO-8L is an AEC Q101 qualified package for high-power, high-temperature automotive
applications. Its key feature is the package's thermo-mechanical resilience, which allows the PowerPAK SO-8L to survive the
designed life cycle of the application. The single-channel PowerPAK SO-8L serves as a drop-in replacement for the
single-channel PowerPAK SO-8. Solder joint reliability test using IPC 9701 guidelines will be tested in the future.
APPLICATION NOTE
Document Number: 64721
Revision: 09-Jan-09
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