Vishay Siliconix
AN821
Document Number 71622
28-Feb-06
www.vishay.com
1
PowerPAK
®
SO-8 Mounting and Thermal Considerations
Wharton McDaniel
MOSFETs for switching applications are now available
with die on resistances around 1 mΩ and with the
capability to handle 85 A. While these die capabilities
represent a major advance over what was available
just a few years ago, it is important for power MOSFET
packaging technology to keep pace. It should be obvi-
ous that degradation of a high performance die by the
package is undesirable. PowerPAK is a new package
technology that addresses these issues. In this appli-
cation note, PowerPAK’s construction is described.
Following this mounting information is presented
including land patterns and soldering profiles for max-
imum reliability. Finally, thermal and electrical perfor-
mance is discussed.
THE PowerPAK PACKAGE
The PowerPAK package was developed around the
SO-8 package (Figure 1). The PowerPAK SO-8 uti-
lizes the same footprint and the same pin-outs as the
standard SO-8. This allows PowerPAK to be substi-
tuted directly for a standard SO-8 package. Being a
leadless package, PowerPAK SO-8 utilizes the entire
SO-8 footprint, freeing space normally occupied by the
leads, and thus allowing it to hold a larger die than a
standard SO-8. In fact, this larger die is slightly larger
than a full sized DPAK die. The bottom of the die attach
pad is exposed for the purpose of providing a direct,
low resistance thermal path to the substrate the device
is mounted on. Finally, the package height is lower
than the standard SO-8, making it an excellent choice
for applications with space constraints.
PowerPAK SO-8 SINGLE MOUNTING
The PowerPAK single is simple to use. The pin
arrangement (drain, source, gate pins) and the pin
dimensions are the same as standard SO-8 devices
(see Figure 2). Therefore, the PowerPAK connection
pads match directly to those of the SO-8. The only dif-
ference is the extended drain connection area. To take
immediate advantage of the PowerPAK SO-8 single
devices, they can be mounted to existing SO-8 land
patterns.
The minimum land pattern recommended to take full
advantage of the PowerPAK thermal performance see
Application Note 826, Recommended Minimum Pad
Patterns With Outline Drawing Access for Vishay Sili-
conix MOSFETs. Click on the PowerPAK SO-8 single
in the index of this document.
In this figure, the drain land pattern is given to make full
contact to the drain pad on the PowerPAK package.
This land pattern can be extended to the left, right, and
top of the drawn pattern. This extension will serve to
increase the heat dissipation by decreasing the ther-
mal resistance from the foot of the PowerPAK to the
PC board and therefore to the ambient. Note that
increasing the drain land area beyond a certain point
will yield little decrease in foot-to-board and foot-to-
ambient thermal resistance. Under specific conditions
of board configuration, copper weight and layer stack,
experiments have found that more than about 0.25 to
0.5 in
2
of additional copper (in addition to the drain
land) will yield little improvement in thermal perfor-
mance.
Figure 1. PowerPAK 1212 Devices
Figure 2.
Standard SO-8 PowerPAK SO-8
