AN-9046 Datasheet, PDF (1/10 Pages) Fairchild Semiconductor – Dual Power56 Packaging

Application Note AN9046
Assembly Guidelines for Dual Power56 Packaging
By Dennis Lang
INTRODUCTION
The Fairchild^® Dual Power56 package is based on
Molded Leadless Packaging (MLP) technology.
This technology has been increasingly used in
packaging for power related products due to its
low package height, excellent thermal performance
with large thermal pads in the center of the
package which solder directly to the printed wiring
board (PWB). Modularity in package design,
single and multi-die packages, is within the
capability of MLP technology.
The Dual Power56 has two large die attach pads
allowing direct soldering to the PWB for best
thermal and electrical performance. These two
pads are the co-packaged high and low side
MOSFETs. The Dual Power56 is designed to be
used in high current synchronous buck DC-DC
circuits, saving board space and component count
by integrating the high and low side MOSFETs
into one package.
This application note focuses on the soldering and
back end processing of the Dual Power56.
BOARD MOUNTING
The solder joint and pad design are the most
important factors in creating a reliable assembly.
The pad dimensions must be designed to allow for
tolerances in PWB fabrication and pick and place,
which are necessary for proper solder fillet
formation. MLP packages, when the pre-plated
lead-frame is sawn, show bare copper on the end
of the exposed edge leads. This is normal, and is
addressed by IPC JEDEC J-STD-001C “Bottom
Only Termination”. In practice it has been found
that optimized PWB pad design and a robust
solder process often yields solder fillets to the ends
of the lead due to the cleaning action of the flux in
the solder paste.
Figure 1: Bottom side view showing pads for Dual
Power56.
Figure 2: Exposed copper on package edge, with
solder wetting after reflow, from singulation
process.
PWB DESIGN CONSIDERATIONS
Any land pad pattern must take into account the
various PWB and board assembly tolerances for
successful soldering of the MLP to the PWB.
These factors have already been considered for the
recommended footprint given on the datasheet. It