Additional Information
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Revision 6.0
2020-11-12
Recommendations for Board Assembly of Infineon Quad Flat
Packages
Package Description
Internal Construction
Infineon QFP are plastic encapsulated lead frame packages. Most of them have an exposed die pad on the
bottom of the package, which is created by an appropriate lead frame down-set. The exposed pads are usually
soldered to the Printed Circuit Board (PCB) for mechanical, electrical and thermal connection.
the typical setup of QFP with and without exposed die pad.
Figure 2
Schematics showing the inner setup of a QFP without (top) and with exposed die pad
(bottom).
Termination Design
The gullwing lead is considered to be one of the most reliable terminations for Surface-Mount Devices (SMD).
To form gullwing terminations, the leads are bent outwards at the tip. These bent Input/Output (I/O) lead foot
and heel areas form the seating plane that is then soldered to the PCB.
The distance between the I/O lead seating plane and the exposed pad landing area at the package bottom is
defined as the package stand-off. On QFP it can vary around the nominal value of 100 µm by ±50 µm.
Consequences to the board assembly are discussed in the following sections.
Termination Plating
Infineon QFP are available with matte tin (Sn) surface finish or with a Pre-Plated lead Frame (PPF). While the
Sn-plating is applied to the base metal by a post-mold process, the PPF provides a solderable surface that is
already deposited on the lead frame prior to the die attach process. The PPF surfaces basically consist of a
nickel/palladium/gold (Ni/Pd/Au) stack-up. While the Sn melts during reflow, the sacrificial Au layer of the PPF
surface is dissolved. The solder connection is then made with the Ni layer.
shows cross-sections of gullwing leads with Sn plated and PPF surface. While the appearance of solder
wetted PPF surfaces is slightly different to Sn surfaces it is in full agreement with IPC-A-610 standard [6]. Images
of the outer solder joint appearance can be found in
