Infineon PG-LQFP, Recommendations For Board Assembly

Page: 7 / 20

Additional Information 7 of 20 Revision 6.0
2020-11-12
Recommendations for Board Assembly of Infineon Quad Flat
Packages
Printed Circuit Board
2 Printed Circuit Board
2.1 Routing
Printed circuit board design and construction are key factors for achieving solder joints with high reliability.
Packages with exposed pads should not be placed opposite to each other on either side of a PCB when doing
double-sided mounting. This will stiffen the assembly and cause solder joints to fatigue earlier than in a design
in which the components are offset. Furthermore, the board stiffness itself has a significant influence on the
reliability of the solder joint interconnect if the system is used in critical temperature-cycling conditions.
2.2 Pad Design
The quality and reliability of interconnect solder joints to the board are affected by:

Pad type (Solder-Mask Defined, SMD or Non-Solder-Mask Defined, NSMD)

Specific pad dimensions

Pad finish (also called metallization or final finish)

Via layout and technology
The NSMD pad design is recommended for QFP components. The approach applies to the peripheral
terminations as well as to the exposed pads. Mixing different pad definition types in one footprint is not
recommended.
The exposed pads of QFP can feature anti-flash profiles. These are meander structures at the outline of the pad
to taper off potential mold flash during fabrication process. In
Figure 4 such an anti-flash profile is shown.
Despite that structure, the exposed pad outline is used for soldering purpose as can be seen in Figure 5 .
Besides their electrical function, the exposed pad areas of QFP packages are designed to conduct high thermal
loads into the PCB in order to achieve an optimal thermal performance. Therefore, the exposed pad area on the
PCB should be congruent with the area on the package at minimum. Using a PCB pad of the same size as the
package exposed pad will also increase the solder joint reliability, and the electrical performance for some
applications.
Figure 5 shows an example of print pattern on a PCB pad for a die pad connection including
thermal vias.
Figure 4 QFP with anti-flash profile in the exposed pad. The outer extension of the exposed pad
including the anti-flash profile should be used as the reference for the PCB pad design.